JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E7, 5077, 2003

The Mars Surveyor Program ’01 Mars Environmental
Compatibility Assessment Wet Chemistry Lab:
A sensor array for chemical analysis of the Martian soil

Samuel P. Kounaves, Stefan R. Lukow, and Brian P. Comeau
Department of Chemistry, Tufts University, Medford, Massachusetts, USA

Michael H. Hecht, Sabrina M. Grannan-Feldman,1 and Ken Manatt
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Steven J. West, Xiaowen Wen, Martin Frant, and Tim Gillette
ThermoOrion, Beverly, Massachusetts, USA

Received 11 September 2002; revised 19 May 2003; accepted 23 May 2003; published 24 July 2003.

The Mars Environmental Compatibility Assessment (MECA) instrument was
designed, built, and flight qualified for the now canceled MSP (Mars Surveyor Program)
’01 Lander. The MECA package consisted of a microscope, electrometer, material patch
plates, and a wet chemistry laboratory (WCL). The primary goal of MECA was to
analyze the Martian soil (regolith) for possible hazards to future astronauts and to provide a
better understanding of Martian regolith geochemistry. The purpose of the WCL was to
analyze for a range of soluble ionic chemical species and electrochemical parameters. The
heart of the WCL was a sensor array of electrochemically based ion-selective electrodes
(ISE). After 20 months storage at -23^oC and subsequent extended freeze/thawing cycles,
WCL sensors were evaluated to determine both their physical durability and analytical
responses. A fractional factorial calibration of the sensors was used to obtain slope,
intercept, and all necessary selectivity coefficients simultaneously for selected ISEs. This
calibration was used to model five cation and three anion sensors. These data were
subsequently used to determine concentrations of several ions in two soil leachate
simulants (based on terrestrial seawater and hypothesized Mars brine) and four actual soil
samples. The WCL results were compared to simulant and soil samples using ion
chromatography and inductively coupled plasma optical emission spectroscopy. The results
showed that flight qualification and prolonged low-temperature storage conditions had
minimal effects on the sensors. In addition, the analytical optimization method provided
quantitative and qualitative data that could be used to accurately identify the chemical
composition of the simulants and soils. The WCL has the ability to provide data that can be
used to ‘‘read’’ the chemical, geological, and climatic history of Mars, as well as the
potential habitability of its regolith.