Living in the Universe

Living in the Outer Solar System

 Second Week of April 2008

What would it be like to live in the outer solar system? It turns out to be not too bad and so life out there might not be as unlikely as we once thought. Past the orbits of Jupiter and Saturn, the Sun is a feeble dot in the sky. Temperatures are extremely cold, and yet under the surface of Titan, Saturn’s large moon, a vast ocean of water and ammonia may be lurking.

Astronomers have not directly observed this ocean, but recent observations with NASA’s Cassini spacecraft of Titan’s rotation and shifts in the location of surface features suggest a liquid ocean perhaps sixty miles under the surface. Titan is Saturn’s largest moon and the second biggest in the solar system, only slightly smaller than Jupiter’s moon Ganymede. It’s larger than Mercury and the recently demoted dwarf planet Pluto. Cassini has been looking at Saturn and its moons for several years and it has collected measurements using radar that penetrate Titan’s thick atmosphere, doing nineteen passes over the moon between 2005 and 2007.

Data from these early observations allowed researchers to locate fifty landmarks, including lakes, canyons and mountains on Titan’s surface. They looked at later radar data and found that prominent surface features had shifted by up to nineteen miles. That’s a lot. The spin of Titan’s crust is linked to winds that blow through its atmosphere, but this large a displacement of surface features would be hard to explain unless the crust were separated from its core by an internal ocean allowing the crust to essentially float. According to Ralph Lorenz of the Johns Hopkins University, who led the study, “It’s because Titan’s crust seemed so mobile that we infer this internal ocean.” He says the ocean is probably water, with a few percent ammonia, while the atmosphere is made up of nitrogen with other hydrocarbons that give Titan its orange color. Titan’s atmosphere consists of compounds that may have existed in the Earth’s primordial atmosphere, but Titan has more of the chemicals ethane and methane.

Titan is perhaps the most Earth-like landscape in the solar system and it probably has the most Earth-like weather. It’s much colder than the Earth, but the same processes that go on in our weather, particularly the formation of clouds and rain, happen on Titan, but in this case with liquid methane and not with water. Titan is thought to have hundreds of times more liquid hydrocarbons than all the known oil and gas reserves on the Earth. On Titan, these hydrocarbons rain from the sky and collect in vast deposits that form lakes and dunes.

Now the evidence of an underground ocean raises anew the possibility that life might exist deep under Titan’s surface. Similar underground oceans have been found on Europa, Calisto, Ganymede, and tiny Enceladus. Saturn’s tiny moon Enceladus is the subject of a second recent story. It has all the ingredients needed for life erupting in geysers beneath its surface and spewing into the atmosphere.  Instruments on the Cassini mission a few weeks ago revealed a concentration of water vapor, carbon dioxide, carbon monoxide, and organic material twenty times denser than expected, and the temperatures were higher than previously measured. Dennis Matson, the project scientist for Cassini, said, “Enceladus has got warmth, water, and organic chemicals, some of the essential building blocks needed for life.  We have quite a recipe for life on our hands.”

Saturn’s moons have long been of interest to scientists, particularly Titan with its enormous and significant atmosphere, but Enceladus’ chemical components are surprising because previously they’d only been found in comets. Cassini also measured surprisingly warm temperatures near the north pole. It doesn’t seem warm to us, but minus ninety-three degrees Celsius or minus a hundred and thirty-five Fahrenheit is tens of degrees warmer than scientists had expected. But it’s the liquid water that’s surprising, and those high temperatures near the surface make it likely that there’s liquid water not far below the surface.

There you have it. In the frigid depths of the outer Solar System, ranging from a large moon Titan to a tiny moon Enceladus, we have liquid water. We also have organic material, and we have energy: all the ingredients necessary for microbial life. Now, we just need a few billion dollars in NASA’s budget to send spacecraft out there with instruments that can make the careful measurements needed to be sure, and that’s at least a decade or more away. Astrobiology is not a subject for those in need of instant gratification.

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Sending Motes into Space

First Week of December 2007

Picture this scene if you will. Just below a half-opened garage door, a tiny device is seen lurking at the feet of someone in the shadows. It looks like a blue dragonfly. Then its miniature wings begin to flap, and it slips under the door and darts along the street. After rising through the air, it hovers outside the window of a building several stories up. There’s an opening on the roof, and it slips inside flitting from room to room with its video camera eye transmitting pictures to a screen on a remote control unit strapped to the wrist of its clandestine operator.

