Trenches dug by the Phoenix lander’s robotic arm (NASA/JPL-Caltech/University of Arizona/Texas A&M University)
06 August 2008 Martian Soil, Chemistry Hold Surprises for Scientists, August 6, 2008
(NASA extends Mars lander mission by five weeks, through September 30)
By Cheryl Pellerin
Washington -- The stubborn stickiness of Martian soil and the unconfirmed discovery of a chemical called perchlorate, which is naturally found on Earth in places like Chile’s cold, extremely dry Atacama Desert, are two findings from NASA’s Phoenix Mars lander that scientists were not expecting.
Since landing on the northern plains of Mars May 25, Phoenix has been studying soil with the wet chemistry laboratory of the spacecraft's microscopy, electrochemistry and conductivity analyzer (MECA); the thermal and evolved-gas analyzer (TEGA); a microscope; a conductivity probe; and cameras.
"Mars is giving us some surprises," Phoenix principal investigator Peter Smith of the University of Arizona-Tucson, said during a July 31 briefing. "We're excited because surprises are where discoveries come from.”
The mission was planned for 90 days, to end in late August, but on July 31 NASA announced that it would extend funding -- about $2 million -- to keep Phoenix running through September 30.
Smith leads the Phoenix mission, with project management at NASA's Jet Propulsion Laboratory in California and development partnership at aerospace company Lockheed Martin in Colorado.
International contributions come from the Canadian Space Agency, the University of Neuchatel in Switzerland, the universities of Copenhagen and Aarhus in Denmark, the Max Planck Institute in Germany and the Finnish Meteorological Institute.
MARTIAN WATER, SOIL
One finding that did not surprise Phoenix scientists was confirmation July 31 by the TEGA instrument -- a series of ovens and analyzers that sniff vapors released from substances in a sample -- that there is water in Martian soil.
Scientists saw evidence of water ice on the planet in 2002 observations by NASA’s Mars Odyssey orbiter and in disappearing chunks that the Phoenix cameras documented in June, but the lab test was the first time that sophisticated instruments had “touched and tasted” Martian water, said TEGA lead scientist William Boynton of the University of Arizona.
The soil sample came from a trench about 51 millimeters deep. When the robotic arm first reached that depth, it hit a hard layer of frozen soil. Two attempts to deliver samples of icy soil on days when fresh material was exposed failed when the samples got stuck inside the scoop.
Most of the material in the examined sample had been exposed to the air for two days, letting some of the water in the sample evaporate and making the soil easier to handle.
Besides confirming the finding from orbit of water ice near the surface and working with the unexpectedly sticky Martian soil, the science team is trying to determine if the water ice ever thaws enough to be available for biology and if carbon-containing chemicals and other raw materials for life are present on the planet.
Within the last month, the MECA wet chemistry lab has analyzed two samples and returned results suggesting that one of the soil constituents may be perchlorate salts. Phoenix scientists are waiting for confirmation of perchlorate by the TEGA instrument.
Perchlorate is an ion, or charged particle, that consists of a chlorine atom surrounded by four oxygen atoms. Such an oxidizing chemical can be toxic to life, yet some Earth-bound microorganisms are fueled by processes that involve perchlorates and some plants concentrate the substance.
The potential finding, Phoenix scientist Samuel Kounaves of Tufts University in Massachusetts said during an August 5 NASA briefing, “doesn’t indicate anything that would be hostile to the extent, for example, if it was sulfuric acid or chlorine or something really lethal to organisms. It’s a benign chemical in terms of most organisms.”
MECA's wet chemistry lab studies soluble chemicals in the soil by mixing a soil sample with a water-based solution with several chemicals brought from Earth. The inner surface of each cell's beaker has 26 sensors that give information about the acidity or alkalinity and concentrations of elements like chloride or perchlorate. The beaker also can detect concentrations of magnesium, calcium and potassium, which form salts that are soluble in water.
The Phoenix science team also is working to make sure the perchlorate readings are not the result of terrestrial sources from the spacecraft.
“This is an important piece in the puzzle as we attempt to determine whether habitable conditions exist for microbes on Mars,” Smith said. “In itself, it is neither good nor bad for life.”
More information about the Mars Lander mission is available at the NASA Web site.