Phoenix Mars lander bakes third soil sample


By Devin Powell (Image: NASA/JPL/University of Arizona) The Phoenix lander is studying its third sample of Martian soil in an onboard oven. The results may confirm the presence of a chemical called perchlorate, which could shed light on the history of water on the Red Planet. In recent days, the lander has also dug its deepest trench yet in the soil, reaching a depth of about 9 centimetres. On Saturday, a soil sample from near the surface of a trench called “Rosy Red” was dropped into an oven on an instrument called TEGA (Thermal and Evolved Gas Analyzer), which heats samples and measures gases released by volatile compounds. Researchers will search the sample for signs of perchlorate, a chemical that can be carried away by liquid water and could thus reveal hints about how water may have flowed in the region in the past. Attempts to detect perchlorate using TEGA in two other soil samples, from different areas, were inconclusive. One released oxygen – a component of perchlorate. But both it and a second soil sample failed to produce chlorine gas, another expected by-product. But two other soil samples taken from this Rosy Red trench and a nearby trench called Snow White showed preliminary evidence of perchlorate when analysed in the lander’s MECA (Microscopy, Electrochemistry and Conductivity Analyzer) instrument. Delivering the latest soil sample to TEGA was not easy. On Thursday, Phoenix’s robotic arm dumped the sample on top of TEGA’s oven number 5. At first, only a few particles made it into the instrument’s cylindrical compartment. Part of the problem was that its double doors – released by spring-loaded mechanism – only partially opened when activated on 20 June. A similar mechanical problem caused only one door to open on the adjacent oven, which was used to study Phoenix’s first soil sample. Nevertheless, the team decided to use oven 5 anyway, to conserve the instrument’s four remaining ovens for high-priority samples of water ice. “We plan to save the cells where doors can open wider for accepting ice samples,” said TEGA team leader William Boynton of the University of Arizona in Tuscon. To make matters worse, the dirt that did squeeze through the crack at the top of the doors initially clumped up on the wire mesh above the oven. So on Friday, team members commanded Phoenix to shake the oven for short, three-minute intervals. The soil fell through the mesh after only a day. That is much faster than the first soil sample, which took about a week to slip through the mesh. This time, the had team carefully sprinkled the dirt onto the mesh to avoid as much clumping as possible. The oven started baking the sample on Sunday. “It will be some time before we have results to release,” says the TEGA team. In the meantime, Phoenix will use its robotic arm to continue expanding another trench called “Neverland” – the deepest it has yet dug. Previous trenches have found evidence of ice 5 centimetres below the surface. But so far Neverland, which has reached a depth of 8 or 9 cm, has found no signs of ice. That may be because it is located between two rocks that should retain heat absorbed from sunlight longer than finer particles of soil, thereby heating the surrounding ground. Studying ice in different parts of the terrain may help scientists understand Mars’s quilted landscape of regular polygons, believed to be created by the expansion and contraction of ice. When the team does attempt to collect its next sample of icy soil, it may keep the scoop out of sunlight when it is carrying the icy sample to the lander’s instruments. That may prevent the sample from becoming sticky, a problem that foiled Phoenix’s first attempt to deliver ice to TEGA. The stickiness prevented the sample from falling from the scoop and may have been caused by partial melting of ice in the sample. “We think once it got into the Sun it got sticky,” says team member Ray Arvidson of Washington University in St Louis, Missouri. Mars Rovers – Mars is full of surprises; learn more in our continually updated special report. More on these topics:
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