This isn’t a scene from a Bond film, but an animated video produced by Onera, France’s national aerospace company, to explain REMANTA, a project to develop technologies needed for miniature robotic spacecraft and aircraft. These bug-like flying devices are being developed in other research labs. Some are small enough to be carried in a briefcase. Others are the size of a jet fighter and need a runway for takeoff. These devices are generically called UAVs, unmanned aerial vehicles. The smallest of them are about six inches across. The bug built by REMANTA has a wingspan that size, and it flies by flapping its wings, a bit like a real insect. This means it needs less power than helicopter type rotors and is better able to withstand winds and being blown off course. Harvard University researchers have developed a fly-like robot that weighs just two thousandths of an ounce and has a wingspan of three centimeters. It’s about the size of a real fly. It cannot, however, fly on its own yet, it needs a power tether.

What have these devices got to do with astrobiology and space travel? Well, the future may be in going small. If we think about the pioneer and landmark missions of the current day, they are huge spacecraft like Cassini at two tons, or the ton and a half of the Hubble Space Telescope. But if we go in the other direction and use miniaturization, there are some interesting possibilities in space travel. Back in the 1970s some MIT undergraduates managed to get an audience with a mid-level NASA bureaucrat and they tried to sell him on the idea of using a robotic ants connected by a neural net to explore Mars and look for life. Well they were a little ahead of the technology, and I guess they were laughed out of the room. But the time has now come to try small robotic space explorers.

Mason Peck, who’s an engineer at Cornell University, envisages thousands of miniature spacecraft drifting to different planets powered only by the Earth’s magnetic field. His novel magnetic propulsion method recently earned him a seventy-five thousand dollar grant from NASA’s Institute for Advanced Concepts. The biggest advantage of using small spacecraft is that it could shave hundreds of millions of dollars off a typical NASA satellite launch because it requires almost no rocket fuel once in orbit. What he’s designed is basically a set of chips that use the Lorentz force, a physics phenomenon that acts on electrically charged particles moving in a magnetic field. In this case, the force would help the chips escape Earth’s gravity and head for a distant planet. On arrival the chips would rain down on the planet, analyze atmospheric or surface samples, and then signal to Earth if they’d found anything interesting.

Peck and his team are testing Lorentz propulsion in the lab, and if all goes well they have plans, ambitious plans, to try this method to go to Europa, probably not for ten or fifteen years. Here’s how it works in a little more detail. Thousands of chips are packed into the nose of a rocket and launched into low orbit. Each chip’s solar panel sends electrons to a capacitor which pumps them through a long trailing wire to charge up the chip. Then, in orbit, the Lorentz force acts on the charged chip through the magnetic field that nudges the space chip to a higher altitude. After about a year the Lorentz force will have given enough energy to the chip to free the tiny device from the Earth’s magnetic gravitational field.

Timed properly, the swarm will fly freely on a trajectory for Jupiter’s large moon Europa. After a two to four year journey, tiny thrusters adjust the chip’s heading as they approach Europa. They are too small to burn up as they enter the atmosphere, and with several thousand en route, the mission will succeed even if some chips don’t make it. The chips then collect molecules from the air or the moon’s surface for analysis. Micro-particles will stick to liquid on the chip’s surface which will be sucked inside the chip. The chip could contain miniaturized versions of PCR, the polymerized chain reaction device that’s used to look for DNA. So this is one of the ways we could look for life on Europa using tiny robotic spacecraft.

More generally, scientists have always taken advantage of the gains implied by Moore’s law, the doubling of processor speed and computing capability every eighteen months. But the second aspect of Moore’s law is miniaturization. Small devices use less power and they are cheaper to launch and accelerate to very high speeds. If other intelligent civilizations are exploring the galaxy, they’re probably not doing it with starships, they’re probably doing it with smart motes.

