The Exploration of Mars’ Largest Moon Will Continue With the Phobos Grunt Mission

Posted on May 17, 2010 by admin

mars phobos 150x150 The Exploration of Mars Largest Moon Will Continue With the Phobos Grunt MissionThe exploration of Phobos, the larger of Mars’ two moons, will continue with Phobos Grunt, a Russian mission to be launched next year.  Roscosmos, the Russian national space agency, is planning to put a lander down on Phobos and return a sample of surface material to Earth.  (The comical-sounding name is Russian for “Phobos Soil.”)  This will be a follow-up to the extensive observations of the moon that are currently being conducted by the European Space Agency’s Mars Express probe.  In our article a few weeks ago, we took a look at the flyby maneuvers recently undertaken by Mars Express and what they are telling us about Phobos.  As we mentioned at the time, part of the purpose of the flybys was to scout out a landing site for the Phobos Grunt lander.  In this article, we will talk about the lander itself and what it hopes to accomplish.

The pictures are in!  The flyby maneuvers of Phobos performed by Mars Express were successful, returning lots of data and some beautiful, clear pictures of the moon.  While details of the radiometric study of Phobos’ density will be coming out later, ESA has already released the pictures showing the proposed landing site for Russia’s Phobos Grunt lander in 2012.  It’s a nice, clear area with a relatively level surface, perfect for a lander.  With this final detail, the Russian mission is set.  Originally scheduled for launch in 2009, the Phobos Grunt mission went through delays and schedule changes, as many space projects do, but now appears to be set for launch next year.  The probe will travel for 11 months, arriving at Phobos in 2012.  When it completes its mission, it will be the longest sample-return mission ever undertaken.

Phobos Grunt is a comprehensive mission to study both Phobos and Mars itself.  It will be conducting studies of Mars, Phobos, and their spatial environment (radiation, plasma, space dust, etc.).  While the return of Phobos surface material will be the tour-de-force, and undoubtedly will be the thing for which the mission is remembered, this is really a larger project regarding Mars and its entire area of space.

The probe will also be carrying a culture of Terrestrial bacteria as a biology experiment.  When the mission successfully returns its samples to Earth, the bacteria will be studied to determine the effects of the long space voyage.

The power for the operation of the probe will be supplied by two rectangular solar panels.  These will be folded down like the eaves of a roof during the voyage to Mars, then deployed in a standard “paddle-wheel” configuration during use.  Between these two panels will be a doughnut-shaped propellant tank, and in the hole of the doughnut will be the rocket that will be used for the return voyage.  This assembly will be connected by eight narrow struts to the ring-shaped landing gear underneath.  Before it is deployed, this entire unit will sit atop a completely separate propulsion system, which will be used for the pre-deployment maneuvers.

Phobos Grunt will go up in the same launcher with Yinghuo-1, China’s first mission to Mars, which will investigate one of the great mysteries of Mars: where did all the water go?  It is now abundantly clear that Mars had much more surface water in its youth than it does today.  The process that deprived Mars of its surface water is still only poorly understood.  Recent findings indicate that some of this water is now locked up in frozen subsurface deposits (see our articles on the Phoenix and Odyssey spacecraft) but exactly how it ended up there, leaving the planet’s seas and river systems dry, is something that will bear much further study.

The origin of Phobos is open to question.  It seems to share surface characteristics with some types of asteroids, which would indicate that it was captured from the nearby asteroid belt.  That scenario is perfectly believable, except for one detail: Phobos orbits Mars in a nearly circular path, exactly on Mars’ equatorial plane.  Now, if this were a random asteroid that had been captured, you would expect its orbit to be random; it probably would not be a perfect circle, and it probably would not be exactly on Mars’ equator.  That kind of symmetry is what we would expect from a body that had been formed along with Mars, in the original planet-forming period of the solar system.  In that case, Mars and its moons could have formed out of one big, spinning glob of dust and gas, and therefore would spin in the same plane.

