Dept. of Defense

Robots can serve as the tip of the spear for U.S. military units.

The veterans being honored over the past couple of days include modern-day warfighters who are using high-tech tools to fight increasingly tech-savvy foes in Iraq and Afghanistan. And among the most essential tools are the robo-warriors that take on dangerous jobs on the front lines.

How essential, and how dangerous? In the course of a legal case involving rival robot companies, the U.S. military has made clear just how much it has come to rely on battlebots.

The case relates to the Pentagon's $280 million xBot program, which is aimed at getting up to 3,000 robots out to hunt for the increasingly sophisticated explosive devices used against military personnel in Iraq. The first 1,000 robots are to be delivered by December 2008.

After rounds of testing and bidding, Illinois-based Robotic FX was selected over Massachusetts-based iRobot, basically because Robotic FX bid $1 million less for the contract, according to court filings. IRobot protested the award and also filed a lawsuit, alleging that its technology was stolen by the former iRobot employee who started up Robotic FX.

As a result, the Army put the xBot contract on hold - and just this month, a federal judge granted a preliminary injunction against Robotic FX, saying that iRobot appeared likely to prevail in its lawsuit alleging theft of trade secrets. A trial date has been set for no later than next April 7. (Check out Xconomy for a backgrounder as well as Robotic FX's side of the story and the PDF file of the court order.)

Robotic FX

Robotic FX makes the Negotiator tactical robot.

The problem is, the military needs those bots pronto. Before the judge's ruling, the U.S. Attorney's Office said the xBot program had to go forward without delay, because otherwise "soldiers will certainly be placed in life-threatening situations when a safer alternative exists."

Marine Col. Edward Ward, the chief for program management at the Army/Marine Robotic Systems Joint Project Office, took a similar tone in another court filing: "If these systems are not sent to the theater [of military operations] in the most expedient manner, a far greater number of soldiers and Marines will be placed in danger."

It's still early in the legal battle, but the Army does have the option of switching the contract over to iRobot if Robotic FX is judged "not responsible" for holding up its end of the deal. And the military has other robotic programs in the works: In fact, iRobot has been supplying its "Packbots" for the Pentagon for five years, starting with bots that hunted Afghan mountain caves for traces of al-Qaida.

"We've delivered 1,200 of them, and we are delivering somewhere between 50 and 70 each month, the majority of which go directly in the theater," said Joe Dyer, president of iRobot's government and industrial division.

iRobot

The SUGV bot is being developed by iRobot.

The Boeing Co. is working with iRobot to hustle Packbot's successors to the battlefront under another program called SUGV, or "Sugvee" - which stands for Small Unmanned Ground Vehicle. SUGV was seen as a development effort for the longer term, but the military wants to put the program into high gear for use in Iraq sooner rather than later.

Yet another program called MAARS, which stands for Modular Advanced Armed Robotic System, could put gun-equipped contraptions into regular combat duty as early as next year, according to Popular Mechanics. These tankbots are said to be "Transformer-like," but unlike the cartoon-world Transformers, they'll be controlled remotely by humans.

It may not be long before we visualize the veterans of the future as gizmo-toting grunts with trusty robots at their side. In fact, Dyer says that day is already here. He recalled the now-classic stories of soldiers who formed emotional bonds with their bomb-hunting bots. They're the kind of bonds that past generations of warfighters formed with their K-9 working dogs, said Dyer, a Navy veteran who worked his way up from aviator to vice admiral.

"And besides that, you know, robots are fearless," he told me. "Consequently, while unmanned aerial vehicles were somewhat slow to evolve because they were so strongly resisted by aviators, the Army mission is so dangerous and so up close and personal ... that the adoption of robots is even quicker."

Dyer brought up one more point about the rise of the machines: You can't talk about the robots without paying tribute to the humans behind them. The bomb technicians who use the robots in Iraq would have to rank as "some of America's most courageous," Dyer said. That could be said about many the folks on the front lines during this long Veterans Day weekend.. 

