Ken Tapping, June 18, 2008

Near the Phoenix Lander, on the edge of the Martian Arctic icecap, there are now two scoop marks in the ground. The spacecraft has successfully fired up its robot arm and scoop, and it has taken two samples of Martian soil. It might not sound like much, but this could lead to a big step forward in our quest for life on the Red Planet.

Some of that scooped up dirt has been put in the "Thermal and Evolved-Gas Analyzer", which is a high tech oven where the soil will be heated and any gases that are released analyzed. One of the pictures transmitted back from Phoenix shows the opening to the oven with dirt scattered around it. What do we hope to learn from an experiment like this?

Imagine some alien version of Phoenix landing in your backyard. Assume it does not have cameras, so it does not notice cars, kids, cats and dogs and other things moving around. A robot arm comes out, takes a scoop of dirt and puts it in an oven, where it is heated and the gases analysed. Because our world is loaded with life, that soil sample is loaded with organic chemicals. Life like ours depends upon the chemistry of highly reactive chemicals that, when released into the environment, disappear very quickly by reacting with something. Their presence in the gases from our heated sample means they are being constantly produced by living things of some kind. Of course there is no reason to assume that chemically-based life on Mars need to be like life on Earth, but we would still expect the signature of this life to be reactive chemicals that do not last long, so that the supply has to be continually topped up.

When the Viking spacecraft landed on Mars some decades ago, they took soil samples, tested them and detected some highly reactive chemicals. At first the conclusion was that life had been detected. However, scientists showed there were other ways of getting the same results. The Martian atmosphere is thin and does little to stop the ultra violet radiation from the Sun. This energetic radiation reacts with chemicals in the soil to produce unstable and highly reactive superoxides and peroxides, which would have produced spurious indications of life. So we could not conclude anything about Martian life from the results of those experiments. We don't expect to make the same mistake this time. The analysis equipment on Phoenix is much more sophisticated and a lot more picky about identifying the chemicals it detects.

Watch this space; the next few months could see some exciting new results. One surprise was how lumpy the Martian soil is. The oven opening is covered by a mesh screen that will admit particles smaller than one millimetre in size, so everyone is hoping that some fine stuff got into the oven. If not, more attempts will be made.

Another nice instrument on Phoenix is a microscope that can be used to look at soil and other particles in fine detail. If there is anything like a bacterium or small soil creature this will spot them. It will also be able to spot particles produced by volcanic eruptions and meteorite impacts, or any other strange events on the Red Planet.

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca