Jupiter is a great big question mark.  Like the king of the gods for whom it is named, the giant planet dominates the solar system, surrounding itself with an entourage of moons and other attendants.  The region of space all around Jupiter is filled with its gravitational field, its magnetic field and its zones of intense radiation.  Its nearer moons are heated by the tidal force of its gravity, allowing them to have inner oceans of water (probably) and sometimes active volcanoes.  Jupiter is our biggest gas giant planet, but we know from our observations of other planetary systems that  there are others that are much bigger.  These enormous planets, Jupiter and its big cousins, are really the main product of planet formation.  They suck up most of the matter that surrounds a planet-forming star, and the crumbs that are left over form the lesser planets.   Jupiter and its cloud of satellites are often called a mini-solar system, with good reason.

One of the main questions that Juno will attempt to answer is, exactly what is Jupiter?  Is there a solid planet down there, or is it just a globe of gas?  You will sometimes hear TV science programs saying that Jupiter has no solid body at its core, but the truth is, we just don’t know.  Understanding that will tell us how the planet formed in the first place.

In its most basic form, the question we’re asking is this: did a rocky core form first, and then attract the rest of the matter around it to form the planet, or did an unstable region of the solar nebula collapse and trigger the planet’s formation?  In the first case, the rocky core should still be there.  In the second case, there will only be gas all the way through, and while it will be extremely compressed at the center of the planet, there will be no rocky core there.

And that’s only one of the topics Juno will be investigating.  In the old myth, Jupiter made a cloud around himself to hide his misdeeds, but Juno was able to pull it aside and see within.  Hopefully, the analogy will prove to be appropriate.

(Just a few days ago, NASA made an announcement that points out our lack of understanding of Jupiter and its atmosphere: one of the iconic stripes has disappeared from the lower hemisphere of the planet.  Scientists confess that they are completely baffled by this event.  When Juno gets there, perhaps it can suggest an explanation of how a feature that has “always” been there can suddenly disappear.)

The Juno probe will be launched in August, 2011, aboard an Atlas V-551 rocket from Cape Canaveral.  The journey will take about five years, with the craft arriving at Jupiter in July of 2016.  The projected mission time (which may be changed, as we know) is one Earth year.  During that time, Juno will orbit Jupiter 32 times in a highly elliptical orbit that will bring it to within 3,000 miles of the planet at closest approach.

The specific goals of the Juno mission are:

1. Measure the amount of water in Jupiter’s atmosphere, which will help us figure out which theory of planetary formation is right, or if we need new theories.

2. Conduct in-depth study of Jupiter’s atmosphere, measuring composition, temperature, cloud motion, etc.

3. Make the first map of Jupiter’s gravity and magnetic fields, which should reveal the planet’s internal structure.

4. Specifically investigate Jupiter’s magnetosphere near the north and south poles, where enormous auroras occur that will hopefully give us new insights into how the planet’s magnetic field interacts with its atmosphere.

Like NASA’s previous Pioneer probes, Juno will spin on its axis to ensure stability and make aiming the craft easier.  Immediately after launch, Juno will be spun up by the rocket motors of its second-stage booster, to which it will still be attached.  When it enters Jupiter orbit, the spinning satellite will sweep space with its instruments once in each rotation.  At three rotations per minute, this means that Juno’s instruments will sweep Jupiter 400 times in the two hours it takes the craft to circle from pole to pole.

Juno will be the first solar-powered satellite made to operate so far from the sun.  Since Jupiter receives 25 times less sunlight than Earth, Juno will need three extra-large solar panels to provide sufficient energy.  These panels will be folded flat against the sides of the probe during launch.  When deployed, they will extend outward from the hexagonal body, giving the craft a span of more than 20 meters.

Thanks to recent technological advances in the field of solar power, Juno’s panels will be 50 percent more efficient and radiation tolerant than solar panels that were used just 20 years ago.  The mission needs only small amounts of electricity, since it will only be in use for about six hours out of each 11-day orbit of Jupiter.  (Juno will be in a highly elliptical orbit, and will only be observing the planet during its closest approach.)  Once it is in its working orbit, Juno will be in total sunlight for the duration of the mission; there will be no time when it is in Jupiter’s shadow.

There are zones of intense radiation around Jupiter which could easily fry the electronics of a space probe, so Juno will have all of its sensitive innards in a shielded vault. Juno is the first space probe to use such heavy shielding, and scientists will be watching carefully to see how well it works.  This line of research is relevant to future missions, since the harsh radiation of space is potentially harmful both to unmanned probes, and to the human crews that will eventually follow them.  To hedge its bets, Juno will try to avoid the worst areas of radiation by making its approaches to Jupiter over the planet’s north pole, dropping below the radiation belts, and then exiting over the south pole.

The smaller planets of the solar system have all seen extensive changes to their atmospheres during their lifetimes.  For instance, we now know that the atmospheres of both Mars and Venus were very different in their early days.  (See our articles on the Mars Express and Venus Express missions.)  But Jupiter, with its enormous gravity, has probably held onto all of the gas that it had at its formation. Planetary scientists will be very interested in studying the big planet’s atmosphere to see what it can tell us about the matter that was around in the solar system’s youth.  Juno will be able to observe that atmosphere in greater detail than ever before, seeing the global structure and motion of gases below the cloud tops for the first time, and mapping variations in the composition, temperature and patterns of motion down to unprecedented depths.

Jupiter has the brightest auroras in the solar system, and Juno will actually take samples of charged particles as it flies over the poles.  Its study of the auroras and the magnetic fields that produce them should increase our understanding of Jupiter and of all other powerful sources of magnetism, such as young stars with their own planetary systems.

So, those are some of the things that Juno will tell us about Jupiter.  This is really basic science, the kind of preliminary investigation that should pave the way for more complex enterprises in the future.  In fact, the mission overview at the NASA website points out that no new technology had to be invented for this mission.  It uses tried-and-true instruments that gather basic information- the kind of stuff that can tell us fundamental things about this giant planet, and about the beginnings of our solar system.

Juno will be launched in August of next year- and of course, you can read all about it here.

Sources:

“Juno: Unlocking Jupiter’s Mysteries” at the NASA website:  nasa.gov/mission_pages/juno/main/index.html

“Juno Mission Overview” at the NASA website:  nasa.gov/mission_pages/juno/overview/index.html

“Juno: Spacecraft and Instruments” at the NASA website: nasa.gov/mission_pages/juno/spacecraft/index.html

“Juno Mission News: Juno Taking Shape in Denver” at the NASA website:

nasa.gov/mission_pages/juno/news/juno20100405.html

For old folks who grew up reading science fiction, this is a wonderful time to be alive. So many of our old dreams are coming true, and others are at least looking more likely than they once did. When reading about the advances of space science in recent years, there is sometimes an odd sense of pride, knowing that we dreamed the right dreams, way back then. Every great advancement of the human race is preceded by mighty dreams, and ours were mighty, indeed.

One of the perennial dreams of old-time science fiction writers was the waterworld, a world completely or mostly covered with water. This type of world was the setting for countless sci-fi stories. Some writers, looking at cloudy Venus, mistakenly thought that this was a waterworld, while others put their hypothetical planet in another system. The waterworld setting allowed the author to pursue a fascinating idea: what if intelligent lifeforms evolved from aquatic organisms rather than from land animals? Many of these old stories were populated by fish people and such.

Well, the fish people may be out there, waiting for us. In 2003, the European Space Agency held a conference called, “Towards Other Earths,” which was attended by more than 200 experts in the budding science of extrasolar planet detection. At this conference, Alain Leger of France’s Institut d’Astrophysique Spatiale presented a report describing a new class of planet that may be awaiting detection. That’s right: it was our old friend, the waterworld.

According to Leger and his research team, such a planet would have roughly six times the mass of Earth, in a sphere twice as wide as our planet. It would have an atmosphere and orbit its primary star at about one AU- the same distance as Earth from the sun. The planet’s entire surface would be covered with liquid water to a depth of about 100 km., 25 times as deep as any of Earth’s oceans.

Recent discoveries right here in the Solar System have shown us that such a body definitely can form. We now know that we have at least two waterworlds in our neighborhood: Uranus and Neptune. Of course, they’re both so far from the sun that the water is frozen, making them iceworlds. But we also now know that planets can migrate closer to their primary stars over billions of years, so a body that formed in the outer reaches of a system can end up much closer to its primary.

We know this, because we have found several examples. Over the last few years, planetary scientists have detected a number of “hot Jupiters” orbiting other stars. They are often even bigger than Jupiter, and orbit their suns more closely than Mercury does. Now, the current science of planetary formation holds that such bodies do not form so close to their suns. Big planets like that form far out in a system, where water can’t exist in liquid form. This is where they start their long migration inward, caused by gravitational interaction with the accretion disc of dust and gas that surrounds their sun.

