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

Even before they were launched, these three missions were successes. Mars Express, Venus Express and Rosetta were all built using the same design and many of the same data-gathering instruments. The same facilities were used to assemble the probes, and even many of the same people worked on all three projects. By using this strategy, the ESA was able to greatly reduce the amount of time and expense required to launch the missions.

But at first, Rosetta had a troubled childhood. It was originally approved in November 1993, and the destination was to be the comet 46 P/Wirtanen- but the project ran into delays and was not able to make that destination. Preparations continued with a new goal: comet 67 P/Churyumov-Gerasimenko. The new itinerary was an ambitious 10-year journey that would include two asteroid flybys: 2867 Steins in 2008 and 21 Lutetia in 2010.

This was the mission that finally made it into space on March 2, 2004, launched on an Ariane-5G rocket from Kourou, French Guiana. After that, the probe spent almost four years modifying its orbit by making two passes near Earth, and one near Mars. This put it on course for its first destination, asteroid 2867 Steins.

This was our first chance to get a close-up look at a rare kind of asteroid, the E-type. These bodies are thought to be fragments of larger asteroids that fragmented. They are highly reflective, with a featureless flat spectrum, and are thought to be the source of a type of meteorite called Aubrites. They are greatly outnumbered by other types of asteroids, mainly the M-types. While other probes had obtained pictures of eight asteroids, none of them was an E-type. As Rosetta approached 2867 Steins, the planetary scientists were keenly anticipating their first peek at one of these rare bodies.

The flyby took place flawlessly on September 5, 2008. The closest approach was 800 kilometers, and the relative velocity was 8.62 km/sec. Rosetta immediately confirmed the calculations of ground-based astronomers by affirming that 2867 Steins rotates once every 6.05 hours. The probe took some beautiful, clear pictures of the asteroid, imaging about 60 per cent of its surface. While the pictures were in color, 2867 Steins still looked gray; there was no significant color variation over its surface. Rosetta measured the asteroid’s albedo (reflectivity) and found it to be .4, meaning that it reflected about 40 per cent of the sunlight hitting it. (This is about four times as reflective as Earth’s moon.)

Steins is shaped like a child’s top: rounded on “top,” pointed on the “bottom.” The rounded end is dominated by a huge impact crater, 2.1 kilometers in diameter. Running down the side of the asteroid is a row of seven circular indentations. While these look like impact craters, their similar size and shape, and the fact that they are in a row, would seem to indicate that there is a fracture along that line, and the indentations are actually collapsed pits where dust has settled into the crack. There is also a similar groove along the other side of the asteroid, which may be the same fracture running completely through the body.

The surface features of Steins can be used to make inferences about its history. Its surface is not saturated with impact craters; in other words, there is some empty space visible between them. But we know that the early solar system was a violent place, with many impacts occurring frequently, so we would expect that an asteroid would be completely covered with impact craters. If we find an asteroid that doesn’t look like that, we must assume that something happened to erase the older craters. When looking for a likely cause of this phenomenon on Steins, our attention is immediately drawn to that 2.1-kilometer crater on its top. This is a puzzle, because the impact was so great, it should have shattered a solid body. Normally, if you take a solid rock that’s about 6 km wide and hit it with another rock that’s also of considerable size, they should both split into lots of little fragments.

The conclusion is inescapable: 2867 Steins was never a solid body. It’s a “rock pile,” a collection of fragments held loosely together by their mutual gravitation. When the big impact happened, these fragments were shifted around; some of them probably even flew away and then came back and re-collided with the larger body. Since the asteroid itself was the greatest source of gravity nearby, all the pieces eventually settled back together. The crater from the big impact was so huge, it was still recognizable after the shift- but any smaller craters were completely obliterated. Except for that big crater, Steins got a completely fresh surface, and any smaller craters that we see on it now have occurred since then.

So now we have another portrait of an asteroid, and we know something about its past. Before now, this type of body was an abstraction that existed only on the pages of astronomy textbooks. Now it is a real object that we can see and study. ESA has posted a video of the approach to Steins, and the sight of this little jewel-like object spinning out of the darkness is truly inspiring.

And Rosetta hasn’t even reached its destination yet! This is a really ambitious project, and the hits just keep on coming. In November of 2009, Rosetta modified its course by flying past Earth one more time, which put it on course for the asteroid 21 Lutetia. That encounter will happen in July of this year, and we will gain another asteroid for our photo gallery. These encounters always give us some interesting science, and this one will certainly be no exception.

