Planets around red dwarfs could be habitable for extraterrestrial life!
Illustration of a major solar flare on an exoplanet orbiting a red dwarf star. © Generated on Bing Creator by Brice Haziza
We earthlings are generally fond of solar flares, because they are, especially at this moment, promises of magnificent northern lights visible even in our latitudes. But elsewhere in space, it's not always good news. Particularly around the most widespread type of star in the Galaxy and the Universe: red dwarfs.
These are low mass stars, much lower than that of our star, the Sun (around 20%, on average). And not so small too. In fact, they are just stars capable of fusing hydrogen and producing electromagnetic radiation in visible light. As they are very numerous and regularly have veritable processions of planets around them, many astrophysicists think that we will discover the first forms of extraterrestrial life around one of them. But, there is a catch.
The Trappist system compared to the Solar System. The green zone is the “habitable” zone where water can exist in a liquid state on the surface. The star is not to scale. © NASA/JPL/Caltech
These stars have a powerful magnetic field and are responsible for violent “angers”: they are particularly eruptive, especially in their youth. As they are small, their planets are often very close to them and always present the same face to their star – like the Moon with the Earth. So, part of the scientific community affirmed on the contrary that if life appeared on these planets, it could disappear very quickly!
A team subjected two types of bacteria to UV radiation equivalent to a “super solar flare” and one of the two bacteria survived!
In this study published on October 24 on the MNRAS, a team of researchers selected two types of well-known bacteria: Escherichia coli And Deinococcus radiodurans. The first is sensitive to UV while the second is known to be very resistant.
Electromagnetic spectrum of the Trappist-1 super flare scaled to the exoplanet Trappist-1e, considered a very Earth-like planet. © XC Abrevaya et al. (MNRAS, 2024)
They then took as a reference a super solar flare from Trappist-1 recorded by the Kepler space telescope. Its energy was 1.24 * 1033 erg, that is to say about 10 times more powerful than a good solar flare from our star. The team simulated the dose of UV radiation received on the exoplanet Trappist-1e, of size and mass comparable to Earth, in the habitable zone and very close to the star. The team says it neglected X-rays because the atmosphere stops most of them.
The curve in the upper graph shows the fraction of D. Radiodurens surviving. The one in the bottom graph is for E.Coli. © XC Abrevaya et al. (MNRAS, 2024)
D. Radiodurens survived long enough to replenish itself between two eruptions…
Without much surprise, Escherichia coli did not tolerate such exposure well. Unlike Deinococcus radiodurans which survived to the tune of 1 million out of 600 million, this may not seem like much, but it is enough to replenish itself within the typical duration of two super eruptions. What if the star was very angry and released a lot of super flares in a row? We can assume that the principle of evolutionary pressure would make these bacteria even more resistant!
Microbial life, if it could appear on these exoplanets, would probably manage to adapt to the harsh conditions imposed by these small but strong stars! All that remains is to discover primitive life elsewhere than on Earth, for example thanks to the Europa Clipper missionin our own Solar System to begin with…
NASA poster of an imaginary trip to Trappist-1e: we see the other exoplanets in the sky because they are close to each other. © NASA
