Block Island—a half-ton meteorite found on Mars by NASA's Opportunity rover.Image credit, NASA/MER OpportunityEver been driving down a lonely desert highway when you suddenly glimpse something in the corner of your eye that makes you think, "What was that?!" You brake, tires screech, you spin the wheel and make a wild U-turn, cutting into the shoulder and leaving a rooster-tail of dust as you floor the gas to get back to what you thought you saw….

Okay, dramatic desert car scene ended. That would be the Hollywood movie version of what NASA's Mars Exploration Rover Opportunity did recently, on the lonely desert highway that it's scouting on Mars.

On its determined long trek from Victoria Crater to the larger Endeavour Crater (a 12-mile span that Opportunity has completed about one fifth of over the past year), the rover passed by an X-box-sized block of iron that presented the appearance of a meteorite. It snapped a picture in passing, which was eventually transmitted to Earth and examined. By this time, Opportunity had already traveled about 180 meters beyond the block (dubbed "Block Island"). This is when the rover was commanded to backtrack all the way to the find (though it's doubtful it worked up a rooster tail).

Upon returning to Block Island—quite obviously an iron-nickel meteorite by appearance alone, but whose composition was confirmed by the rover's alpha particle X-ray spectrometer instrument—Opportunity took more pictures, including extreme close-ups with its microscope camera, which revealed surface patterns similar to those found on Earth iron-nickel meteorites that have been exposed to long-term weathering by wind and sand.

As interesting as stumbling upon a half-ton meteorite on the dusty plains of Mars' Meridiani Planum is, what this particular chunk of weathered iron is telling scientists sparks the imagination. In a nutshell, given the thinness of Mars' current atmosphere, scientists wouldn't expect a meteorite of this size to survive impact intact, at the speed it would be going. One of the possible explanations for Block Island's rock-houndable state is that when it fell to Mars, Mars' atmosphere was substantially thicker than it is now.

Further examination of the meteorite may reveal clues as to how long ago it fell through Martian skies. Evidence that Mars' atmosphere was warmer and thicker in the distant past, as well as the possibility that there was liquid water on the surface, has been mounting over the years. The age of this meteorite-fall could shed more light on the history of Mars' environment. If it fell billions of years ago, Block Island would weigh in as more evidence to support our current suspicions. If, however, we find that it fell more recently, then this could indicate that the atmosphere was more substantial later in Mars' history than we thought.

Imagine, if you will, a Mars that looks even more Earthlike than it does now: seas of water with waves rolling into shorelines, great clouds sending downpours of rain and snow onto mountains and plains, streams and rivers snaking through the landscape. Maybe, maybe, even some form of life?

All that from a rock? Yes, rocks talk, if we listen.

Mars as seen through Chabot Space & Science Center’s 20-inch telescope near the 2003 close encounter. Credit: Conrad Jung/Chabot Space & Science CenterIf you take away no other message from this blog, just remember this: the planet Mars is NOT passing close to Earth this August and will NOT appear as large as the Full Moon. There; disclaimer delivered.

As August approaches, the ghost of Mars returns to haunt us, in the form of emails and phone calls from people asking if it's true that Mars is about to get closer to Earth than it has been in a gazillion years—so close that it will look as big as the Full Moon.

I say "ghost" because it simply isn't true, here in 2009. I say "haunt" because, six years ago, it was true—at least, partly.

The time: August 27, 2003. The scene: Earth and Mars. The event: Mars is coming into opposition—the time when Earth passes directly between Mars and the Sun, and consequently Mars is closest to us and at the opposite point in the sky from the Sun—hence "opposition." A routine encounter, one that happens about every 2.2 years. But what's different with this Mars opposition is the distance between Earth and Mars at closest approach: the two planets are closer together than they have been in a very long time: a bit less than 35 million miles.

This was a very big deal, you may recall. We remember it very well at Chabot: On one of the evenings that weekend, we had 2000 people who came up to see Mars through our telescopes…. A close opposition is the best time to see a planet, and this was closer than average for Mars by maybe 10 million miles. (It was at another very close opposition of Mars when Percival Lowell made his famous "Martian canals" observations and Martian civilization hypothesis, back in 1894.)

At the time of the 2003 opposition, there were a lot of reports—emails, websites, blogs—flying around describing the event, in some cases with exaggeration. One exaggeration is the amount of time since the previous closest encounter with Earth. Different accounts suggested a thousand years, ten thousand years, even one hundred thousand years. Technically this may have been true, if one were calculating down to the inch. Practically speaking, however, the opposition in 1924 was almost as close, by a difference of only 12,000 miles (one and a half Earth diameters).