After this, the probe will go into a period of hibernation. When it wakes up, it will be at it final destination, the comet 67P/Churyumov-Gerasimenko. If all goes well, the probe will go into orbit around the comet and put down a lander, which will anchor itself by shooting harpoons into the comet’s surface. The lander and the probe will stay with the comet through its entire approach to the sun, observing the changes that occur as it heats up and begins to give off the gasses that form the comet’s “tail.” If this is successful, we will finally know in detail exactly what happens to a comet as it approaches the sun.

The show is just starting! Watch for updates at this website.

Sources:

Rosetta homepage at the website of the european Space Agency: sci.esa.int/science-e/www/area/index.cfm?fareaid=13

Space Topics: Rosetta at the website of the Planetary Society: planetary.org/explore/topics/rosetta/

Rosetta: the United States’ Contribution at the NASA website: search.nasa.gov/search/search.jsp?nasaInclude=rosetta+comet+mission

The first object was spotted by the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey. This project was set up by the United States Air Force, NASA and MIT’s Lincoln Laboratory with the aim of discovering and tracking near-Earth asteroids and it has had much success over the years. Observations are carried out by a pair of Ground Based Electro-Optical Deep Space Surveillance (GEODESS) telescopes which are located in Socorro, New Mexico. On January 6 the telescopes achieved their latest success when they observed a new object in the asteroid belt which is a region of the solar system located between the orbits of Mars and Jupiter. This new object was named P/2010 A2 and its appearance has caused some excitement in the astronomical community.

While it is not uncommon that a new object should be identified in the asteroid belt the unusual thing about P/2010 A2 is its appearance. Generally asteroids have a relatively circular orbit and are not volatile in nature. These show up as a speck of light on pictures taken from telescopes. Comets on the other hand tend to have an elliptical orbit around the Sun and exhibit a visible tail due to the effects of solar radiation on their nuclei. These tend to have a fuzzy appearance in pictures. The mystery with P2010 A2 is that it exhibits the traits of both an asteroid and a comet. While it has an orbit which is consistent with an asteroid the picture taken of the object appeared fuzzy which gives it the appearance of a comet. This came as a surprise in that comets do not normally reside in the asteroid belt and scientist have been working to come up with an explanation of why this should be.

Initial observations indicated that the aphelion (furthest distance from the Sun) of the object is only 2.6 Astronomical Units (AU). This would mean that it remains within the warmer inner regions of the asteroid belt where ice is less likely to form. The frost line is located at 2.7 AU and it is beyond this that more volatile ices are expected to form which are typical of a comet. With ice probably not forming on its surface, this has led to the theory that the unusual appearance may be as a result of a recent asteroid collision which exposed ice that had been originally trapped beneath the surface of the object. Melting of this ice and the resulting gas and dust which would be released would help to explain the tail of the object.

If this explanation is indeed true then it would be the first confirmed collision event between two asteroids. Although a similar event has probably occurred in the past, this would be the first time observations of the phenomenon had been made. Monitoring of the object is expected to continue in the near future to try and establish more details. Specialists hope that either the Hubble or Spitzer Space Telescopes can be brought to bear on the puzzle although this has yet to be confirmed.

In future another space telescope which may view the object is the WISE Telescope. This was launched into space at the end of 2009 and only a few weeks after the lens cover was removed from the instrument it is already starting to produce results. The official start of the WISE mission to map the entire night sky was January 14. However in tests prior to this the telescope showed why it will be an important part of detecting near-Earth asteroids in future. Two days before the official mission was to begin it was reported that WISE had already sighted its first asteroid. The sighting was confirmed by the University of Hawaii’s 2.2m visible light telescope and the asteroid was named 2010 SB78. Initial estimates indicate that the asteroid is around 1 kilometer in diameter and is currently at a distance of 158 million kilometers from Earth. It is not considered that the orbit of the asteroid will bring it near to Earth and while it is not considered to be a danger it will continue to be monitored.

With two new objects being discovered in a relatively short time period it is to be hoped that the pace at which asteroids are detected will accelerate in the future. The work of the many existing projects which detect and track near-Earth objects will be enhanced by the capabilities of the WISE telescope and this should mean our knowledge of asteroids in the vicinity of Earth should be greatly increased in the coming years.