So with Phobos (and its sister moon, Deimos, too) we see a body that looks like an asteroid, but orbits like something that formed along with Mars.  If it’s an asteroid- or a rubble pile composed of several chunks of asteroidal rock- then it’s hard to explain the orbit.  If it formed along with Mars in the distant birth of the solar system, then it’s hard to explain its surface characteristics.  This is the great enigma that is emerging about the two moons of Mars, and all research regarding them will be aimed at clearing up the question.  We haven’t even looked at Deimos in-depth yet, but when we do, all of the questions that are now being asked about Phobos will also be asked about it.  Where did these moons come from?  Exactly what are they?  In the years to come, we will be trying to find out, and Phobos Grunt will be an attempt to get closer to an answer.

There is also another mystery about Phobos: it just looks funny.  There are long, straight grooves running for many kilometers across its surface, as if it had been sandblasted.  That may be literally what happened: asteroid impacts on Mars in the distant past may have thrown up huge amounts of ejecta, reaching so high that it scored the moon’s surface.  Such asteroid collisions may have happened repeatedly throughout Mars’ early history, and provide us with still another possible origin for the Martian moons: they could be formed out of material thrown up from Mars by early collisions, then scored again and again by the ejecta from later collisions.

Alternatively, it is theorized that these grooves may be long, straight fissures in the underlying rock, into which surface dust has settled.  Phobos Grunt will be taking a closer look at these formations to determine which theory is correct.

Upon arrival in Mars orbit, Phobos Grunt will first study Mars’ magnetosphere and atmosphere, and release the Chinese Yinghuo-1 into Mars orbit.  When these operations are completed, the landing on Phobos will be attempted.  This operation is a bit challenging, simply because of the small size of the target.  Phobos is a rugged little rock about 20 or 30 km. wide (depends on which way you measure it; Phobos isn’t even close to a sphere) and simply hitting it will require some sharpshooting.  Landings on small objects are always a time of uncertainty and anxiety for the crew back on Earth; there are so many things that could go wrong.  If you’re a little off-target, you’ve missed the moon altogether, and if you hit it a bit too hard, you’ve smashed your multi-million-dollar probe.  Assuming that Phobos Grunt can get past this nail-biter, it will arrive on the surface of Phobos and collect its samples.  While the object of the mission is to return the samples to Earth for further study, the probe will be able to do some preliminary work on the spot.

Phobos Grunt will be carrying three instruments contributed by France’s Centre Nationale d’Etudes Spatiale.  One of these is a microscope that can see in visible and infrared wavelengths, which will be used to spot interesting places to collect soil samples.  An identical instrument was used with great success on the Rosetta mission (see article at this site).  The other French instruments are a gas-phase chromatograph and a laser spectrometer, which will be used to determine soil composition.   While the samples returned by Phobos Grunt will undoubtedly be studied for years to come, the preliminary examination by these instruments will give us some idea of what we have, without having to wait for the samples to arrive.

Simply getting the samples is only part of the job; they will then have to be returned to Earth.  The long voyage back will be the easy part.  The real anxiety starts when the ground crew starts to think about reentry.  Getting delicate samples to the ground intact has proven a problem in the past.  For instance, in the return of the samples from the Stardust comet mission (see our article), the sample capsule was damaged during the impact, nearly compromising the samples.  Disaster was narrowly avoided that time, but it’s a safe bet that the Phobos Grunt crew will be thinking about it when they try to bring their probe down.

Hopefully, everything will come out all right, and the Russians will have the world’s first samples of Phobos.  As part of their agreement with France, Roscosmos is sharing the samples with CNES.  Within days or weeks at the most, scientists all over the world will finally be able to learn something about this strange little body.

Even if the sample return is unsuccessful, this mission will give us some data about Mars and its largest satellite that will prove valuable for future researchers.  It’s a neat mission, and the spacecraft is a classy device that will probably be copied for other sample-return missions in the future.

As developments happen, you can read about them here.

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Waterworlds: New Research Says We Will Probably Find Them Someday

Posted on May 14, 2010 by admin

water world 150x150 Waterworlds: New Research Says We Will Probably Find Them SomedayThis is an article about waterworlds, and the search for them. It now appears likely that such planets do exist somewhere in the universe, and if we go far enough, we will undoubtedly find some of them. Scientists have recently calculated that such a body is not only likely, but probable in some planetary systems. Once again, we see an old fantasy which may turn out to be true.