The other (gross) exaggeration was a statement made that at opposition Mars would appear as large as the Full Moon. That would be spectacular! However, at some point a piece of information was lost from the original message: the part about needing to look at Mars through a telescope to achieve the advertised view.

The final piece of information missing from that message—which gave birth to the annual Mars Hoax –was the year, 2003, omitted along the way and making every August 27th a day to view the splendor of Mars in all its glory. But, alas, the ghost of Mars.

For the record, the next extra-close opposition of Mars will occur on August 15th, 2050, when it will be only 200,000 miles farther than the 2003 near-miss….

Google Mars view from the slopes of the Olympus Mons caldera. Credit: Google Earth

I was sitting at my computer the other day, quietly exploring minute details of the surface of planet Mars, when I realized once again that in my lifetime planetary exploration has gone from telescopic-view-only to robotic rovers poking microscopes close up at Martian geology!

Did I say quietly exploring the surface of Mars? Yes I did—and you can, too. First of all, if you're not familiar with Google Earth, please go and google Google Earth and get your free download today (this is NOT a sales pitch!). A modestly powered computer with a decent graphics card is all you need to probe every nook and cranny of planet Earth, sometimes to the detail of spotting people walking in the streets….

But there's a magic button on Google Earth (it looks like planet Saturn, for some reason) that instantly transports you to planet Mars—Google Mars, that is. It's a simple button click to explore Mars, Google Earth style.

This detailed digital Mars has been created with all of the data collected by the fleet of robots we've sent—from Viking to Mars Global Surveyor to Mars Odyssey to Mars Express to Mars Reconnaissance Orbiter (MRO), and of course Pathfinder, Phoenix, and the Mars Exploration Rovers, Spirit and Opportunity.

First on my itinerary was Olympus Mons, that extinct, Arizona-sized shield volcano that rises 15 miles above the average global terrain. Swooping into the San Francisco Bay-sized caldera, I got a sense of what it would be like to be there, standing on the caldera rim. There were even strips of super-high resolution imagery provided by MRO's HIRISE camera, allowing me to hover maybe a hundred feet above the ground and see rocks and piles of sand!

Next on the list had to be that other famous gargantuan feature, Valles Marineris, the "Grand Canyon of Mars" which, if it were moved to Earth, could stretch from Oakland, California to New York City—putting Grand Canyon National Park within a day's drive of anyone in the US…. Google Earth/Mars has a flight simulation mode that allows you to pilot an aircraft over and through (and into) the terrain.

Like a kid in a science supply shop (okay, that's the kind of kid I was), next I hopped on up to the landing site of NASA's Phoenix lander, on the wide flat plains near the Northern Polar Ice Cap. Yup, those plains are really flat. To my delight, I found that someone had inserted a panoramic picture taken by the orbiting MRO spacecraft when it captured Phoenix descending through the atmosphere.

Onward, planetary explorer…. I had to feel—not just see, but feel—what the landscapes that Spirit and Opportunity have been exploring for 5 years are like. On Spirit's side of the globe, Gusev Crater, I poked about the Columbia Hills, following in the tracks of the robot. Over at Opportunity's digs, I dropped into Victoria Crater, enveloping myself in "Street View"-style panoramas that almost set my feet down on Martian soil.

Okay, I could go on telling you about my adventures on Mars for days—but since you can do it yourself now, I'll let you go to it. Have fun, and send back a postcard! (Which, by the way, you can do from Google Mars….)

NASA/Mars Reconnaissance Orbiter; Fans of dark dust on Mars'
southern ice cap, apparently blasted from beneath the ice
by thawing carbon dioxide."

It's spring again, that time of year when my thoughts return to…blasts of carbon dioxide gas jetting up from beneath the frigid layer of dry ice below, carrying rusty red dust in plumes that jet toward the pale skies….

At least, that's what happens at the polar ice cap on the planet Mars. I'd sure love to be there to see it, even if there are no flowers in bloom. Still, there seems to be plenty of "blossoming" going on….

NASA's Mars Reconnaissance Orbiter—the spacecraft with that high powered camera that could spot a beach ball on Mars' surface—has captured images of the aftermath of some of Mars' springtime polar action. Appearing as dark fan-shaped bursts strewn across the thinning springtime polar ice, these features are explained as plumes of Martian dust that have settled after being blasted into the air by releases of gas pressure from under the surface of the ice.