HAYABUSA was launched on May 9, 2003 on an M-V-5 launch vehicle from Uchinoura Space Center on Kyushu Island, Japan. About a year later, the probe modified its orbit by performing a flyby of Earth, and was sent on a trajectory for its destination. It arrived at Itokawa on September 12, 2005.

It was a perilous journey. Along the way, HAYABUSA had to endure two solar flares, one of which damaged its solar panels, resulting in a delay in arrival. Despite the problems, the mission was a technological success, premiering an array of new devices that will also be used on future space missions. The craft is a beautiful piece of equipment, featuring four ion drive propulsion units and an autonomous guidance system allowing the probe to guide itself without directions from Earth. Its flyby of Earth was the first such maneuver to be achieved using only ion drive as the propulsion.

(For the rest of this article, you must bear in mind that there was a 30-minute signal delay, so the events that are related here in a few paragraphs actually took place over many worried hours, with much nail-biting by the mission control crew.)

So far, so good. HAYABUSA had arrived a little battered, but still capable of performing its mission. It made observations of the asteroid from a few kilometers out. (Itokawa looks a bit like a cucumber: elongated and slightly bent, with little lumps here and there on its surface.) The next part of the mission was to deploy a small hopping robot to rove over the asteroid’s surface. On rough terrain, hopping is sometimes a better way to get around than rolling. It was hoped that this little device would be able to get to places that the larger unit couldn’t.

Unfortunately, this part of the mission was a failure. A technical malfunction caused the hopper to fire in the wrong direction, missing the asteroid completely. It’s still out there somewhere, whizzing around the sun: an artificial asteroid. That was a disappointment, but the main part of the mission was still to come. HAYABUSA prepared for its landing on the surface of Itokawa.

At this point, there was a malfunction that almost ended the mission prematurely. HAYABUSA made two landing attempts, and on the second one, a leak developed in a fluid line within the probe, causing a cascade of damage. After that, there was a period of confusion.

The probe continued to approach the asteroid. The moment of landing came and went, and the probe kept signaling that it was descending. Why was it still descending? Had it missed the asteroid completely, or was the signal simply incorrect? The mission control team decided to give the probe instructions for an emergency ascent in the direction of Earth. It was a gamble, since they were not sure of the status of their probe and were not even certain if it could respond, but it was their only chance.

To their enormous relief, it worked. Communication was reestablished with the probe, which sent an update relating the exact sequence of events:

The first landing attempt was aborted by the probe itself, because it detected an obstacle during the descent and recognized it as a danger. On the second landing attempt, apparently the signal indicating that the probe was still descending after the expected landing time was incorrect. The landing was successful, and the probe remained on the surface of the asteroid for about half an hour. The probe then lifted off from the asteroid.

It was at this point that the leak in the fluid line had developed, resulting in a period of signal loss. During this time, the probe’s onboard computer had rebooted once, causing the loss of all data that was stored at that time. This left the central question unanswered: did HAYABUSA successfully collect its sample of asteroid dust? The team members pored over their data, and there were conflicting press reports which first indicated that the sample had been taken, then that it had not.

The plan had been for HAYABUSA to fire one or two pellets into the ground, throwing up a plume of dust which would be captured and stored in the probe’s sample container. In examining the data from the probe, the scientists were unable to determine if this had been carried out. However, it was ascertained that during the 30 minutes that HAYABUSA was on Itokawa, its sample collector was open and in contact with the ground. It is hoped that even if the pellets were not fired as planned, some dust from the surface may have been disturbed by the landing and drifted into the container. Even a microscopic amount would be of enormous scientific importance.

The problems were not over for HAYABUSA. A malfunction developed in the craft’s ion drive, raising the possibility that it might not be able to put itself into orbit for return to Earth. (We can guess that this may be related to the original fluid leak.) In a heroic save, the team managed to link parts of two of the craft’s four ion engines, thus achieving the thrust of one engine. The reduction in thrust would delay the probe’s return to Earth, originally planned for 2007, until June of 2010.

That day is coming in just a few months now, and provided that the probe’s return to Earth is successful, we will finally learn if it contains the dust of an asteroid. Even if it doesn’t, the Japan Aeronautical Exploration Agency has earned praise from the scientific community for their heroic and ingenious efforts in overcoming the many obstacles that this mission faced. Regardless of the result of the HAYABUSA mission, Japan has suddenly moved into the forefront of space exploration.