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

Posted in Astronomy, Planets | Tagged , , , , , | Leave a comment

ESA’s Herschel Space Telescope Is Off to a Great Start

Posted on May 6, 2010 by admin

galaxy universe 150x150 ESA’s Herschel Space Telescope Is Off to a Great StartOn May 14, 2009, the European Space Agency launched two revolutionary space telescopes aboard the same launcher.  These were Planck and Herschel, new eyes on the universe which will hopefully revolutionize our view of the galaxy and beyond.   The dual launch was a cost-saving measure, but the two missions do have one thing in common: they give us a view of the universe in wavelengths that are invisible to our eyes, and which reveal things that visible light does not.  In our article a few weeks ago, we took a look at Planck and its mission; this time we will look at Herschel.

Herschel is a tall cylinder, about 7.5 m tall and 4 m wide.  Its launch weight was 3.4 tons, and the telescope itself weighs 315 kg.  It is orbiting the sun at the L2 point, just beyond the orbit of Earth.  In this position, the sensitive instruments are in Earth’s shadow, which will protect them from the heat of the sun, and far enough from the Earth and the moon to avoid their interference, too.  Its lifetime was originally projected to be 3.5 years, but as we have seen with other probes, this may be extended.

At 3.5 meters in diameter, Herschels’ main mirror is more than four times as large as any previous infrared telescope.  It will capture almost 20 times more light than any of its predecessors.

Herschel is part of a larger movement toward multi-wavelength astronomy.  The sad truth is that we humans are almost blind.  Most of the energy in the universe is completely invisible to our eyes.  If you look at a chart of the electromagnetic spectrum, you can see that visible light is only a tiny sliver of the whole range of wavelengths.  Some phenomena emit very little in this range, concentrating most of their emissions in parts of the spectrum that we can’t see: X-rays, infrared, radio waves etc.  If we are only looking at visible light, we are only seeing a small part of what’s really going on in the universe.  To remedy this situation, we have invented new eyes that can see in those other wavelengths, and launched them into space.  Above the murky atmosphere, they can show us things we’ve never seen before.

Granted, this line of research is not new.  Astronomy in the X-ray, radio wave and infrared regions of the spectrum has been around for a while, and has already given us new views of some objects.  But the new wave of space telescopes, of which Herschel is one of the pioneers, will greatly expand the range of wavelengths being observed, and will be capable of studying many more targets than previous missions.  For the first time, we will at least be getting close to a complete view of the universe around us.

For example, Herschel is the first observatory to cover the entire range from far-infrared to sub-millimeter wavelengths and bridge the two.  It will observe further into the far-infrared than any other mission, studying the dusty regions of the cosmos, both near and far.  Many of the wavelengths that Herschel can see have not been exploited so far, so the things revealed there will be completely new.

Herschel’s work will be conducted all the way from the local level to the intergalactic level:

Within the solar system, the telescope will study asteroids, Kuiper belt objects and comets.  All of these objects absorb solar radiation and then emit it in the infrared, and their emissions carry information about the emitting body.  (In this, Herschel is taking part in a larger drive to gain greater understanding of the small bodies of the solar system- see our articles on the Dawn probe and the Hayabusa asteroid mission.)

On a larger level, but still within our Milky Way galaxy, Herschel will turn its attention to the star-forming regions, to reveal different stages of early star formation and observe the youngest stars in our galaxy for the first time.   Herschel will also be able to study the dust clouds and accretion rings around stars, the very things that make planets.  By doing this, it is hoped that Herschel will be able to study the birth and evolution of planets in unprecedented detail.

Expanding its view still more, Herschel will look at the vast reservoirs of dust and gas in the Milky Way and in other galaxies, conducting astrochemical analysis which will hopefully give us new insight into the complex chemistry of these dust clouds.

