There's been an uptick in speculation lately about whether life could exist on Mars, the moon, or one of Jupiter's satellites. Too inhospitable, you say? Earth has places that are just as bad, yet rich with organisms.
As someone, possibly Jake from Animorphs, once observed, Earth is a tough neighborhood. A feature at Smithsonian magazine illustrates this memorably, noting the regions and circumstances where it doesn't make sense for life to exist, yet where it somehow turns up.
There are a few great counterintuitive examples, like the pupfish colonies soldiering on in Death Valley's aquifers and springs, or the Desulforudis audaxviator bacteria that lives in complete biological isolation at the bottom of a gold mine in South Africa. (D. audaxviator is named after a passage in — what else? — Jules Verne's Journey to the Center of the Earth, from the Latin for "bold traveler.")
Other places where life springs eternal: on the surface of pools of acidic mining runoff; drifting in the stratosphere at altitudes of more than eleven miles; and in facilities at the Carnegie Institution, where scientists accidentally exposed strains of E. coli to pressures of 16,000 atmospheres, theoretically more than life can withstand, only to find that a number of the samples had survived.
Then there are the Jurassic bacteria, preserved in spore form in Antarctic ice for millions of years and resuscitated in modern labs — not unlike Philip J. Fry, except less likely to leave a hat full of milk in a storage locker.
If nothing else, this extremophiles' hall of fame lends some hope to those awaiting reports of extraplanetary biota. There's water on the moon, possible Martian microbe fossils in a crashed meteorite, and the potential for oceans of Jovian fish on oxygen-lousy Europa. If a previously unknown phylum of bacteria can be discovered in Yellowstone's near-boiling hot springs, why couldn't there be something waiting out there in the star-system suburbs?