NEWS NATURE|Vol 453|8 May 2008

Phoenix descending NASA’s Mars strategy goes from “follow the water” to “arrive at the ice”.

Since 2001, the slogan for from hardware and software.

NASA’s Mars programme has “We may not succeed, but we NASA been “follow the water”. deserve to succeed,” he says. With Phoenix, a US$420- Engineers at the Jet Propul- million mission to the edge of sion Laboratory in Pasadena, the planet’s north ice cap, the California, which runs most of agency hopes to finally touch NASA’s planetary missions, will its quarry, in the form of dirty have their last chance to tweak water ice scraped from the the trajectory on 24 May. The subsurface and melted in the next day, Phoenix is expected probe’s on-board ovens. to use the planet’s atmosphere, If all goes as planned, Phoenix and its own heat shielding, will reach the end of its 680- parachutes and retrorockets, to million-kilometre, 10-month- slow itself down from an orbital long journey on 25 May. Its speed of 20,000 kilometres per landing site is in a region where hour to a soft, safe landing at NASA’s orbiting Mars Odyssey just 2.4 metres per second. spacecraft has detected gamma-ray and neu- Phoenix, a 350-kilogram lander, inherited Smith and his team hope that the ice and soil tron signatures suggesting a significant amount hardware from the Mars Surveyor Lander, a samples they will study with the spacecraft’s of hydrogen — thought to be a constituent of mission cancelled in 2000 after the failure of mass-spectrometer and chemical analysis sys- frozen water — near the surface. Soon after the Mars Polar Lander, with which its design tems will contain hints of organic molecules, unfurling twin solar arrays, the lander will had much in common. As a result of its sibling’s of which the Viking landers found no trace at extend a robotic arm to dig down as far as half demise, Phoenix’s principal investigator Peter lower latitudes. The polar environment might a metre in search of that ice. Smith of the University of Arizona in Tucson be more hospitable to persistent organics — Older missions, including the rovers Spirit and his team eliminated more than two dozen either from incoming meteorites or primordial and Opportunity, have shown that there was flaws that might have conceivably led to failure to Mars — than the corrosive and radiation- water at and near the planet’s surface billions blasted surfaces which the Vikings scratched. of years ago. Phoenix will be rooted in the Phoenix can measure salts, pH levels and present, sampling ice that may have frozen individual chemicals, but can’t analyse the in place mere tens of thousands of years building blocks of life, such as proteins. ago and also sifting the soil for organic “We’re an ideal stepping stone for more chemicals and substances, such as expensive and sophisticated missions sulphur, that life might use as an such as the Mars Science Laboratory, energy source. “Phoenix will, for which can really look at molecules the first time, give us the opportu- and say, ‘This is DNA’,” says Smith, nity to directly assess habitability,” referring to the Cadillac of NASA says Doug McCuistion, NASA’s Mars missions — a long-duration Mars-exploration programme rover weighing 850 kilograms director. and budgeted at nearly $2 bil- Before that, though, it has lion — which is due for launch to get down safely. Five NASA next year to one of a shortlist spacecraft have landed suc- of six sites closer to the planet’s cessfully on Mars in the past: equator. two 1976 Viking landers, the By August, Phoenix will have 1997 Pathfinder and the two used up its ovens and laboratory rovers that arrived in 2004 and equipment. It will hang on as a polar are, remarkably, still going strong. weather station for a few months But there have been misfires. The before the severe cold of the high-lati- most successful of the Soviet Union’s tude winter in all likelihood ends its mis- various attempts at landing in the 1970s sion. But its results may lure other probes sent back only seconds of data from the sur- back to the poles. “If we find an abundance of face — but that was better than NASA’s Mars organic matter in this ice,” Smith says, “you Polar Lander, which was never heard of again can bet your bottom dollar there’ll be another after entering the atmosphere in 1999, and the Phoenix hopes for a picture-perfect landing (top) mission going there someday.” ■ British-run Beagle 2, lost in 2003. on Mars’s northern plains (above). Eric Hand

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