Free Astronomy Magazine January-February 2019

43 JANUARY-FEBRUARY 2019 ASTROBIOLOGY A photo of the bacteria colony surviving the experiment called OU-20, which lasted a year and a half outside the ISS. Below, Professor Charles Cockell, from the Open University, with a sample of rock impregnated with the bacteria pro- tagonists of the OU-20 experi- ment. [NASA, Open University] and the outcome of each of them depends on numerous varying factors. Only recently, researchers attempted to merge the various solutions into a single model, however unavoidably generic. A push in this direction has been from the dis- covery, between 2015 and 2017, of seven planets in orbit around the red dwarf TRAP- PIST-1. This system has awakened the inter- est in panspermia, because its planets are all comparable in size to Earth (from 0.77 to 1.14 times the Earth’s diameter) and five of them also have masses comparable to that of Earth. But the most interesting feature of the TRAPPIST-1 system is represented by the orbits of the planets, very close to each other and decidedly coplanar. The semima- jor axes range from 1.73 million km for the innermost planet, TRAPPIST-1b, to 9.27 mil- lion km for the outermost planet, TRAPPIST- 1h. The planets graze each other at dis- tances between 2 and 6 times the Earth- Moon distance! Despite being so close to their star, TRAP- PIST-1 is so weak an energy source that some of its planets orbit in its habitable zone, making this system theoretically ideal for carrying out panspermia studies, as high- lighted in a work published at the end of Oc- tober in Astrobiology Magazine with the title “Dynamical and biological panspermia constraints within multi-planet exosystems”.