On Earth, these gases are almost always produced only by organisms.
Attention alien hunters: If you want to find life on distant planets, try looking for signs of cleaning with toxic chemicals.
Gases that organisms produce when they clean up their environment, can give clear signs of life on planets orbiting other stars , researchers announced on January 9 at a meeting of the American Astronomical Society. All we need to do to find signs of extraterrestrial life is to look for these gases in the atmospheres of these exoplanets, in images from the James Webb Space Telescope or other observatories that may soon be online.
With the exception of interstellar radio transmissions, the chemistry of a distant planet is one of the most promising ways for researchers to detect extraterrestrial life. On Earth, life produces many chemicals that change the atmosphere: for example, plants give off oxygen, and many animals and plants give off methane. Life in other galaxies can do the same leaving chemical signatures that humans can detect from afar.
But many vital gases are also released in processes that have nothing to do with life at all. Their detection can give the false impression of a living planet in the distant solar system, when in fact it is just a barren rock.
However, at least one type of compound that some organisms produce to protect themselves from toxic elements may provide unequivocal signs of life.
Life-hardening compounds are called methylated gases. Microbes, fungi, algae, and plants are terrestrial organisms that create chemicals by bonding carbon and hydrogen atoms with toxic substances such as chlorine or bromine. The resulting compounds evaporate, sweeping away the deadly elements.
The fact that living things are almost always involved in the creation of methylated gases means that the presence of these compounds in a planet’s atmosphere is a strong indication of some kind of life, planetary astrobiologist Michaela Leung of the University of California, Riverside, said at the meeting. .
The same is not true of oxygen and methane. Oxygen, in particular, can build up when a hot star heats a planet’s oceans. “You have a steamy atmosphere, and [ультрафіолетове] the radiation from the star splits the water” into its constituent parts of oxygen and hydrogen, Leung says. Hydrogen is light, so a large amount of it is lost to space on small planets. “What you’re left with is all this oxygen,” which she says leads to “really compelling signals of oxygen in this process that never once involved life.”
Similarly, although living organisms produce methane in large quantities, non-living geological phenomena such as volcanoes also produce methane.
At concentrations of methylated gases typical of Earth, these gases will be difficult to see in the atmospheres of distant planets, even with such a powerful device as the Webb telescope. But Leung has reason to believe that there may be planets where the gas content is thousands of times greater than Earth’s.
“The most productive environment [для виділення метильованих газів], which we see here on Earth,” she says, “are things like estuaries and wetlands.” A watery planet with lots of small continents and a correspondingly larger coastline, for example, might be filled with organisms that scavenge toxic chemicals using methylated gases.
One of the advantages of looking for compounds as a sign of life is that life does not need to be like what we have on our planet. “Maybe it’s not DNA-based, maybe there’s some other weird chemistry going on,” Leung says. But assuming that chlorine and bromine are likely to be toxic in general, the methylated gases offer what Leung calls an agnostic biosignature that can tell us there’s life on the planet, even if it’s completely alien to us.
“The more signs of life we know how to look for, the better our chances are of recognizing life when we find it,” says Vicki Meadows, an astrobiologist at the University of Washington in Seattle, who was not involved in the study. “It also helps us understand what telescopes we should build, what we should look for and what the instrument requirements are. For this reason, Mikaela’s work is really important.”
