Single biggest obstacle to Earth bacteria thriving on Mars

[Torbjorn_L]

The question reminded me of the article that BillTree mentions, that shows how UV light is probably the largest problem on the surface. (Mind that the experiment is limited as of yet using just one hardy strain; though since it was drought resistant it should also be radiation resistant due to the copious DNA repair mechanisms.)The question is hard to answer since it maps a lot of source ecologies of thermophiles onto a lot of potential cornucopia of ecologies on Mars from the top of its atmosphere way down in the crust. The most promising current habitat would be deep in the crust, in which case any living populations would share much the same conditions as deep in our crust. Though Yggdrasil's article may point in other directions...On another matter, though I appreciate curiosity on behalf of science I also appreciate (due) diligence. Here are some curious references that a modicum of googling would have rejected:

Interesting... there were meteorite rocks with bacteria found within these rocks blasted from Mars during a strike from a meteor long ago.See: http://www.lpi.usra.edu/lpi/meteorites/The_Meteorite.shtml

The modern consensus is that it was neither nano-cells (too small to be anything like "bacteria") nor fossil remains of them. Every property found has an abiotic explanation. [ https://en.wikipedia.org/wiki/Allan_Hills_84001 ]

http://www.iflscience.com/space/marine-plankton-found-surface-international-space-station/How could such plankton survive ...

There are - as far as I know - no peer review articles that has shown any such data.

I understand that bacteria were found on a TV camera that was returned from the Moon by one of the Apollo misions

Due to failures of protocol lab contamination after opening the camera cannot be excluded and is the most likely explanation. [ https://en.wikipedia.org/wiki/Reports_of_Streptococcus_mitis_on_the_Moon ]