2023-05-31 11:45:50
The Sun is not the most common type of star in our galaxy. The most typical class is that of red dwarfs, with lower mass and lower temperature. It is estimated that in the Milky Way there are billions of planets orbiting red dwarfs.
In order to capture enough heat to make them potentially habitable, these planets have to be very close to their small stars, which makes them more vulnerable to certain destructive effects derived from that closeness.
In a new analysis of data obtained from multiple astronomical observations, astronomers Sheila Sagear and Sarah Ballard, both from the University of Florida in the United States, have concluded that in our galaxy two-thirds of the planets that rotate with such closeness around red dwarf stars must have suffered these destructive effects, rendering them incapable of supporting life. However, the remaining third of such planets (hundreds of millions of planets) may be in an ideal orbit for liquid water to exist on their surface and also have escaped those catastrophic effects derived from the proximity of their sun; in short, they are potentially habitable.
These stars are excellent targets for searching in the right orbital fringe for small planets whose surface would conceivably host liquid water and support life, as Sagear argues.
Until now, it was not clear what percentage of planets around red dwarfs could be at the correct distance to allow the existence of liquid water on their surface and at the same time be free of the destructive process described. And indeed, rather pessimistic estimates were circulating.
Artist’s impression of a planet in the habitable zone around its star, a red dwarf. (Illustration: NASA’s Ames Research Center / Daniel Rutter)
Sagear and Ballard measured the orbital eccentricity of a sample of more than 150 planets around red dwarf stars (spectral class M), which are about the size of Jupiter, but considerably more massive than it. The more oval an orbit is, the more eccentric it is. If a planet orbits close enough to its star, roughly the distance Mercury orbits the Sun, an eccentric orbit can subject it to a process known as tidal heating. As the planet is stretched and deformed by changing gravitational forces in its irregular orbit, friction heats it up. At its most violent, the process can cook the planet, eliminating all possibility of liquid water and making it sterilizing.
Sagear and Ballard found that stars with multiple planets are most likely to host the kind of circular orbits that allow planets to retain liquid water. In solar systems where the stars are accompanied by a single planet, it is where the planet is most likely to experience extreme tides that remove its water and render it sterile.
The study is titled “The orbital eccentricity distribution of planets orbiting M dwarfs“. And it has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS). (Source: NCYT de Amazings)
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