To describe what's going on, let me paint a picture of the Martian polar region as it emerges from the deep freeze of winter into spring.

Mars' year is almost twice as long as Earth's—and so too are its seasons. Winter at the southern pole of Mars lasts almost six months. In that time, the normally freezing temperatures on the Red Planet plummet to as low as -225 degrees Fahrenheit at the pole. During this time, Mars' permanent water ice cap acquires a layer of frozen carbon dioxide (dry ice) on top, formed from carbon dioxide freezing directly out of the atmosphere.

This seasonal dry ice cap also forms around the edges of the water ice cap, covering adjacent ice-free surfaces as well. The carbon dioxide ice cap may grow to as much as a meter thick.

Then, as spring approaches and the ice cap gradually comes out of the dark and receives more and more sunlight, it begins to warm up (though don't get the impression that it is ever "warm" anywhere on Mars' surface! Air temperatures recorded by the Viking landers in Mars' more temperate latitudes was barely ever higher than 1 degree Fahrenheit). Spring Equinox in Mars' southern hemisphere was on December 26th.

As the layer of solid carbon dioxide heats up, its ices turn to gas, both at the top of the layer and beneath it as well. The gases forming underneath build up pressure, which seeks a path to escape. Evidently the pressurized carbon dioxide gas can actually carve channels in the Martian soils under the ice as it flows—said channels have been seen in the past after the seasonal ice cap dissipates entirely.

When the gases find a weak point in the ice, they can erupt upward, bursting into the air, sometimes carrying dust with it. The dust rockets skyward and is blown by prevailing winds, settling out on the ice in great dark fans—which is what Mars Reconnaissance Orbiter has shown us.

Ah, to be on Mars in springtime….

Methane concentrations revealing a plume in Mars' northern
hemisphere during its summer season. Credit: NASAMethane on Mars? Really? What does that mean?

We've known about the existence of methane gas on Mars for several years now, from independent observations.  Further observations have led to the detection of "plumes" or clouds of methane gas apparently emanating from specific locations on Mars.  One plume is estimated to contain 19,000 metric tons of the stuff.

Why is this exciting news? If you know anything about the source of most of Earth's atmospheric methane gas, you already know the answer:  possible life.  Not, I should say, necessarily life on Mars, but maybe a strong piece of evidence in that direction.

On Earth, methane (CH₄) is produced by living organisms—mostly by the activity of microbes, but some by the digestive processes in larger organisms (yes, like humans, and cows).  Methane is the major constituent of natural gas, which fuels gas powered ovens and heaters in homes, as well as natural gas power plants.  Methane is also produced by decaying organic matter—that's where "swamp gas" comes from.

On Mars, methane gas cannot exist for long in the atmosphere; it is relatively quickly broken down by solar radiation.  So, the methane detected in Mars' atmosphere must be replenished by something, continually.

So the big question right now is, where is the methane coming from? Under the surface of Mars, almost certainly.  By biological processes—life—underground? Could be.  By non-biological means? Could be, too; methane can be produced through inorganic chemical processes.  We don't know yet.  The next step in finding out more will be the Mars Science Laboratory, a large rover scheduled to be launched to Mars sometime in the near future.

In one form or another, humans have been trying to see, or find, life on Mars for a long time.  Percival Lowell squinted at Mars' small, blurry disk through his 24-inch telescope in Flagstaff, and perceived markings he saw to be vast canal complexes, ostensibly built by a desert Martian civilization thirsty for water harvested from their planet's polar ice caps. This led to much of the science fiction relating to life on Mars in the 20^th Century.

Earth-bound telescopes noted seasonal changes in Mars' color and brightness, and some attributed this to possible seasonal growth of Martian vegetation—though it was later found that these variations were the effects of seasonal planet-wide dust storms.

The Viking landers' primary mission in the 1970's was to search for life.  They didn't find any by scratching around Mars' surface and testing the soils there.

The 1990's saw the controversy over microscopic structures in meteorites found on Earth but determined to have originated on Mars.  Some argued that these structures were fossils of Martian microbes that lived on Mars long ago.  Whether these findings were in fact fossils and not just geologic structures was never conclusive.

The determination that liquid water once flowed on the surface of Mars, and still exists under its surface at least as ice, is pretty much scientific fact today.  Evidence of past liquid flows have been imaged and mapped from space, and the Phoenix lander found water ice in the north polar regions last year.  And there's the rover Opportunity that has confirmed gray hematite, a mineral that forms in the presence of water.

