Exoplanets in TRAPPIST-1 are warming up due to solar flares, and that's a good thing

What makes planets habitable?

Planetary researchers have always looked at geologic activity on Earth as a model for finding habitable environments on other planets. While this activity is driven by planetary cooling, the Earth's interior also has radioactive elements that generate heat and enable geological processes in the long run.

If this model were the only way for the establishment of habitable environments, it would require all planets to have radioactive elements in their core for life to evolve. An international team of researchers at the University of Cologne, though, looked at the potential of solar flares to heat up planets.

Solar flares, the intense eruptions of electromagnetic radiation from the Sun, are often looked at as a destructive force that can cause damage to humans in space and spacecraft located in thinner layers of the atmosphere. These flares have also been associated with the stripping off of atmospheric layers making them less habitable.

However, the researchers found the solar flares emitted by a star much smaller than the Sun could actually help warm up the planet.

How do solar flares warm up the planet?

Solar flares in the TRAPPIST-1 system can heat up planets as a result of Ohmic dissipation. Also known as Ohmic loss, this is the loss of energy experienced in a circuit when current flows through a resistance. Scientists use this definition to determine how much energy a planet loses as it cools down, but in the case of the TRAPPIST-1 system, it is actually helping the planets warm up.

The driving up of temperatures on these planets could lead to geological activity, which could result in thicker atmospheres, the researchers noted. The presence of a magnetic field around the planet could also enhance the results of such heating.

The findings of the research team are significant in light of another discovery made by the James Webb Space Telescope as it looked at the TRAPPIST system for the first time. The space telescope observed that planets in this system had a lower probability of possessing a hydrogen atmosphere. This is much like gas planets in our solar system, meaning that planets in the TRAPPIST-1 system could end up being more terrestrial, like Mars, Venus, or even Earth, in the future.

These findings will pique the curiosity of astrobiologists who would want to know more about the likely atmosphere the planets could have.

The research findings were published in the Astrophysical Journal Letters.

Abstract

Many stars of different spectral types with planets in the habitable zone are known to emit flares. Until now, studies that address the long-term impact of stellar flares and associated coronal mass ejections (CMEs) assumed that the planet's interior remains unaffected by interplanetary CMEs, only considering the effect of plasma/UV interactions on the atmosphere of planets. Here, we show that the magnetic flux carried by flare-associated CMEs results in planetary interior heating by ohmic dissipation and leads to a variety of interior–exterior interactions. We construct a physical model to study this effect and apply it to the TRAPPIST-1 star whose flaring activity has been constrained by Kepler observations. Our model is posed in a stochastic manner to account for uncertainty and variability in input parameters. Particularly for the innermost planets, our results suggest that the heat dissipated in the silicate mantle is both of sufficient magnitude and longevity to drive geological processes and hence facilitate volcanism and outgassing of the TRAPPIST-1 planets. Furthermore, our model predicts that Joule heating can further be enhanced for planets with an intrinsic magnetic field compared to those without. The associated volcanism and outgassing may continuously replenish the atmosphere and thereby mitigate the erosion of the atmosphere caused by the direct impact of flares and CMEs. To maintain consistency of atmospheric and geophysical models, the impact of stellar flares and CMEs on atmospheres of close-in exoplanetary systems needs to be studied in conjunction with the effect on planetary interiors.