Based on the TRAPPIST-1 system, scientists have modeled how the atmospheres of Earth-sized planets can coexist with the radiation of similar stars. It emerged with huge problems.

In order for there to be liquid water on the surface of the planet, it must have a very dense atmosphere. Fortunately, astronomers can probe and study atmospheres to find changes in the star’s radiation as an exoplanet passes in the background. But there are many planets and long-term observations are required to collect relevant data. One such target for observation is the TRAPPIST-1 system, which consists of seven rocky planets; four of these are comparable to Earth in mass and are in the “populated” region.

The authors of the new study, whose preprint is available at arXivdecided to test whether these planets had atmospheres by simulating the conditions of the system. To be able to scale the study’s results to other potentially habitable worlds, they did not strictly adhere to the parameters of the specific planets of the TRAPPIST-1 system. So scientists ignored the density estimates and calculated the radii of the simulated planets by mass (0.8, 1, and 1.2 of Earth’s mass) based on our planet’s density (5.5 grams per cubic centimeter).

The researchers’ goal was to see how the atmospheres of such planets withstand the influence of a low-mass spectral class M star like the one at the center of TRAPPIST-1. For this, they used the upper atmosphere model called Kompot Code, which describes the one-dimensional thermochemical structure of the surface of the atmosphere at the border with space.

The model used includes more than 500 reactions of 63 chemical elements. It takes into account the effect of various heating and cooling mechanisms. In particular, X-ray and infrared radiation, as well as the cooling effect of carbon dioxide in the upper layers of the atmosphere.

Comparing the simulated data with TRAPPIST-1 parameters, scientists concluded that most of the planets in this system cannot maintain their atmospheres, regardless of their composition. Under the star’s radiation, the upper layers of the atmosphere must have heated up so much that molecules began to fly out of the planet’s gravitational field.

Given the age of the system (about 7.6 billion years by one estimate), even if there was an atmosphere 100 times larger than Earth’s, it would have all dissipated by now. According to the authors’ assumption, a similar story should happen with all terrestrial planets with stars of spectral class M.

Simulation results confirm the observational results. No trace of a hydrogen atmosphere has been found on any of the system’s planets. According to the James Webb telescope, the planets TRAPPIST-1b and TRAPPIST-1c do not have dense atmospheres. According to other studies, neither CO2 nor CO2 dominates TRAPPIST-1c’s atmosphere.

Although the authors of the new paper state that none of the TRAPPIST-1 planets could retain their atmosphere, we see that the density of these planets suggests otherwise. Although the mass of many of them is comparable to that of the Earth, they all have a density lower than that of the Earth and Venus. It’s hard to imagine how this would be possible without an atmosphere of light elements. It remains to wait for new observations of these objects.