MOSCOW, Oct 30, Salma Sultanova. NASA recently announced that the giant exoplanet K2-18 b has a water ocean, as evidenced by images taken by the James Webb telescope. This means it can be habitable. How and where scientists are looking for extraterrestrial life — in the material .
Bet on the ocean
Astronomers have discovered about four thousand planets orbiting stars. However, on most of them, life is practically impossible due to the special composition of the atmosphere and significant temperature changes. Meanwhile, on a potentially habitable planet, conditions must be more moderate, otherwise there will be no liquid water there.
In 2015, in the direction of the constellation Leo, scientists discovered an exoplanet 8.6 times larger than Earth. It orbits the red dwarf K2-18 in the habitable zone. The distance from K2-18 b (as the planet was designated) to Earth is 120 light years. Such worlds are called sub-Neptunes, and so far they have been poorly studied.
K2-18 b attracted the attention of the scientific community due to the fact that traces of water vapor were found in its atmosphere. Theoretically there could be rain and clouds. In addition, the distance separating the planet from its parent star prevents water from freezing or evaporating. However, the exact composition of the atmosphere is unknown.
Recently, an international team of astronomers, using data from the James Webb Space Telescope, came to the conclusionthat the gas envelope of the celestial body contains methane and carbon dioxide. This allows us to classify K2-18 b as a hypothetical class of worlds with oceans — the Hyceans.
«Our results show how important it is to study a variety of habitable environments when searching for extraterrestrial life. Traditionally, it is searched for on small, rocky exoplanets, but Hykeans are suitable for atmospheric observations much better,” saysEuropean Space Agency press office Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper.
The lack of ammonia also indirectly confirms that there may be an ocean beneath the hydrogen-rich atmosphere of K2-18 b. In addition, there are signs of dimethyl sulfide — on Earth, this organic compound is released only by living organisms, or more precisely, by phytoplankton. Only further studies will be able to definitively confirm the presence of these molecules on K2-18 b.
According to Dr. Phys. mathematical sciences, leading researcher at the Laboratory of Thermodynamics and Mathematical Modeling of Natural Processes of the Geochemical Institute of the Russian Academy of Sciences Sergei Ipatov, gikeanas are of interest to scientists for several reasons.
“First of all, due to the fact that a search is being carried out for planets where life is possible. Therefore, any exoplanets are being tracked, not just Hykeans. For life similar to that on Earth, liquid water is needed. The larger the planet — and we know that Hyceans are larger than a terrestrial planet, which makes it easier to detect and observe with telescopes,” notes Ipatov.
The habitability of exoplanets depends not only on the presence of liquid water, but also on a number of other factors: the level of radiation from the star, the composition of the atmosphere and the temperature of the planet, whether it always faces one side to the star, and so on. In each case, the combination of conditions is unique.
“Therefore, for accurate estimates of the probability of habitability, it is necessary to study a sufficiently large number of exoplanets, including Hyceans. We can expect that this probability is non-zero,” the scientist concludes.
Not only Hykeans, but also planets of smaller mass can be potentially habitable, as the example of Earth successfully proves. An important condition: they must contain water and be in the habitable zone (have conditions similar to our planet). By the way, there may be water under the surface of the planet, which makes it difficult to find traces of life.
«The question of the possibility of life without water is still being debated. Some scientists believe that there are many more options for life, but our level of knowledge is not allows us to assess the habitability of other planets,” Ipatov clarifies.
In the habitable zone
The closest exoplanet to us is called Proxima Centauri b. Scientists have been studying it closely since itsdiscoveryin 2016. It is located in the habitable zone of its parent star, the red dwarf Proxima Centauri, so its surface temperature is suitable for liquid water to be present there.
It is impossible to say unambiguously whether Proxima Centauri b is inhabited or not. The presence of liquid has not been proven, and it is unclear what happens to the atmosphere in such an orbit. It is critical for the origin of life: it regulates the climate, maintains pressure on the surface favorable for water, and protects against dangerous space weather.
“The distance from Proxima Centauri b to Earth is four light years. Therefore, it takes a long time to fly to it, because the speed of the spacecraft is much less than the speed of light,” says Sergei Ipatov.
Recently, astronomers led by Emily Gilbert from NASA's Jet Propulsion Laboratory released < u>article, where they reported the discovery of another exoplanet located in the habitable zone of the star TOI-700. Previously, three similar planets had already been found in this system, which were called TOI-700 b, c, and d. TOI-700e's surface is likely rocky and is 95 percent the same size as Earth.
«TOI-700 system — «One of the few where many small planets with a habitable zone have been discovered, so we will continue to observe it. Planet e is about ten percent smaller than planet d. Thanks to the TESS telescope, we can see such small worlds,» explains Emily Gilbert.
According to Sergei Ipatov, flights to exoplanets are a matter of the very distant future. First you need to master several bodies and planets of the solar system.