I think the post is relevant (and hope this post is also). If we have difficulty identifying signatures of viruses from early Earth evolution then how can we find them on Mars - for example (but, then again, aren't viruses dependent on cellalar organisms to exist - which might be easier to identify?)
Maybe deviating here, some bacteria are really quite resiliant. Bacteria from the cliffs of a village called Beer (hmmm... b e e r !) on the South Coast of England survived on the outside of the ISS for 533 days
http://www.bbc.co.uk/news/science-environment-11039206
And prior to that when Apollo 12 recovered the camera of Surveyor 3 it was found that it was contaminated on Earth prior to being sent to the moon and the bacteria, when rehydrated, was alive (was on the Moon for nearly three years).
http://science.nasa.gov/science-news.../ast01sep98_1/
The Bacteriophage T4 is really fascinating - an animation of one infecting a bacterium is well worth watching here:-
http://www.seyet.com/index.php?optio...101&Itemid=204
The last one isn't really astronomy related except for the incredible similarity to a man-made probe landing on a moon etc. It's hard to believe that this little virus isn't technically alive (if one requires metabolism) - but is a superb little machine regardless.
With respect to the question of whether viruses are alive - try finding a universal or widely accepted definition. It's a challenge.
Mark C.