It's almost certain that there are no Martian cows grazing the rusty desert plains out there.  But there seems to be a lot of evidence for the possibility that something is going on below Mars' surface—perhaps the presence of liquid water, perhaps the presence of some form of life.  We don't know yet, but it sure feels like we're onto something here….

Terrestrial snow at Chabot on December 16, 2008
Photo by Craig CoryellDriving to work today, I was amused to notice that the raindrops falling on my windshield were a bit grainy–and getting more so the higher up the hill I drove. I starting to think, is it starting to sleet? By the time I reached Chabot–at 1500 feet elevation–the precipitation had turned to bona fide snow!

This is quite unusual for the Oakland Hills, of course. In the ten years I've worked here, this is the second, maybe third, dusting I've witnessed. I recall the great freeze of '74, when it actually snowed in Oakland close to sea level—that's the year all the eucalyptus in the hills froze and died.

My mind wandered—pretty far out in space (an occupational hazard at Chabot). I started thinking about all the recent news and discoveries from around the Solar System, my thoughts guided by the fat white flakes drifting down all around the observatory domes.

Last September, NASA's Mars Phoenix Lander detected snow falling high in the atmosphere–about 4 kilometers high. This Martian snow, however, quickly evaporated in Mars' thin, dry air, never reaching the ground. Phoenix used a laser probe to make the detection–so we don't actually have picture to look at!

Snows of the Solar System may also fall out of the plumes of "cryovolcanoes"–the frigid outer Solar System's version of volcanism (may it live long and prosper). On moons such as Saturn's Enceladus and Neptune's Triton, plumes of material have been detected spouting from fissures and cracks–probably fueled by heat generated by tidal forces from their parent planets.

On Enceladus, the geyser plumes contain water vapor and ice crystals, and are believed to come from subsurface lakes of "warm" water (32 degrees Fahrenheit–in other words, ice water… but that's a veritable hot spring, or magma chamber, on a cold moon like Enceladus!).

The ice crystals in the geysers' plumes mostly fall back to Enceladus–maybe in a diffuse fall of "snow" across the globe? I'm waiting for those pictures…

Saturn's large moon Titan is speculated to possibly have a form of cryvolcanism, though no direct detection has yet been made. Still, any water vapor that might erupt from a Titanian cryovolcano might be expected to fall in a form of snow….

Triton, much farther from the Sun than Saturn, is even colder than Enceladus. In fact, it's been called the coldest measured surface in the Solar System, at -391 degrees Fahrenheit. Here, nitrogen freezes solid. Triton cryovolcanoes, or geysers, may be partially solar-heated, but tidal heating within Triton is probably dominant. Triton's geysers spout nitrogen gas and dark material, which falls across the landscape in dark streaks and lighter deposits of frozen nitrogen–a form of extreme cryo-snow, to my imagination!

Now, are you as cold as I am just thinking about it? Time for a cup of cocoa…

The Mars Science Laboratory. Credit: NASA/JPL-Caltech

When I hear about the search for alien life, it's hard not to think about all the science fiction movies with little green men and Earth-destroying spacecraft. But it's an idea that's far from science fiction for scientists at NASA Ames.

NASA is preparing to send their next rover to the surface of Mars, known as the Mars Science Laboratory. It follows the legacy of the twin rovers Spirit and Opportunity, who have survived far longer than NASA scientists expected. After four years, they're still sending data from the Martian surface. (For an update, check out this post from QUEST blogger Ben Burress).

The Mars Science Lab rover will have a few upgrades, though. It's much larger than Spirit and Opportunity and will be nuclear-powered — meaning no solar cells that are vulnerable to dust storms. It will also be carrying the most advanced lab equipment yet, some of which will look for organic matter on the surface. The goal to discover how habitable the surface could have been for life.

When it comes to what kind of life, it's microbial life that many scientists believe is the best case scenario. There have been a number of recent discoveries that are promising evidence that liquid water once existed on the surface. But if even the conditions were right for life then, they're certainly not right today. Thanks to a thin atmosphere, Mars is bombarded by solar radiation and conditions are dry and cold. Still, many scientists think there's a possibility that life could survive in the subsurface, where it's warmer and more sheltered.

