It’s about four months until Curiosity, NASA’s new Mars rover, plunges into the thin Martian atmosphere at a good few thousand miles per hour, releases a parachute and then finally uses a retro-rocket jet pack to place her safely down on the surface…hopefully (watch this great video of the landing sequence). She’s a well equipped machine with a radioisotope thermoelectric generator as her power source and a large swathe of spectrometers, microscopes, cameras and sensors. All these gadgets aren’t going to help her look for life though. Why is that? Why hasn’t NASA loaded a Martian rover, sent it Mars (somewhere where we think life may be) and decided not to go hunting for it? It all stems back to NASA’s first missions to land on Mars, the Viking missions, back in 1976. These were two landers that were equipped to look for life. What went wrong?
Mars from Viking 2
The Viking landers consisted of 3 biology experiments along with two other supporting instruments. I want to focus on one of the biology experiments and one of the supporting instruments. I should note first though that two of the biology experiments provided results consistent with non-biological processes. The two aspects I’m focusing on are the labelled release (LR) biology experiment and the gas chromatograph-mass spectrometer (GCMS).
A GCMS is a device used to identify different substances in a test sample and the LR experiment was designed to test for metabolic activity of any microorganisms that consumed nutrients that were provided by the experiment. The results were confusing and yet intriguing.
The LR experiment produced results showing positive life detection. The experiment basically involved a small sample of ‘soil’ being moistened with a nutrient of distilled water and organic compounds that had been labelled with radioactive 14C. Any microorganisms that appeared would consume the nutrient and give off gases containing 14C. In the actual experiment labelled gas was emitted (suggesting the presence of microorganisms) but further additions of nutrient caused the gas level to decrease and then increase slowly again. This was very bizarre if this was due biological activity.
The GCMS, however, didn’t find any evidence of organic compounds at the surface thus making all the biology experiments redundant as they were designed to test organic matter.
This is all a very confusing result. One experiment saying there’s no organic matter so there can be no life whilst another says there could be life here. It’s now thought however the the LR experiment can be explained non-biologically and that all the biology experiments showed chemical processes.
So the overall result? Inconclusive. Although some scientists have started to question the LR experiment recently saying that it did actually find life (see ‘Is this proof of life on Mars?‘). They don’t seem to answer questions about there being no organic matter though.
NASA have since taken the view of ‘follow the water’. They don’t want to spend millions or billions of dollars on a mission to get another inconclusive result. So they’re more recent missions have been to understand the geology and chemical processes, and to figure out where the water has been. After a while we may find evidence of an area that could have extant or extinct life, only then will NASA be confident enough to send a life searching mission to Mars.
Gale crater with Curisoity’s landing site
Gale crater, Curiosity’s destination, is an interesting place though. It appears to have been an old lake bed where sediments have been laid down over long periods of time when Mars had water. A good habitat for life? Possibly, but we’re not going to find out conclusively for a long time yet.