Watch for an update at this site when HAYABUSA returns to Earth in June.

Sources:

Website of the Japan Aerospace Exploration Agency (JAXA): jaxa.jp/projects/sat/muses_c/index_e.html

Current Status of the Asteroid Explorer HAYABUSA in Space Daily: Your Portal to Space, February 6, 2009: spacedaily.com/reports/Current_Status_Of_The_Asteroid_Explorer_Hayabusa_999.html

Space Topics: HAYABUSA (Muses-C) at website of the Planetary Society: planetary.org/explore/topics/hayabusa/

Cain, Fraser: HAYABUSA Successfully Collects an Asteroid Sample in Universe Today: universetoday.com/2005/11/29/hayabusa-successfully-collects-an-asteroid-sample/

When it was first identified in 2004 Apophis caused some concern as initial observations indicated a small chance that it would collide with Earth during its 2029 pass of the planet. At an estimated size of around 1000 feet this had the potential to be a serious impact event. However additional observations discounted the possibility of a collision in 2029 although they showed that the course of the asteroid could possibly take it through a gravitational keyhole at this time. These are small regions in space that can alter an asteroids course in such a way that on its subsequent pass it could collide with the Earth. If Apophis passed through such a region it was considered that it could set up an impact event in 2036.

This threat was taken seriously enough that Apophis remained on the Torino impact Hazard scale until 2006. This scale is a method of categorizing the potential danger of an asteroid and runs from 0 to 10. An asteroid classified with a 0 rating has a negligible chance of colliding with Earth while a classification of 10 means that a collision is certain. Asteroid Apophis was classified as a 4 for a short time although further study showed that it was unlikely that it would pass through a gravitational keyhole and it was subsequently downgraded to a 0.

However a number of scientists still consider that Apophis warrants further study to assess its threat. In 2008 the Planetary Society organized a competition to design a space probe which could be used to track the asteroid and awarded $50,000 in prize money to the winners. The European Space Agency, NASA and other research groups have also studied ways in which Apophis or other similar asteroids could be deflected from an Earth bound course.

The latest view of the threat that Apophis poses came from the Russian Space Agency at the end of December 2009. Anatoly Perminov currently heads this organization and in a radio interview he indicated that they were planning a meeting to discuss the possibility of a mission to Apophis. Although no detailed information was given, Perminov indicated that other agencies such as NASA and the Chinese and European Space Agencies may be invited to join any subsequent project that the Russian Space Agency plans. Whether this comes to fruition remains to be seen.

Whatever the outcome of the latest discussions regarding Apophis, it is generally accepted that at some point in the future an asteroid is likely to be found that is on a collision course with Earth. Recent advances in technology such as the WISE telescope and projects such as NASA’s Near-Earth Object Program are likely to identify many new asteroids in coming years. While the majority of these will pose no threat to Earth it cannot be discounted that a number of dangerous asteroids will be identified. Studying strategies for dealing with such a threat is best done as early as possible and while Apophis itself may not turn out to be dangerous it may help to spur agencies and research groups into taking action which could prove to be beneficial in the long run.

WISE was launched on a Delta rocket on December 14, and after a few weeks of prepping the satellite, NASA jettisoned the cover that had kept the sensitive instrument cold. Since WISE sees in the infrared, it could pick up its own heat, which would ruin the data being collected. To guard against this, it was cooled with frozen hydrogen and sealed in a vacuum container similar in principal to a Thermos bottle. Now that it is in orbit and without its cover, the vacuum of space will serve the same purpose, but even better. At the moment, the instruments on the satellite are being calibrated, and observations will begin shortly. WISE will spend eighteen months surveying the sky, at which time it should have exhausted its supply of internal coolant. At that time, the mission will be over.

What are some of the things that WISE might find? Scientists have high expectations. This mission will build on the findings of two earlier infrared missions, COBE and IRAS. To get an idea of how big an improvement WISE is over its predecessors, consider this: while IRAS, which went up in the 1980′s, had only 62 pixels in its cameras, each of WISE’s four cameras has over a million. With eyes like that, it should be able to see a lot.

