Oct. 8th, 2002

Nathalie A. Cabrol

D-8 before departure!

Studying Earth to Understand Mars...and Vice-Versa. For those of you who have already read the summary of the expedition project, you can see that one of our great motivations to go to this altitude, breath so little air, sleep in the cold, and be exposed to harmful UV (although we will use protection against UV) is because we want to learn more…about Mars! It does not seem to make lots of sense…Or does it? This is also true that the organisms living in the lake survive in such incredible conditions that by going there we will also learn a lot about the limits of life on Earth. That alone would be worth undertaking this adventure.

But what about Mars…What is it about the Licancabur lake that makes it a unique analog to the Red Planet? What does analog mean and what it does not? Analog does not mean similar. For instance, it is clear that Mars is not similar to Earth. It is Earth-like (e.g., seasons, channels, dunes, poles, ancient lakes) but it has its own characteristics (e.g., thin atmosphere, cold average temperature, extremely variable obliquity, etc.). There are processes that can be analogous on both planets because, for instance, there is gravity, volcanoes, water and many other common things. Now, the Earth not being Mars and vice-versa, an analog will never be perfect. Many times researchers will try to find a place on Earth where some of the characteristics (e.g., temperature) remind Mars and its potential habitability (possibility for organisms to find favorable environmental conditions to survive)

Water is of course the common link here as it is a pre-requisite for life. There was water on Mars in the past, lots of it and it flowed through channels and ponded in lakes [see Fig. 1]. We know from the study of lakes on Earth that they are good places for life to develop. Moreover lake sediments are very good at preserving the record of life as fossils [see Fig. 2]. When organisms living in a lake die, they fall at the bottom. They are quickly buried under the lake sediments. This rapid burial generates an anoxic (without oxygen) environment that prevents decay and favor the fossilization process. So, lakes are good to search for life in general but there are not all as good. What makes Licancabur so special?

Licancabur is the highest lake on Earth at almost 6000 m (~20,000 ft). At this elevation, the atmospheric pressure is about 480 mb (millibars). This is very thin air for human beings to breath when you think that the average pressure of the atmosphere at sea level is 1013 mb (a little bit than twice more!). With 480 mb, the summit of Licancabur is like going back in time about 3.5 billion years ago on Mars and this is when it gets even more exciting. At that time on Mars, there were still plenty of rivers and lakes.

Another good analogy is the UV radiation. It is very high at Licancabur, much higher than in most of the other places on Earth and this for two reasons: (a) the summit of the volcano is very high and the air is then very thin, thus, it protects less; and (b) the lake is located in the intertropical region where the ozone layer is not that thick. This means that the UV radiation passes even more easily through the atmosphere in this region. There are all sorts of UV but one is very harmful to life: this is the UV-B. We want to understand how much gets to the surface and in the water and learn how the organisms in the lake defend themselves against it. Maybe, just maybe, it would teach us some interesting UV defense strategies that potential martian life in lakes would also have developed 3.5 billion years ago in their environment where there was no ozone layer to protect them.

Another good analogy is the fact that the Licancabur lake is ice-covered most of the year (about 9-10 months a year). These are conditions that were certainly common on martian lakes because of the average temperature. How do organisms deal with limited sunlight and exchange with the surface? It will be interesting to compare our results with those obtained from lakes in Antarctica and in the Arctic.

There is also the fact that the lake sediments are volcanic in origin, material which would have been very common in the martian lakes. What type of habitats do these sediment provide? What kind of record can they keep of dead organisms? All this information will be so useful for the exploration of Mars.
Finally, there is also the possibility that the lake could be sustained by hydrothermal activity or simply heated by geothermal activity [see Fig. 3]. On Mars, 3.5 billion years ago, lakes and volcanoes were still active and there might have been many places like the Licancabur up there [see Fig. 4]. This is how and why going to Chile and Bolivia helps us going back 3.5 billion years in time on Mars. Mother Nature on Earth is our time machine!

