There are large spaces in space that life can call its home, and the view from such a house will be simply breathtaking. In the Milky Way galaxy, many millions of cold brown dwarfs float on their own - sub-stellar objects that are many times the mass of Jupiter, but not large enough to become a star. According to new research, the atmosphere in their upper layers has about the same pressure and temperature as on Earth, and therefore microbes floating in the ascending air currents can live there.
This study expands the concept of a habitable zone to include a vast array of worlds that were previously not even considered as candidates for a habitat. "A planet like Earth with a solid surface is not necessary at all," says Jack Yates, planetary scientist at the University of Edinburgh, who is leading the study.
Life in the atmosphere isn't just for birds. For many years, biologists have known about microbes that drift with air masses high above the earth's surface. And in 1976, Carl Sagan (Carl Sagan) suggested the existence of an ecosystem that can evolve in the upper layers of Jupiter, receiving energy from sunlight. It is not excluded the existence of a kind of heavenly plankton - small microorganisms, which he called "sinkers". And there may also be "floats" similar to balloons, which either rise or fall in the atmosphere, changing their internal pressure. Over the years since then, astronomers have also considered the possibility of microbes in the carbon dioxide atmosphere above the inhospitable surface of Venus.
Yeats and his colleagues used these ideas and assumptions for worlds that Sagan was not aware of. Some cold brown dwarfs discovered in 2011 have surface temperatures around room temperature or lower, so conditions in the lower atmosphere can be quite comfortable. In March 2013, astronomers discovered the brown dwarf WISE 0855-0714, which is only seven light-years away and has water clouds in its atmosphere. Yeats and his colleagues decided to modernize Sagan's calculations to determine the size, density, and life strategy of microbes that can be found in the habitable parts of the vast atmosphere, consisting mainly of hydrogen. Go too low and get crushed or toasted. Go up too high and you can turn into ice.
In such a world, small "sinkers" such as microbes in the earth's atmosphere or even smaller ones are more likely than Sagan's "floats". The authors of a new study wrote about this in the new issue of The Astrophysical Journal. But a lot depends on the weather. If the updrafts on free-flying brown dwarfs are strong (and it looks like they are when looking at gas giants such as Jupiter or Saturn), heavier creatures may find their niche there. In the absence of sunlight, they can feed on chemical nutrients. Observations of cold brown dwarfs show that they contain most of the ingredients on the basis of which earthly life arose and exists: carbon, hydrogen, nitrogen and oxygen, but not phosphorus.
It's a purely speculative idea, but worth considering, says Duncan Forgan, an astrobiologist at the University of St Andrews in Britain, who was not involved in the study but knows the participants. "This opens up new horizons in terms of the number of objects that we can look at, assuming they are livable."
So far, only a few dozen cool brown dwarfs have been discovered, although statistics indicate that there should be about 10 of them within 30 light-years from Earth. These are good objects to study with the James Webb Space Telescope, which is very sensitive in the infrared range. where brown dwarfs glow the brightest. Following the launch of the space observatory in 2018, the telescope will help determine the weather and atmospheric composition of these dwarfs, says astronomer Jackie Faherty, who works at the Carnegie Institution for Science in Washington, DC. “We will soon have excellent spectral characteristics of these objects,” she says. "I think about it all the time."
The search for life will require finding the strong spectral characteristics of microbial byproducts such as methane or oxygen and then separating that from other reactions and processes, Faerty says. Another task is to explain how life could arise in an environment where there are no rocks interacting with water in the form of hydrothermal vents - after all, it is believed that it was in them that earthly life originated. Perhaps life could have evolved through chemical reactions on the surface of dust particles flying in the atmosphere of brown dwarfs. Or maybe she arrived as a traveler on an asteroid, and then secured a foothold on the captured bridgehead. “The presence of small microbes that fly in and out of the brown dwarf atmosphere is great,” Forgan says. "But first you have to get there."
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