For much more about military robots, click on over to Wired Danger Room - and check out Robot Stock News for the latest on the bot biz. Here at msnbc.com, the Invention section is the place to go for your robot fix. And as always, feel free to add your comments below about the changing high-tech battlefield.

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I'm off to British Columbia to tour the TRIUMF physics lab and attend a conference on "Future Directions in Science Journalism." My plan is to go dark on Friday (unless, say, an asteroid ruins somebody's day) and resume regular postings on Monday.

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Ferris Valyn

A video displayed on a giant screen at the X Prize Cup shows the Rocket Racing League's X-Racer taking off for a test flight from California's Mojave Airport, with a bright flame shooting out from the rocket engine at the back.

If the Rocket Racing League followed the time line it announced when it was created two years ago, we'd be seeing 10 fire-breathing rocket planes competing for prizes like a "NASCAR in the sky." Instead, the league's first X-Racer plane is just now making its first honest-to-goodness test flights, under a veil of secrecy.

Eleven days ago, the Rocket Racing League let that veil slip just a little bit, and since then bloggers and photographers have been tearing away at it right and left. In the months and years to come, we could be hearing about the X-Racer - and about the Xerus, a suborbital spaceship that's likely to take advantage of X-Racer technology as well.

Both the X-Racer and the Xerus are being developed by XCOR Aerospace, a rocket company just down the street from SpaceShipOne's birthplace in Mojave, Calif. While other rocketpreneurs make a big splash with artist's conceptions and computer-generated animations, XCOR tends to keep a lower profile, chipping away at the technical challenges by taking on smaller contracts that are consistent with its big rocket vision (like the methane-fueled engine it's making for NASA).

The X-Racer builds on the work that XCOR did several years ago with its EZ-Rocket: The company is developing a new rocket engine called the XR-4K14, and fitting it into a frame based on the Velocity airplane kit. The project finally got off the ground, literally, on Oct. 25 for three rocket-powered hops.

Video from those test flights was shown on the Jumbotron screen during the X Prize Cup that weekend, but the Rocket Racing League hasn't yet made that video available. Daily Kos blogger Ferris Valyn snapped a screen grab of the video, however, showing bright kerosene-fed flames shooting out of the back of the plane. Another rocket-watcher, Ben Brockert, posted his own long-range video of the Oct. 25 tests.

The tests didn't stop there: Michael D'Angelo, the Rocket Racing League's vice president of technology, said more test flights have been conducted, pointing up the kind of "squawks" that are typically found during any aircraft development effort. Last week, Mojave photographer Alan Radecki took some choice snapshots of the plane on the ground and in the air, which are now posted freely on Wikipedia.

The league itself, however, isn't saying much about the test flights or releasing any imagery. Why is that? The league's executives are trying to follow a carefully laid-out schedule for the media rollout, including demonstration flights - first for journalists, then for the public. That means the pictures are being held back for what the league feels will be maximum impact.

Granger Whitelaw, the league's co-founder, president and chief executive officer, said the timing depended in part on the negotiations for broadcasting the races on television. "I won't launch the league until I have my TV deal," he told journalists.

The current timetable calls for starting exhibition races next year, then moving to a full racing schedule with a point system for prizes, Whitelaw said. "We will have one, two, three, four vehicles racing each other in the air during the spring, at air shows and other places ... but the points series won't start until '08, '09," he said.

Toward that end, Whitelaw announced that three more racing teams were being added to the mix: Rocket Star Racing, led by former Navy test pilot Todd White; Team Extreme Rocket Racing, headed by Navy aviator Bryan Schwartz; and Beyond Gravity Rocket Racing, led by Canadian X Prize competitor Brian Feeney. The new teams join Bridenstine Rocket Racing, Santa Fe Racing and Thunderhawk Rocket Racing.

Whitelaw admitted that he was "a little bit behind where I thought I'd be" on getting the league going, in part because he dwelled too much on the sponsorship end of things and not enough on the rocket end during the early going. But he said XCOR was making good progress on the X-Racer and its other projects, such as the Xerus suborbital spaceship.