At some point in the planet’s inward spiral, the ice melts and our iceworld becomes a waterworld. To make the dream a little more pleasant, let’s say that our hypothetical world goes inward just far enough to have a nice, balmy climate, sort of like Hawaii without the islands. Since this migration is happening very gradually over billions of years, there might be a long period where the planet has a climate suitable for the evolution of life-as-we-know-it. In fact, the time might be long enough for life to develop to a considerable degree of complexity. We’re talking fish people!

There is an interesting variation on the waterworld which may exist closer to home. There is mounting evidence that some of the moons of Jupiter and Saturn, including Enceladus, Callisto and Europa, have internal oceans covered with thick layers of ice. This was a surprise, as these bodies are so far from the sun that any water should be frozen- but nature is full of surprises, isn’t it? While future probes will give us confirmation and more details, it now seems that these worlds offer much more opportunity for life than we once thought. Who knows, the fish people may be closer than we think.

Granted, that’s a longshot, but eventually we may encounter many of these planets, and at least some of them may have life. However, this is not a certainty, since these worlds will probably lack a feature that figured prominently in the origin of life on Earth: hydrothermal vents.

Hydrothermal vents, sometimes called “black smokers,” are openings on the ocean floor that are constantly pouring out vast amounts of hot gas and minerals from deep beneath the Earth’s surface. Here on Earth, such formations have proven to be zones of intense biological activity, with a profusion of lifeforms fed by the energy and minerals of the vent. One theory of the origin of life on this planet is that it started at these vents and spread outward from there. But according to the report presented by Alain Leger and his colleagues, hydrothermal vents would not exist on their hypothetical waterworld.

Remember what we’ve got here: a planet that formed originally as an iceworld, then migrated inward and melted. But when it was at a distance from its star that would allow Earthlike temperatures near its surface, all of the ice would not have melted yet. While a layer of liquid water would cover the surface to a depth of about 100 km., there would still be a thick layer of ice below that, and at the center of that would be the planet’s core. That core would be molten- but all that ice on top of it would effectively cap any volcanic vents, sealing in their heat. Of course, if the planet continued its journey inward toward its star, it would eventually reach a point where all of the ice would melt and the volcanic material would come gushing out, but by that time, the surface would be too hot for the kind of life we’re familiar with. So our balmy world with its Hawaii-like climate probably would not have hydrothermal vents; they would still be buried under many kilometers of ice.

Supposing that these vents were the source of life on the primordial Earth, we are left with the question, would life evolve on a planet that doesn’t have them? We don’t know the answer to this, but scientists are hoping that when they find such a planet, life will have taken the more obvious route: evolving on or near the water’s surface and using the planet’s sun for its energy source.

If humans decided to colonize a waterworld, they would have to live in floating communities. The very idea of living on the frozen ocean floor would be preposterous- imagine the pressure of 100 km. of water! We can envision colonies like enormous buoys, tethered by cables to the distant ocean floor. Or perhaps nature will provide convenient platforms in the form of floating plants. The “lily pad” shape has been quite successful on Earth; maybe our planet will have something like that, only bigger. Our colonists could built their settlement on top, and as long as they didn’t cover up too much of the plant’s sunlight-gathering surface, they would be fine.

Living on a world without dry land would, of course, require some new, outside-the-box technology. Obtaining metals on such a planet would be extremely difficult, since a thick layer of ice would cover the rocky core. Mining operations would have to drill through it to get to any metals underneath- a stupendous challenge. Rather than going through all that, our colonists might be able to find a convenient, metal-rich asteroid that they could move into orbit around the planet and mine.

All this is assuming that our colonists come fully prepared. As we unfortunately know, space missions can sometimes go catastrophically wrong. Equipment fails, and crashes happen occasionally. If we imagine a scenario in which colonists crash-landed on a waterworld with only minimal equipment, the challenges would be formidable. Even if nature had provided them with those giant lily pads, these people would have a rough time. Since one of the very few hard substances in their world would be human bone, it is probable that the bones of the dead would be recycled to make tools. We can picture a case in which Granddaddy’s leg bone gets made into a harpoon, then gets passed down the generations as a family heirloom.

(While it is not the purpose of this article to offer book reviews, it should be noted that the novel The Blue World, by noted science fiction writer Jack Vance, is an excellent treatment of some of the ideas expressed here, especially those in the last paragraph.)

We will find waterworlds, sooner or later. Sooner is a distinct possibility; we are reaching the point where our space telescopes could find such a body orbiting another star. The COROT satellite, a collaboration between the ESA and France’s CNES, is sensitive enough to spot a body that small, and determining how much water is on its surface. (See our article on COROT from a few weeks ago.) The discovery of our first waterworlds could be right around the corner.

And what about those fish people? Well, they may sound pretty far-fetched now, but when you consider that our species evolved from a tiny, shrewlike ancestor with a brain smaller than a marble, the idea of fish evolving into intelligent, technological lifeforms sounds quite believable.

Maybe we’ll meet them someday!

Sources:
ESA Space Science: “Searching for the Real Waterworld” at website of the European Space Agency: http://www.esa.int/esaSC/SEMR96XO4HD_index_0.html

ESA Space Science: “How Do ‘Waterworlds’ Form?” at website of the European Space Agency: http://www.esa.int/esaMI/COROT/SEMYM6XO4HD_0.html

NASA News & Features: “Water World? New Discovery Heats Up Search for Life” at the NASA website: http://www.nasa.gov/vision/universe/newworlds/EnceladusWorld.html

Some of the invaders are already there; others are in the planning stages. One project which is currently being planned, and which will hopefully be launched next year, is the ExoMars mission. This is a project of the European Space Agency, with contributions by NASA. Its purpose is to subject Martian soil and rocks to the most precise and detailed tests yet, in an attempt to discover if they contain the chemical signatures of past or present life. ExoMars will involve both an orbiter and a lander, with the most sophisticated and sensitive detection devices ever sent to Mars. If there is anything alive there, or if there ever was, this is the device that could find it.

The search for life on Mars has had its ups and downs. When the Viking landers arrived in 1976, the samples of Martian soil that they collected showed none of the chemical traces that would be left by life. At that point, all of the planetary scientists on Earth let out a collective groan: Mars was a dead planet! For some years these results stood, leading to the prevailing opinion that Mars did not have life now, and probably never had it.

However, the Viking results, and their interpretation, have come under criticism in the intervening years. For one thing, Viking contained three separate tests for signs of life, and while two of them gave negative results, the third one, called the Labeled-Release Experiment, gave ambiguous results that might be indicative of life. Scientists have never gotten very excited about this, because there is a high probability that the results were produced by natural chemical processes unrelated to life- but the fact remains that the three instruments did not produce uniformly negative results. Until further investigations are conducted, it is impossible to say with absolute certainty that Mars is a dead world, and always has been.

When contemplating the Viking results, these objections have also been raised:

Maybe the instruments on the Viking landers just weren’t sensitive enough to pick up faint traces of biological chemicals in the Martian soil. Since then, new devices have been developed which can detect chemicals in amounts of only a few atoms. If instruments like that were used on Mars, the results might be different.

Perhaps the Viking samples just weren’t taken in the right place. There are certain extreme environments on Earth- the Atacama Desert in Chile, for instance- where soil samples might yield the same results, but that doesn’t mean that Earth is a dead planet.

Another interesting point is that since Viking, we have learned that life is more versatile than we used to think. Extremophile organisms have turned up in places on Earth that are at least as hostile as the environment of Mars. They have been found in places of extreme heat and cold, in permanent darkness, and in chemical environments that would kill most other life. They have even been found encased in rock, where they apparently live by metabolizing the very rock itself. If life can exist in those places, why not on Mars?

A third point, which could invalidate the Viking results, is that even if the chemical signatures of life are not detectable on the surface of Mars, they might be found just underground. Maybe they were present on the surface at one time, but have since been broken down by the harsh UV radiation of the sun, or by oxidation. In that case, they might not be detectable unless you take a sample from underground, or from the inside of rocks.

ExoMars will attempt to address these issues. The lander will be equipped with a drill that can penetrate up to two meters of soil or rock. Samples from that deep should be safe from the both the sun’s UV rays and the effects of oxidation.

The drill is actually three devices in one: a drill, a sample collector and an infrared spectrometer. Once it drills below the Martian surface, it can actually perform spectroscopic analysis within the bore hole. If it spots something that looks interesting, there is a chamber within the drill shaft with an internal shutter which can be used to get a sample.

However, once the sample is taken, the next challenge is to figure out what we’ve got. One problem in identifying primitive organisms, even on Earth, is that they are so simple that their remains can be mistaken for non-living mineral precipitates. Because of this, a visual examination, even on a microscopic level, probably will not be enough to be conclusive. In fact, given the extreme importance of this evaluation, it is likely that no single piece of evidence will be enough to convince all scientists. Therefore, the ExoMars lander will employ several different lines of investigation in determining if a sample contains evidence of life,
including geological and environmental investigations to evaluate possible habitats, visual examination of samples (morphology) and spectrochemical composition analyses.