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Follow the Water

Fourth Week of November 2007

The theme this week is water, which is considered to be one of the fundamental and essential ingredients for life in the universe. In a story based on an Ohio State University news release, scientists for the first time have directly observed how water lubricates the motions of protein molecules to enable their different functions to occur. Scientists are one step closer to understanding how proteins move when they perform essential life functions. This finding was based on using ultra-fast light pulses to reveal how the water molecules link up with proteins and enable them to move around.

The research has practical benefits. Researchers hope to find new treatment for diseases such as Alzheimer’s, Parkinson’s, cataracts, cystic fibrosis, and diabetes. In addition, understanding the role of proteins in living cells can help scientists decipher how the first cells on our planet began to function. The work also sheds light on the role liquid water plays in living organisms. Scientists were able to map the motions of water molecules at different locations on a very much larger protein molecule. The team took laser snapshots of a single myoglobin molecule, which is the protein that carries oxygen inside muscle tissue, while it was immersed in water in the laboratory. They were able to observe how fast the water molecules were moving around the protein and see how those rapid motions related to the characteristics of the protein at that moment, the electrical charge at a particular site for example, or changes in the protein shape.

Proteins can execute motions in as little as a few billionths of a second. Water normally moves a thousand times faster on a scale of a trillionth of a second. In previous work, researchers showed that water molecules slow down substantially as they get close to a protein. This new study shows that water molecules slow even more once they reach the protein. The water forms a very thin layer only three molecules thick around the protein, and this layer is the key to maintaining the protein structure and flexibility and lubricating its movements. These findings challenge the conventional wisdom of theorists trying to envisage what occurs on these tiny scales. They usually use computer simulations to fill the gap, but now the observations are direct.

We move from this story of how water works within the context of life to a more distant location: Europa. Europa is perhaps Jupiter’s most exciting moon, the water moon. Its icy shell is scarred with a crazy quilt pattern of cracks and grooves, and beneath that outer layer of ice hides a global ocean. Astronomers would love to know if there is life swimming in that ocean. The answer partly depends on the flavor of the water. Earth’s oceans are full of minerals that have shed into the water from the erosion of rocks or from volcanic eruptions. Chlorine and sodium are the primary elements in the solution, and they give our ocean its distinctive salty taste. Europa’s ocean too is believed to be salty, but is it just like the Earth’s ocean? Or does it have its own unique recipe based on different ingredients, and how would those different ingredients affect the likelihood of life in the Europan ocean?

Kevin Hand, who’s a planetary scientist with NASA’s JPL says, “The conventional wisdom is that Europa’s ocean is dominated by magnesium sulfate. The reason for that,” he says, “if you take a bunch of chondrite, space rocks, and crunch them all together to form a planet or a moon as we think occurred around the Jovian system, the dominant cation and anion that come out of that leached material is magnesium and sulfate.” He says that while scientists have seen evidence for the sulfate, the anion or the negatively charged ion, in spectroscopic measurements of Europa’s icy surface, they’ve not been able to discern what the dominant positively charged cation is. There’s active debate over whether that cation is really magnesium or if it could instead be sodium as it is on Earth. A third possibility is that it might even be hydrogen. There is a lot of hydrogen in the Jovian system because the planet that it belongs to is ninety percent hydrogen, and hydrogen is available on the surface of Europa. If that’s the case, then Europa’s ocean could be a searing cauldron rather than a placid sea because hydrogen combined with sulfate creates sulfuric acid.

Europa’s ice chemistry is further complicated by its neighboring moon, Io. This volcanic moon is constantly spewing particles out into space, and those particles become trapped in Jupiter’s rapidly rotating magnetosphere. Europa is continually bathed in this charged ionic stew. Another researcher in the team chips in, “Io contributes sodium, sulfur, chlorine, and other ions to Europa’s surface. These charged particles, along with electrons and protons from the hydrogen ions, stimulate chemistry in the surface material and have probably altered its chemical makeup.” Another complication is that Europa’s oceans still could be adding its own salts to the surface ice because scientists have shown that the ice has more salt than can be explained by simple radiolytic processing from Io’s contribution. To determine the ocean’s chemistry from remote spectral data, scientists would need to tease out that native source of salt from the other salts present in the surface.