Although XCOR hasn't said much about the Xerus lately, there have been hints that the X-Racer would move the company well more than one small step closer to space. The Xerus design might well take a page from the X-Racer effort, and some observers have noted that a cluster of four X-Racer engines could work quite well as Xerus' propulsion system. 

"My guess is, they're the first guys to go suborbital," Whitelaw said.

Update for 1:20 p.m. Nov. 8: Space consultant Charles Lurio points out this inside-scoop reference to the Xerus in his e-mail newsletter about private-sector spaceflight, The Lurio Report:

"I'm told that the engine for the XCOR 'Xerus' suborbital vehicle will be a derivative of the engine for the Rocket Racer.  I suspect strongly that such a derivative engine may have already been tested - or at least is well along toward that milestone.

"I know a few technical data points about the projected Xerus engine but can't be specific about them publicly.  What I can mention is that in addition to an increase in thrust over the Racer's engine, four or five of the derived rockets will be used in the Xerus. The number of engines is still an open question at this point for reasons of both operational safety and (presumably) engineering uncertainties.

"The Racer engine has undergone extensive duration and Racer flight profile testing on the ground.  What I hear about the durability results of these tests could hardly be better, but again I can't mention any specifics."

• The Heavy Stuff: The O'Hare UFO incident ... one year later
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• ONN: Mean automakers dash nation's hope for flying cars 

NASA / JPL-Caltech

This artist's conception shows four of the five planets that orbit 55 Cancri, a star much like our own. The most recently discovered planet looms large in the foreground. The colors of the planets were chosen to resemble those of our own solar system. Click on the image to watch a video from MSNBC's "Countdown."

Planet-hunters say they have detected a giant world that is nestled among four others in a planetary system 41 light-years from Earth. This newfound world is in the "Goldilocks zone" - a place that's not too hot, not too cold, but just right for the existence of liquid water and conceivably life.

The fresh discovery, announced Tuesday during a NASA teleconference, focuses on a star and planetary system called 55 Cancri, in the constellation Cancer. The system is already well-known to astronomers who search for the telltale signs of planets beyond our own solar system - but the newly detected planet has taken the search to a new level.

"We're announcing the discovery of the first quintuple-planet system," Debra Fischer, an astronomer at San Francisco State University and lead author of a paper due to appear in the Astrophysical Journal, told reporters.

Geoff Marcy, a pioneer planet-hunter from the University of California at Berkeley who contributed to the paper, said the planetary system is a "souped-up" version of our own. Like our own solar system, these planets make nearly circular orbits around the parent star - but they're super-sized.

The innermost planet is about the size of Neptune and whips around the parent star in less than three days, at a distance of about 3.5 million miles. The farthest-out planet is four times as massive as Jupiter and takes 14 Earth years to orbit, at a distance of about 539 million miles - or just a little farther out than our solar system's Jupiter.

The planets in between are in the range of Jupiter and Saturn, but the most interesting one is the fourth rock from its sun: a world 45 times the mass of Earth, perhaps a gas giant similar to Saturn or Neptune in composition and appearance. That planet is about 72.5 million miles out from the parent star, in an orbit that's similar to Venus' orbit.

55 Cancri is slightly fainter than our own sun - and that would put the newly detected planet in a habitable zone that should allow water to remain liquid on a rocky surface, astronomers say.

NASA / JPL-Caltech

This diagram shows the 55 Cancri system at top and our own solar system at bottom. In each view, the "habitable zone" is marked as a green band.

A gas giant isn't a likely suspect in the search for life - but any rocky moons around it would be. Just as Jupiter's moon Europa and Saturn's moon Enceladus hold promise for astrobiologists, a moon around the newly detected planet could conceivably be a prime suspect in the search.

"Such a moon would have to be fairly massive," Marcy cautioned. "In fact, it would have to be about as massive as the planet Mars … in order to retain its water."

Jonathan Lunine, a planetary scientist at the University of Arizona, said temperatures on this hypothetical moon might be just a little bit warmer than temperatures on Earth. But like Marcy, Lunine said a bit of caution was in order. "I would recommend not buying real estate on any of these planets" until more readings were available, he said.  

