After the euphoria, the disenchantment. Last February: NASA made a sensational announcement : a system of seven rocky planets similar in size to Earth had been discovered orbiting a single star, TRAPPIST-1 . This red dwarf – an ultracold star slightly smaller than Jupiter – is only 39 light years from our planet. And also, as if that were not enough, their worlds (especially the three closest to the star) could house water in a liquid state, an inescapable condition for life as we know it to develop. “Today, this extrasolar system is our best bet,” said Brice-Olivier Demory, one of the authors of the finding. The exobiologists’ eyes must be pointed there .
But two independent studies, published in the International Journal of Astrobiology and Astrophysical Journal Letters, have just spilled a glass of cold water on hopes of finding some trace of extraterrestrial life alongside TRAPPIST-1. Both teams have detected several factors that would preclude the emergence of biology even in the three worlds located in the “habitable zone.”
Punished by UV radiation
As the first of the works indicates, which has been carried out by scientists from the Harvard-Smithsonian Center for Astrophysics (CfA), the main problem is that being a small and cold star, its temperate zone is dangerously close to it. The farthest planet is only nine million kilometers away; by comparison, Mercury, which is closest to the Sun, orbits at 58 million kilometers. This supposes an excessive exposure of the seven exworlds to the radiation of TRAPPIST-1, something, in principle, incompatible with life. According to the computational models that astronomers have made, they receive a rate of ultraviolet (UV) rays much higher than that which reaches the Earth , and therefore would not have been able to develop any type of atmosphere .
The second study, carried out by astronomers from the CfA and the University of Massachusetts at Lowell, emphasize this absence of a gaseous layer. The experts examined the effects of solar winds, whose particles would be punishing the seven exoplanets at magnitudes between 1,000 and 100,000 times higher than those suffered by the Earth. And also, due to the proximity between TRAPPIST-1 and the worlds that orbit it, their magnetic fields would be fused , so they have no protection.
“The magnetic field of our planet acts as a shield against the potentially damaging effects of the solar wind,” explains Cecilia Garraffo. “If the Earth were much closer to the Sun and subjected to attack by particles like those of the star TRAPPIST-1, our planetary shield would fail.”
Researchers fear that these life-hostile scenarios will be repeated on the exoplanets of other red dwarfs , such as Proxima-b, which is just 4.3 light-years from Earth and has also raised the interest of the scientific community. It so happens that red dwarfs are the most frequent stars in the solar system.
Anyway, and despite the poor prospects, astronomers assure that they will continue looking for traces of extraterrestrial biology in the TRAPPIST-1 system.
Reference:
Manasvi Lingam, Abraham Loeb. “Physical constraints on the likelihood of life on exoplanets” International Journal of Astrobiology (6 de julio, 2017) DOI: https://doi.org/10.1017/S1473550417000179
Cecilia Garraffo, Jeremy J. Drake, Ofer Cohen, Julian D. Alvarado-Gómez, Sofia P. Moschou. “The Threatening Magnetic and Plasma Environment of the TRAPPIST-1 Planets”. Astrophysical Journal Letters (12 de julio, 2017).
Foto: R. Hurt / NASA /JPL- Caltech
