This, Sarah Stewart Johnson, an assistant professor of planetary science at Georgetown University in the US, argues in her beguiling first book is precisely why the search for life on other planets matters. It is not just that finding so much as a dormant speck of protein in this planetary tomb would be a peerless scientific wonder. It is that if life can emerge and survive on Mars — “the smallest breath in the deepest night”, as Johnson writes — it can do so in a trillion other places. It raises the likelihood of a universe positively frothing with biology. It would mean we are not alone.