Marcy said the discovery of the fifth planet "has me jumping out of my socks" - not just because of the habitable-zone angle, but because it indicates that planetary systems like our own appear to be more common than astronomers thought just a few years ago.

The new planet, like the four other ones, was detected using the Doppler radial-velocity technique, in which a planet's gravitational tug is detected by the wobble it produces in the parent star. In a long-running project funded by NASA and the National Science Foundation, observations of 55 Cancri were collected using telescopes at the Lick Observatory in California and the Keck Observatory in Hawaii.

The method is one of the most time-honored tricks for finding extrasolar planets - but it takes a long time to gather enough information about the complex wobbles to identify multiple planets in a system. More than 350 velocity measurements were required to untangle the wobbly pattern created by the planets at 55 Cancri.

"Discovering these five planets took us 18 years of continuous observations at Lick Observatory, starting before any extrasolar planets were known anywhere in the universe," Marcy said in a NASA announcement. "But finding five extrasolar planets orbiting a star is only one small step. Earthlike planets are the next destination."

As currently used, the Doppler technique isn't sensitive enough to detect planets around the mass of our own - but Fischer said an intriguing orbital gap in the 55 Cancri system is big enough to harbor Earthlike planets that could be found in the future using more precise techniques.

"There could be 10 Earthlike planets there, but we've just not detected them yet," Fischer said.

Finding new Earths around sunlike stars would be a "holy grail" for planet-hunters, Lunine said. Such worlds could harbor alien life, or not. Either way, the quest could answer humanity's deepest questions about life, the universe and everything.

But like all quests, this one has its bumps in the road: Marcy and Fischer noted that one of the extrasolar planets that was once thought to be potentially hospitable to life, Gliese 581c, is now said to be too hot rather than just right. (There's a debate about that.)

To reach the true grail, scientists will have to develop new ground-based telescopes and launch new spacecraft such as NASA's Kepler probe and Europe's Darwin flotilla. Most importantly, they'll have to cast a wide, wide net.

"If you  asked me where the right place would be to look for Earthlike planets," Lunine said, "my answer would be anywhere, and everywhere."

Update for 9:35 p.m. ET: Be sure to check out this video segment from MSNBC's "Countdown." Host Keith Olbermann discusses the newfound planet and other space news with Derrick Pitts, chief astronomer at the Franklin Institute.

• Popular Mechanics: Robot surgeons for Baghdad ... or Mars
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GeoEye via NASA

This view of Indonesia's Anak Krakatao volcano was captured by the Ikonos satellite in 2005.

Catching a volcano just before it explodes isn't always as easy as, say, predicting the weather. And that's a problem for scientists as they gauge the current upswing of activity going on within Indonesia's volcanoes.

Mount Kelud is already pushing out magma and thick steam - while an island volcano called Anak Krakatao ("Child of Krakatoa") is reminding experts about a famous blast from the past.

Tens of thousands of people living around the flanks of the Kelud volcano are wondering whether they should heed the evacuation orders - and based on the strong uptick in temperature as well as seismic activity, the big blast could come at any time. Or not. The uncertainty points to gaps in our understanding of how volcanoes work - gaps that could be filled if only scientists had more data.

"It requires some forethought and resources to have instruments in the ground, and have the information that you need to have," said John Ewert of the Volcano Disaster Assistance Program, based at the U.S. Geological Survey's Cascades Volcano Observatory in Washington state.

The ideal would be to give potentially threatening volcanoes a thorough checkup every once in a while, so that scientists can get a fix on what represents normal activity. Ewert drew an analogy to getting an annual physical.

"Often what happens is that you see the patient with really bad pain in his abdomen," he told me. "It's a lot better if you know the history of the patient."

Slow burn vs. fast blast
When it comes to Mount Kelud, volcanologists know the patient is in a bad way. They just don't know how much worse it's going to get. In 1990, Kelud erupted explosively, killing more than 30 people. Since then, however, it's been relatively dormant, which makes it hard to determine exactly where the volcano is in its eruptive cycle.

