What do we know about the TRAPPIST-1 system’s habitability?

The TRAPPIST-1 system is notable for having Earth-like planets that may be habitable. They are rocky and in the so-called “habitable zone” where water may exist to support life. But the star in this system is active, much more so than our own Sun. What does this mean for habitability in the TRAPPIST-1 system? We spoke with Federico Fraschetti, an astrophysics professor at the University of Arizona who studies the system. We asked him about his work, and also for his recommendations to aspiring astrophysicists.


What specifically do you study about the TRAPPIST-1 system?

TRAPPIST-1 is a planetary system comprised of a cool star hosting seven Earth-sized rocky planets at a distance of 12 parsecs, which is about 36 light years, from Earth. The planets are packed within a very small region – just 0.06 astronomical units, where 1 astronomical unit is the distance between the Earth and the Sun! Three of these planets are considered to be in the habitable zone, namely the region of space where the stellar radiation is neither too strong nor too weak for liquid water to exist on the surfaces of the planets. Despite being cool, the central star is very active and emits a large quantity of high-energy particles. Such particles cause auroras on Earth but also are hazardous to astronauts in space. We believe that those particles might have played a role in the early development of life on Earth.

The team I am working with has, for the first time, calculated in detail how these particles impinge on the nearby planets by using a realistic model for the turbulent magnetic field generated by the star.

What have your findings indicated about the habitability of the system?

We have found that the fourth planet, the closest one to the star in the TRAPPIST-1 habitable zone, may experience a dramatic bombardment of particles, up to a million times more than Earth. Flares on the surface of the star or travelling shock waves emanating from explosions on its surface produce those particles.

The journey of the particles away from the star depends on the angle of the star’s magnetic field with the stellar rotation axis. In the TRAPPIST-1 system, the most likely orientation of this field will bring energetic particles directly to the fourth planet’s face along polar streams, where they would break apart complex molecules that are needed to build life. Others believe that those particles might instead seed catalysis of pre-biotic molecules, helping life to proceed. In either scenario, these results are very important because they change our vision of the effect that energetic particles have on the habitability of planets in a quantitative way. Surprisingly, if the alignment is off the most likely one by a few tens of degrees, the particles might not reach the planet at all.

In the case of our Earth, the magnetic field protects most of the planet from energetic particles emitted by the Sun. A field strong enough to deflect TRAPPIST-1’s particles would need to be improbably strong – hundreds of times more powerful than Earth’s.

What advice do you have for people who would like to become astrophysicists?

Scientists, including astrophysicists, should always question themselves and challenge the current vision or scenario in their field, even the broadly accepted ones. Big discoveries may originate in apparently insignificant observational or experimental results or theoretical inconsistencies that deviate from the most credited theory in that particular moment.

Although it seems an obvious and reiterated recommendation by scientists to general audiences, in fact most professional scientists tend, in my opinion, to re-obtain previous results with more advanced techniques, disguising their findings as ground-shaking. The objective of doing this is probably to stabilize one’s job situation or to achieve awards. Conversely, the motivation behind such behavior is essentially the fear of failing. However, the essence of science is mostly to look for new paths, explore new ideas, and create new visions. So, don’t fear to fail.
In particular for those aiming to become astrophysicists, I would like to call attention to the fact that in the last few decades, numerical techniques have advanced noticeably. As a consequence, problems are now starting to be cracked that previously seem unsolvable. This has created what I would call a third generation of human-computer relations. In the first generation, the human wrote a code to solve a problem and then used the code to solve the problem. In the second generation, the human wrote a code to solve a problem, gave the code to another less experienced human (a student) who did not engage in understanding how the code works in detail, but who nevertheless acted under the guidance of the code-writer to use it to solve the problem.

We are now in the third generation, in which the human writes a code and makes it available to anybody on the Internet so that anybody can use and modify the code with the risk of introducing unexpected and undetected bugs. In essence, anybody can now solve the problem. On the one hand, this is good because it allows surprisingly fast growth of workforce and of number of publications. On the other hand, this new way of doing things is problematic because it risks creating spurious numerical and not physical results. A suggestion is therefore that you should always master the numerical code that you use and never use it as a black box, as much as possible.

A final suggestion is: don’t be afraid to have broad scientific interests and try to expand your scientific horizons. There are two reasons why I make this suggestion. First is that science is driven by passion. Second is that ideas can cross-fertilize between different scientific fields.