Herschel will allow us to expand our perspective.  So far, most of our science about interstellar physics and chemistry has been learned from observing our own galaxy.  This is very limiting, since different galaxies have different chemistries.  For the first time, Herschel will allow us to conduct observations of other galaxies, some of which are very different from our own.  For instance, some galaxies have much lower amounts of metal than the Milky Way does.  Any stars and planets that formed in those galaxies would be very bizarre from our point of view, having few if any of the metals that form such an essential part of all kinds of chemistry in our world.  (Creatures like us, with our iron-rich blood, would not even exist.)  By studying such galaxies, Herschel will finally expand our knowledge of interstellar chemistry and physics beyond our own neighborhood.

Moving to a still larger level, Herschel will be able to look far back in cosmic time, to a period when star formation was happening at a much higher rate than it is today.  The star formation occurring now is really just the aftermath of this burst, which happened when the universe was about half its current age.  With Herschel as our time machine, we will be able to see this period and study it in new detail.

Herschel will also conduct studies of the cosmic infrared background, a function which complements the mission of Herschel’s launch mate, the Planck space telescope.

This is heavy stuff: the processes that made the galaxies, stars and planets.  It is cosmic science, in the truest sense.  It was just a few years ago that the science of cosmology was largely a matter of theory.  We thought we knew how the universe had come to be, but we had no way of checking our theories for accuracy.  Now, with Herschel and its breed, we can fill in some of the blanks in our knowledge.

Besides that, Herschel’s work closer to home will also show us some interesting things.  The dust clouds that it will pierce have been opaque to us until now, and for the first time, we will see what is within them.  Closer still, Herschel will contribute to our knowledge about the composition and structure of asteroids and comets.  This will be really interesting, but it may also help us out in the future.  If one of those objects is detected heading for Earth, it will be nice to know something about it- and Herschel may help to provide some of that knowledge, either by studying that body specifically or by providing us with general information about the characteristics of such objects.

All that is in the future, but Herschel is in operation right now, and is already proving its worth.  It opened its “eyes” and took a test image on June 19, 2009, and ESA proudly released the picture to the press: an absolutely beautiful shot of the spiral galaxy MS1, which will undoubtedly grace many calendars and posters for years to come.  It looks like a piece of exotic jewelry, a swirl of eye-popping blue, yellow, pink and white against the blackness of intergalactic space.

Since then, Herschel has performed even better than expected.  For its first assignments, it was trained on more galaxies, star-forming regions and dying stars.  It provided spectacular data from the start, finding water and carbon and revealing dozens of new galaxies.

ESA has already started compiling a picture gallery of images Herschel has taken.  The latest of these just came in a few days ago: the star-forming region in the Rosette molecular cloud, revealing a previously unseen cluster of stars roughly ten times the mass of our sun.  This is another stunner: swirls of blue, gold and red, set with stars like diamonds.  Wow!  The guys who do screen savers will go crazy over this stuff.

We’re going to see lots more from Herschel in the years to come.  You can read about it here- and the picture gallery at the ESA website is highly recommended.

Sources:

“Herschel at a Glance” at the website of the European Space Agency:  esa.int/SPECIALS/Herschel/SEMBM00YUFF_0.html

“ESA Herschel: Science Objectives” at website of the European Space Agency:

esa.int/SPECIALS/Herschel/SEMSN00YUFF_0.html

“Herschel Highlights” at the website of the European Space Agency:  esa.int/SPECIALS/Herschel/SEMEN00YUFF_0.html

“ESA Herschel: Vital Stats” at website of the European Space Agency: http://www.esa.int/SPECIALS/Herschel/SEM4T00YUFF_0.html

ESA News: “Herschel’s Daring Test: a Glimpse of Things to Come” at website of the european Space Agency:  esa.int/SPECIALS/Herschel/SEM76A0P0WF_0.html

ESA News: “Baby Stars in the Rosette Cloud” at the website of the European Space Agency:  esa.int/SPECIALS/Herschel/SEMWQ59MT7G_0.html

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Scientists and Politicans Discuss the Threat of Near-Earth Objects

Posted on May 3, 2010 by admin

asteroid dino 150x150 Scientists and Politicans Discuss the Threat of Near Earth ObjectsThis article is about NEOs- Near Earth Objects- and possible steps that could be taken to deflect one of these objects if it should appear in danger of colliding with Earth.  A major impact by an NEO is not just a possibility, it is an absolute certainty.  The only question is, when will it happen, and how prepared will we be when it does?

