On which exoplanets can there be terrestrial life

NASA Ames / JPL-Caltech / T. Pyl Planet Kepler-452b as an artist

Astronomers have already found quite a lot of exoplanets that are potentially viable. In the new work, experts focused on the amount of ultraviolet radiation emanating from the parent star and is supposed to contribute to the development of life: on this basis, researchers identified planets on which life could appear like life on our planet.

“Life, as we know, requires many molecular structures that perform various functions within the cell, ” explains astrophysicist Paul Rimmer of the University of Cambridge. - Including DNA, RNA, proteins and cell membranes, which consist of relatively simple building blocks (lipids, nucleotides and amino acids). For a long time, where these building blocks came from remained a mystery, but recently important discoveries have helped determine how they appeared on the surface of the Earth. ”

“For example, ” explains Rimmer, “ultraviolet irradiation of hydrocyanic acid (a chemical compound that exists in nature) in water, in the presence of a negatively charged ion such as bisulfite, leads to the appearance of simple sugars.” Under suitable conditions, hydrocyanic acid - which is found in large quantities in protoplanetary disks - and a negatively charged ion can produce huge concentrations of building blocks for life, but they need ultraviolet light to do this.

In 2015, researchers demonstrated this experimentally. So, with the help of UV radiation and hydrocyanic acid, they were able to create lipids, amino acids and nucleotides, which are components of living cells, but without the use of ultraviolet light, the reaction did not take place.

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Rimmer and other scientists used this data for a new study. Experts compared the amount of UV radiation used in the 2015 experiment with the radiation emanating from stars in the Kepler candidate planet systems (potentially viable exoplanets detected by the Kepler space telescope). Based on the calculations, the researchers determined the so-called abiogenesis zone - the distance from the star at which the planet would receive enough UV radiation. (The Kepler’s list of candidates includes rocky planets in the habitable zone: not too close and not too far from the star — so that liquid water could exist on the planet.)

It is important, as noted, that the star has a temperature similar to that of the Sun: then the habitable zone and the abiogenesis zone intersect. Cooler stars, on the other hand, usually emit insufficient amounts of UV radiation - unless, of course, frequent flashes occur on them: can the latter lead to the appearance of building blocks for life, while, as the researchers note, it remains unknown.

The planet Kepler 452-b (due to its possible similarity to the Earth, it was called "Earth 2.0"), as experts have established, is included in both the habitable zone and the abiogenesis zone. In addition, according to researchers, the planet Kepler-62e is likely to be in the zone of abiogenesis, however, it may not be rocky.

The Kepler telescope, which has discovered many planets outside our solar system, will soon stop working (the apparatus, as you know, runs out of fuel). However, to replace it, the TESS space telescope was already launched (he recently officially started searching for exoplanets). In addition, NASA is preparing to launch the most powerful James Webb telescope - its launch, however, is constantly being transferred and now it is expected in May 2020.

The study was published in the journal Science Advances . Briefly about the results of the work is reported in the material on the website of The Conversation.

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