  We shortly discuss the observable consequences of the two hypotheses about
the origin of life on Earth and Mars: the Lithopanspermia (Mars to Earth or
viceversa) and the origin from a unique progenitor, that for Earth is called
LUCA (the LUCA hypothesis). To test the possibility that some lifeforms similar
to the terrestrial ones may survive on Mars, we designed and built two
simulators of Martian environments where to perform experiments with different
bacterial strains: LISA and mini-LISA. Our LISA environmental chambers can
reproduce the conditions of many Martian locations near the surface trough
changes of temperature, pressure, UV fluence and atmospheric composition. Both
simulators are open to collaboration with other laboratories interested in
performing experiments on many kind of samples (biological, minerals,
electronic) in situations similar to that of the red planet. Inside LISA we
have studied the survival of several bacterial strains and endospores. We
verified that the UV light is the major responsible of cell death. Neither the
low temperature, nor the pressure, nor the desiccation or the atmospheric
changes were effective in this sense. We found that some Bacillus strains have
a particular capability to survive for some hours in Martian conditions without
being screened by dust or other shields. We also simulated the coverage
happening on a planet by dust transported by the winds, blowing on the samples
a very small quantity of volcanic ash grains or red iron oxide particles.
Samples covered by these dust grains have shown a high percentage of survival,
indicating that under the surface dust, if life were to be present on Mars in
the past, some bacteria colonies or cells could still be present.