The bad thing about science is that it lets us know just how precarious our position is.  Our ancestors were blissfully ignorant, thinking they were living in a safe and unchanging world.  Now we know that this was only a misconception caused by lack of knowledge.  As we get smarter, we realize just how dangerous this universe is, and how quickly and completely our little corner of it could change.  All the bodies of the solar system, including Earth, are pockmarked with the prints of past impacts, and more of them are being discovered all the time.

There are many examples.  In 2004, for instance, a systems analyst in Buenos Aires, Max Rocca, was indulging his hobby of poring over Landsat images online, when he noticed something unusual.  There is a river in Colombia called the Vichada which travels through miles of dense jungle before finally reaching the Orinoco.  For most of its course, the Vichada travels in a very predictable way, following the natural shape of the land.  Max Rocca had some training as a geologist, and he could tell where the path of the Vichada River should be in that landscape.  For most of the river’s course, he was absolutely right.  Only at one point did it deviate from the expected course, and that was where it turned at almost a right angle, traced a perfect semicircle through the jungle, and then returned to its former path.

Apparently there was a semi-circular feature on the land at that point, which had never been found before because the jungle growth obscured its outline.  Rocca knew it shouldn’t be there.  There was nothing in the normal seismic and erosional forces shaping this landscape that should have made a perfectly round depression there.

Further investigation showed that the crook in the Vichada River was following a ridge along one side of a circular depression 50 kilometers wide.  A shallow depression surrounded by a ridge of hills is the classic signature of an impact crater, and this was the biggest one every found in South America, 50 kilometers wide.

While Mr. Rocca certainly deserves kudos for his discovery, such features are not rare.  One truly spectacular example is Vredefort Crater in South Africa, which at 300 kilometers wide, is the largest confirmed impact crater on Earth.  (The Wilkes Land Crater in Antarctica is even larger at 500 km., but has not yet been confirmed to be an impact crater.)   Luckily, this event occurred some two billion years ago.  If such an impact happened today, it would induce an “impact winter” effect that would disrupt agriculture on a global scale, resulting in widespread famine and the probable extinction of many of the lifeforms on the planet- especially big ones at the top of the food chain (that’s us).

Of course, the situation is much better now than it was back then, because many of the rocks that were whizzing around two billion years ago have already hit something, but there are still plenty of rocks flying around the sun that are big enough to cause vast destruction.  When you consider the consequences of a single event of the magnitude of Vredefort or even the Vichada impact, it is impossible to ignore the threat.

With this in mind, there has been a lot of very serious discussion in recent years about what we can do if an asteroid or comet is found to be on a collision course with Earth.

The issue is being addressed by various organizations around the world, some associated with specific national governments and others of an international nature.  In 1998, NASA established its Near-Earth Object Program and set a goal of locating at least 90 percent of the estimated 2,000 asteroids and comets larger than one kilometer that approach Earth by the end of the following decade.  Unfortunately, it is now 2010 and this goal has still not been reached, but it probably will be realized in the next few years (see the article on the WISE space probe at this site).

Despite the fact that it has had to revise its original timetable, the NEOP is still alive and well.  In a 2007 report to Congress, NASA refined the goal of the project to the mapping of all bodies larger than 140 meters across whose orbits pass within .05 AU of Earth’s orbit.  At that time, the date of completion was estimated to be 2020.

In its web page about the establishment of this organization, NASA points out that the detection of NEOs also has a possible good side.  We now know that comets and asteroids are rich in substances that will prove useful to future space exploration efforts.  One of the most important of these is water, which exists in frozen form on many of the small bodies of the solar system.  In addition to its obvious usefulness for human consumption, water can be processed to yield oxygen and hydrogen, which also have multiple uses.  Besides this, there may be metals and minerals on some of these bodies that can be mined by future explorers.