However, yet another complication is that over long timescales the ocean and the surface may exchange material thanks to the cracking and shifting of the ice shelf. By now you’ve probably got the sense that this is a difficult problem to solve. To summarize, Hand says, “Right now, many people think that the spectra on Europa may be best matched by a one-third mixture of magnesium, sodium, and hydrogen as cations.” It’s going to be awhile before we know exactly what Europa’s ocean water is like. In fact, to really know we’ll have to send a mission there designed to pierce through the ice. Scientists don’t even agree on how thick that ice shell is, but it likely varies a great deal from one place to another. The best Galileo data suggest an average thickness of four kilometers or two and a half miles. Hand says, “That’s comparable to the Antarctic ice sheet, and we’re boring down through that now on our way to Lake Vostok. It may be comparable to what we need to do on Europa.” Around the year 2015, hopefully NASA will launch the Europa explorer mission, which could include a lander that will melt through the ice pack, allowing us to answer these questions directly for the first time.

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The Great Lakes of Titan

Third Week of October 2007

This week’s news comes from the outer reaches of the solar system. JPL released some newly assembled radar images from the Cassini spacecraft that provide the best view so far of the hydrocarbon lakes and seas on the north pole of Saturn’s moon Titan. Another new radar image reveals that the south polar region also has lakes. These images give new insights into the cycling of hydrocarbons on Titan, which are in some ways analogous to the water cycle on Earth. Titan is a uniquely active environment in the solar system, along with Io as another example with its active volcanoes. Titan is the only moon known with a significant, substantial atmosphere. Scientists think that it might in some ways resemble aspects of the early Earth and provide clues of how precursor molecules for the origin of life were formed.

The images that we’re seeing now were sent back from an October 2 flyby where the primary goal was the hunt for lakes at the south pole. The new mosaic has been stitched together from radar images from seven Titan flybys over the past eighteen months and it shows a north pole pitted with giant lakes and seas, at least one of which is larger than Lake Superior. About half of Titan’s north polar region has been mapped by Cassini’s radar instrument, and about fifteen percent of that region is covered with what scientists interpret as liquid hydrocarbon lakes. The lakes and seas are very common at the high northern latitudes of Titan, which is mired in the depths of winter now. Scientists say that it rains methane and ethane there, filling in the lakes and seas. These liquids then carve meandering rivers and channels on the moon’s surface.

Now Cassini is moving into unknown territory, the south pole of Titan. One of the mission specialists said, “We wanted to see if there are more lakes present, and sure enough there they are, three little lakes smiling back at us.” Titan is indeed the land of lakes and seas, and it will be interesting to see the differences between the north and south polar regions. Scientists have made progress in understanding how these lakes have formed. On Earth, lakes fill low spots or are created when local topography intersects a groundwater table. Mission specialists now think that the depressions containing the lakes on Titan may have formed by volcanism or a type of erosion called karstic on the surface, leaving a depression where the liquids can accumulate. Karstic lakes are common on the Earth. For example, Minnesota and central Florida have hundreds of lakes like this.
The lakes observed on Titan appear to be in varying stages of fullness suggesting their involvement in a complex hydrologic system akin to the Earth’s water cycle, and that really does make Titan unique amongst the extraterrestrial bodies of the solar system. The lakes seen so far vary in size from the smallest that can be observed, about a kilometer square, to greater than a hundred thousand square kilometers which is slightly larger than the great lakes in the Midwest U.S. Of the four hundred observed lakes, seventy percent of their area is taken by large seas. These flybys will continue, and they will continue to pencil in our view of this strange world. Titan’s nitrogen atmosphere, its geography, and its complex weathering are familiar, but the chemistry is completely different.

Another story this week from Cassini involves the surprising moon Enceladus, which was shown to have jets of fine icy particles spraying up. Members of the imaging team have used two years worth of data from the geologically active moon to find the sources of the most prominent jets sprouting from the moon’s surface. They compared these surface source locations to hotspots that had been previously detected in 2005. They found that almost all the jets appear to come from four prominent tiger stripe fractures in the moon’s active south polar region, and in almost every case in the hottest areas detected by Cassini’s infrared spectrometer.