The question most of us would ask, though, is: even if we found extraterrestrial life someday, how would we recognize it? NASA scientist Chris McKay explained his take to me. It turns out there are some basic things scientists believe they could look for. You can hear what he has to say in this audio clip:

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McKay brought up another interesting point — we've already sent earthlings to Mars. The NASA rovers were built in clean rooms, but they're not completely sterile. Chances are there are microbes from Earth on Mars now, protected inside machinery we built. McKay believes this contamination is reversible, and there's already a policy in place to protect both Earth and Mars known as planetary protection.  You can hear McKay explain why it's so important in this clip.

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No matter what the outcome of the Mars Science Lab mission, there's a lot more to discover about what Mars is like today and about its past.

Watch the Looking for Mars Life on Planet Earth report online.

Artist concept of the Phoenix lander,
sleeping under the darkening polar skies of Martian autumn.It seems like only last month that we witnessed the drama of NASA's Phoenix landing on Mars. We were on the edge of our seats in Chabot's planetarium during those "seven minutes of terror" as Phoenix burned a meteoric path through Mars' atmosphere.

But that was last May, and Phoenix has operated near Mars' northern polar ice cap going on six months now! The mission has continued a couple months longer than originally planned, giving Phoenix more time to dig in the icy soil, bake scooped up samples to detect what chemicals sublimate, track the polar weather day and night, and look to the skies with its various instruments.

Phoenix sent back some very interesting news. Indeed, it had landed on what turned out to be dust-coated water ice; ice that contains chemicals like calcite and perchlorate– the former of which may indicate past liquid water on Mars, the latter of which, however, is generally toxic, and may complicate arguments for life, past or present, on Mars.

One of the more "fanciful" detections by Phoenix was falling snow: two or three miles above, Phoenix detected ice crystals falling from clouds– albeit flakes that never made it to the ground, instead evaporating like Earthly virga back into the atmosphere.

But Phoenix’s mission has a built-in conclusion (unlike the seemingly perpetual Energizer Bunnies exploring the Martian tropics, aka the Mars Exploration Rovers). Phoenix landed at 68 degrees north latitude– that’s equivalent on Earth to the north coast of Alaska, Norway, or south central Greenland– prior to Martian northern summer solstice (which was June 25). As with Earthly summertime, the polar days were unending, the Sun above the horizon 24 hours a day (yes, Mars' day is about 24 hours long, just as on Earth). This provided Phoenix with its electrical power, generated by photovoltaic panels.

But now the Sun is dipping below the horizon several hours a day as the Martian northern hemisphere slides in the direction of autumnal equinox (December 26, 2008), at which time the Sun will spend half the time below the horizon, the other half never rising very high. Already, Phoenix's solar panels are generating considerably less power than in the heyday of its mission. A dust storm, filling the air and blocking some of the already weak sunlight, has also cut available power to the lander for a time in October.

The diminishing conditions also caused Phoenix to put itself into an automatic "sleep" mode in late October, waking up for only a short time each day, when solar energy was at a peak. To give a flavor of the temperatures Phoenix is enduring, on Sol 151 (the 151^st Martian day since landing-October 27^th, Earth time), the daily high reached a balmy 50.8 degrees F-negative 50.8 that is! The night time low hit -128 degrees F… .

With every day possibly being the last we hear from Phoenix, scientists are collecting as much data as possible, mostly focusing on meteorological conditions. Reporting from the Martian polar ice cap, as the icy darkness of winter begins to settle in, this is Phoenix Lander, signing off….

Forward camera view from Opportunity as the rover attempts to
climb up a slope toward the wall of Victoria Crater.
Photo by NASA/MER/Opportunity.Is there life on Mars? Well, that investigation is still ongoing–but from a cybernetic perspective, the surface of Mars is literally crawling with it: in the form of robots!

Four years after their planned three-month tour of duty began, NASA’s Mars Exploration Rovers (MER) Spirit and Opportunity roll doggedly on like a pair of aged, dusty desert prospectors looking for gold. In this case the "gold" is evidence for past water on Mars, and signs of that seem to abound.

What sparked this blog for me was the announcement of the plan to send Opportunity out of the depths of Victoria Crater, the half-mile impact crater that the rover has been exploring for almost a year now. Last September, when it was decided to send Opportunity into Victoria to get a close-up view of the sedimentary rock layers exposed in the crater walls, there was a lot of talk about this expedition possibly being the rover's last–it almost sounded like the robot was being sent into its own grave, its final resting place on Mars. After all, the rover had already operated ten times longer than what it was designed for!

What did Opportunity's year-long sojourn yield? By examining the multitude of exposed sedimentary layers, it is believed that those layers were probably originally laid down by wind (not a surprise on Mars, which even today is a world of wind-blown dust: dust devils, sand dunes, planet-wide dust storms). But there are also clues written in the rocks that the layers of sediment have been modified by the action of water.