The United Nations started an organization in 2001 called Action Team-14, which is dedicated to international discussions of the NEO issue.

This is all good, but it does raise an obvious question: when we find a NEO that is clearly going to impact Earth, what can we do about it?  Bear in mind that if we just shoot a missile at the thing, it will only make matters worse by creating a multitude of smaller pieces, all of which would follow roughly the same path as the parent body.  That would be turning a cannonball into buckshot- not a good idea.

Recent scientific findings have shown just how likely such an outcome would be.  We now know that “rubble piles” are very common in the solar system- see the article at this site about Mars’ moon, Phobos.  These are groups of rocks that stick to each other because of their slight gravitation, but are not actually attached.  If nothing happens to separate these rocks, they might stay together for billions of years; but if something hits them and jostles them apart- say, a missile fired by foolish little germs on some nearby planet- then they could fly apart very easily, and the buckshot analogy would be quite appropriate.

In its 2007 report to Congress, NASA listed different techniques that might be used to deflect a NEO that is on a collision course with Earth, and assessed the potential effectiveness of each one.  Because of the rubble pile problem, they immediately dismissed any idea of detonating an explosive on or under the surface of the body.  However, the report did propose an alternative: bring a nuclear device close to the NEO- but not too close- and set it off.  The force of the blast would nudge the NEO into a different orbit, but if you positioned the explosion right, it might not blow the object to pieces.

What we do depends, to some extent, on how much time we have to get to know our intruder.  In a best-case scenario, we would spot the object some years before it was to make impact.  Then we would be able to send an unmanned probe to study the threatening object.  By transmitting a continuous radio signal during a flyby of the body, the probe would allow Earth-based scientists to measure the Doppler shift of the signal, and calculate the body’s mass.  This would give us a pretty good idea of whether we were dealing with a rubble pile or not.  (As we saw in our Phobos article, rubble pile objects tend to have very low gravity because so much of their interior is empty space.)  If it turns out that we are dealing with a solid body rather than a rubble pile, our troubles are over (almost).  NASA estimates that for such a body, the best approach would be to shoot a non-explosive impactor, or more likely a series of them, at the body and knock it into a new orbit like an oversized pool ball.

Various “slow push” techniques have been proposed.  One of these is to find another asteroid and modify its orbit so that it acts as a tugboat, pulling the threatening object into a new orbit.  Another idea is to put down a robot lander which would actually mine rock from the body and fire it off in high-velocity “bullets,” in effect turning the NEO into a rocket.  Another idea is to send a spacecraft to rendezvous with the NEO and spray-paint it with some coloring agent which would make one side brighter than the other, so that radiation from sun-heated material would provide a small thrust.

One particularly novel proposal has come from America’s Planetary Society: mirror bees.  These are small, unmanned craft that use mirrors to focus sunlight on the NEO, causing material to boil off and create jets which, if carefully positioned, could change its orbit.  Alternatively, they might use lasers rather than mirrors.

The 2007 Congressional report said that while slow push techniques would work in theory, they could only be used if we had plenty of warning, since they all involve getting spacecraft to the object and performing operations that would take some time to be effective.  If we only have short warning- which is likely, unfortunately- then a stand-off nuclear explosion is probably our best bet.

The report also pointed out that up to 80 percent of NEOs might be in orbits that could not be attained by current launch vehicles, which would mean that new launchers would need to be developed.  Even then, it would be necessary to use gravity-assist maneuvers to the fullest advantage to reach some of them.

So the bad news is, if it happens, we’re in big trouble.  The good news is, at least the governments and other institutions of the world are aware of the problem, and are trying to do something about it.  These discussions have yielded some good ideas, but now those ideas must be acted on.  Our planet has been pounded many times before, and each time, many species became extinct as a result.  If we are lucky, maybe it will be different next time.