This is the first time that these visible icy jets have been tied to the tiger stripes. Scientists suspect that these jets collectively feed a plume that towers thousands of kilometers above the moon. This is the first proof, however, that makes a causal connection between the jets and unusual heat radiating from the fractures. All the measured jets fell on a fracture, but not all jets fell on a previously discovered hotspot, and so the team concluded there are other hotspots to be found. The possibility suggested by the imaging team is that the jets may erupt from pockets of liquid water. That, together with the unusually warm temperatures and organic material detected by Cassini in the vapor accompanying the ice particles, pushes this small Saturn moon into the spotlight as a potential habitable zone object, but what happens beneath the surface to power the jets remains a mystery.

Carolyn Porco, lead of the imaging team on Cassini, says, “These are findings with tremendously exciting implications. To say that I’m eager to get to the bottom of it would be a cosmic understatement. Do the jets derive from near surface liquid water or not, and if not then how far down is the liquid water that we all suspect resides within this moon? Personally, I’d like to know the answer yesterday.” Me too, but patience is required. The next opportunity for answering these questions will not be until March 2008, when Cassini dips low again over Enceladus and flies through the plume. Astronomers will be waiting anxiously for this moment to learn more about the most intriguing small moon in the Solar System.

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Ice in the Outer Solar System

Second Week of August 2007

We all know about global warming, and most people suffering through the summer will recognize that it’s one of the hottest on record, perhaps the hottest on record. You probably don’t have it as bad as we do in Arizona. Up the road in Phoenix, this year so far they’ve had twenty-one days with a high temperature above a hundred and ten degrees. That’s three times more than the largest number ever on record. In Tucson we consider we’re lucky if we get away with a hundred degrees, and this year we may have a hundred days over a hundred degrees. It’s pretty nasty here. Humans are not really built for such heat.

What better than to think of the coolest place possible? No, not your swimming pool or freezer. I mean the outer parts of the solar system, the coolest place there is. So let’s talk about the distant realms of the solar system, Pluto and its small moon Charon. I know, Pluto’s not even a planet anymore; it was demoted a year or so ago so it’s almost beneath our respect, but it sure is a nice, cold place. So let’s talk about ice.

Charon is like an ice machine sitting in the outer part of the solar system. Recent observations have shown that frigid geysers spew material up through the cracks in the crust of Pluto’s companion and recoat parts of its surface in ice crystals that could make this little distant world into the equivalent of an outer solar system ice machine. The evidence for these ice deposits comes not from any spacecraft, although there is a spacecraft on the way to Pluto, but from a ground-based telescope at the Gemini observatory in Hawaii. It’s their adaptive optics system coupled to a near infrared instrument called NIRI. These observations were made with the 8-meter telescope on Hawaii’s Mauna Kea, and they showed that spectral fingerprints of ammonia hydrates and water crystals are spread in patches across Charon and have been described as the best evidence yet for the existence of these compounds on tiny worlds such as Charon.

The observations suggest that liquid water mixed with ammonia from deep within Charon is pushing out onto the ultra-cold surface. This action could be occurring on timescales as short as a few hours or days and at levels that re-coat the little moon to a depth of one millimeter every hundred thousand years. This discovery will have implications for other cold worlds in the outer solar system, particularly in the Kuiper Belt, which is a region of the solar system that extends beyond the orbit of Neptune and contains a number of small bodies, the largest of which include Pluto and Charon. It also, famously, includes several objects that are larger than Pluto, hence the demotion of Pluto from planet status. Jason Cook, a graduate student on the project who works up the road at Arizona State University, says, “There are a number of mechanisms that could explain the presence of crystalline water ice on the surface of Charon, but the most interesting explanation points to cryovolcanism which brings liquid water to the surface where it freezes into ice crystals, and that implies that Charon’s interior possesses liquid water.

Liquid water is essential for life as we know it, and understanding the distribution and behavior of liquid water beyond Earth can help scientists understand where to search for habitable environments.” To reach the conclusion that cryovolcanism was producing ice on Charon, Cook and his collaborators studied all the possible mechanisms that could explain water ice. The crystals are unlikely to be made of primordial ice from the time the solar system formed, because such ice would become amorphous, that is it would lose crystalline appearance in a few tens of thousands of years due to solar UV radiation and cosmic ray bombardment. Processes that create fresh, icy patches on other worlds, such as impact gardening by meteorites and convection of subsurface materials to the surface, are not supported by the particular chemical fingerprint they saw.