You can get an idea of the kind of science that will be done with WISE by considering the things it can see. The wavelengths that the satellite can detect fall into four bands:

Band 1: 3.4 microns- This is a broad filter to detect stars and galaxies.

Band 2: 4.6 microns- This is radiation from things that are too cool to be stars, but have some internal heat- in other words, brown dwarfs.

Band 3: 12 microns- This is the wavelength at which asteroids radiate in the infrared.

Band 4: 22 microns- At this wavelength, relatively cold things will be revealed, such as the dust of star-forming regions.

WISE will orbit Earth from pole to pole, surveying strips of the sky with each passage. This will allow each spot in the sky to be imaged many times, and by comparing the images, NASA scientists will be able to detect any that show visible movement over a short period of time. By doing, this, they will identify asteroids within the solar system, most of which are in the main asteroid belt between Mars and Jupiter. This will give us our first really accurate map of the asteroids in our system.

In addition to these nearer objects, WISE will be able to pick up the faint warmth of brown dwarfs. As stated above, these are bodies that are almost massive enough to become stars, but not quite. They never achieve nuclear fusion, the fundamental characteristic of stars, but they do emit some infrared radiation. It is possible that one or more brown dwarfs exist close to the solar system, but have remained undetected before now. WISE will find these objects, if they’re out there, and should even be able to pick up the glow from any planets that orbit them. (There is no reason why a brown dwarf should not have planets, though it is unclear whether they could support life.)

It is also hoped that WISE will show us the brightest galaxies in the universe. In addition to the faint objects that it will detect, the telescope will pick up infrared radiation from brighter sources, such as galaxies bursting with the heat of trillions of suns. These ultraluminous infrared galaxies, or ULIRGs, are almost undetectable in visible light surveys, and may not have been found before.

Other things that WISE is expected to see include young stars and the discs of planetary debris that surround them, clusters of galaxies in the distant, early universe, and a detailed view of our own Milky Way galaxy. In doing this, it will give the best view yet of the evolution of stars, protoplanetary discs, galaxies and clusters of galaxies- in other words, the universe from the bottom up.

The WISE mission promises to be a gold mine, providing enough data to keep the worthy scientists of NASA working for years. Unfortunately, we will have to wait a little while to see any results. The WISE data will be released in two stages. A preliminary release is scheduled to take place six months after the end of the mission, or about 16 months after launch, and a final release is scheduled for 17 months after mission’s end, or about 27 months after launch.

Watch for future articles about WISE at this website.

Sources:

WISE mission page at NASA website: wise.ssl.berkeley.edu/

Ten Things You Should Know About WISE at website of the Jet Propulsion Laboratory: jpl.nasa.gov/wise/facts.cfm

WISE Overview at website of the Jet Propulsion Laboratory: jpl.nasa.gov/wise/overview.cfm

WISE public website: astro.ucla.edu/~wright/WISE/

Lakdawalla, Emily: WISE Guys, at the Planetary Society Blog, August 27, 2009: planetary.org/blog/article/00002070/

Whereas asteroids are protoplanets that were prevented by gravitational disturbance from reaching their maturity, comets come from an even earlier stage. They are actually frozen droplets of ice and dust from the original cloud that surrounded the early sun, from which the planets and all the other bodies in the solar system would later form. Comets are the solar system’s baby pictures, offering a view of the primordial material which grew into all that we see today. And unlike the material on larger bodies, the stuff of comets has not been changed by geological forces. It hasn’t been melted and reformed, as the matter on the planets has. By looking at it, we can get the earliest possible view of where everything else in the solar system came from.

Nasa’s Stardust, launched in February 1999, has been a huge success and a technological tour-de-force. It has already yielded revolutionary data on how and where comets form, and its mission has now been extended into a project called StardustNExT. The probe’s original mission was to capture dust from the comet Wild 2. To do this, it used a groundbreaking piece of technology that will certainly be used again on future missions: aerogel.

Aerogel is a substance that almost isn’t there at all; it is more than 99 per cent empty space. It looks like a faint fog, like your breath on a cold morning, but motionless. When particles of fast-moving dust hit a thick layer of aerogel, they penetrate the surface and get embedded inside, but they are not broken or deformed by the impact. The aerogel becomes a convenient storage medium, holding the dust particle until it is retrieved by scientists.

