Mars Exploration: Secrets of the Soil

Is there life on Mars today? This question has been fiercely debated by scientists for the past thirty years.

The evidence sent back from Mars by two Viking Landers in 1976 and 1977 was inconclusive. In fact, NASA's first press release about the Viking tests announced that the results were positive. The "labeled Release" (LR) experiments had given positive results. But after lengthy discussions in which Carl Sagan participated, NASA reversed its position, mainly because another experiment detected no organics in the soil.

Yet to this day, Gilbert Levin, the principal designer of the LR experiment, believes the tests pointed to life on Mars (7). When the same two experiments were run on soil from Antarctica, the same conflicting results were obtained (LR - positive; organics - negative.) Soil and ice from Antarctica certainly contains life. The test for organics was negative because it is far less sensitive than the LR experiment. The same problem could have caused the organics test on Mars to give a false negative.

Before oxygen could accumulate in Earth's atmosphere, all the exposed iron had to rust. During that process, lasting hundreds of millions of years, Earth was also a red planet. In the current issue of the journal Nature, Corinna Wu asks: Could the oxygen that rusted the iron on Mars have been produced biologically? Could life on Mars have simply "run out of steam" after that stage of its development?

The answers to these profound questions will hopefully be made by the Phoenix Probe's Thermal and Evolved Gas Analyzer (TEGA) built by the University of Arizona and University of Texas, is a combination high-temperature furnace and mass spectrometer instrument that scientists will use to analyze Martian ice and soil samples. The robotic arm will deliver samples to a hopper designed to feed a small amount of soil and ice into eight tiny ovens about the size of an ink cartridge in a ballpoint pen. Each of these ovens will be used only once to analyze eight unique samples.

Once a sample is successfully received and sealed in an oven, the temperature is slowly increased at a constant rate, and the power required for heating is carefully and continuously monitored. This process, called scanning calorimetry, shows the transitions from solid to liquid to gas of the different materials in the sample: important information needed by scientists to understand the chemical character of the soil and ice.

As the temperature of the furnace increases up to 1000°C (1800°F), the ice and other volatile materials in the sample are vaporized into a stream of gases. These are called evolved gases and are transported via an inert carrier to a mass spectrometer, a device used to measure the mass and concentrations of specific molecules and atoms in a sample. The mass spectrometer is sensitive to detection levels down to 10 parts per billion, a level that may detect minute quantities of organic molecules potentially existing in the ice and soil.

With these precise measurement capabilities, scientists will be able to determine ratios of various isotopes of hydrogen, oxygen, carbon, and nitrogen, providing clues to origin of the volatile molecules, and possibly, biological processes that occurred in the past.

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