The only mechanism that could explain the data is cryovolcanism, which is the eruption of liquids and gases to the surface in an ultra-cold environment. It seems now that cryovolcanism is a fairly common occurrence in the outer solar system. Enceladus, a tiny moon of Saturn, and Europa, which orbits Jupiter, both show evidence of water ice oozing or spewing out from beneath their surfaces. The so-called tiger stripes on Enceladus were reported in 2006 by Carolyn Porco. They may have been created by geysers that send water out through surface cracks. Similar markings are seen on the Uranian moon Ariel in Voyager 2 flyby images.

Enceladus and Europa are tidally squeezed by the gravitational forces of their giant planets and in some cases by large nearby moons. This squeezes the water through the cracks. Ariel may have been affected by tidal squeezing in the past. By contrast however, Kuiper Belt objects such as Charon, Quaoar, Orcus and others are not tidally squeezed, and yet they seem to show evidence of cryovolcanism as well. In the case of Charon, it’s thought that heat from internal radioactivity creates a pool of melted water mixed with ammonia inside the ice shell. As the subsurface water cools and approaches the freezing point, it expands into the cracks in the ice shell above it. Due to the expansion, even a small vertical crack of half a kilometer in the base of the ice will allow material to propagate to the outer surface in a matter of hours. As the water sprays through the crack, it freezes and immediately snows back down onto the surface creating the icy patches that can be distinguished in near infrared light. Well, that’s the explanation from theory. The real proof will come from the deep space NASA probe New Horizons which will arrive at this system in 2015 and send back images to verify what’s been seen from the ground.

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Phoenix Soars for Mars

First Week of August 2007

This weekend was a great success for planetary science in general, exploration of Mars, and my university in particular, the University of Arizona. The Phoenix Mars Mission blasted off aiming to arrive at the red planet on May 25 next year to closely examine the northern polar region. Sitting atop a Delta II rocket, it left Cape Canaveral Air Force Base at 5:26 am on Saturday morning. It was a very exciting launch for anyone who was there to witness it.

The principal investigator of this mission is my colleague Peter Smith from the University of Arizona’s Lunar and Planetary Laboratory. The spacecraft launched flawlessly and established communications quickly with its ground station in Goldstone, California. Phoenix will be the first mission to touch water ice on Mars. Its robotic arm will dig into an icy layer believed to just lie below the surface. The mission will study the history of the water in the ice, monitor weather in the polar region, and investigate whether the subsurface environment in the far northern plains of Mars has ever been favorable for sustaining microbial life.

People shouldn’t get the wrong impression. This mission was never designed to look for life itself. It has no detailed biological analysis facility, but it will produce enough diagnostics to show whether this very promising region of Mars, just under the surface and therefore protected from the extreme cold, vacuum, and ultraviolet radiation of the surface itself, is potentially a place that could sustain life or has sustained it in the past. As Peter Smith says, “Water is central to every type of study we will conduct on Mars.” Phoenix is the first of NASA’s competitively proposed and selected Mars scout missions, designed to supplement the agency’s core Mars mission, with the theme: “follow the water.” The University of Arizona was selected to lead the mission in August 2003, and now we are the first public university to lead a Mars exploration mission. The grant that supports this mission was three hundred and thirty million dollars which is also the largest grant the U of A has ever had.

Phoenix uses the main body of a lander originally made for a 2001 mission that was canceled before launch, hence the name Phoenix. During the last year before launch Phoenix was run through a rigorous testing regimen for people who wonder about using a failed mission. The spacecraft and its instruments went through actual mission sequences allowing them to assess the entire system through the life of the mission while here on Earth. In fact there’s a test rig, a facility built in an empty warehouse just down the road from the U of A where they’ll simulate, recreate the Martian surface and run the Mars lander through its paces of landing and sampling soil, and people will be able to go down the road and watch it.

Samples of soil and ice collected by the lander’s robotic arm will be analyzed by instruments mounted on the deck. A key instrument will check for water and carbon containing compounds by heating the soil samples in tiny ovens and examining the vapors that are given off. Another will test soil samples by adding water and analyzing the dissolution products. There are cameras and microscopes to provide information on scales spanning ten powers of ten from features that could fit into hundredths into a period at the end of a sentence, microns, to the aerial view it will take during descent. There will also be a weather station to provide information on atmospheric processes in the arctic region.