For the Stardust mission, the collection device was a metal framework resembling an oversized tennis racket, with blocks of aerogel in the squares of the grid. The probe passed through the comet’s coma with this framework extended, allowing bits of comet dust to strike the aerogel and get embedded. The samples obtained this way were sealed in a capsule and returned to Earth, but Stardust stayed in space and continued along its orbit.

This operation was tricky, and it was uncertain whether the samples could be returned to Earth undamaged. Because of aerogel’s fragility, there was a possibility that the substance would simply shatter from the stress of the landing. Tension was high when the capsule came down in the Utah desert, but when it was retrieved, scientists were relieved to find that their precious samples were undamaged.

Before these samples were obtained, scientists thought they knew what comets were made of. The conventional wisdom held that these bodies had formed on the distant edge of the solar system and had remained there ever since, frozen in cosmic cold storage. It was assumed that because of their extreme distance from the sun, comets had never received much heat or light.

But when some of the dust was retrieved from the aerogel and examined, scientists were amazed to find rounded particles called chondrules. These are already well known, as they are a common component of certain meteorites. They are bits of rock that melted, formed round bubbles and then solidified again.

Obviously these dust particles had not spent their entire existence beyond the orbit of Pluto.

Also found in the comet dust were Calcium Aluminum Inclusions (CAIs). These are thought to be the oldest solar system materials, and are composed of exotic substances that can only form under extreme heat.

The region of space where comets exist has always been extremely cold. It is absolutely impossible for chondrules and CAIs to form there. The NASA scientists were forced to admit something that sounded impossible: these particles were formed very close to the sun, under heat that could melt rocks. However, a large part of a comet’s mass is water ice, which obviously would not form in such heat. The inescapable conclusion was that the constituents of a comet did not form all at once, in the same place. Rather, the dust particles formed very near the sun, and then somehow migrated out to the edge of the solar system, where they became encased in ice.

While this result was not expected, even before this there were several theories which suggested that large-scale mixing may have occurred in the early solar system, with rocky particles forming very close to the sun and then migrating out to more distant regions. These results clearly confirm this, and indicate that the constituents of comets were formed in different places, and possibly over a very long period of time.

More recently, Stardust has given us another revelation. In their continuing examination of the collection device and the samples it contains, scientists have now found the amino acid glycine adhering to the aluminum grid that holds the aerogel blocks. Further analysis confirmed that this substance, which is one of the basic consitutents of life, has a different isotopic ratio from glycine that originates on Earth, and so must be of extraterrestrial origin. This lends support to the theory that life on Earth may have been seeded by amino acids from comets.

This is not the last we will hear from Stardust. The mission has now been extended into Stardust NExT, a mission in which the probe will perform a flyby of the comet Tempel 1, taking pictures and gathering other data. This is the comet that was deliberately struck by the Deep Impactor probe in January 2005. By the time Stardust arrives there in 2011, six years will have passed since that encounter, and scientists will be able to see if any surface changes have occurred in that time. They will probably also be able to see the impact crater caused by Deep Impact; this crater was obscured by dust at the time, and was never actually seen. When Stardust encounters Tempel 1, it will be the first time a comet has been visited twice by spacecraft.

Stardust will be telling us things for years to come. The dust samples will continue to be examined and analyzed, and the probe has new places to go. Watch this site for future updates.

The WISE Telescope is the latest in a long line of instruments that have been launched into space as part of NASA’s Explorer Missions. The instrument was designed, fabricated and tested by the Space Dynamics Laboratory in Logan, Utah and includes a 16 inch diameter telescope and four infrared detectors.

It has been launched into an orbit 525 kilometers above the Earth and will circle the planet 15 times a day, during which it will capture images of the night sky on an infrared sensitive digital camera. An image will be captured every 11 seconds with each picture covering an area of the sky around 3 times the size of the moon.

The operational phase of the mission is planned to last for 10 months and during the first 6 months of this the telescope will scan and map the entire night sky. Each position in the sky will be mapped at least eight times during this process and following its completion the telescope will begin a second scan which will continue for the remainder of the mission. The second scan will be used to try and identify further objects in the night sky and also to check if any changes have occurred since the first scan.

