March 22, 2023
m dwarf stars destroy atmospheres.

A nearby star has completely blown the atmosphere off its planet

What if you put an Earth-sized planet in a tight orbit around an M-dwarf star? It is more than an academic question, as M dwarfs are the most numerous stars we know of. A team of astronomers studying the planet GJ 1252b found an answer, and it’s not pretty.

Since this planet is so close to its star, it receives a lot of heat. And this closeness is deadly in another way. “The radiation pressure from the star is enormous, enough to blow a planet’s atmosphere away,” said Michelle Hill, an astrophysicist at the University of California, Riverside and co-author of a recent paper focusing on GJ 1252b. The planet is about 65 light-years from Earth and orbits its star twice every 24 Earth hours. The heat from the star makes this world inhospitable.

Illustration of the atmosphere being blasted off a planet by a nearby star. (NASA)

This is not terribly different from Mercury in our solar system. There is no atmosphere and the planet alternately heats and cools as it orbits the Sun. In fact, Earth also loses some atmosphere from solar activity. However, volcanism and other processes release gases back into our atmosphere. Earth is lucky. planets like Mercury and GJ 1252b are not. And, this has profound implications for the search for life-friendly worlds.

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What is M Dwarf Stars?

There are millions and millions of M dwarf stars in our galaxy alone. Their size ranges from about one-tenth to two-thirds the mass of the Sun. These can be active, sending flares and bursts through their systems. Most have at least one planet in their habitable zones and others at various distances.

This is not a great combination if you want to find life on their planets. The stellar activity that blasts planetary atmospheres apparently also destroys any chance for life on those worlds. And, since M dwarfs are so numerous, their ubiquity can reduce the number of planets in the galaxy that actually support life. This is not great news for planets like GJ 1252b.

“It’s possible that the condition of this planet is a bad sign for planets even further away from this type of star,” Hill said. “That’s something we’ll learn from the James Webb Space Telescope, which will be looking at planets like these.”

Although M dwarfs could be atmosphere killers, it’s not all doom and gloom. For example, many of the 5,000 stars in Earth’s solar neighborhood are M dwarfs. Even if a large fraction of them eject their host planets, at least 1,000 others (not all M dwarfs) could create conditions suitable for life on their worlds. “If a planet is far enough away from an M dwarf, it could potentially retain an atmosphere. We cannot yet conclude that all rocky planets around these stars are restricted to the Mercury fate,” Hill said. “I remain optimistic”

I am looking for an atmosphere in GJ 1252b

The science behind the situation in GJ 1252b is interesting. Astronomers used data from the Spitzer Space Telescope to assess infrared radiation from the planet as a secondary eclipse blocked its light. The measurements showed that the star is ejecting the planet. Daytime surface temperatures hover around 1227 C (2242 F). It is hot enough to melt gold, silver and copper.

The heat, combined with the supposed low surface pressure, led researchers to believe that there was no atmosphere there. But, let’s assume for a moment that there was an atmosphere of carbon dioxide. This would trap the heat at the surface and perhaps allow this blanket to exist for a while. However, it turns out that GJ 1252b is not so lucky. “The planet could have 700 times more carbon than Earth and still have no atmosphere. It would build up initially, but then diminish and erode,” said Stephen Kane, a UCR astrophysicist and co-author of the study.

In the long run, if this study applies to a significant population of M dwarf stars, it will shift the search for habitable planets to other candidates around less volatile stars.

For more information

Discovery could dramatically narrow the search for space creatures
GJ 1252b: A hot terrestrial super-Earth with no atmosphere
M Dwarfs Stars

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