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, not just assuming that the things we see in the solar system are similar to one another," said Andrew Lincowski, PhD student at UW and lead author of 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 early oceans had evaporated and 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 "M 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 insight into their evolution, especially around a star very different from ours, with a different light coming from it," Lincowski said. . "It's just a gold mine."

According to Mr. Lincowski, previous articles have modeled the TRAPPIST-1 worlds, but he and his research team "have tried to do the most rigorous physical modeling possible in terms of radiation and chemistry, trying to optimize maximum physics and chemistry ".

The team's radiation and chemistry models create spectral signatures, or wave lengths, for each possible atmospheric gas, allowing observers to better predict where to look for these gases in atmospheres. ; exoplanets. Lincowski said that when gas traces are actually detected by the Webb telescope, or by others, one day, "astronomers will use the bumps and ripples observed in the spectrum to infer which gases are present – and compare it to function as 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 some of the TRAPPIST-1 planets might look like Venus, any water or ocean having been burned for a long time. He explained that when water evaporates from the surface of a planet, the ultraviolet light from the star breaks water molecules, releasing hydrogen , the lightest element that can escape 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 act today as an aquatic world, entirely covered by a global ocean. In this case, the climate could be similar to that of the Earth. "

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

"Before knowing this planetary system, the estimates of atmospheric detectability for Earth-sized planets seemed much more difficult," said co-author Jacob Lustig-Yaeger, an UW PhD student in astronomy.

The star being so small, he said, the gas signatures (like carbon dioxide) in the atmospheres of the planet 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."

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

"The processes that shape the evolution of a terrestrial planet are essential to know whether it may 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.

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More information:
Andrew P. Lincowski et al. Advanced and discriminating observational climates for the TRAPPIST-1 planetary system, The astrophysical journal (2018). DOI: 10.3847 / 1538-4357 / aae36a