The mission has a number of objectives which include finding and studying asteroids and comets in our solar system, identifying the nearest and coolest stars which are know as brown dwarfs and to find the most luminous galaxies in the universe. It is expected that the mission will capture the images of hundreds of millions of objects in the night sky and the sensitivity of the infrared equipment is such that it will discover many objects that have previously gone unseen.
The finds that the telescope will make closest to our own planet will be near-Earth objects such as asteroids and comets which have orbits that bring them close to us. It is expected that hundreds of previously undetected dark asteroids will be identified by the mission and this will help in the search for potentially dangerous near-Earth objects which may be on a collision course with our planet.

The mission will also identify most of the asteroids with a size of 3 kilometers or greater in the main asteroid belt of our solar system and by measuring the infrared light from these will provide a good estimate of the size distribution of the asteroid population. Scientists should be able to use this information to make an estimation of how often it is likely that the Earth will have an encounter with a potentially dangerous object. The data collected should also provide an insight into the composition of asteroids and give clues as to whether they are solid or more like giant snowballs. Both the size and composition of an asteroid are important in determining its threat to our planet. The information from the mission will therefore assist future studies of potentially dangerous asteroids and also help in formulating a strategy for any that are found to be heading towards Earth and need to be dealt with.

The WISE Telescope will also be sensitive enough to identify brown dwarfs which form like stars but do not pick up enough mass to ignite nuclear fusion at their cores. It is suspected that around 1000 of these objects lie within 25 light years of planet Earth and the telescope should be able to provide confirmation of this. It has also been speculated that WISE may identify a ninth planet in our own solar system. The pattern of comet orbits around the Sun suggest that there may be a giant gas planet on the outskirts of our solar system about 25,000 times as far from the Sun as planet Earth and if this is the case then WISE should be able to confirm its existence.

Other finds are expected to include millions of energetic galaxies which are known as ultra-luminous infrared galaxies, newborn stars and disks of planetary debris around young stars. The most interesting finds that the WISE Telescope makes will be followed up by other missions including the Hubble Space Telescope, the Spitzer Space Telescope and ground based observatories. Information from the mission will also be used to target interesting areas of the universe by the James Webb Space Telescope when it is launched in 2014.

Data from the mission will be released in two stages. A preliminary release is scheduled for 6 months after completion of the mission and the final release will follow on 11 months after this. The results will be eagerly awaited by the scientific community and hopefully the mission will be a stunning success, providing new and exciting information that will broaden our knowledge of the solar system and universe in which we live.

The protoplanets are baby planets whose development was stopped by the gravity of Jupiter, which disturbed the dust in that region and prevented it from forming into full-size planets. What was left were small bodies that could have been the cores of larger planets, if Jupiter hadn’t been there. It is thought that Earth, Venus and Mars started from similar bodies, but continued their evolution into true planets. So the protoplanets are like snapshots from the early history of the solar system, frozen in perpetual babyhood, and it is hoped that by studying them, scientists will be able to learn something about the conditions under which they were formed. Another objective of the mission is to determine the nature of the building blocks from which the terrestrial planets formed, thus increasing our understanding of the process. A third objective is to contrast two bodies which seem to have followed very different paths in their development, in an attempt to understand the evolutionary processes involved.

The mission is timely because astronomers are beginning to detect planetary systems around other stars, and in the near future we should be able to answer one of the most fundamental questions of space exploration: is our solar system typical, or unusual? Are there other planetary systems out there that are similar to ours? If so, why? If not, why not? Understanding the processes that form such systems is obviously fundamental to answering these questions.

Ceres is the largest of the asteroids. It was the first to be discovered, found on New Year’s Day, 1801 by Giuseppe Piazzi of the Palermo Observatory. Its year is 4.6 times as long as Earth’s, and it has a diameter of about 960 km. (600 miles.) Vesta is the brightest of the asteroids and the only one that is ever visible with the naked eye. It was discovered on March 29, 1807 by Heinrich Olbers. Its year is 3.6 terrestrial years long, and it has a diameter of about 520 km. (320 miles.)

Simply giving the diameter of these bodies is a bit misleading, since they are not flat landforms such as we are used to here on Earth, but three-dimensional objects. While many asteroids are really just pebbles whizzing through space, Ceres and Vesta are big enough to be considered true worlds. To date, the largest asteroid to be approached by a space probe is Mathilde, which was studied by the NEAR-Shoemaker probe in 1997. That asteroid had a very irregular shape, with its largest dimension being about 66 km. (41 miles.) Compare that to the size of Ceres and Vesta, and it becomes obvious that they really are worlds. Vesta has a surface area more than three times that of Arizona, while Ceres’ surface is as big as Alaska, Texas and California combined. Ceres is so large that it may have a wispy atmosphere, and there is even the possibility that it may have permanently frozen polar caps composed of water frost.