"We're at the point now where it could be basically hanging fire for days, or a week or two," Ewert said.

If Mount Kelud doesn't erupt sometime in the next two weeks, that would be a good sign, even though the magma has risen, Ewert said. He explained that the key to an explosive eruption is the gases within the magma: water vapor, carbon dioxide, sulfur dioxide and the like. Those gases are what give an eruption its pop - and if you give the magma enough time, the gases will dissipate and the molten rock will go flat.

"It's a little bit like ripping the top off a champagne bottle because you won the World Series, or slowwwwwwly easing the top off because you paid 50 bucks for the bottle," Ewert explained.

The good news is that catching a volcano becomes easier once it shows what it's made of. "Typically what happens is, once you get into the eruptive cycle of a volcano, real predictions become easier to obtain," Ewert said.

Revolution in volcano science
And that demonstrates how far volcano science has come since Mount St. Helens erupted 27 years ago - which was just about the time Ewert began his work at the Cascades Volcano Laboratory. Back then, scientists were lucky to have a few spectrometers, seismometers and early tiltmeters on the ground.

"It's funny to look back at the systems and where they were, " Ewert said. "This was a time when a megabyte was a vast amount of memory. St. Helens happened right on the cusp of the computer revoluton and the digital age. We still relied pretty heavily on direct observation and direct measurements."

Today, Indonesian scientists can draw upon the new tools that have been developed since then. Mount Kelud has been watched particularly closely because it has killed before, back in 1990. Those tools include a variety of eyes in the sky:

• Locator devices on the ground that can provide real-time readings on ground deformation, using the Global Positioning System. Radar-sounding satellites can also look for the signs of rising ground that often precede an eruption.
• Infrared satellite imagery that can detect telltale variations in temperature variations.
• Orbiting sensors that essentially sniff the air below for the signs of volcanic sulfur dioxide emissions - another precursor of an eruption.

Indonesian scientists are doing what they can to keep track of Mount Kelud. "At Kelud, they have more sensors than they have at many of their other volcanoes. ... They had a system in the [crater] lake that was monitoring chemistry and temperature," Ewert said.

But Ewert said much more could be done to keep tabs on killer volcanoes - in Indonesia, and even in the United States.

"A lot's been learned in the last 27 years," he said. "Unfortunately, it's not enough to allow us to make predictions in every case. And a lot of that is because we don't have all the monitoring history that we'd like to."

Wanted: Early warning system
In 2005, a National Research Council committee report called for the development of a new generation of Earth-observing satellites - including a radar satellite that Ewert said could help with eruption prediction as well as other scientific tasks. "The Canadians have one. The Europeans have one. The Japanese have one. The U.S. does not have one," Ewert said.

Just last year, Ewert and some of his colleagues put out their own report for a National Volcano Early Warning System. The report said that just three of the United States' 18 most dangerous volcanoes - Kilauea in Hawaii, California's Long Valley caldera and Mount St. Helens - were being monitored adequately.

"There's a lot of unmet need on the part of the scientific community to have better monitoring on a large number of volcanoes," Ewert said.

To learn more about a volcano's inner workings, check out our interactive "Anatomy of a Volcano." For NBC's take on the current Indonesian cliffhanger, check out Ian Williams' posting on the World Blog. Find out more about the "Ring of Fire" that includes Indonesia's volcanoes as well as Mount St. Helens by clicking onto this archived article. And for the personal touch, read about my very own Mount St. Helens adventure 27 years ago.

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In the wake of the X Prize Cup, one reader wrote in to ask why anyone would pay $200,000 for a quick space trip on a rocket plane. "I assume it means much quicker travel time coast to coast, but your story never mentioned anything about why this is the next step in aviation evolution," said Cutter Garcia of Los Angeles.

Point-to-point travel is definitely on the minds of spaceship developers - but before they get to that point, all they can offer are up-and-down sightseeing trips. At least at first, rocketeers will be banking on a luxury market ... the kind of people who are willing to pay $95,000 to go on a North Pole expedition, or buy a cell phone for $20,000. So who better to design the interior of the spaceship than Frank Nuovo, the man behind that $20,000 cell phone?