The Phoenix Mars Mission will not answer the question of whether there’s life on Mars. It will take a more sophisticated series of missions later in the decade, but it’s going to be an exciting new insight on to the one place we think might have life in the solar system.

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A Proxy for Europa

Fourth Week of May 2007

At a place called El Zacaton in Mexico, NASA is testing an underwater robot in one of the Earth’s deepest sinkholes as a first step towards searching for life on Jupiter’s icy moon Europa. El Zacaton is near the Gulf Coast of northeastern Mexico. It’s about three hundred and thirty feet wide and more than thirty-three hundred feet deep. It could easily hold the Washington Monument or the Eiffel Tower. Scientists plan to map and take samples in this dark water-filled fissure with the one and a half ton DEPTHX robot over the next two weeks, as a prelude to navigating Europa’s ice capped oceans in about twenty years.

That mission is the latest step in a four hundred year old endeavor to understand Jupiter and its distant moons. Chris McKay of NASA Ames Center in California says we’re so sure there’s water on Europa that the real question is whether there is also life, whether there’s something in the ocean that bugs can eat. The robot is the ideal way to search. The robot is lowered by a sixty ton crane, and it’s powered by batteries. It’s nicknamed Clementine for its round shape and orange color, and it’s going to make daily descents into the vertical cave known in Mexico as a cenote. In fact the cenotes known in this part of Mexico are often formed from the debris of giant impacts, and many were caused by the impact that extinguished dinosaurs and other mammals sixty-five million years ago.

The robot will take three dimensional images, collect rock samples, and using floodlight film nooks and crannies too deep for divers to reach. Plants, animals, fungus, microbes, and bacteria are the known forms of life, but there may be more branches to the tree of life on Europa. Learning more about life tells us about our own heritage and the benefits for health and medicine that it could bring, according to researchers in the project.

The idea of mapping Europa’s oceans with an automated robot was dreamed up by a Texas scientist called Marcus Gary at a barbeque in 2001. Two years later his team won NASA funding for the five million dollar project. Gary chose El Zacaton for the first major test of the robot, which is about the size of a small car, because its sheer depth at the site was an unknown quantity. In 1994, an American diver died trying to swim to the bottom. According to Gary, it’s an ideal testing ground because we can test the robot’s mapping powers in untried waters. Its great depth means that many of its microbes live without oxygen or light and could be similar to that which could exist on Europa.

Europa’s thought to have twice as much water as the entire Earth, and it’s intrigued scientists ever since Italian astronomer Galileo Galilei observed Jupiter’s large four moons for the first time in 1610. NASA has hopes to take the probe to Antarctica in November 2008 to test it in the much colder waters below the frozen ice that resembles Europa, and if funding can be found, the scientists could send a much smaller version of the robot to Europa in about twenty years. That’s a long time to wait for a measurement of life, but water much closer at hand features in another story from this week, further evidence of a wet past on Mars.

The Mars rover Spirit has uncovered possibly the strongest evidence that the planet was much wetter than previously thought, by analyzing a patch of soil in Gusev crater and finding it unusually rich in silica. The presence of water would have been necessary to produce such a large silica deposit, according to team scientists. Principle Investigator Steve Squyres of Cornell University said in a statement to the news media, “This is a remarkable discovery. It makes you wonder what’s still out there.”

Spirit previously found clues of ancient water in the crater through the presence of sulfur rich soil, water altered minerals, and explosive volcanism, but this latest find is compelling because of the high silica content, which raises the possibility that conditions may have been favorable for the emergence of primitive life. It’s not clear how silica deposits form. One possibility is that the soil mixed with acid vapors in the presence of water. Others believe the deposit was created from water in a hot spring surrounding. The durable Spirit and its twin Opportunity have been working on overtime since completing their primary three month mission all the way back in 2004. For eight months opportunity has explored the rim of Victoria Crater on the opposite side of the planet. Scientists are exploring for a safe opening to send the rover in. These missions are managed by NASA’s JPL laboratory, and we can expect further discoveries from these intrepid rovers searching for evidence of previous life and wet conditions on Mars.

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