Sources:

Lendroth, Susan: Press Release- “Saving Earth One Asteroid at a Time” at the website of the Planetary Society:  planetary.org/about/press/releases/2010/0212_Saving_Earth_One_Asteroid_at_a_Time.html

Alexander, Amir: “Project: Asteroids- the Potential Threat” at the website of the Planetary Society:  planetary.org/programs/projects/targetearth/20100213.html

Projects: “Mirror Bees: Planetary Defense” at the website of the Planetary Society:  planetary.org/programs/projects/mirrorbees/

Murrill, Mary Beth and Whalen, Mark: “JPL Will Establish Near-Earth boject Program Office for NASA” at the NASA website:  neo.jpl.nasa.gov/program/neo.html

“Near-Earth Object Survey and Deflection Analysis of Alternatives” (report to Congress, March 2007):  neo.jpl.nasa.gov/neo/report2007.html

Vredefort Crater entry at Wikipedia:  wikipedia.org/wiki/Vredefort_crater

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ESA’s Envisat Is Watching Eyjafjallajoekull Erupt

Posted on April 30, 2010 by admin

volcano image 150x150 ESAs Envisat Is Watching Eyjafjallajoekull EruptOver the last several days, the world has been given a small glimpse of the power of nature on a planetary scale.  The Eyjafjallajoekull Volcano in Iceland, which had not erupted since 1821, has suddenly awakened from its sleep and started pouring vast amounts of volcanic ash into the atmosphere.  Worldwide air traffic was thrown into a state of chaos, with stranded passengers sleeping in airports.  The entire world will undoubtedly experience elevated levels of atmospheric dust for some years to come, and while this incident will not be big enough to induce a serious wintering effect on the planet, larger eruptions could certainly do so.

Much of our information about this eruption has come from the European Space Agency’s Envisat satellite, which is a state-of-the-art meteorological instrument in orbit around Earth.  In this article, we’ll take a look at this device, the awesome phenomenon of the eruption itself, and the larger scientific value of studying events like this.

In the study of our planet, we humans are hampered by our very smallness, and the brevity of our lives.  To us, 1821 seems like a long time ago.  If a volcano waits that long between eruptions, we might get a false sense of security- but the people of Iceland have been watching volcanoes for a long time, and they know better.  They know that to a volcano, 1821 was only yesterday.  It’s just long enough for the pressure to build up again- and Iceland has an awful lot of pressure.

The reason is a stroke of amazingly bad luck.  This poor island is the only piece of real estate on the planet that exists directly over not one, but two, of Earth’s pressure vents.

One of these pressure vents is the boundary between two tectonic plates.  America is on one plate and Eurasia is on another.  These plates literally float on the liquid rock of the planet’s mantle, and at the boundary between the two, that liquid rock sometimes seeps through.

Now, there is also another formation called a hotspot, which is made by a huge column of molten rock welling up under the surface.  As you might imagine, this makes the rock above the column bulge up.  If it happens on the ocean floor, it can make an island.

Now, just imagine these two things happening in the same place: a hotspot makes an island right over the boundary between two tectonic plates.  This incredibly unlikely coincidence would create an island which was constantly leaking magma and gases from deep within the Earth.

OK, you don’t have to imagine it; you can just look at the globe.  The winner of our Unluckiest Island in the World Award is Iceland, which is created by an enormous hotspot, and also exactly straddles the Mid-Oceanic Ridge which separates the American tectonic plate from the Eurasian one.  At some unknown time in the future, that column of magma under the hotspot is going to blow, and the resulting eruption will be one of the most destructive events in the life of the planet.

To their great credit, the Icelandic people have made good use of this energy.  Iceland currently leads the world in the generation of electricity by geothermal means.  Sitting on top of a hotspot does have its advantages.

And there’s another good side to all this, if you’re a planetary scientist: Iceland gives you a lot to study.  The island is like a geothermal laboratory where the workings of a planet can be studied in detail.  By looking at Iceland, we can see the interplay of forces that also exist on other small, rocky bodies.  Volcanoes, both active and extinct, have been observed on several other worlds in the solar system.  For instance, Mars has a huge mountain called Olympus Mons (appropriate, don’t you think?) which is a volcanic cone so high that its peak is outside the atmosphere.  Volcanoes have also been observed on some of the system’s moons, and recent evidence indicates that Venus may have active volcanoes, too.  This is one of those lucky instances where Earth presents us with an analog of something that exists on other worlds.  By studying the one we’ve got here, we can, in a way, study the ones out there, too.  The things that we learn about planetary forces and how they interact will also be true on those other worlds.

