The search for another Earth continues at an incessant pace, thanks to new methodologies, new scientific instruments and a lot of enthusiasm. A lot of things happened since 1992, the year in which Aleksander Wolszczan discovered the first exoplanet in orbit around a pulsar, PSR B1257+12. After the first years of slow progress, the discovery of exoplanets has increased exponentially in the last decade, leading to over 4,100 exoplanets discovered and over 2,000 still awaiting confirmation. Most of them, due to the enormous distances involved, are gaseous giants, large enough to be spotted. However, by now the research techniques are so advanced that several rocky planets of dimensions comparable to those of the Earth have also been discovered which, needless to say, are the primary objective of this research.
The latest discovery will represent a turning point in the search for exoplanets and life on other worlds. Using data from the Hubble Space Telescope, two independent groups of scientists, one led by Björn Benneke, of the Montreal University of Canada, and one led by Tsiaras and Ingo Waldmann of University College London, discovered the presence of water vapor in the atmosphere of the planet K2-18b.
The presence of water vapor in the atmosphere of an exoplanet is not new, in fact NASA had already made a similar discovery in 2018. However, the planet WASP-39b was certainly unsuitable for life, as the models indicated an equal temperature at about 800 °C. In this case, however, the planet K2-18b is inside the habitable zone of its star, that is the region of a solar system in which the presence of liquid water is possible. According to astronomers, the temperature of this planet would be between -73 °C and 46 °C. Terrestrial temperatures in practice.
The planet K2-18b is about 8 times larger than the Earth, a dimension comparable to that of Neptune, and places it within the group of super Earths. It orbits in about 33 days around its star, a cold red dwarf 111 light years away from us, in the constellation of Leo. The discovery of the planet took place in 2015, at the La Silla Observatory in Chile, using the radial velocity method.
Using data from the Hubble space telescope, astronomers were able to study the spectra of the K2-18b atmosphere by discovering the presence of hydrogen, helium and water vapor. Attention therefore to enthusiasm. On this planet life does not exist as we know it, and perhaps life does not exist. But this discovery shows once again that a distant cousin of the Earth certainly exists, at the right distance from its star, with the right temperature and the presence of water.
Here are the words of Angelos Tsiaras, one of the authors of the discovery:
At the moment this is the only exoplanet that we know to have the right temperature to guarantee the presence of water, it has an atmosphere and this contains water, making it the best habitability candidate known so far.
The coming years will be very prolific for the search for exoplanets. In November, ESA will launch, for example, the CHEOPS space telescope, dedicated to measuring the rays of exoplanets of mass already known thanks to spectroscopic investigations made by the Earth. Knowing the radius and density, it will be possible to determine the density and then classify the exoplanets into rocky and gaseous.