What if you put an Earth-sized planet in close orbit around an M dwarf star? It’s more than just an academic question because M dwarfs are the most star-studded we know. A group of astronomers studying the planet GJ 1252b has found an answer and it’s not pretty.
Since this planet is so close to its star, it receives a lot of heat. This closeness is deadly in another way. “The pressure from the star’s radiation is enormous, enough to blow the planet’s atmosphere away,” said Michelle Hill, an astrophysicist at the University of California Riverside, co-author of a recent paper focusing on GJ 1252b. The planet is located 65 light years from Earth and orbits its star twice every 24 hours from Earth. The heat of the star makes this world inhospitable.
This is not terribly different from Mercury in our solar system. There is no atmosphere and the planet alternately heats up and freezes as it orbits the sun. In fact, Earth also loses a little bit of its atmosphere due to solar activity. However, volcanoes and other processes release gases back into our atmosphere. Earth is lucky. Planets like Mercury and GJ 1252b are not. This has profound implications for the search for life-friendly worlds.
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How about M Dwarf Stars?
There are millions upon millions of M dwarf stars in our galaxy alone. They range in size from about one-tenth to two-thirds of the mass of the Sun. These can be active, sending flares and explosions through their systems. Most of them have at least one planet in their habitable zones and others are at varied distances.
This is not a great combination if you want to find life on their planets. It’s also clear that stellar activity that blows the atmospheres of planets away destroys any chances of life on those worlds. And due to the multiplicity of M dwarfs, their ubiquity may reduce the number of planets in the galaxy that actually support life. This isn’t great news for planets like GJ 1252b.
“It’s possible that the state of this planet is a bad sign for planets far from this type of star,” Hill said. “This is something we will learn from the James Webb Space Telescope, which will look at planets like this.”
Although M dwarfs can be lethal to the atmosphere, it’s not all doom and gloom. For example, many of the five thousand stars in the solar neighborhood of the Earth are M dwarfs. Even if a large portion of them blow up their planets in a hospitable place, at least 1,000 more people (not all of them M dwarfs) could provide suitable conditions for life in their worlds. “If a planet were far enough away from an M dwarf, it would probably retain an atmosphere. We cannot yet conclude that all rocky planets around these stars have the fate of Mercury,” Hill said. “I’m still optimistic.”
Looking for Joe on GJ 1252b
The science behind the position in GJ 1252b is interesting. Astronomers used Spitzer Space Telescope data to assess infrared radiation from the planet where the secondary eclipse obscured its light. Measurements showed that the star was blowing up the planet. Daytime surface temperatures range around 1,227 °C (2,242 °F). It is hot enough to melt gold, silver, and copper.
The heat, along with the supposedly low surface pressure, led the 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 heat on the surface, and possibly allow that blanket to stay in 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 it wouldn’t have an atmosphere. It would build up at first, but then dwindle and erode,” said Stephen Kane, an astrophysicist at the University of California, co-author of the study. “.
In the long term, if this study is validated across a large group of M dwarf stars, it will shift the search for habitable planets to other candidates around less volatile stars.
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GJ 1252b: Super Hot Earth Without Atmosphere
dwarf stars m
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