That's exactly what Oklahoma-based Rocketplane Global is doing for its XP rocket plane: Although the final design isn't yet set, Nuovo's rough outline shows swoopy mesh seats (like Herman Miller's Aeron chairs), wide windows, personalized video displays and hush-hush technologies that the company declines to talk about for fear of tipping off its competition at Virgin Galactic.

"I like to work with technology that's supported at the highest level of experience, so effectively it becomes luxury technology," Nuovo told me last weekend at the X Prize Cup in New Mexico.

Nuovo, who packs a titanium Vertu phone for voice as well as a palm-sized PDA for e-mail, said his work with Rocketplane Global is a "passion project" - and he's expecting a future spaceflight aboard the XP as part of his payoff.

"You're working on an extraordinary experience, and that extraordinary experience is what I'm trying to capture in my career going forward," Nuovo said. "How can you turn it down?"

Although Rocketplane Global has redesigned its rocket-jet hybrid to be somewhat larger than the Learjet template that the designers started out with, the interior layout is still similar to that of a six-seat private jet. Virgin Galactic's SpaceShipTwo design concept may provide empty space for floating around, but that's not the way Rocketplane Global's top pilot, former NASA astronaut, intends to run his ship.

"From a safety perspective, I'm not letting anybody out of their seat," Herrington, who is vice president for flight operations as well as chief test pilot, told reporters at the X Prize Cup. At least in the beginning, the suborbital passengers' safety harnesses will loosen up, and they'll be able to get that weightless feeling at the top of their ride. They won't be allowed to float free around the cabin, however.

That may change after the XP goes through its shakedown period, Herrington acknowledges. Rocketplane Global is considering a trick that's long been familiar to minivan owners: that is, taking out the middle two seats and giving some extra zero-G room for the backseat passengers. Of course, the company would charge a premium for that experience.

Rocketplane's rationale is that if you're really interested in weightless acrobatics, you're better off doing that on a zero-G airplane flight. The company intends to include that kind of flying time - as well as other spacey experiences such as altitude-chamber sessions or centrifuge rides - during a four-day preflight training program.

The preflight training should also include a generous helping of other luxury experiences, according to Olle Norberg, head of the Esrange Space Center in Kiruna, Sweden. The Swedish center is angling to become Virgin Galactic's first spaceport in Europe.

"It's not enough to just provide the runway and the fueling facilities," Norberg told me. "You have to really provide the full experience, not only for the passengers but also for the family and the friends."

For Norberg, the full experience would include a stay in Kiruna's swanky Icehotel, and perhaps outings to see auroral light shows, wildlife and other winter delights. "We are mainly focusing on the winter experience," he said. The Swedish spaceport had hoped to offer zero-G flights as well, but Norberg said that part of the plan "unfortunately crashed" due to high insurance costs.

Rocketplane's home base in Burns Flat, Okla., has a ways to go to match the Icehotel - but eventually, the company will have to offer ground-based luxuries to supplement the spaceflight. Virgin Galactic is already thinking about those luxury options as it lays out its plans for Spaceport America in New Mexico, said Alex Tai, the company's chief operating officer.

"The experience has to be seamless from beginning to end," Tai told me. Future passengers should have enough to keep them busy for a visit ranging from three days to a couple of weeks, he said.

"It's really up to New Mexico to step up and say, 'OK, these are the other things you'll want to do while you're here,'" Tai said. That would certainly include a resort experience, and either Virgin Galactic's external partners or the Virgin Group's travel subsidiaries could fill the bill there.

I have to admit that it was hard to think about luxury experiences as I watched Armadillo Aerospace go about their grimy rocket business at the X Prize Cup - but perhaps people thought the same thing as they watched the Queen Mary (and, um, the Titanic) being built - or as the Wright brothers struggled with their first airplanes. Eventually, that tinkering brought us luxurious cruises and (at least for a time) Concorde flights.

