A study presents new climate models from the seven fascinating worlds of the little star TRAPPIST 1

Not all stars are like the sun, so all planetary systems can not be studied with the same expectations. A new study by a team of astronomers led by the University of Washington provides updated climate models for the seven planets around the star TRAPPIST-1.

This work could also help astronomers to more effectively study the planets surrounding stars unlike our sun and better utilize the limited and costly resources of the James Webb Space Telescope, which is scheduled for launch in 2021.

"We are modeling unknown atmospheres, and not just assuming that what we see in the solar system will look the same as another star," said Andrew Lincowski, Ph.D. student at UW and senior author of the Solar System. an article published on November 1 in Astrophysical Journal. "We conducted this research to show what these different types of atmosphere might look like."

The team discovered, to sum up, that because of an extremely hot and brilliant early star phase, the seven worlds of the star could have evolved like Venus. All the oceans of the first hour had evaporated and had left a dense and uninhabitable atmosphere. However, a planet, TRAPPIST-1 e, could be an oceanic world similar to that of Earth that would merit further study, as has also indicated previous research.

TRAPPIST-1, at 39 light-years away or about 235 trillion kilometers away, is as small as a star can be and remains a star. A relatively cool "dwarf" star – the most common type in the universe – represents about 9% of the sun's mass and about 12% of its radius. TRAPPIST-1 has a radius only slightly larger than the planet Jupiter, although it is much larger in mass.

The seven planets of TRAPPIST-1 are about the size of the Earth and three of them – the planets labeled e, f, and g – would be in its habitable zone, this band of space around A star where a rocky planet could have liquid water on its surface, thus giving a chance to life. TRAPPIST-1 d travels the inner edge of the habitable zone, while TRAPPIST-1 h, farther away, revolves around the outer edge of this zone.

"It's a whole sequence of planets that can give us a glimpse of their evolution, especially around a star very different from ours, whose light differs," said Lincowski. "It's only a gold mine."

Lincowski explained that previous articles had modeled the TRAPPIST-1 worlds, but that he and his team "have tried to do the most rigorous physical modeling possible in terms of radiation and chemistry – trying to optimize at best physics and chemistry ".

The team's radiation and chemistry models create spectral or wavelength signatures for each possible atmospheric gas, allowing observers to better predict where to look for these gases in exoplanet atmospheres. Lincowski said that when gas traces are actually detected by the Webb telescope, or by others, someday, "astronomers will use the bumps and ripples observed in the spectrum to infer which gases are present – and will compare it to work like ours, the composition of the planet, its environment and perhaps its evolutionary history. "

He said that people are used to thinking about the livability of a planet similar to that of the sun around stars. "But dwarf M stars are very different, so you really have to think about the chemical effects on the atmosphere and how that chemistry affects the climate."

By combining terrestrial climate modeling with photochemistry models, researchers simulated environmental states for each of the TRAPPIST-1 worlds.

Their modeling indicates that:

• TRAPPIST-1B, the closest to the star, is a blazing world too hot, even for clouds of sulfuric acid, as on Venus, to form.
• The planets c and d receive slightly more energy from their star than Venus and the Earth from the sun and could look like Venus, with a dense and uninhabitable atmosphere.
• TRAPPIST-1 is the most likely of the seven to harbor liquid water on a temperate surface and would be an excellent choice for further studies taking into account habitability.
• The outer planets f, g and h could look like Venus or be frozen, depending on the amount of water formed on the planet during its evolution.

Lincowski said that in fact, all or part of the TRAPPIST-1 planets might look like Venus's, with water or oceans burned for a long time. He explained that when water evaporates from the surface of a planet, the ultraviolet light of the star breaks water molecules, releasing hydrogen, which is the lightest element and can escape to the gravity of the planet. This could leave a lot of oxygen, which could remain in the atmosphere and irreversibly eradicate water from the planet. Such a planet can have a thick oxygen atmosphere – but not generated by life and different from all that has already been observed.

"It could be possible if these planets initially had more water than Earth, Venus or Mars," he said. "If the planet TRAPPIST-1 had not lost all its water during this phase, it could today be an aquatic world, completely covered by a global ocean. In this case, it could have a climate similar to the Earth. "

Lincowski said that this research is more focused on climate change than on the habitability of the planets. He plans future research by focusing more directly on the modeling of aquatic planets and their chances of survival.

"Before we knew this planetary system, the estimates of atmospheric detectability for Earth-sized planets seemed much harder," said co-author Jacob Lustig-Yaeger, an astrophysics PhD student at UW.

The star being so small, he said, the signatures of gases (such as carbon dioxide) in the planet's atmosphere will be more pronounced in the telescope data.

"Our work informs the scientific community of what we could expect from the TRAPPIST-1 planets with the next James Webb Space Telescope."

Lincowski's other co-author is Lincoln, Victoria Meadows, professor of astronomy and director of the astrobiology program at the University. Meadows is also Principal Investigator for NASA's Astronomy Virtual Global Virtual Laboratory Virtual Planet Lab, based at the University. All authors were affiliated with this research laboratory.

"The processes that shape the evolution of a terrestrial planet are critical to whether it can be habitable or not, as well as for our ability to interpret possible signs of life," Meadows said. "This article suggests that we may soon be able to search for potentially detectable signs of these processes on extraterrestrial worlds."

TRAPPIST-1, in the constellation Aquarius, was named after the planets on the transiting surface and the small planetary telescope, the installation that first discovered traces of planets around him in 2015.