This artist’s concept shows the TRAPPIST-1 system as seen from the surface of one of its planets. Credit: NASA/ESA/HST.

A group of researchers has published a study in which they review what impact solar flares, from the star TRAPPIST-1, can have on their surroundings. Specifically, how they might affect the internal heat of the exoplanets around them. The study is attractive for several reasons. For example, it could help to better understand how solar flares affect planetary evolution. It must be remembered that TRAPPIST-1 is 39 light-years from the Solar System and that it has seven rocky worlds in its environment.

It must be remembered that the star is much smaller than the Sun. It is, in fact, a red dwarf, the least massive and longest-lived type of star in the cosmos. It has twelve times less mass than our star. Being so small, the orbits of the planets around it are consequently much smaller than those we observe in the Solar System. So the question is unavoidable. How can this study help to better understand the habitability conditions of the planets in the TRAPPIST-1 system? The researchers explain that we can use Earth as a starting point. In our world, geological activity has shaped its entire surface. Geological activity is ultimately fueled by planetary cooling. The Earth has radioactive elements in its interior. They generate heat and allow geological processes to last for billions of years. The question, however, is whether all planets need radioactive elements to trigger the geological processes necessary to create a habitable environment.

Other mechanisms for generating internal heat There are other mechanisms that can generate heat inside a planet. The disadvantage is that they generally have a short duration and require very specific circumstances. Something that would give strength to the hypothesis that geological activity (and consequently habitable environments) are rare. What is intriguing about this study, they add, is that TRAPPIST-1 is a well-known red dwarf. It is a much smaller star than the Sun and emits less solar radiation. Red dwarfs are also the most abundant stars in our environment.

The role of ohmic dissipation Ohmic dissipation (also known as ohmic loss) is defined as the loss of electrical energy due to conversion to heat when a current flows through a resistance. In essence, it’s what researchers use to calculate how much heat a planet loses. It is a phenomenon known as planetary cooling. All rocky objects, including Earth, experience it. The study indicates that planetary cooling on the TRAPPIST-1 worlds is sufficient to trigger geological activity.

This would allow the existence of denser atmospheres. The researchers’ models also predict the presence of a planetary magnetic field, which may help reinforce such warming. To this we must add that, recently, the James Webb telescope has made the first observations of the TRAPPIST-1 system. One of the planets has a low probability of having a hydrogen atmosphere, like that of the gas giants in the Solar System. This opens up the possibilities for other worlds.

Perhaps one of them, at least, has an atmosphere more similar in composition to that of Earth, Mars, or Venus. The attractiveness of the TRAPPIST-1 system, from the point of view of astrobiology, is undeniable. So it’s not surprising that the researchers have already set their next targets. There are two great paths that you can follow. On the one hand, the abundance of red dwarfs in the stellar neighborhood invites us to analyze the behavior of those other stars present in our galactic environment.

The impact of stellar flares on the search for life in TRAPPIST-1 On the other hand, a more detailed study of the TRAPPIST-1 planetary system, through observations and models, will allow us to better understand what the interior of its planets is like. This will allow the researchers to refine their model regarding questions such as the existence of an iron core, or if they could have a large layer of silicates, as happens on Earth. Its goal is to perform more elaborate physical simulations. Thus, they hope to better understand the intrinsic effects of the magnetic fields of these planets.

The long-term goal, they add, is to be able to couple their model with others that focus on the formation and destruction of atmospheres. In any case, the road ahead in the TRAPPIST-1 study is still long. The observations of the James Webb telescope will undoubtedly be an interesting point to get a better idea of ​​what we could find there. The presence of an atmosphere more similar to that of worlds like Earth or Venus will be good news. It will not be enough, however, to know if they could be habitable.

The activity of red dwarfs, moreover, continues to be one of the great points of debate about the habitability of the worlds around them. These stars are the most abundant (in the main sequence phase) in the universe. Therefore, the abundance of life, in the cosmos as a whole, is linked in a very direct way to the possibility that life can appear in such systems. If the possibility of life appearing around red dwarfs is high, life could be present in almost any corner of a galaxy.

Study The study is A. Grayver, D. Bower, J. Saur et al.; “Interior Heating of Rocky Exoplanets from Stellar Flares with Application to TRAPPIST-1”. Published in The Astrophysical Journal Letters on December 7, 2022. It can be viewed at this link.