One of the indicators of life that ExoMars will look for is homochirality. This is based on the fact that two of the main chemicals involved in making life, amino acids and sugars, can exist in left- and right-handed forms which are mirror images of each other. Amino acids and sugars can be created by non-living processes, but when that happens, the resulting substances are split evenly between the two forms. However, living organisms on Earth all use one form or the other- left-handed for amino acids and right-handed for sugars. This is necessary so that the molecules can fit into the biochemical mechanisms of living organisms. If an amino acid or a sugar is of the wrong form, it won’t fit, and the organism can’t use it.

So, if ExoMars finds amino acids or sugars on Mars, and the chirality is evenly split between right-handed and left-handed forms, we will know that the chemicals were made by some non-living chemical process. But if samples are found which have sugar or amino acids that are all left- or right-handed, it will be a conclusive sign that the chemicals were created by biological processes.

To conduct these chemical studies, ExoMars will use an instrument called the Urey Mars Organic and Oxidant Detector (named for Dr. Harold Urey, biochemist at the University of Chicago). This device uses several flat surfaces coated with chemical films, which are attached to each other to form a box. When a sample is placed in the box, the degree of reaction on each surface will be monitored, and this will tell us if there are any biochemicals present.

Besides the basic search for biochemicals, ExoMars will also be trying to spot potential problems for future human explorers. For instance, are there corrosive substances on Mars that could degrade equipment, or cause health hazards for humans? And what about the Martian dust? When astronauts went to the moon, the moondust got into everything, even in places that were supposedly sealed airtight. If that’s going to happen on Mars, we need to know about it ahead of time, and take measures to prevent it.

ExoMars is a big step forward in our journey to the red planet. It will tell us what Mars used to be like, and it may even find the signs of life, past or present. It will also tell us what we can expect there, and what we will have to do to survive. ExoMars and its mechanical brethren are paving the way for us, and the information it obtains may be crucial in the survival and prosperity of future colonies.

In addition to that, ExoMars is looking back into the past of Mars. It is now well established that Mars looked a lot more like Earth at one time: there were large bodies of liquid water, and that means that the air pressure was much higher than it is today. We can’t help but wonder: just how similar was it? Was there life, and did it look like us?

The answers are waiting on the red planet, and ExoMars is going to help us find them.

Sources:
NASA Science Missions: ExoMars Urey Instrument at the NASA website: science.nasa.gov/missions/exomars/

Mars Oxidant Instrument at the NASA website: nasa.gov/centers/ames/multimedia/images/2007/moi.html

“Sensor Being Developed to Check for Life on Mars” at the NASA website: nasa.gov/centers/ames/research/2007/mars_sensor.html

ESA Aurora Program: ExoMars at the webiste of the European Space Agency: esa.int/esaMI/Aurora/SEM1NVZKQAD_0.html

“ExoMars: Searching for Life on the Red Planet” (information packet downloaded from ESA website)

The idea of putting a telescope in space, above the blurring effects of Earth’s atmosphere, was first proposed in 1923 by Hermann Oberth, one of the pioneers of rocketry. Unfortunately, Oberth was one of those true visionaries whose imagination far outpaces the technology of his age, and the idea was ignored at the time- but in 1946, Lyman Spitzer, an American astrophysicist, wrote a paper proposing the same thing.

Spitzer became a crusader for his idea. Over the coming decades, his quiet advocacy was the main force behind a whole generation of orbital observatories, including the Copernicus Observatory and the Orbiting Astronomical Observatory. It was his authoritative voice that spurred NASA to approve the Large Space Telescope project in 1969. Unfortunately, Spitzer’s original proposal got downsized due to budget problems, and took some years to get off the ground. (Another bad pun!)

In 1974, the planning group for the project made a modification to the original idea: the satellite would carry not just one telescope, but a number of instruments which could be removed and changed. When new devices were developed, they could be added onto the existing structure, so the satellite would not become obsolete when new technology was invented.

In 1975, NASA and the European Space Agency began a collaborative effort that would eventually become the Hubble Space Telescope. Congress approved funds for the project in 1977.

NASA first planned to launch the telescope in 1983, but as often happens in space science, there were delays. The entire optical assembly was not put together until 1984, and the whole spacecraft was not assembled until 1985. However, 1983 did have one important event: that was the year when the name of the device officially became the Hubble Space Telescope, in honor of Edwin Hubble, the imminent American astronomer.

The revised launch date was in October, 1986- but then disaster struck. The space shuttle Challenger exploded just one minute into its flight, and all shuttle flights were cancelled for the indefinite future. Since Hubble was supposed to be launched from the shuttle, nobody knew when or if it would go up.

Years passed; shuttle flights were eventually continued. Planning for the Hubble telescope was resumed.

All the planning finally came to fruition in 1990. There was quite a bit of hype preceding the launch; in a world where astronomy rarely gets the front page, Hubble was as famous as a rock star. Particular attention was given to the big mirror that would focus light onto the light-sensing elements, which was praised as a masterpiece of precision workmanship.

Unfortunately, this mirror did not live up to its image (still another low-flying pun!) Due to a manufacturing error, one edge of it was off by about one-fiftieth of the width of a human hair. In astronomy, that’s enough. Some science could still be done, but the faulty mirror severely compromised the quality of the images, and parts of the mission would have to be canceled.

Somebody should write a book about the valiant and almost superhuman efforts of ground crews in correcting or compensating for problems with spacecraft. On many occasions, missions that seemed to be hopelessly doomed have been resurrected and successfully completed, because the folks on the ground just refused to give up. This was one of those occasions.

Hubble was scheduled to get its first servicing mission in 1993. Rushing to meet this deadline, engineers designed a device to fix the optical problem. The system was called the Corrective Optics Space Telescope Axial Replacement, or COSTAR.

In December of that year, COSTAR went into space. Working in two teams, the astronauts performed a record of five back-to-back spacewalks, during which COSTAR was installed and the Wide Field/Planetary Camera was replaced with an improved unit. In addition, there were routine maintenance jobs to be done, such as putting in new solar arrays and replacing four of the satellite’s gyroscopes.

The fix worked. After that, Hubble started sending back sharper images, and NASA (possibly in an attempt to salvage its damaged image) released reams of them to the press. One of the earliest and most popular was the gorgeous picture of the star-forming region in the Orion nebula, which ended up on countless calendars, posters, screen savers, etc. After that, there were many others: stars like diamond dust set against swirls and streamers of nebular gas, so detailed and delicate that it could have been painted.

Some of us had always known that space was beautiful, but now the whole world knew it.

The pictures are famous now; some of the best ones have been compiled into a gallery at the NASA website, which is certainly worth a look. But as nice as they are, pictures aren’t everything. This was supposed to be a science mission, and while the folks who make calendars, posters and screen savers must have been grateful for the new material, that really wasn’t the point of all this. 20 years on, we can now ask: just what have we learned from Hubble?

In reading over the history of Hubble at the NASA site, a few highlights stood out. Here are a few of them:

1. Observing the evolution of accretion discs around stars. The current theory of planet formation says that it all starts with the accumulation of a cloud of gas. The gas gets denser and denser, especially at its center, which finally gets so compressed that the atoms start to fuse. When that happens, light, heat and other products are emitted, and the result is a star at the center of this condensing gas cloud. Because of the increasing gravity, the rest of the gas begins to spin, just as water spins when it goes down the drain of a bathtub. The spin makes the cloud of gas get flat and disc-shaped, which causes it to be more concentrated. This concentration makes the gas molecules collide with each other and begin to form dust grains, which will eventually clump together to form planets. In observing other stars, astronomers would expect to find discs in various stages of evolution, and Hubble has done that. In January of 2005, NASA scientists announced that Hubble had found several stars with dust discs, and that some of these discs have a flared, thick edge, while others don’t. This shape was expected from computer simulations. The scientists think that the stars with the thick edges are in the early stages, and probably have not formed planets. It is thought that all of the other stars originally had flared edges, too, but the dust that was in them has already formed planets. While this theory of planet formation has been around for some time, this was the first time that “before and after” pictures have been taken of actual stars going through the process.

2. Observing the seasons of Pluto. In February 2010, NASA released pictures of Pluto taken by Hubble. These are our most detailed pictures of that body ever taken, and they show Pluto changing colors over a period of time. During the period of observation (2000 to 2002), Pluto became significantly redder, while the northern hemisphere got brighter. It is thought that the color change is the result of surface ices evaporating over one pole and then refreezing over the other pole, as Pluto starts the next phase of its year, which lasts for 248 Earth years. Just taking these shots was a challenge, since the resolution necessary is comparable to that needed to read the brand name on a soccer ball 40 miles away.

