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A Plan to Drill Mars
By Mark Schrope
Special to SPACE.com
posted: 07:02 am ET
26 September 2000
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Locked inside the ice at Mars' north pole, protected from the destructive surface conditions, lies a preserved record of what life has been like on Mars for millions of years, and possibly whether there was any life to experience it Locked inside the ice at Mars' north pole, protected from the destructive surface conditions, lies a preserved record of the planet's climate history for millions of years, and possibly whether there was any life to experience it. Using a unique robotic hammering drill to burrow into the ice cap, a team at NASA's Jet Propulsion Laboratory (JPL) hopes to unlock that geological treasure chest by the end of the decade.The JPL team is currently devising plans for a Mars Climate History Mission, which would depend on the SSX subsurface explorer, under development through a separate project. The SSX concept calls for a unit that looks like a metal model rocket without the fins, just 3.2 feet (meter) long and almost an inch (a few centimeters) wide. Inside is an 11-pound (5-kilogram) weight that spins to high speed at the top of a shaft and then engages threads that throw it down, converting this rotational energy into a powerful punch that crushes everything in its path. 
A drawing of the proposed Mars Climate History Mission lander with its large round solar collector, bow-tie sounding radar antenna, and subsurface explorer, deployed, at lower center. This hammer scheme, already tested in prototype form, is more than three times as efficient as other drilling mechanisms used on Earth. This is crucial because the SSX would have to operate on a tiny trickle of power supplied by wires unrolled from a surface lander equipped with solar panels. Crushed bits of dust, ice and whatever lies within and below the cap would be sent to the lander for analysis via a small tube. Equipping the SSX with a device to take small cores from its side is also a possibility, according to designer Brian Wilcox, supervisor of JPL's Robotic Vehicle Group.Researchers hope that sending such a device deep into the Martian north polar cap would help solve a variety of mysteries regarding its history. "If you could really do that, anything you get would be good information," says James Rice, an astrogeologist at the University of Arizona, Tuscon. "Our knowledge of the polar regions is almost zero." Based on indirect evidence, the bulk of the north cap is around 2 miles (3 kilometers) thick, though the mission will be aimed at a site about 0.6-mile (1-kilometer) thick. Current theory holds that the cap is made mostly of water ice with some carbon dioxide as ice or locked in water ice cages known as clathrates. The permanent portion of the cap is about 682 miles (1,100 kilometers) across, although it grows and recedes seasonally across the planet. Pictures of the edges of the cap show thick, dark layers that researchers assume are dust mixed with ice. But the cap currently only grows about 0.04 inches (1 millimeter) thicker each year. " The layering we see from orbit is at the several to tens of meters scale," says mission planner Frank Carsey, "so we're not seeing one dust storm." Determining what they are seeing would be one of the many goals of the mission.Neon-helium dating A key element will be dating ice layers to see if growth rates have varied over time. This could also determine whether the dark layers line up with known historical events such as changes in the tilt of the planet that could have changed the Martian climate and atmosphere dramatically, possibly leading to increased dust accumulation at the poles. ~ The favored dating method is comparing ratios of helium to neon in samples, both of which are bombarded by cosmic rays into rock and ice when they are exposed at the surface. Over time and at a regular rate, the much lighter helium diffuses out while the neon stays trapped, so less helium means an older sample. This process, assuming there are no as yet unknown factors on Mars to throw it off, has already written a rough chemical date on every layer of the cap. The samples sent to the lander will also be run through a slew of other tests to determine their composition. Researchers will learn if the dust is really dust, and they should discover the history of volcanic eruptions on the planet by identifying ash from specific layers.
The layout of a Mars surface analysis laboratory. Particles from the subsurface explorer would be moved in a capillary filled with high-pressure gas through a suite of instruments. While such climate-related information is the focus of the mission, team members also hope to search for signs of life to a limited extent by analyzing samples for organic molecules. Non-biological processes tend to produce a uniform distribution of organic molecules with smaller ones most abundant. "But life doesn't do that," says Carsey. So, the mission might identify non-uniform distributions that would suggest current or past life in the ice. This would not be definitive proof of life on Mars, he says, but it would be tantalizing evidence to guide future missions.Non-biological organic material would also be an important find. Right now Mars' thin atmosphere lets through so much ultraviolet light that organic molecules are essentially eaten alive. So, significant amounts of organic material in certain layers would indicate that the atmosphere was at times thicker and more protective.Hunting for limestone The plan also calls for exploration below the cap. Based on what appear to be ancient shorelines, many scientists believe Mars once had a liquid ocean. "There's a body of circumstantial evidence that points in that direction and basically it's a question of waiting for the smoking gun," says Paul Schenk, a geologist at the Lunar and Planetary Institute in Houston. The JPL team hopes that the chemical composition of material just below the cap would be just that. One possibility is that if there were an ocean, the high concentration of carbon dioxide in the atmosphere would have led to high concentrations of it in the water. This would make the water acidic, causing it to react with material on the seafloor to form limestone or other carbonate rocks. So, if the SSX found carbonate rocks it would suggest that the bottom of an ancient ocean had been found.If the Mars Climate History Mission should eventually receive funding, the tentative launch date is 2009. Whether such a mission will be considered a priority is difficult to say, as the entire Mars Program is currently being re-evaluated. A report on the new priorities is due out in October. "Certainly, I and other people believe that the polar caps are a good place to go for astrobiology and climate study," says Stephen Clifford, a Martian hydrologist at the Lunar and Planetary Institute.Even if the mission is never funded, Carsey says just showing the space community that technology has reached the point where subsurface missions can be conceived and planned is important. "The meat on the table for Mars," he says, "is almost certainly going to come from subsurface exploration."
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