Digging Deep on Mars
A NASA spacecraft preparing to launch will use novel technology to search for signs of life on the red planet.
A new Mars spacecraft called Phoenix, created largely from leftovers from one mission that failed and another that was canceled, is set for takeoff on Saturday from Cape Canaveral, and it could provide more information than ever before about just what Mars is made of.
In particular, the red planet’s enigmatic, highly reactive soil is about get its first in-depth investigation, and may finally give up its secrets–particularly whether it does, or once did, hold life–after Phoenix lands in a previously unexplored area near Mars’s north pole next May.
Phoenix is equipped with a trenching tool that can dig down half a meter into the dirt–far lower than the few centimeters of previous missions–and a grinding tool that can penetrate even superhard ice. Phoenix carries a battery of instruments that go far beyond anything previously taken to another planet, including the most advanced weather station yet sent to Mars. It also carries two different kinds of microscopes: an optical microscope with its own multispectral light source, and an atomic-force microscope that can see details as small as 200 nanometers–one-hundredth the diameter of a human hair.
Both microscopes are capable of revealing details of soil structure never even glimpsed before, which may help bring to light important details about the past geology and climate of the planet. For example, the shapes of particles can reveal whether they were exposed to flowing water, or were repeatedly frozen and thawed, or remained soaking in water for extended periods.
The cameras and microscopes will study the freshly exposed surfaces, and then the really new science begins. Scoops of soil and ice will be picked up and analyzed by various devices, including a wet chemical lab that will dissolve particles and study their chemistry, and another device that will vaporize the soil and melt the ice to study the molecules within it.
This instrument, called the Thermal and Evolved Gas Analyzer, or TEGA, is capable of determining exactly how much ice is in the soil at various depths and the ratios of various isotopes, including hydrogen and its heavier form, deuterium. And if there are organic chemicals lurking in that ice, Phoenix could discover their presence on Mars for the first time and learn a bit about the details of their composition.
Organic molecules–any compounds containing carbon–constantly rain down on Mars, as they do on Earth, from meteors burning up in the atmosphere, which is why scientists were so startled when Viking didn’t find any. A new analysis last year suggests that that failure may have been because the Viking instrument didn’t heat its samples enough to detect certain kinds of “refractory” organics that might be there.
“If organics are present, we’ll detect them,” says Bill Boynton, a biochemist at the University of Arizona who led the team that developed the TEGA instrument. It works by putting a tiny scoop of soil into a chamber, sealing it shut, and then slowly heating it and measuring the vapors given off as the temperature rises all the way to 1,000 ºC.
While TEGA can’t tell the difference between organics resulting from chemical processes and those made by living organisms, it could at least provide enough information to allow researchers to decide whether its landing area is worthy of later exploration by landers equipped to search directly for traces of life. “If this is a region where organics can survive, it might be a region one could go back to with a roving mission to see if there are indications of life or not,” Boynton says.
Although it’s a long shot, TEGA might also be able to find more direct traces of life. Three different groups have reported the detection of methane gas in the Martian air, although the amounts are low and the evidence remains controversial. With luck, the Phoenix device might pick up those traces, especially if, as some researchers suggest, they may sometimes reach higher concentrations in some places. Methane in the air, since it breaks down quickly, would be a clear sign of a very active process–either current volcanism, which has not been detected there, or the metabolism of living organisms.
Phoenix, a project led by University of Arizona planetary scientist Peter Smith, will be the first planetary probe whose operations will be run from a university-based control room rather than a space-agency center. This is a step toward making planetary exploration a normal, operational process and taking it beyond the experimental development phase. A similar setup has worked well for the Chandra X-ray Observatory, which is run from a control center in Cambridge, MA, and operated by MIT.
Phoenix also represents an unusually inexpensive approach to such a complex mission, partly because it was able to make use of spacecraft and instruments developed for the Mars Polar Lander, which crash-landed in 2002, and from the Mars Surveyor Lander, a project that was canceled by NASA in 2001. This rebirth with parts from lost missions gave the new mission its name.
Scientists have been puzzled by Mars’s ruddy soil ever since the Viking mission in 1976 investigated the planet from ground level for the first time. The results from the twin Viking landers, which have been heatedly debated ever since, suggested the presence of some powerful oxidizing agent on the soil surface that very quickly decomposes any organic compounds there–an environment highly toxic for life.
But many scientists suspect that just a few inches below the surface, things may be very different. Radar and gamma-ray inspections from orbiting spacecraft have revealed a layer of subsurface ice on much of the planet, in some places just a few inches deep. In the near-polar region where Phoenix will land, ice may extend more than a half-mile down, and parts of it may occasionally melt in certain seasons. It’s a place where, if life ever gained a toehold on Mars, its last straggling microbes may have survived for eons, and where some might even persist today.
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