3. Imaging of cross-shaped “comet-like object”. This one has both scientific value and visual appeal. It is a picture of a structure shaped like a cross, with trails swept back by the solar wind. NASA scientists think this is the remnant of a recent collision between two asteroids. The lines of the cross are trails left by the two objects, and the long trails behind the object are particles of debris from the impact. It was an amazing stroke of luck to catch the object right after such an impact, and we may never see another one. The picture is stunning. It’s a safe bet that this one will end up hanging on a few walls, too.

4. First detection of organic molecules on a planet orbiting another star. Last but not least, this one has enormous implications for future space exploration. If nature is going to create life, it has to have the right ingredients. While it is possible to imagine exotic forms of life with bizarre chemistries, the only kinds of life that we know are made from what we call organic molecules. If we can find planets with organic molecules, there is a chance we may be able to find lifeforms there. Until recently this was just theoretical, but in March of 2008, Hubble detected the organic molecule methane in the atmosphere of a Jupiter-size planet in the constellation Vulpecula, some 63 lightyears from here. While this planet is too hot for the kind of chemical reactions that would create life, just finding an organic molecule on another planet is a big step.

The list goes on, and Hubble isn’t done yet. In May of 2009, astronauts made a repair mission to Hubble, refurbishing it for further duty. Now it’s sending back lots of wonderful pictures again, and hopefully will continue to do so for years to come. At 20 years and counting, it is certainly one of the most successful missions in the history of space exploration- and we haven’t seen the last from it yet.

Sources:

“Hubble Space Telescope History” at aerospaceguide.net: aerospaceguide.net/spacehistory/hubble-history.html

“Hubblesite: Hubble Discoveries” at the NASA website: hubblesite.org/hubble_discoveries/

Feature: “Hubble Finds MIssing Link in Planet Formation” at NASA website: nasa.gov/vision/universe/newworlds/0112_missing_link.html

“20 Years of Hubble: Hubble Finds First Organic Molecule on an Exoplanet” at NASA website: nasa.gov/mission_pages/hubble/science/hst_img_20080319.html

“20 Years of Hubble: New Hubble Maps of Pluto Show Surface Changes” at NASA website: nasa.gov/mission_pages/hubble/science/pluto-20100204.html

“20 Years of Hubble: Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris” at NASA website: nasa.gov/mission_pages/hubble/science/asteroid-20100202.html

This is an exciting time.  As we have seen in previous articles, there are a lot of fascinating projects going on right now, with robot probes exploring places in the solar system and beyond.  Places that used to be just names in textbooks are now real places to us, and we are learning more about them all the time.

However, it should never be forgotten that the exploration of the mysterious third planet on which we live can be just as interesting, and of even more vital importance.  To help us understand more, there is now a legion of satellites orbiting Earth to study various aspects of its environment.  Many of these are assessing the consequences of environmental tampering by humans, and finding that those consequences are proceeding at a faster pace than was originally thought.

In assessing the consequences of global warming, one of the indicators that is available to us is the Earth’s ice.  We already know that ice in the polar regions is shrinking to levels unknown in recorded history.  Ships can now sail through places that were completely blocked by ice only a few years ago, but this is only anecdotal evidence, and does not tell us how fast the problem is moving or how far it has already gone.  Before 2000, it was thought that the interiors of the major ice sheets were largely stable.  This was based on data gained by satellite altimetry, but the capability of those satellites to measure change at the margins of ice caps, where most of the change was occurring, was limited by their design. By 2006, new information was emerging which was causing scientists to doubt the stability of the ice caps.  In that year, analysis of radar readings of the Pine Island Glacier in Western Antarctica showed a definite thinning of the ice layer. Data from other satellites, such as ESA’s Envisat, mapped the Earth’s ice and found that annual average Arctic sea ice extent had shrunk by 2.8% per decade since 1978.

But even with that information, we still don’t have the full picture.  To get that, it’s necessary to measure the thickness of the ice.  That’s the only way to get an accurate estimate of the amount of ice that is left, and how quickly it is retreating.

To address this need, CryoSat-2 was designed as part of Earth Explorer, a larger project which addresses key questions regarding the natural processes of our planet, and in some cases, how they are changing in response to the stresses placed on them by human activity.

CryoSat was originally intended to be the first of these probes, not the last.  In one of those terrible disappointments that occasionally happen in space exploration, the first version of CryoSat was lost due to launch failure in October 2005.  The ESA immediately started planning for a relaunch.  Cryosat-2 took four years of preparation, and during that time, the other phases of the Earth Explorer Series proceeded as planned.  While CryoSat was being rebuilt, the GOCE gravity mission and the SMOS water mission were launched successfully, and when CryoSat-2 went up today, it completed the series that it was supposed to start.

Cryosat-2 carries technology to measure changes in two types of ice: the huge sheets covering Greenland and Antarctica, and floating ice in the oceans.  The satellite will travel in a highly inclined polar orbit which will reach 88 degrees latitude north and south, to get maximum coverage of the poles.  Its main instrument is the Synthetic Aperture Interferometer Radar Altimeter (SIRAL).  Radar altimeters used in the past have been designed for use over ocean or land, but SIRAL is the first one to be specifically made for use on ice.

SIRAL has a higher resolution than earlier radar altimeters.  Whereas conventional radar altimeters send out radar pulses that are, on average, 500 microseconds apart, SIRAL send its pulses at intervals of only 50 microseconds.  The onboard data processor can separate the echo into strips which are about 250 m. wide.  Since the interval between bursts is arranged so that the satellite moves forward by 250 m. each time, the strips laid down by successive bursts can be superimposed on each other and averaged to reduce noise.   This is known as the SAR (Synthetic Aperture Radar) mode.

In order to get accurate readings, it is necessary to pinpoint the position of the satellite with great precision.  To accomplish this, CryoSat-2 uses the DORIS (Doppler Orbit and Radio Positioning Integration by Satellite) system.  The satellite’s radio receiver measures the Doppler shift of signals from a network of more than 50 radio transmitters around the globe.  The true accuracy of the reading can only be obtained by processing on the ground, but the raw data provides a usable estimate, good to about half a meter.  The DORIS network has been in use for more than ten years, and has been used for various satellites, including ESA’s Envisat.

This locates the satellite itself, but in addition to this, it is necessary to determine the precise orientation of the baseline of the two antennas that receive the signal.  To obtain this baseline, CryoSat-2 uses the sailor’s old friends, the stars in the sky.  There are three startrackers on the antenna support structure, and each of them takes five pictures per second.  The onboard computer compares the images to a catalogue of star positions.  The orientation of the baseline of the receiving antennas is determined using this positioning data.

Unlike many other Earth-orbiting satellites, CryoSat-2 does not have a sun-synchronous orbit- in other words, it does not orbit in such a way as to receive sunlight all the time.  Instead, the satellite’s path is such that there will be times when Earth is between it and the sun.  This presented some design challenges, as the satellite will regularly be subjected to extreme temperature shifts.  Because of this, it was necessary to insulate the precise instrumentation to maintain optimal operating temperature.

Except for a few valves in the propulsion system, CryoSat-2 has no moving parts at all.  Even the solar panels, rather than being deployable as in most other satellites, are rigidly fixed to the body of the craft, forming the “roof” of the structure.  The lack of moving parts allowed a significant cost savings in the satellite’s manufacture.

Knowledge is our best weapon in the fight against the long-term consequences of global warming.  It is a sad truth that we gained the ability to destroy our world before we learned how to fully assess the damage, so the process went on for years before we realized it.  Now we are in the uncomfortable position of having to measure just how far the process has progressed, and what, if anything, we can do about it.  CryoSat-2 is a new tool for that measurement, and from it, we will gain a new understanding of our planet and its processes.  If we could see the history books of tomorrow, how would they speak of this project, and the other Earth-sensing projects that are going on now?  Will they see this as the beginning of recovery, or just a futile assessment of our hopelessness?  Perhaps these measures will only provide us with a precise gauge of the inevitable end, or perhaps not.  Much environmental damage has already been done, and will not be corrected soon- but the knowledge we gain from CryoSat-2 may help us to lessen the impact, at least.

And it will give us a lot of interesting things to ponder, too.  From it, we may pry a few more secrets from this world on which we have always lived, but which we still do not know very well.  In that sense, this is another fascinating, alien planet to explore, because the things we are learning now are totally new.  It’s all part of our growing knowledge of the mysterious third planet.

Sources:

“Successful Launch for ESA’s CryoSat-2 Ice Satellite” at website of the European Space Agency:  esa.int/esaCP/SEMH5ZZNK7G_index_0.html

“ESA CryoSat: an Earth Explorer” at website of the European Space Agency: esa.int/SPECIALS/Cryosat/SEMHSTOJH4G_0.html

“ESA CryoSat: an Icy Mission” at website of the European Space Agency:  esa.int/SPECIALS/Cryosat/SEMFJ4908BE_0.html

“ESA CryoSat: Earth’s Changing Ice” at website of the European Space Agency:  http://www.esa.int/SPECIALS/Cryosat/SEMQK4908BE_0.html

“ESA CryoSat: Platform” at website of the European Space Agency:  esa.int/SPECIALS/Cryosat/SEMFN4908BE_0.html

“ESA CryoSat: the Instruments” at website of the European Space Agency:  esa.int/SPECIALS/Cryosat/SEMRQ4908BE_0.html

In one of our earlier articles, still posted here, we took a look at the European Space Agency’s Venus Express probe, which is already in orbit around Venus.  These two projects are not redundant, nor are they in competition with each other.  The projects have been in close communication with each other since their beginning phases, and have been planned to complement each other in the construction of the most complete picture possible of the Venusian environment.  In some cases, the two Venus probes will work together on composite science projects, while in other cases, they will be doing separate work of a complementary nature.

