Science Magazine‘s Joshua Sokol shares the wonderfully plausibly bizarre idea of alien life floating in the upper atmospheres of brown dwarfs.
There’s an abundant new swath of cosmic real estate that life could call home—and the views would be spectacular. Floating out by themselves in the Milky Way galaxy are perhaps a billion cold brown dwarfs, objects many times as massive as Jupiter but not big enough to ignite as a star. According to a new study, layers of their upper atmospheres sit at temperatures and pressures resembling those on Earth, and could host microbes that surf on thermal updrafts.
The idea expands the concept of a habitable zone to include a vast population of worlds that had previously gone unconsidered. “You don’t necessarily need to have a terrestrial planet with a surface,” says Jack Yates, a planetary scientist at the University of Edinburgh in the United Kingdom, who led the study.
Atmospheric life isn’t just for the birds. For decades, biologists have known about microbes that drift in the winds high above Earth’s surface. And in 1976, Carl Sagan envisioned the kind of ecosystem that could evolve in the upper layers of Jupiter, fueled by sunlight. You could have sky plankton: small organisms he called “sinkers.” Other organisms could be balloonlike “floaters,” which would rise and fall in the atmosphere by manipulating their body pressure. In the years since, astronomers have also considered the prospects of microbes in the carbon dioxide atmosphere above Venus’s inhospitable surface.
Yates and his colleagues applied the same thinking to a kind of world Sagan didn’t know about. Discovered in 2011, some cold brown dwarfs have surfaces roughly at room temperature or below; lower layers would be downright comfortable. In March 2013, astronomers discovered WISE 0855-0714, a brown dwarf only 7 light-years away that seems to have water clouds in its atmosphere. Yates and his colleagues set out to update Sagan’s calculations and to identify the sizes, densities, and life strategies of microbes that could manage to stay aloft in the habitable region of an enormous atmosphere of predominantly hydrogen gas. Sink too low and you are cooked or crushed. Rise too high and you might freeze.
On such a world, small sinkers like the microbes in Earth’s atmosphere or even smaller would have a better chance than Sagan’s floaters, the researchers will report in an upcoming issue of The Astrophysical Journal. But a lot depends on the weather: If upwelling winds are powerful on free-floating brown dwarfs, as seems to be true in the bands of gas giants like Jupiter and Saturn, heavier creatures can carve out a niche. In the absence of sunlight, they could feed on chemical nutrients. Observations of cold brown dwarf atmospheres reveal most of the ingredients Earth life depends on: carbon, hydrogen, nitrogen, and oxygen, though perhaps not phosphorous.