Perhaps the luxury market is one small step toward a wider-based technological leap - the same kind of leap we saw with the spread of affordable air and sea travel, consumer electronics and, yes, cell phones. At least that's what I'm hoping. To me, $200,000 still sounds like a lot of money for a ride on a rocket plane - even a luxurious one.

For further reflections on the hits and misses of the X Prize Cup, check out these links:

• 'We Failed': Postmortem from Armadillo Aerospace's John Carmack
• Space Revolution News at Daily Kos: Recapping the X Prize Cup
• The Space Review: Hard start, tough finish 
• X Prize Cup retrospective at The Pomerantz Report
• Matt Falk's photos from the X Prize Cup

• CollectSpace: How to make 'cufflinks' to save the space station
• Slashdot: The economic development of the moon (or not)
• 'Nova' on PBS: 'Sputnik Declassified'
• The Economist: The fly's a spy

NASA / JPL-Caltech / Cornell

NASA's Opportunity rover sent back this view of a Martian promontory at Victoria Crater named Cape Verde. The picture is in soft focus due to the scattering effect of dust on the camera's front window. Click on the image for a larger version.

The mysteries from the Red Planet just keep on coming: On the ground, NASA's Opportunity rover is carefully picking its way down a deep crater, sending back a stunning postcard along the way.

Meanwhile, high above, the European Mars Express orbiter has sent back curious evidence of equatorial deposits of material that go more than a mile beneath the Martian surface. Is it water ice? Dust? Volcanic ash? Scientists can't yet answer that question, but they really want to. If it's ice, that could help answer questions about Mars' past - and its future.

First, about NASA's rovers: For some weeks now, Opportunity and its twin, Spirit, have been focusing on long-term science projects. Spirit is looking at an intriguing layered rock formation nicknamed "Home Plate" that may shed light on ancient volcanic activity - and also looking for a safe, sunny place to spend the Martian winter.

On the other side of the Red Planet, Opportunity has driven down the inside slope of half-mile-wide Victoria Crater and is looking at a mysterious light-toned band of rock just below the crater's rim.

"We think it's made of the same stuff that all the other rock around here is made of, but something different happened to it during its history," Cornell astronomer Steve Squyres, the principal investigator for the rover missions, told me today.

The band is several meters wide, and consists of three "subbands" with different characteristics, Squyres said. The top band seems to consist of material from before the impact that created Victoria Crater, and the material may look different because it interacted with the Martian atmosphere millions of years ago, he said.

Could this show scientists whether the air on Mars was different back then? All Squyres would say is, "You could speculate like crazy."

Another hypothesis is that water seeped up from below and interacted with the rock, changing its texture and chemistry. If this suggestion is borne out, "the base of the bright band is effectively a bathtub ring," Squyres said.

"We saw something very much like it back at Endurance Crater," he said.

Scientists aren't yet close to figuring out exactly what caused the bright band to look the way it does. "It's a very laborious problem to try to solve this. ... Sometimes it's just grind-it-out science and it takes a while," Squyres said. The fact that Opportunity is sitting on a potentially perilous slope doesn't make the job any easier.

As of this week, Opportunity and Spirit have spent two full Martian years on the Red Planet, and they're both still going strong. To celebrate the milestone, NASA released a stunning picture of a promontory at Victoria Crater called Cape Verde. Those two years on Mars translate into nearly four years on Earth - not bad for a mission that was initially slated for just 90 days.

Deep deposits
Now for the results from the MARSIS radar altimeter aboard the Mars Express orbiter: For decades, scientists have been intrigued by an equatorial region known as Medusae Fossae, which marks a transition of sorts between the Martian highlands and lowlands. Even back in the 1970s, they suspected that there might be large deposits of water ice there, although they couldn't explain how those deposits got there.

ESA / ASI / NASA / Univ. of Rome / JPL / Smithsonian

This color-coded view shows the Martian surface and subsurface in the Medusae Fossae region. The MARSIS radar sounder found echoes from the lowland plains buried by mysterious deposits. The top arrows show the surface echo, and the bottom arrows indicate the subsurface echo of one of the hills made up of the deposits.