The Venus Climate Orbiter, also called Akatsuki, will weigh 480 kg. with fuel, and will carry a science payload of 34 kg.  Basically, it will be a rectangular box with “paddle wheel” solar panels extending on either side.  There will be small thrusters at all eight of the corners for minor attitude adjustments, and a larger engine for orbital maneuvering in the rear of the unit.  There will be five instruments onboard, taking observations at different wavelengths to obtain various types of information.

Departing from Earth in May of this year, Akatsuki will first deploy all of its secondary payloads.  These include some experiments proposed by prominent Japanese universities relating to information encoding and transmission, observation of the Earth’s atmosphere for meteorological purposes, and the testing of computer technology for space use.  The last of the secondary payloads to be deployed will be the IKAROS lightsail, an exciting experiment to test the use of the pressure of sunlight to propel a spacecraft.  (See our article on lightsails at this site.)  On the journey to Venus, Akatsuki use the travel time to perform various astronomical observations and to study the interplanetary dust cloud.

Akatsuki will arrive at Venus in December 2010 and settle into a long, elliptical orbit near the planet’s equatorial plane.  This will be a 30-hour orbit in a westward direction.  The apoapsis (farthest point from the primary) will be 79,000 km., and the periapsis (nearest point to the primary) will be 300 km.  Global images of the atmosphere and the ground surface will be taken every two hours continuously.  Because of its stretched-out orbit, the probe will be making close-up observations of mid-scale features at periapsis, and more long-range observations at apoapsis.  It will take advantage of periods when it is in the planet’s shadow to make low-light studies of phenomena such as lightning and air-glow.  (Lightning has never been observed on Venus, and there is some question as to whether it even exists there at all.  Scientists will be eagerly waiting to see if Akatsuki spots any.)

Akatsuki is being called an “interplanetary meteorology” mission, because its main function is to peer deep into Venus’ murky cloud cover and obtain 3-D images of the phenomena happening there.  It is hoped that the probe will be able to see the different layers of the atmosphere, how they are moving, and how they interact with each other and with the planet’s surface.

The whole purpose is to try and understand the amazing movement of the Venusian atmosphere.  As we saw in our article on the European Space Agency’s Venus Express probe, the big mystery about this planet that has emerged in recent years is that the entire atmosphere is racing around the globe in a planet-wide gale that moves at 60 times the rate of the planet’s rotation.  If you were unlucky enough to be standing on the surface of Venus, you would literally be knocked flat by a non-stop wind of 100 meters per second.  This is called “super-rotation,” and it is a complete mystery.  There is nothing in our Terrestrial meteorology to explain such rapid motion of an entire planet’s atmosphere.  Where is all that energy coming from?  Granted, Venus is close to the sun and has an average temperature of 460 degrees C both day and night, but even that isn’t enough to explain this amazing movement of air.

In some ways, Venus and Earth are very similar.  They are small, rocky planets with roughly the same mass, and it makes sense to think that they should be fairly similar.  The weird thing is, they’re not.  These two planets have taken very different paths in their evolution, and ended up in very different states.  In contrast to our own pleasant world, Venus is a pressure-cooker with a carbon dioxide atmosphere of enormous density.  And now we learn about this super-rotation, and the mystery deepens.  We certainly don’t have anything like that here at home.  How did these two planets, which probably started out as very similar little pebbles in the beginning, end up so completely different?

And as we saw in our Venus Express article, there is another factor that makes the whole thing even more intriguing.  There now seems to be convincing evidence that there are continent-size masses of granite on Venus.  Granite only forms in the presence of water, but due to the heat and pressure, liquid water can’t even exist on Venus today.   If there’s so much granite on Venus, there must have been an awful lot of water there at one time, and that implies a different environment from what we see now.   It must have been an environment with much lower air pressure and much lower temperatures- a planet more like Earth, in fact.

Just how much like Earth?  We don’t know yet, but it is that central question, and other questions connected to it, that will dominate Venusian research in the coming years.  And this thing with the super-rotation has to do with that, because it is very unlikely that this movement of the air was happening with such energy in the earlier, more Earth-like world we’re thinking of. When did it start, and why?  Why does it continue, with no obvious source of energy?  For that matter, why did the whole environment change from a world with water and granite continents into the oven-like place we see today?

Venus is turning out to be a big box of questions, and so far, we don’t have many answers.  However, there is an ominous note in all this: while there are many things we don’t know about Venus, we do know why it is so hot.  The cause of its 460-degree heat is runaway global warming caused by carbon dioxide buildup in the air.  This probably doesn’t result from the same source as our global warming here on Earth.  Since we have absolutely no evidence that Venus ever supported an industrial society, it is far more likely that its carbon dioxide buildup is the result of some natural process.  What process, we don’t know.  Could it happen here?  Of course it could- but will it?  We don’t know, but perhaps it would be prudent to find out.  When you think of it that way, this line of research suddenly becomes more than just an academic question.

If we imagine this ancient Venus, so different from the one we see today, we are tempted to think of a place very much like Earth: balmy islands with palm trees swaying in the breeze.  In all likelihood, this view only shows our provinciality, the fact that we only know one planet.  If there is anything that our study of Venus has already taught us, it is just how different two similar planets can be.  Whatever Venus was like in that long-ago age, it probably wasn’t just like Earth.

As for what it really was like, we will have to guess for the moment.  However, someday in the not-too-distant future, landers will descend to the surface of Venus and start taking samples of the soil and rocks.  At that point, we will finally begin to unravel the evolution of this planet.  If it turns out that those ancient oceans really did exist, perhaps we will find the fossilized remains of things that swam in them.

Between now and then, smaller revelations will be coming out, some of them perhaps in the near future.  When that happens, you can read about it here.

Sources:

Akatsuki Special Site at the website of the Japan Aerospace Exploration Agency:  jaxa.jp/countdown/f17/index_e.html

“JAXA Explores the Planets of the Solar System- Anticipating Amazing Discoveries” at the website of Japan Aerospace Exploration Agency:  jaxa.jp/article/special/explore/imamura02_e.html

“Satellites and Spacecraft- Venus Climate Orbiter ‘Akatsuki’” at website of the Japan Aerospace Exploration Agency:  jaxa.jp/projects/sat/planet_c/index_e.html

“Akatsuki- Planet C” at website of the Institute of Space and Astronautical Science:  isas.jaxa.jp/e/enterp/missions/planet-c/index.shtml

The COROT Space Telescope has been in orbit around Earth since 2006.  The satellite was launched by CNES with equipment contributed by other ESA members, and is only one of a growing array of satellites designed to find planets orbiting other stars.  So far, it has been highly successful, performing even better than expected and locating an interesting assortment of planets which will be studied for years to come.  COROT is also using a method of star study called asteroseismology, which was first employed  in the study of our own sun and is now being used to study others.

The detection of exoplanets has come a long way in a short time.  It’s hard to believe it’s only been 15 years since the first planets outside our solar system were found.  Since then, hundreds of new exoplanets have been spotted, most of them very different from the ones we are more familiar with.  In fact, it’s already time for the next step in this field, the use of new techniques and the development of new equipment that will greatly expand our planet-finding capabilities.  Already the equipment used for the early detections is looking antiquated, and is rapidly being outstripped by a new generation of devices and methods.  While the old techniques will still be used, they are becoming much more sensitive than they were in the beginning, allowing the detection of bodies that could not have been seen before, and giving us more detailed information about them.

As we saw in last week’s Kepler article, the early efforts to find planets orbiting other suns were hampered by the limitations of the technology available.  Early detections were made by using the wobble (radial velocity) method, which takes advantage of the fact that very large planets cause their primary stars to wobble as they orbit them.  This worked great for finding monster planets that orbit very close to their primaries, because they make the most pronounced wobble in the star.  Smaller planets like Earth could not be seen by this method, since they did not cause a big enough wobble to be detected.

Already this situation is changing, in two ways.  As we saw in the Kepler article, the wobble method is now being used in conjunction with the transit method, by which planets are found because of the dimming of the light of their primaries as they pass in front of them.  If a star is found that dims periodically, and the amount of dimming is the same every time, we can be sure that there’s a planet there, passing between us and the star.  This method allows the detection of smaller bodies, since it is not dependent on the mass of the planet.

