Is there life on Mars? We don’t know yet. If there is, it isn’t very big. In fact, if there’s (still) any life at all, it will be bacteria or something even more primitive and small. Whatever there is, it’s also not likely to be on the surface. That’s not because of the cold; it’s the radiation – specifically the ultraviolet (UV) radiation. That’s part of the results of an Italian study, led by researcher Giuseppe Galletta, University of Padua (Italy), which simulated Martian surface conditions and their effects on bacteria populations.

To conduct their experiments, the researchers built a special atmospheric chamber, which they dubbed LISA (an acronym for Italian Laboratory for Environmental Simulation). The LISA chamber(s) could be programmed to produce a variety of atmospheric pressures, humidity conditions, temperatures, and radiation (UV) levels. Various conditions that reflected known conditions on Mars were reproduced and various species of bacteria (as bacterial cells and as spores) were kept in the environments for different lengths of time. The samples were then tested for the ability to resume growth (in essence, come back to life when re-plated on a favorable growing surface).

As on Earth, bacteria can be very resistant to cold. When stressed, many kinds of bacteria produce an endosperm (spore) from which all water has been removed. These are particularly impervious to cold. Similarly, pressure change has little effect, nor does humidity (especially relative to the very cold temperatures). Conditions on Mars are relatively brutal, with temperatures running from 20C on the high end to -80C on the low end. There is little to no moisture available in the atmosphere or at the immediate surface. Pressure changes are by Earth standards abrupt and dramatic. However, individually the extremes had little impact on spores and even some of the living cells were able to survive.

Adding intense UV radiation to the mix of conditions was decisive. The intensity of unfiltered ultraviolet light that bombards the surface of Mars is unknown on Earth, and it is fatal for nearly all forms of bacteria. The combination of UV with some of the other conditions, especially cold, was usually fatal; however, some bacteria survived hours and one species survived 28 hours – a remarkable toughness.

Perhaps the key element of the study was the introduction of a coating of fine dust (simulated by volcanic powder and iron oxide). This is a condition that would be very common on Mars, where the global winds and massive storms carry dust clouds everywhere. It was found that even a very thin coating was sufficient to protect most bacteria species from UV radiation. This meant that even in today’s conditions, it is possible that bacteria may survive on Mars and may possibly revivify whenever enough warmth and moisture are available.

The researchers were careful to point out that these are experiments with Earth microbes. There is no evidence for any bacteria on Mars, as yet. There is also no way to tell, without specimens, if Martian microbes are like those on Earth. If, as the hypothesis called panspermia is correct, then bacteria may have been wafted among the stars, moons, and planets on debris thrown out by meteorite impacts. In such a way, life could have migrated from Mars to Earth or vice versa. If so, then the types of bacteria – their molecular composition and DNA – should be similar, and tests like the Italians used should be valid. However, if life arose independently on Mars, there would be its own version of LUCA (Last Universal Common Ancestor). Such life might have substantially different biochemical composition – possibly one not even detectable by our earthly biological devices.

The Italian experiments are part of an ongoing research into the nature and living conditions of extremophiles, forms of life that exist under extreme conditions – in volcanic vents, under glaciers, at the bottom of oceans, and even inside rocks. In this case, the experiments relate to Mars; but in the broader picture what they discover, at least in the case of life forms with similar biochemical makeup to that of Earth, could be applicable to many other locations in our solar system, including the moons Io, Titan, Europa, and Enceladus.

Terrestrial lifeforms show a strong capability to adapt to very harsh environments and to survive even to strong shocks as those
derived from meteorite impacts. These findings increase the possibility to discover traces of life on a planet like Mars, that had past
conditions similar to the early Earth but now is similar to a very cold desert, irradiated by intense solar UV light.

[Source: arXiv]