Monday, July 7, 2008

Another martian twist at the PLRP

Alfonso Davila

It's about to get really nasty. Tomorrow some of us are heading to the Basque Lakes, a group of lakes characterized by a high concentration of magnesium-sulfate salts, which at this time of the year precipitate here and there and everywhere, forming small brine pools. Bacteria feed on these sulfate salts, leaving behind a collection of sulfide minerals and gases. Getting your nose too close to these pools will engrave long-lasting, stinky memories in your brain. Watch your step, or they may leave long-lasting stains on your boots and trousers too. Nothing in these black and white smelly ponds will be of interest to your eyes, unless your interests lie in finding out if life was ever present on Mars.
Magnesium sulfate salts, mainly epsomite (MgSO4-7H2O) and its dehydrated twin kieserite (MgSO4), are the most common evaporitic minerals identified on Mars so far. They have been found in the vast flat lands of Meridiani Planum and in the steep walls of Valles Marineris. These minerals are a window into a period of the history of Mars when liquid water was stable and abundant on the surface. In the Basque Lakes, magnesium sulfate salts are breakfast for many microorganisms, which in turn are lunch for others and so on down the menu. To many of you the resulting ecosystem may not be the prettiest expression of mother nature's masterpiece, but perhaps the simplicity of a mathematical equation will change your mind:

Mg-sulfate + H2O + Life on Earth = Mg-sulfate + H2O + X on Mars

Figure out X and you may find beauty. This is one of the many equations that justify Mars analogue research. It is based on the fact that there is many places on Earth that resemble Mars today or sometime in the past. Pavilion Lake may be an example. The Basque Lakes may be another. Studying these analogue environments brings us a step closer to understanding Mars, its evolution and its potential for life. It helps us guiding and designing the next robots that will be sent to Mars, and are the perfect grounds for testing the instruments that they will carry, or the life support systems that humans will use themselves one day. This year we brought a portable version of one of these instruments: a Raman Spectrometer. We use the Raman to identify special compounds within bulk samples that are of interest for one reason or another. Organic compounds are one example, sulfate salts are another. The working principle of a Raman Spectrometer is the same as bouncing a ball against something. Bounce it against a concrete wall and it will come right back at you. Bounce it against a pillow and it will come back much more slowly (or it won't come back at all!). After bouncing the ball many times against many different things, you may be able to recognize the type of material you are hitting just by seeing how fast or slow the ball is coming back to you. A Raman does not throw balls but instead it shines a laser into the sample. After interacting with the sample the laser comes back with a different wavelength (wavelength shift), the equivalent to the speed of our ball. Organic compounds and sulfate salts induce characteristic shifts on the laser, which can be easily identified on the screen of the computer attached to the Raman. This way we hope to be able to easily identify any sulfate salts and organic compounds in the lakes. I can almost smell them...

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