The other way in which the situation is changing is that the wobble method is getting more precise and sensitive now.  In our earlier article, we asserted that in the early years of planet detection, it was impossible to see planets the size of Earth with this method, since they are not big enough to cause a perceptible wobble in their star.  That was true back then- but in doing the research for this article, we found that the wobble method is now becoming sensitive enough to pick up the movement of a star as an Earth-size planet moves around it.  We stand corrected; science is moving fast, and sometimes it’s hard to keep up.

These changes are now embodied in COROT and the program of which it is a part.  The new generation of exoplanet detection starts here.

COROT was launched onboard a Soyuz-Fregat rocket from the Baikonur cosmodrome in Kazakhstan on December 27, 2006, and entered a near-circular orbit which ranges from 537 to 544 miles above Earth’s surface.  Its method of observation was to point itself at a specific section of the sky and simply keep pointing at it for 150 days.  During this time, hopefully some of the stars in that section would experience a planetary transit, and COROT would detect them.  When that observation period was over, the satellite would turn itself toward another part of the sky and observe it for another 150 days.

As we said earlier, COROT actually has two scientific goals.  While it’s observing a star in search of that telltale dimming, it will also be conducting asteroseismological measurements of the star.  This is an exciting new area of research which promises to give us much knowledge about the inner workings of stars.  Here’s how it works:

The inside of a star is a turbulent place.  Matter there is subject to intense gravitational forces, Coriolis forces and pressure.  As these factors interact with each other, they cause the star to vibrate in a changing series of patterns, or modes.  While the forces that generate these vibrational modes may be happening deep inside the star, the vibrations reach all the way to its surface, and cause slight changes in the star’s brightness.  The frequency, amplitude and duration of these modes, as revealed by the changes in the light of the star, can tell us things about the star’s mass, age and chemical composition.

This technique provides us with a source of information on the inner workings of stars, and as we learn to read that information better, it promises to give us much data on stellar evolution.  For some years, the ESA’s Solar and Heliospheric Observatory (SOHO) has been using asteroseismology to study our own sun.  What we need to do now is conduct the same kind of study of other stars, to find out how typical our sun is, and to compile a catalogue of different vibrational signatures for a wide variety of stars.

COROT is starting this work.  Since it will be staring at the same stars for a long time, it will be able to observe the slight changes in brightness that are used for asteroseismology.  By mission’s end, it should have compiled a sizable catalog of stars’ vibrational signatures, which will actually begin the science of interstellar asteroseismology.

The COROT mission started off in a spectacular way.  Once in a while, you get one of those rare surprises, a piece of space equipment that actually performs better than expected.  Within 60 days of its deployment, COROT was sending back data of exceptional clarity and detail, amazing even its designers.  The first planet that it found, called COROT-Exo-1b, was a gas giant with about 1.78 times the radius of Jupiter, orbiting a yellow star similar to our own.  The unexpected accuracy of the data made scientists hopeful that it might be able to detect planets even smaller than they had thought.  While they had conservatively hoped that COROT would be able to see planets a few times bigger than Earth, these results showed that it should be able to see them all the way down to Earth-size or even smaller.

The asteroseismological part of the mission was also an immediate success.  While observing this star, COROT showed large variations in the light of the star over a time scale of several days, driven by magnetic activity deep within the star.  This information was of outstanding accuracy, with an error of only five parts in 100,000.  While the information will be studied for years to come, scientists can already say that this star is very similar to our own sun, both in its outward appearance and its asteroseismic characteristics.

So far, so good- but there is one drawback to the transit method of detecting planets.  Even if you find a star with a periodic pattern of dimming, you still can’t be sure there’s a planet there.  Some stars have a variable output, which causes a very similar dimming- so when you find a star that shows this kind of behavior, you can’t be sure you’ve hit paydirt unless you get corroboration by some other method.

The stars found by COROT are examined by ground-based telescopes, and this is where we see the new sensitivity of the wobble or radial transit method, because one of the ways of corroborating these findings is to look for the slight change in the star’s velocity that is caused by the orbiting of a small, rocky planet.  All stars move, of course.  They are all whirling around their galactic centers, and the galaxies themselves are moving in a vast, universe-size ballet.  This change of the star’s velocity that they’re talking about is really just another way of expressing the wobble: the alteration of the star’s movement caused by the gravity of an orbiting body.  That’s why they call it the radial velocity method (though even the NASA literature will often use the term “wobble method”).

COROT has found several more planets to date, including one which is almost as small as Earth.  It’s way too close to its star to have life like us, but it’s a big step in the right direction.  Someday soon, this telescope may find a tiny, wet pebble surrounded by a bubble of air- and when we look at it, maybe something similar to ourselves will be looking back at us.

Exoplanet detection is an exploding field, and new findings are constantly coming in.  Each telescope is more sensitive than the last, and we can now say with confidence that it is only a matter of time before we find Earth analogs orbiting other stars.  If that happens, you know we’ll tell you about it, right here.

Sources:

COROT: “COROT Team Announces the Detection of Smallest Exoplanet to Date” at website of the European Space Agency:  sci.esa.int/science-e/www/object/index.cfm?fobjectid=44131

ESA News: “COROT Surprises a Year After Launch” at website of the European Space Agency:  esa.int/esaCP/SEMF0C2MDAF_index_0.html

Ellison, Doug: The Planetary Society blog: “Europlanet: COROT- Preliminary Results” at the website of the Plantary Society:  planetary.org/blog/article/00001089/

Lakdawalla, Emily: The Planetary Society blog: “COROT Has Bagged Its First Planet” at website of the Planetary Society:  planetary.org/blog/article/00000960/

Planetary News: Extrasolar Planets (2007): “COROT Sees First Light” at website of the Planetary Society:  planetary.org/news/2007/0124_COROT_Sees_First_Light.html

Cowen, Ron: “The Hunt For Habitable Planets” in Science News magazine, December 20, 2008:  sciencenews.org/view/feature/id/39031/title/The_Hunt_for_Habitable_Planets

ESA Space Science: “COROT Objectives” at website of the European Space Agency: esa.int/SPECIALS/COROT/SEM20ZC4VUE_0.html

ESA Space Science: “COROT Overview” at website of the European Space Agency:  esa.int/esaSC/120372_index_0_m.html

“COROT Astronomy Mission: From Stars to Habitable Planets” at the website of the Centre National d’Etudes Spatiales:  smsc.cnes.fr/COROT/index.htm

In conducting these flybys, the ESA is working in cooperation with ROSCOSMOS, the Russian Federal Space Agency.  Russia is planning to place an unmanned lander on Phobos by 2012 to collect soil samples, and images taken on these flybys will be used to select the landing site.

It is hoped that all of this scrutiny will unlock the secret of this moon’s origin, which is a point of much speculation now.  There are three conflicting theories about this, which we will examine in more detail in a moment, and while the final verdict won’t come out until the actual return of soil samples, these flybys are already filling in some of the blanks in our understanding of this body.

We talked about the Mars Express probe in a previous article (still posted at this site).  This spacecraft was launched by the ESA on June 2, 2003, and arrived at Mars in December of that year.  Since then, it has returned huge amounts of data on the red planet, including many beautiful and striking images of Martian landforms.  One of the accomplishments of this mission has been the detection of methane in some areas of Mars, which may be an indication of some sort of biological activity.  Mars Express has also contributed to the growing body of evidence for frozen water just beneath the Martian surface.

This is not the first time Mars Express has encountered Phobos.  In fact, it’s a regular event for this probe, whose orbit periodically brings it close to the moon.  The folks at ESA call it “Phobos flyby season,” and typically use this time to study the body.  But this time is the closest approach to the moon yet, and will present a chance for more exact measurements than ever before.  The observations will include very precise radiometric readings to determine exactly what the gravity of Phobos is, and how mass is distributed within the body.  This information will be useful to the Russians in planning their lander expedition, and will also address a key fact which has come to light about Phobos: it seems to be hollow.

Well, maybe not completely hollow.  Scientists are estimating that between 25 and 35 percent of Phobos’ interior is empty space.  They have arrived at this conclusion because Phobos simply doesn’t have as much gravity as it should.  The dimensions of this moon are quite well established, so it’s possible to get a rough estimate of how much gravity there should be if the whole body is solid rock.  While the flybys that are happening now will give us our most precise measurement of the moon’s real gravity to date, less precise measurements have already revealed that the gravity of Phobos is much less than it should be.  The conclusion is inescapable: this body doesn’t have as much matter as it seems to have.

This is not as big a mystery as it seems.  In fact, Phobos appears to be a type of body that was predicted before any were actually found, and which now seems to be quite common in the solar system.  Scientists call them “rubble piles,” and that’s exactly what they are.  You see, there are an awful lot of rocks flying around out there, especially in the asteroid belt, which is between the orbits of Mars and Jupiter.  In the early solar system, there were even more of them than there are today.  (Nowadays, the majority of these rocks have already crashed into some larger body, and the asteroids that are left are just the small percentage that have managed to avoid this fate.)

