Free Astronomy Magazine September-October 2014

33 SEPTEMBER-OCTOBER 2014 ASTROBIOLOGY The similarity of the temperature and spectrum of the white dwarf with that of the Sun, and the roughly equivalent size of the dwarf and its planet, imply that if the latter has an atmosphere, the photo- chemical processes inside it should re- flect those of our atmosphere, so that the possible discovery of CFCs should not be equivocal. There is no denying that the above strat- egy has some weaknesses; from the large quantity of pollut- ants needed to ensure prop- er detection, to the need for the planet to transit on the white dwarf, up to limited time period within which a civilization will “broad- cast on that channel”. But perhaps the weakest point concerns the forma- tion of the supposed habit- able planet, which can only have taken place after the contraction of the white dwarf’s progenitor, conse- quent to the red giant phase. Any planet habitable before those transformations could no longer have been so there- after, and no planet could have existed before at 1-2 million km from the centre of the star, as it would have been rapidly destroyed. That the residual dust and gas from a white dwarf formation can aggregate in a new planet (or more planets) is amply demon- strated, but that such planet could resem- ble Earth to the point of hosting an in- dustrial or post-industrial civilization seems somewhat unlikely, given the very differ- ent starting conditions and the non-super- imposability of the two scenarios. An objection above all: the systems in which to look for CFCs must inevitably be a few billion years old, but it takes a lot less time for the mass of the white dwarf to synchronize the rotation and revolution periods of the planet. This leads to the con- tinual exposure of one of the two hemi- spheres to the stellar radiation and to the creation of environmental conditions so hostile to crush any life attempt to reach a state of awareness. Nevertheless, the pro- ject of Lin’s team is worthy of support and deserves to be given a chance, both be- cause it costs almost nothing to carry out and because in case of (unlikely) positive results we would be facing the greatest discovery that mankind has ever made. n