One particular thing Opportunity has discovered are rock features dubbed "fins." These fins are raised edges around rock boundaries that are rich in the mineral hematite–a mineral that often forms in the presence of water. Opportunity found hematite on Mars early in its exploration, which supports the speculation that at least that rover’s region on Mars (Meridiani Planum) may have harbored at least shallow and intermittent bodies of water in the past.

The "fins" may have been formed when water dissolved away areas of sediment and then "filled in the holes" with deposited minerals–forming a kind of "fossil" of what was once an empty space.

When I lived in Northern Arizona, I remember driving across the plains east of Flagstaff and finding long, wide ridges of what looked like sandstone, snaking across the dusty desert like enormous gopher trails. I learned that these were the fossil remnants of what were stream beds: the streams formed deposits of sand and mud in their bed, which over time hardened into sandstone and mudstone. Later, the softer surrounding soils and sands eroded away, leaving the hardened stream beds as raised ridges of rock–dry evidence in a dry desert of past liquid water action. Though this is not the same process that formed the fins on Mars, it is analogous.

But now Opportunity's mission in Victoria Crater is done, and NASA is making plans to have the robot crawl back up the slope and exit the crater at the same place it entered last September. It will continue its mission by examining "cobbles"–small, loose stones on the surrounding planes, some of which were probably ejected by meteorite impacts in Mars' distant past.

Spirit, on the other side of the planet in Gusev Crater, is also still alive, and is making ready to do a bit more roving after a Martian winter of relative inactivity. With one of its six wheels no longer functioning, Spirit will limp along and continue prospecting–next stop: some white, silica-rich material that may have formed in hot water.

The ‘Snow White' excavation trench, after rasping
and digging by Phoenix. Credit: "NASA/Mars Phoenix"

Since witnessing the historic landing of NASA's Mars Phoenix Lander on May 25, I've been holding my breath to learn if Phoenix has made the discovery it set out to make: whether it landed on a vast deposit of water ice near Mars' northern polar cap.

It took several weeks after landing for the declaration to finally be made-and without further ado, YES, definitely, water ice was found by Phoenix. But even now, in August, it seems the declaration of Phoenix's great discovery is still in the process of unfolding, one careful and tantalizing announcement after another.

From a lay point of view one might think, why did it take weeks for Phoenix scientists to announce that, yes, the white stuff scraped up by the lander's instruments, from under a thin topping of soil, is water ice? And why do there seem to be unanswered questions about the nature of that ice even now, three months after landing?

For those familiar with how a remote robot probe like Phoenix makes its investigation, this is not surprising at all. In fact, serious scientific measurements by Phoenix didn't happen immediately after landing. The mission team had a lot of work to do to make sure the spacecraft was healthy and undamaged, ready to explore.

Then, the team worked Phoenix's robot arm and soil scooper to dig, scrape, and eventually scoop up soil and bits of the white substance and drop it into Phoenix's onboard laboratory compartments. At first, there wasn't much of the white substance included in the scooped up samples. Then, the sample stuck to the scoop. So, just getting an adequate sample into the spacecraft where it could be analyzed wasn't a simple matter of scoop and dump….

Eventually, though, the white substance was identified as water ice. The first clue came when the white substance was exposed to the air and sunlight after being dug up, when it began to slowly disappear: it sublimated (went directly from its solid state to a gaseous state, without passing through a liquid state, without passing Go and collecting $200…). If the white substance were, say, a type of salt, it wouldn't have done that.

Inside Phoenix's chemical laboratories, more definitive tests were performed. One instrument is essentially a small oven in which a sample is slowly heated and any gases that boil off (excuse me: sublimate) are identified by a gas analyzer.

But there were still plot complications! One is the possible detection of the chemical "perchlorate" in the ice sample: an oxidizing ion (a compound of chlorine and oxygen) which, if it does turn out to exist in the Martian ice, will give scientists new food for thought on Martian chemistry and the implications for possible Martian life. It wouldn't rule out the possibility of life (past or present), but is an additional factor in the equation.

So, the search for life on Mars-the big-picture-reason we've been looking for water there-goes on. We have to keep in view the fact that finding microbial life, or fossils thereof, on Mars isn't as simple a matter as snapping a picture and looking for plants and animals; it's more like a 19^th Century story I heard of where a race of mile-high beings from Jupiter land on Earth, and at first don't realize there is life here, under their feet….