Since all matter exerts some gravitational attraction, every one of those rocks has its own gravity, and when rocks come close to each other, they tend to attract.  If two of these space rocks drift together and stick to each other because of their mutual gravitation, then of course, they’re exerting a stronger gravitational attraction than either one did separately, so they tend to attract still more rocks.  Eventually, if more and more of them come together and stick to each other, you end up with a big mass of rocks loosely held together by gravity.  Of course, they don’t fit together very well, and while they are touching each other in some places, there will also be a lot of gaps.  What you’ve got is a classic rubble pile.

Over millions or billions of years, more rocks will keep hitting this pile, smashing up the outer surface and spraying a lot of asteroid dust around.  Eventually, our rubble pile acquires a coating of this dust which fills in the cracks on the outside of the body, giving the illusion of a solid, unbroken surface.  To an outside observer, there is no obvious sign that this body is not solid- but deep inside, all those gaps are still there.  You wouldn’t suspect a thing unless you measured the body’s gravity, at which point it would become evident that there was an awful lot of empty space inside it.

So, that’s the giveaway: if you find a body that has a much lower gravity pull than it logically should have, you know you’ve got a rubble pile.  We have already found a few of these bodies out there.  For example, it is strongly suspected that Jupiter’s moon, Amalthea, is a rubble pile.

This brings us back to a point mentioned earlier: the fact that there are conflicting theories about the origins of the Martian moons.  One of them is the scenario that we’re looking at here: Mars, being so close to the asteroid belt, has attracted some far-roaming rocks into orbit around itself.  The fact that Phobos- and possibly the other moon, Deimos- is a rubble pile instead of a solid chunk doesn’t really effect this scenario; the rocks may have formed into a pile in the asteroid belt, or after they were captured by Mars.

Another theory about the formation of the Martian moons is that some large body slammed into Mars in the remote past, and Phobos and Deimos are fragments from the collision, thrown off the planet with enough speed to achieve orbit.  If this is the case, it is probable that we won’t know for certain until soil samples can be collected from Mars and both moons, so they can be compared.  If Mars and its moons were originally part of the same body, they should have similar compositions.

However, even if this is the case, it still will not be conclusive, and further research will have to be done to get a definitive answer.  If Mars and its moons are made of similar stuff, there is another possible explanation for it, and this gets to the third theory about the formation of these moons.  This theory holds that the planet and both moons were all formed at the same time, from the same primordial accretion disc that gave birth to all the other planets.  In other words, they may be first generation objects (formed in the birth of the solar system) rather than second generation (formed later from smaller fragments coming together).

So far, it’s all a big mystery, but we are fast closing in on the answer.   The information gained from this series of flybys has already taught us a few things about Phobos, and further analysis of it will reveal more.  Radiometric data from these flybys are being studied right now, and should be precise enough to tell us where the gaps are within the moon.  As said earlier, the gravity analysis from Mars Express will be used to help ROSCOSMOS select the spot to set down its lander in 2012, and the samples from that encounter will answer more questions.  In time, we will pry all of the secrets out of Phobos.

One final note about the possible future of Phobos: it may be a ready-made home for settlers.  What you’ve got is a big rock with a lot of holes in it, and some of those holes can probably be smoothed out and modified to make living spaces.  Since it now appears that at least a quarter of Phobos’ area is empty, that amounts to a lot of space.  If we should ever want a convenient space station orbiting Mars (and we will, eventually) Phobos might be it.  Using a body that’s already there would be a lot easier and cheaper than building something from scratch.  In some far-future time, this little rock might be riddled with underground colonies.

As you can see, the work is just starting on Phobos- and we haven’t even looked at Deimos yet.  The data from the recent encounters will be studied for years to come, and new findings will undoubtedly come to light.  Stick with us; we’ll keep you posted.

The Odyssey mission went exactly as planned.  Using the survey information that it had gathered, NASA scientists picked a landing site for Phoenix: a region where there was a high probability of finding frozen water just beneath the surface.  Phoenix was intended to provide the final, positive proof: a sample of ice taken from the Martian soil.

We will take up our story with the launch of Phoenix from Earth.

Phoenix was launched on a Delta II rocket from Cape Canaveral, Florida, on August 4, 2007.  The name was a reference to the fact that this mission was actually a resurrection of some of the equipment from two unsuccessful earlier missions.  The Mars Polar Lander failed to return data after its landing, and this shattering failure caused NASA to cancel plans for Mars Surveyor 2001.  Phoenix used some of the designs from each of these missions, and represented a new birth pulled from the ashes of disappointment.

The Phoenix mission had two objectives: (1) to study the history of water in the Martian arctic and (2) search for evidence of a habitable zone and assess the biological potential of the ice-soil boundary.

The spacecraft arrived at Mars after a 10-month voyage, slowed itself with airbraking and then finished its descent by parachute.  On May 25, 2008, it landed successfully in the Martian arctic.  (The location was at a latitude which, on Earth, would have been in northern Alaska.)

The projected mission was short, only three months.  It was expected that the frigid Martian winter would cause terminal damage to the lander.  As it turned out, Phoenix survived for two months longer than expected, getting in a full five months of work.

Now that the information is all in, we can see what a big success the Phoenix mission was.  It found the ice it was looking for, and it also found evidence that ongoing, long-term climate cycles might sometimes provide favorable conditions for life on Mars.

Speaking in an article published in the journal Science, Phoenix Principal Investigator Peter Smith of the University of Arizona said, “Not only did we find water ice, as expected, but the soil chemistry and minerals we observed lead us to believe this site had a wetter and warmer climate in the recent past- the last few million years- and could again in the future.”

The article goes on to cite evidence that the Martian soil has had films of liquid water at times.  This, plus the presence of potential nutrients in the soil, “implies that this region could have previously met the criteria for habitability” during parts of cyclic climate shifts, the article concludes.

We know from examples here on Earth that some forms of life can go into periods of dormancy that last indefinitely.  Microbes which were apparently dead have been found encased in rock and made to grow in the laboratory; ancient seeds taken from archaeological sites have been shown to be viable.  The possible duration of dormancy for living cells is not established, but is obviously very long.  The Phoenix findings raise the tantalizing possibly that some forms of life, at least on the microscopic level and possibly larger, may have the ability to remain dormant through these long-term cycles.

It paints a beautiful picture, doesn’t it?  At some time in the remote future, the Martian climate may shift, vast amounts of subsurface ice may thaw, and the plains of Mars spring into life like the desert after a rainstorm.  Let your mind play with that idea for a moment: what kind of life might be buried in the Martian dust, just waiting for a little moisture to help it come alive?

Another pleasant surprise was the presence of perchlorate in the soil samples collected by Phoenix.  If combined with water in the right concentrations, it could form a brine that would allow water to stay liquid at lower temperatures than normal.  On Earth, some microorganisms use perchlorate as food. Humans could get oxygen from it, or process it into rocket fuel.

Phoenix also documented an event that is both scientifically interesting and aesthetically beautiful: snowflakes falling in the thin Martian air.  This was the first documented precipitation on Mars.  Before this, we knew that the polar caps were composed of frozen water, but we didn’t know whether it was frost that had condensed on surfaces, or precipitation that had fallen from the sky.  Now we know: it actually snows on Mars.

Finally the deep cold of Martian polar winter overtook Phoenix, and the lander stopped operating.

As we said earlier, this outcome was expected.  But space probes have been known to defy expectations and continue functioning long after their projected lifespans, and with this in mind, NASA has been using the Mars Odyssey satellite to listen for a signal from the lander.  Odyssey listened as it passed over the site in January, then again in February, and it will try again in March.  So far there have only been negative results, and hope is fading for Phoenix.

It’s the end of a great mission.  Phoenix has found what it was looking for: subsurface water ice on Mars.

And where there’s water, there may be life.  The first Martians that we encounter may be extremophile organisms lying in that frozen soil, waiting for the next swing of the climatic cycle.

And now we know what one of the major industries will be for future Martian colonies: ice mining.  This will undoubtedly prove to be one of the most valuable natural resources on the red planet, and may form the basis of a planet-wide economy in the same way petroleum does here (but without the pollution.)

Phoenix will sit on that windswept plain for a while, but in time, people will go there and retrieve it.  When they do, they should put in a museum or shrine- some place of honor, as it deserves.  Phoenix has made a vital step in our march to the stars, and the world of the future will owe it a debt of gratitude.

Odyssey is still orbiting Mars and functioning fine.  We will undoubtedly hear from it again.

Preview: The European Space Agency’s Mars Express probe, which was featured in a previous article at this site, has recently been conducting a series of flybys of Phobos, one of Mars’ moons.  The info from these is starting to come out, and our next article will take a look at it.

