In the next decade, astronomers have powerful telescopes that analyse the atmospheres of exoplanets, the thousands of millions of worlds that are in the orbit of the stars of the Milky Way. Thanks to that, you will be able to study their nature and to suggest which ones could harbor life as we know it (of which we know nothing, we have nothing to say). This is more important than it seems: if we had a twin of the Earth to the extent, our present-day instruments would be unable to study its atmosphere; it could be a world with oceans and the beings living there "to the side" and we would not be aware of it.
despite the limitations of the existing instruments, a team of researchers has just discovered water in a world that has the right temperatures to support life.
For the first time, have detected water vapor in the atmosphere of a world rocky , in addition, it is to be in the zone of habitability of its star, the region in which a planet can have liquid water on the surface. This is K2-18b, a supertierra eight times more massive than our planet and located 110 light years and that has become the exoplanet most promising in the search for habitable planets. The discovery has been published in Nature Astronomy. Another team from the university of Montreal (Canada) has made the same observations, which has been published in arXiv.
"This is the first detection of water vapor in the atmosphere of a planet that is not a gas giant," explained Angelos Tsiaras, first author of the study and researcher at the University College of London (Uk). "It is a planet that is within the habitable zone of its star, which means you can have liquid water. So, right now, is the only planet outside the solar system that has the right temperature to support liquid water, which has an atmosphere and that, effectively, has water vapor."
Since it was discovered in 2015, K2-18b became one of the exoplanets most promising to search for traces of water in an atmosphere, but this new discovery places him as a priority target for further observations with powerful telescopes.Another representation of K2-18b - Alex Boersma
in Addition have detected water vapor in its astmósfera, whose concentration, according to the researchers going from one to 50%, the authors have concluded that K2-18b get as much radiation from its star as the Earth from the Sun , so you might have water on the surface. The authors consider that it is very likely that this exoplanet has clouds. However, they have clarified that without more data you cannot place a bet if K2-18b is a ocean world or if you have a surface dry.Not an "Earth 2.0"
despite this, K2-18b is very far from being a brother of the Earth . It is twice as big and has eight times its mass, which makes him a supertierra. In addition, it is very close to its star, so that it takes only 33 days to complete a lap around it. Your "sun" is a red dwarf, a star that is half the size of the Sun, which is red and which bombards the surface of K2-18b with large doses of ultraviolet rays. In other places, these stars raze their planets with countless flares, stellar, although on this occasion this seems not to be the case, according to the researchers.
"K2-18b is not an "Earth 2.0", because it is significantly heavier and has an atmospheric composition different", has had the effect of Tsiaras. "However, helps us to answer a fundamental question: what Is the Earth unique? ".The three atmospheres of the supertierra
The researchers used data collected by the Hubble space telescope between 2016 and 2017 and were processed with a program designed for the occasion. So, they analyzed the footprint left by the atmosphere of the exoplanet when it was crossed by the light of his star during the transits, the "eclipses" in which the planet comes between the Earth and the star. With this information, scientists developed a series of computer models according to which K2-18b can have three different atmospheres.
"There are three chemical weather possible", explained Ingo Waldmann, a co-author of the study. "A very dominated by water, with some hydrogen. Another dominated by a gas transparent, possibly nitrogen, and another in which there are clouds," he said. "All of them fit equally well with the data available now, but all indicate a high abundance of water ".Uncertainty surrounding K2-18b
And still there are more important mysteries to unravel. The data collected by the scientists suggest that K2-18b could be a world rocky with an extensive atmosphere, but, as has been pointed out to ABC Enric Pallé, a scientist at the Institute of Astrophysics of Canarias (IAC) an expert in atmospheres, "K2-18b is a supertierra on tenterhooks" .
As has been said, is very close to the upper limit after which it begins to be considered an exoplanet, not as a land of gigantic, a supertierra, but as a small gaseous planet, a minineptuno. "You could have a wrapped gas very important. I would not be considered as a candidate exoplanet is habitable, although it is only my opinion and depends on the physical properties that really have".
In any case, the authors have explained that the calculated density for this world closer to a world rocky world of a gas. In fact, according to their calculations, the density of K2-18b is similar to that of the Moon and Mars.In search of the atmosphere of a living planet
Be that as it may, it seems that these puzzles cannot be resolved, for the time being.
The Hubble space telescope, launched in 1996, has reached its limit . Has revealed countless secrets of the Universe and provided amazing images of the solar system, but is unable to seek the footprint that it would leave in the atmospheres molecules such as nitrogen or methane.
In fact, as explained Pallé, to find an atmosphere compatible with the presence of life would have to "find an atmosphere in disequilibrium, generated by the life, with the presence of oxygen, water and methane.
the authors of The study have highlighted the need to observe K2-18b with new instruments to be able to go beyond and know what is the chemistry and the structure of its atmosphere, which is fundamental to understanding the nature of the surface of this exoplanet.
Instruments like the space telescope James Webb , which NASA will launch in 2021, or the mission ARIEL, of the ESA that will analyze hundreds of planetary atmospheres beginning in 2028, will be critical. In addition, the new generation of observatories giant land , as the "Extremely Large Telescope", that is being built in Chile, or the "Thirty Meter Telescope", to be built in Hawaii, if the protests of some local permitting, will also be revolutionary.What lies ahead
In connection with K2-18b, Waldmann has pointed out that, "given that we expect to discover many supertierras in the next two decades, it is likely that this is the first discovery of many potentially habitable planets". And not only because the supertierras are among the planets most abundant of the galaxy, but because the sun that enlightens K2-18b, a red dwarf, is the type of star most common in the galaxy.
According to Giovanna Tinetti, co-author of the study and principal investigator of the mission ARIEL, of the THAT: "Our discovery makes K2-18b one of the most interesting for future studies . Have been detected around 4,000 exoplanets, but we do not know much about their nature or composition. But, by observing a large sample of planets, we hope to reveal the secrets of their chemistry, formation and evolution".
that's why, according to Tsiaras, K2-18b is crucial to our understanding of the worlds habitable beyond the solar system, and, finally, to "put the Earth, our only home, in the image of the cosmos." Time will tell what is also the site it occupies K2-18b, but for the moment, it is the world that most requirements meets to be a world habitable.
Updated Date: 20 September 2019, 12:01