And that brings us to Envisat.  This satellite, which was designed for studying the weather, has proven invaluable in observing the Eyjafjallajoekull eruption.  This is a good example of a spacecraft that has been adapted to a job which is beyond its originally intended design.

Envisat, launched by the European Space Agency in 2002, is the largest Earth-observing spacecraft ever built.  It is equipped with 10 instruments which perform both optical and radar observations of Earth and give a wealth of data on how the planet works, including factors contributing to global warming.

While a list of all the devices on Envisat would be tedious and exhausting, we can take a look at the two most important ones, both of which are new pieces of technology:

The biggest single instrument on Envisat is called Advanced Synthetic Aperture Radar (ASAR).  It is a significant improvement over any previous meteorological radar unit, with enhanced ability in coverage, range of incidence angles, polarization and modes of operation.  The elevation of the radar beam can be steered, and the observations can be made in swaths of varying width, either 100 or 400 km wide.

MERIS, the Medium Resolution Imaging Spectrometer, is designed to measure the solar radiation reflected by the Earth.  It can observe the entire planet in three days.  Its primary mission is studying the color of the water in oceans and coastal areas.  From this it is possible to derive measurements of chlorophyll pigment concentration in algae, suspended sediment concentration and aerosol loads over marine seas.  In addition, it is used for atmospheric and land monitoring.

Envisat has given us a view of this event that we have never had for any other volcanic eruption.  The satellite, of course, was specifically calibrated for measuring the characteristics of clouds, and a new algorithm had to be devised to adapt it to the volcanic ash plume.  This has been working very well, providing detailed information on the movement, altitude and size of particles involved.  Since the blanket of ash that is spread by an eruption is one of its most destructive aspects, knowing how it moves and where it settles will be of great importance in preparing for future events of this type, and in understanding volcanoes everywhere.

And by studying this one, we are studying a scaled-down model of Olympus Mons on Mars, the volcanoes of Jupiter’s moon Io, and all the other volcanoes of the solar system.  How convenient!

One good thing: amazingly, there have been no casualties from this eruption.  Several hundred households in the vicinity of the volcano had to be evacuated, but all survived.

At this writing (April 24) the eruption is still happening.  The initial plume of ash has subsided enough for air traffic to resume, but it will take days or even weeks to get all those stranded passengers to their destinations.  A news report from two days ago (see sources) says that there are still ominous rumblings coming from the volcano.  Events of this type sometimes continue sporadically for some time, so we may not have heard the last from this one.

Whatever happens, Envisat will be there to watch it.  Thanks to the ESA and their outstanding satellite, future vulcanologists will have an in-depth profile of this eruption to study for years to come.

Sources:

“ESA Observing the Earth: New Satellite Image of Volcanic Ash Cloud, 15 April 2010″ at website of the European Space Agency:  esa.int/esaEO/SEMFYR9MT7G_index_0.html

“ESA Observing the Earth: New Satellite Image of Ash Spewing From Iceland’s Volcano, 19 April 2010″ at website of the European Space Agency:  esa.int/esaEO/SEMM16XN58G_index_0.html

“ESA Missions Observing the Earth: Envisat Overview” at website of the European Space Agency:  esa.int/esaEO/SEMWYN2VQUD_index_0_m.html

“Tremors on the Increase at the Eyjafjallajoekull Volcano” at newspublic:  news-public.com/index.php?option=com_content&view=article&id=1707:tremors-on-the-increase-at-the-eyjafjallajoekull-volcano&catid=34&Itemid=65

“Icelandair reschedules Flights out of Glasgow Despite Keflavik Airport Closure” in IceNews: News From the Nordics 24 April 2010:  icenews.is/index.php/2010/04/24/icelandair-reschedules-flights-out-of-glasgow-despite-keflavik-airport-closure/

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