Sources:

Phoenix Mars Lander: Mission Overview at NASA website:  nasa.gov/mission_pages/phoenix/mission/index.html

Phoenix Mars Lander: Launch Coverage at NASA website:  nasa.gov/mission_pages/phoenix/launch/index.html

Phoenix Mars Lander: Exploring the Arctic Plain of Mars at NASA website:  nasa.gov/mission_pages/phoenix/news/phoenix-20090702.html

Phoenix Mars Mission: “Mars Odyssey Still Hears Nothing From Phoenix” at website of the University of Arizona:  phoenix.lpl.arizona.edu/index.php

Phoenix Mars Mission: Mission Phases at website of the University of Arizona:  phoenix.lpl.arizona.edu/phases.php

Space Topics: Phoenix at website of the Planetary Society:  planetary.org/explore/topics/space_missions/phoenix/

Phoenix Mars Lander News: “NASA Phoenix Results Point to Martian Climate Cycles” at website of the Jet Propulsion Laboratory, California Institute of Technology:  jpl.nasa.gov/news/phoenix/release.php?ArticleID=2210

This is the story of two such missions, so closely linked that they might be viewed as two parts of the same whole. They are the 2001 Mars Odyssey satellite and the Phoenix lander. As we will see, these two projects were designed to work together, with Odyssey paving the way for Phoenix, then serving as its communication relay. They worked together toward a single goal: proving that there are large deposits of frozen water beneath the Martian surface. In this, they were successful.

This article is the first of two parts. In this one, we will look at the 2001 Mars Odyssey satellite and the science it accomplished. In our next article, we will look at the Phoenix lander. As we will see, their combined effect is a new and better understanding of Mars and its water processes.

The 2001 Mars Odyssey was launched on April 7, 2001 from Cape Canaveral, Florida. It was an ungainly assembly of rods, panels, antennae and other devices, but in general terms, it measured 2.2 meters long, 1.7 meters tall and 2.6 meters wide. At launch, it weighed 725 kilograms, which included the 331.8-kilogram spacecraft, 348.7 kilograms of fuel and 44.5 kilograms of instruments. In an effort to keep the weight down, the satellite’s designers built its framework mostly from aluminum and titanium.

Mars Odyssey carried three instruments:

1. Thermal Emission Imaging System (THEMIS)- would acquire high spatial and spectral resolution images of the surface mineralogy, and provide information on the morphology of the Martian surface. Different elements radiate thermal energy in identifiable patterns, so by studying the thermal emission of the Martian surface, it’s possible to determine which elements are present. A thermal survey would also be able to locate areas of volcanic activity, as well as geothermal zones similar to Yellowstone Park on Earth.

2. Gamma Ray Spectrometer (GRS)- would also contribute to a map of the elemental composition of the surface, and determine the abundance of hydrogen in the shallow subsurface. Hydrogen is used as an indicator of the presence of water.

3. Mars Radiation Environment Experiment (MARIE)- would characterize the Martian near-space radiation environment as related to radiation-induced risk to human explorers.

The two-part plan, mentioned earlier, was present from the beginning. Odyssey was intended to locate areas where frozen water might be present in preparation for a lander which would go down and actually take samples. By mapping the surface morphology and mineralogy, rough areas would hopefully be eliminated from the list of possible landing sites. Once the lander was on the ground, Odyssey would act as its relay to send data back to Earth.

In addition to the presence of hydrogen as an indicator of water, it was expected that the thermal survey would find other signs such as sedimentary deposits of water-soluble minerals in areas where underground ice could have melted and come to the surface at some time in the past. This would provide a long-term history of water activity on the Martian surface.

It is now generally accepted that Mars had large amounts of surface water in its distant history; many of the planet’s land-forms were obviously shaped by flowing water. However, recently there has been a growing body of evidence for the presence of deposits of frozen water on Mars now, not just in the past. For instance, data gathered by the European Space Agency’s Mars Express probe, as discussed in our article from a few weeks ago, strongly indicates that there are large amounts of water frozen just under the surface in some parts of Mars.

Once Mars Odyssey had found some interesting areas, a landing site would be chosen for the lander. This was another job where THEMIS would be useful. Big chunks of rock tend to absorb more heat than the surrounding soil, and retain it longer. Because of this, rocky places would be hotter, and would clearly show up in the thermal survey. Rocky areas tend to be rougher than sandy areas, which would make them too dangerous to be considered as landing sites.

The science to be done by this mission could be summed up as four main goals:

1. Determine whether life ever arose on Mars. Odyssey did not carry instruments to directly detect life, but data gathered by this mission would help to determine whether the Martian environment could have ever supported life. For the first time on Mars, a probe was equipped to map the presence of near-surface water and mineral deposits from past water activity.

2. Characterize the climate of Mars. Odyssey would try to understand the evolution of the Martian climate, and how water activity has effected that evolution.

3. Characterize the geology of Mars. Odyssey would determine the chemical elements that make up the Martian surface, and help explain how the planet’s land-forms developed over time. That information should provide clues to the geological and climatic history of Mars and the likelihood of finding past or present life.

4. Prepare for human exploration. Part of the Odyssey mission, as we mentioned earlier, was the Mars Radiation Environment Experiment. This would determine the levels of harmful radiation on the Martian surface, with the thought of preparing future explorers for the hazards they would face.

The Odyssey mission was a huge success, achieving all of these goals and more. Odyssey entered Mars orbit on October 24, 2001. Over the next 76 days, it performed orbital modifications which finally placed it in a two-hour science orbit. Results started coming in almost immediately. Some of the early data from Odyssey’s THEMIS device showed the presence of chloride mineral deposits in the southern Martian highlands. These are salt beds similar to the ones seen in some areas on Earth, and their presence on Mars means the same thing it means here: there was once a lot of water here. In all, THEMIS found about 200 areas with chloride mineral deposits.

The hydrogen mapping part of the mission was also successful, locating areas with elevated hydrogen levels which indicated a high probability of frozen water just underground.

While the early images of the Martian surface were taken from directly above, with Odyssey looking straight downward, later images were obtained by changing the satellite’s orbit and taking pictures of surface features from an oblique angle. By viewing a spot from directly above, and then shifting the orbit and viewing the same spot from an angle, it was possible to construct three-dimensional images of land-forms.

Here’s another important point: these images not only allow the study of the land-forms of Mars, but also of the atmosphere above them. When the light passes through the air, it is modified by the gas molecules and whatever dust and other particles are in the air. Different sizes and types of particles absorb or reflect light in different ways, so if you subtract the information about the actual ground itself, you are left with a picture of the modifications caused by air molecules and suspended particles. This can tell us a great deal about air currents and the movement of dust etc. in the atmosphere of Mars- factors which can have a huge influence on the climate, and which are necessary for a full understanding of the dynamics of the Martian atmosphere.

As we saw earlier, some of this activity had a specific purpose: locating a landing site for a future lander. A suitable site was found, and in time, the Phoenix lander was launched from Earth. This would provide the final, conclusive piece of evidence: an actual sample of ice taken from the Martian soil. Eventually Phoenix arrived and landed in the place selected for it. During its mission, Mars Odyssey provided the communications link which transmitted the data back to Earth.

But that’s another story, as they say. To find out about Phoenix, you’ll have to read our next article.

Odyssey was also the communication relay for the two famous Mars rovers, Spirit and Opportunity, whose ramblings have provided us with such spectacular pictures and data on the Martian surface.

The Odyssey satellite is still working fine, and will undoubtedly perform other jobs relating to future missions. It is the Energizer Bunny of space probes, still going and going even though its official mission is now over. Hang in there, Odyssey!

In our next article, we will take a closer look at the Phoenix lander and the science it has given us. Don’t miss it!

Sources:
Mars Odyssey: Mission Spacecraft at website of the Jet Propulsion Laboratory, California Institute of Technology: mars.jpl.nasa.gov/odyssey/mission/science/
Mars Odyssey: Mission Science at website of the Jet Propulsion Laboratory, California Institute of Technology: mars.jpl.nasa.gov/odyssey/mission/science/

Mars Odyssey: Mission Overview at website of the Jet Propulsion laboratory, California Institute of Technology: mars.jpl.nasa.gov/odyssey/mission/overview/

Mars Odyssey THEMIS: “New Orbit Gives THEMIS Better Looks at Mars Minerals” at website of Arizona State University: themis.asu.edu/news/new-orbit-gives-themis-better-looks-mars-minerals

Mars Odyssey THEMIS: “Sideways Look From THEMIS Probes Mars’ Atmosphere” at website of Arizona State University: themis.asu.edu/sideways

Mars Odyssey THEMIS: THEMIS Helps Phoenix Land Safely on Mars” at website of Arizona State University: themis.asu.edu/news/themis-helps-phoenix-land-safely-mars

Mars Odyssey THEMIS: Mars Salt Deposit Discovery Points to a New Place to Hunt for Life’s Ancient Traces” at website of Arizona State University: themis.asu.edu/news/mars-salt-deposit-discovery-points-new-place-hunt-lifes-ancient-traces