Ken Tapping, July 9, 2008

Dry river valleys and canyons, dried up lakes and seas all show that billions of years ago Mars was a wet, warmer world than it is today. One of the million-dollar questions has been where did the water disappear to? If there is life on Mars, we would expect it to be where the water is, if there is any. In addition, if one day we are to live on Mars for long periods, locally available water will be essential.

The two most likely possibilities are that the water was lost to space, or that it is now underground, as a huge amount of buried ice. The latter theory is the one we would prefer to be the case. Until this summer, the only information we had were observations made on the surface and studies of the Polar Regions made from orbiting spacecraft and from Earth by means of large telescopes. The spacecraft sitting on Mars' surface showed us a cold, dry desert with a dusting of frost on the rocks in the mornings. We could see the polar caps, but there was a lot of argument as to how much of that ice was frozen water and how much could be frozen carbon dioxide. Some craters have beautiful frozen turquoise lakes at the bottom. However, when you total all that observed water, it does not add up to a significant lake, let alone an ocean.

Orbiting radars showed us something more encouraging. Pulses of radio waves sent down from space penetrated below the dry surface and then bounced back from something deeper down that could well be ice. However the only way to prove that one way or the other was to have a look.

One of the main instruments on the Phoenix lander is a small but powerful scoop that can be used to scrape away the surface sand to see what is buried underneath. Over the last couple of weeks, this is exactly what Phoenix has been up to, and not far below the surface is a layer of ice. One observation does not really justify making conclusions about the history of an entire world, but this discovery is very exciting. However, now that we have some ice to play with, this is only the beginning of the story. For example, we can melt some of it and find out what chemicals are in it. Are there traces of life in it? In addition, is this ice one big layer, or a series of layers? If we find layers, are they the result of a series of freeze-ups that laid the ice down a layer at a time? Have they melted and refrozen? These ice layers could tell us the story of climatic changes during that part of Mars' history where the planet changed from a lush, wet, warm friendly world to the frozen, almost airless desert we see today. 

A couple of weeks ago we heard that Phoenix had successfully scooped up some soil and tipped it onto the mesh grill covering the thermal and evolved gas analyser. However, the soil was lumpier and less powdery than expected and it was not clear that any soil got though the grill. The latest news is there is soil in the analyser and we will soon hear whether there is evidence that in the distant past Mars was a living world, and at least equally exciting, whether it still is.

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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