Free Astronomy Magazine January-February 2019

JANUARY-FEBRUARY 2019 T he impact of an asteroid on a young Mars could have thrown many rocks into space, perhaps containing colonies of ex- tremophile bacte- ria, which contin- ued to proliferate for decades. When part of those rocks fell to Earth, the surviving bacteria found a hospitable environment to conquer. [NASA] a philosopher of ancient Greece and very careful observer of celestial phenomena. One must wait until the 19 th century to see the proposition of panspermia in a more sci- entific context, then further strengthened in the following century, mainly thanks to two giants of astronomy − Fred Hoyle and Chandra Wickramasinghe. In the 1970s, they hypothesized that interstellar dust could contain organic molecules (a hypoth- esis then verified) and that forms of ele- mentary life are continuously entering the atmosphere (a hypothesis never verified). More recently, in 2009, Stephen Hawking also came out in support of panspermia as a possible explana- tion for the spread of living organisms between planets and solar systems. In October 2017, with the discovery of `Oumuamua, we re- ceived confirmation that a meteoroid (or a cometoid) can ac- tually travel from one planetary system to another, and these wandering ob- jects might exist in the billions of bil- but it was nonetheless suitable for hosting species from outside. As we do not know the environment in which that “adopted” life may have been born, we are not able to recreate it in the laboratory. This is evidently a hypothesis of conven- ience, a solution that does not solve the problem, but instead transfers it to un- known times and places. The concept of panspermia is, however, interesting be- cause, from a theoretical point of view, life could certainly move from one celestial body to another. This idea dates back to 25 centuries ago. The first to spread the notion was Anaxagoras,