Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site
Phoenix Ascending
The Phoenix mission landed on Mars in March 2008 with the goal of studying the ice-rich soil of the planet's northern arctic region. Phoenix included a robotic arm, with a camera attached to it, with the capacity to excavate through the soil to the ice layer beneath it, scoop up soil and water ice samples, and deliver them to a combination of other instruments—including a wet chemistry lab and a high-temperature oven combined with a mass spectrometer—for chemical and geological analysis. Using this setup, Smith et al. (p. 58) found a layer of ice at depths of 5 to 15 centimeters, Boynton et al. (p. 61) found evidence for the presence of calcium carbonate in the soil, and Hecht et al. (p. 64) found that most of the soluble chlorine at the surface is in the form of perchlorate. Together these results suggest that the soil at the Phoenix landing site must have suffered alteration through the action of liquid water in geologically the recent past. The analysis revealed an alkaline environment, in contrast to that found by the Mars Exploration Rovers, indicating that many different environments have existed on Mars. Phoenix also carried a lidar, an instrument that sends laser light upward into the atmosphere and detects the light scattered back by clouds and dust. An analysis of the data by Whiteway et al. (p. 68) showed that clouds of ice crystals that precipitated back to the surface formed on a daily basis, providing a mechanism to place ice at the surface.
Abstract
The Wet Chemistry Laboratory on the Phoenix Mars Lander performed aqueous chemical analyses of martian soil from the polygon-patterned northern plains of the Vastitas Borealis. The solutions contained ~10 mM of dissolved salts with 0.4 to 0.6% perchlorate (ClO4) by mass leached from each sample. The remaining anions included small concentrations of chloride, bicarbonate, and possibly sulfate. Cations were dominated by Mg2+ and Na+, with small contributions from K+ and Ca2+. A moderately alkaline pH of 7.7 ± 0.5 was measured, consistent with a carbonate-buffered solution. Samples analyzed from the surface and the excavated boundary of the ~5-centimeter-deep ice table showed no significant difference in soluble chemistry.
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Published In
Science
Volume 325 | Issue 5936
3 July 2009
3 July 2009
Copyright
Copyright © 2009, American Association for the Advancement of Science.
Submission history
Received: 18 February 2009
Accepted: 26 May 2009
Published in print: 3 July 2009
Acknowledgments
We thank J. M. Morookian, C. Cable, P. Grunthaner, A. Fisher, X. Wen, D. Morris, M. Lemmon, the Phoenix Robotic Arm team, and other contributors to MECA and Phoenix. The Phoenix Mission was led by the University of Arizona, Tucson, on behalf of NASA and was managed by NASA’s Jet Propulsion Laboratory, California Institute of Technology, of Pasadena, CA. The spacecraft was developed by Lockheed Martin Space Systems, Denver.
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