But in general, there is so much that the study of terrestrial analogs can bring. What can we learn about Earth from the study of Mars? There are two main things that we could learn. First, we will acquire lots of knowledge about the formation of our own planet. Earth is a geologically very active planet. Many geological eras have come and gone. Our early past is buried under considerable volumes of sedimentary deposits. Sometimes, we can access this past thanks to outcrops and exposures in valley walls, canyons, etc. However, beyond 3.9 billion years in the past we would not be able to find anything. Why? Because Earth has plate tectonic that recycles the rocks through plate collisions and subduction. Our past has simply disappeared. The most ancient rocks have been melted again in the depth of our planet. There is hope though that someday we still could learn about that time way…way back in our history when everything started. Mars has been formed from the same material as Earth. The big difference is that Mars did not have plate tectonics and there, the "genesis" rock, a rock that would go back 4.2 billion years ago when the planets started to cool down, is still waiting for us to find it. When I say "the" genesis rock, I do not mean of course that there is only one such rock. We would be in trouble to find it! No. It means that there must be entire exposures and many blocks exposed at the surface. Discovering and studying such rock would teach us a lot about our own very ancient geology and mineralogy, the formation of Mars and Earth, and possibly also about life as geology dictates in part the environment and habitat that life will find on a planet.

Second, we could find out a lot about the history and evolution of life on Earth, whether or not we are finding life on Mars. What do I mean?

If we find life on Mars, there could be two main possibilities (there are some of intermediate cases but let's start with the two more probable):

(1) Martian life is completely different to that of Earth. This would be a clear evidence that life started independently on the two planets. If life did that on two planets out of a system of nine, we should be very optimistic that life could be a common occurrence in the Universe and not just an exception on Earth;

(2) Martian life is analogous to Earth's life (and I am making mention here to microorganisms because there is no evidence of advanced life on Mars). What could we conclude. (a) A first conclusion could be that life has started independently on Earth and Mars but evolution has found the same responses to environmental constraints. The end products look comparable, except that the conditions on Mars changed dramatically (loss of atmosphere, cold, UV) and life on Mars stayed at a micro-organic stage instead of evolving towards higher life forms; (b) Another possibility is that life has started on either Mars or the Earth and has been "transported" to the other planet. At the beginning of the history of the solar system, there was a common line of transportation between those two planets, a natural one. Big asteroids and comets were still travelling in the interplanetary space and from time to time impacted planets, including Earth. If the impact was violent enough, the impacted material was ejected into space out of the limits of the planet's attraction and traveled until it was captured by the gravity of another one. It would have taken 2 or 3 million years to a block possibly carrying resistant microorganisms inside to make the travel between Earth and Mars and vice-versa. The next question is then: are we martians? Did life in fact appear on Mars but found more favorable conditions to develop on Earth? Or are the martian microorganisms (if they exist) earthlings? I find this idea a very profound one and in some sense an amusing possibility. We are always looking for extraterrestrial life and maybe, just maybe, we are some sort of extraterrestrial ourselves!

Now, there is another possibility and this is that we will not find life on Mars because maybe it never appeared. How can we learn from this (lack of) discovery? Well…We will learn that we are very precious as we tend to forget too often. We will learn that life is maybe the results of very complex circumstances and not so abundant. That would not mean though that we are alone in the Universe at all. It would just mean that…Mars did not develop life. Discovering the reasons why will help us to really understand and narrow down what are the right conditions for life to appear. In the long-range, this will help us design better strategies to look for life in our Universe and also elsewhere in the solar system. For instance, Europa and Titan are two great candidates to look for evidence of life too.

The lesson here is that it is important to learn. "Yes" or "no" responses are equally good as we learn from each of them different lessons. Of course, deep in our heart, we hope that the answer will be "yes", there is life on Mars and going to places like Licancabur is just what we need to do to develop the right exploration strategies and instruments to find it.