Dawn’s ambitious itinerary, with all the course adjustments that it involves, would not be possible with old-style chemical propulsion. Dawn was first lifted into space by a Delta rocket, but since leaving that rocket, it has been relying on its ion drive. This is an advancement that was anticipated by science fiction writers for many years, and it works just as well in real life as it did in fiction. First used to great advantage by the Deep Space 1 probe, ion drive allows far greater flexibility and maneuverability than a chemical rocket would. Whereas chemical rockets are able to deliver large amounts of thrust for a short time, the ion drive is able to deliver lower thrust for a much longer time. The system is powered by solar panels. The power from these ionizes the fuel (xenon) and then accelerates it with an electric field between two grids. The resulting jet shoots out the rear of the engine at a speed of 60,000 miles per hour.

The idea of the ion drive has had a long history. Hermann Oberth, one of the pioneers of rocketry, proposed such a system in the 1930′s, but because chemical rockets were easier to design, the development of rocketry went in that direction instead. Now the technology has finally caught up with the vision, and we see that Oberth was right: this is a reliable and efficient propulsion system. Given its excellent performance so far, it will certainly be used on many spacecraft in the future.

In more ways than one, Dawn is the fulfillment of dreams. Many a science fiction story has been written about the settlement and mining of the asteroid belt. With the Dawn mission, we are taking a step toward that dream.

Sources:
Website of the Jet Propulsion Laboratory, California Institute of Technology dawn.jpl.nasa.gov/

Dawn: a Journey to the Begining of the Solar System ssc.igpp.ucla.edu/dawn/

Ambrosiano, Nancy: Dawn Space Mission is a Go in Los Alamos National Laboratory News Bulletin lanl.gov/news/index.php/fuseaction/nb.story/story_id/11526

Dawn Spacecraft at Aerospaceguide.net aerospaceguide.net/spacecraft/dawn.html

Many people may have missed the news but an asteroid was detected passing less than 9000 miles from the Earth on Friday 6 November and it was only 15 hours before this happened that the comet was actually detected. The asteroid was first picked up by researchers at the University of Arizona as part of their Catalina Sky Survey and following this was detected by the Minor Planet Centre in Cambridge Massachusetts. The asteroid was then picked up by the National Aeronautics and Space Administration (NASA) and its trajectory plotted.

The 23 foot wide asteroid has been christened 2009 VA and at its closest it was only 8700 miles from the Earth. This is 30 times closer than the Moon which lies approximately 250,000 miles from the Earth and it was the third closest approach of an asteroid ever recorded. However it is not considered that the asteroid would have made much of an impact and in actual fact it probably would have burned up in the Earth’s atmosphere long before it reached the ground.

However the more worrying aspect of the story is the fact that it was only detected 15 hours before it passed the Earth. This demonstrates that there are still objects out there that we know little about and shows how close they can approach before actually being detected. Although 2009 VA actually posed little threat, a larger asteroid could have potentially devastating consequences if it were to collide with planet Earth.

NASA was tasked by Congress with identifying at least 90% of the asteroids that are considered to pose a threat to our planet by 2020. They were assigned the task in 2005 and initially estimated there were around 20,000 dangerous comets and asteroids, with those that are 460 feet or greater in size being considered a risk. To date scientists have accurately located around 6000 of these and the scheme which is known as the Near-Earth Object Program continues.

However the passing of 2009 VA shows how difficult this task will be. For an asteroid to get so close to the Earth without being detected is not something that should be taken lightly. NASA monitored a 100 foot asteroid in March this year as it passed around 45,000 miles from the Earth. An asteroid of similar size crashed into planet Earth in 1908 although it landed in a remote part of Siberia. The impact however devastated an area 1,200 square miles in size and if such an object landed near an area of dense population there would be severe consequences.

The NASA project is therefore important and if an early warning of an imminent strike was given this could greatly reduce the human consequences involved. 2009 VA was a lesson that the task of identifying near earth comets and asteroids is not an easy one although the hunt will go on.