In a report published today on Science Express, the MARSIS team provides an estimate of just how deep the deposits go, based on radar sounding data. The answer? Pretty darn deep: about 1.6 miles (2.5 kilometers).

"If these materials are ice-rich, it's a significant amount of water that would be added to the inventory of water ice that we know about on Mars," Thomas Watters of the Smithsonian Institution, lead author of the Science study, told me today. "It would be something like a 36 percent increase in the total amount of water ice that we know about at the surface of Mars. Again, that's all qualified with a big if."

The "big if" relates to whether or not the deposits really do consist mostly of water ice. The radar readings indicate that the Medusae Fossae deposits have the density and electrical properties of water, but they also could conceivably consist of fluffy volcanic ash or dust. That doesn't seem likely: If the ash or dust is that deep, you would think it would compact into denser stuff. But the geology of Mars isn't like Earth's, and confirming the composition would require more detailed readings - by MARSIS or a higher-resolution radar imager aboard NASA's Mars Reconnaissance Orbiter, called SHARAD.

Even if it is water ice, the deep deposits appear to be covered with a layer of wind-sculpted soil that might be meters thick. "That could be the veneer or the covering that is insulating the thicker deposits that have ice in them," Watters said.

The presence of that top layer makes it harder to know for sure exactly what lies beneath. "We're really not going to be able to determine it definitively until we actually go there and sample below this desiccated outer layer," Watters said.

Past and future of the Red Planet
If it is water ice, that raises yet another question: How did all that water get there in the first place? Scientists believe the deposits are only a couple of million years old, based on the lack of cratering and the fact that they're sitting on a geologically recent lava plain.

NASA / ASU

Wind has sculpted the terrain in the Medusae Fossae region, as seen in this view from the THEMIS imager on NASA's Mars Odyssey orbiter.

"The fact that this exists at the equator is very intriguing, because there has to be some sort of climatic condition that allows accumulation and preservation of water ice in a tropical area on Mars," said Jeffrey Plaut, a planetary scientist at NASA's Jet Propulsion laboratory who is co-principal investigator for the MARSIS experiment and a co-author of the Science paper.

One hypothesis is that the tilt of Mars' axis was more pronounced millions of years ago.  "If the spin axis rotates to a high value, then you actually warm up the poles and cool down the midlatitudes and the equator," Plaut explained. Water ice at the poles might sublimate into vapor, make its way toward the equator and freeze out of the atmosphere as ice deposits.

Over time, ice crystals would mix in with soil deposits. As the planet's tilt became less oblique, temperatures would become warmer at the equator, and the ice near the surface would disappear - leaving that layer of soil on top to be sculpted by the wind.

It all makes for an intriguing story about Mars millions of years ago - but if the deposits really are ice-rich, that also could tell us something about the future exploration of the planet.

"The one advantage of having ice in the lowlands is that it's a much easier place to get to [than the poles]," Watters said. "The lowlands are an attractive place for robotic landers or human-piloted landers."

Plaut agreed, noting that his colleagues at NASA are already doing a lot of research into what it would take for humans to live off the land on Mars.

"Those folks are very interested in any evidence that there may be water ice reservoirs in these more temperate parts of Mars, because it's certainly easier to operate equipment in those regions of Mars than in the polar regions," he told me.

So it might be worth getting to know Medusae Fossae better in the years to come. It's definitely a weird-looking place, based on photos like this one, and this, and these. Oh, and this zoomable picture, too. To keep up with the saga of Mars exploration, be sure to check in on our special report, "Return to the Red Planet."

In addition to Watters and Plaut, authors of the Science study include Bruce Campbell and Lynn Carter of the Smithsonian Institution; Carl Leuschen of the University of Kansas; Giovanni Picardi and Roberto Orosei of the University of Rome;  Ali Safaeinili and Anton Ivanov of the Jet Propulsion Laboratory; Stephen Clifford of the Lunar and Planetary Institute; William Farrell of NASA's Goddard Space Flight Center; Roger Phillips of Washington University in St. Louis; and Ellen Stofan of Proxemy Research.

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