Astronomers have found that an Earth-sized exoplanet has no atmosphere. This supports a theory that planets around small stars usually lack an atmosphere.

Recently, a team of astronomers has been able to observe the surface of a rocky exoplanet, LHS 3844b. They were looking for signs of an atmosphere but instead found none. It turns out this planet is a bare rock.

This is the first time astronomers have been able to pin down whether an Earth-sized, terrestrial planet outside our solar system has an atmosphere.

NASA’s Transiting Exoplanet Survey Satellite (TESS) discovered this planet back in 2018. It is 1.3 times larger than Earth.

LHS 3844b orbits around a small, cool M-dwarf star every 11 hours. This makes it one of the fastest orbiting exoplanets known. This system lies almost 50 light-years beyond our solar system.

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The planet resembles Mercury, which is a bare rock without an atmosphere. Even if it had one in the past, the star’s radiation likely blasted it away early in the planet’s formation.

“We basically found a hot planet with no gases around it,” says co-author Daniel Koll, a postdoc in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “This is the first time we’ve known anything in detail about the atmosphere of a planet around these M-dwarfs, which are the most common type of star, making LHS 3844b the most common type of rocky planet in the galaxy.”

A lack of atmosphere indicates there’s no chance life as we know could survive there. That’s because the radiation coming from the star would cook off any organisms on the planet’s surface.

“We never thought this particular planet would be hospitable for life,” says lead author Laura Kreidberg, a researcher at the Harvard Center for Astrophysics. “It’s more a question of whether this whole category of planets around smaller stars has atmospheres or not. And our technique is a robust way of assessing whether an atmosphere is present or not.”

Detecting The Radiation

For this discovery, the team trained NASA’s Spitzer Space Telescope toward the planet for 100 hours. Thus capturing about 10 orbits of the planet in total. The telescope measured infrared radiation, or heat, given off by the planet’s surface.

“This has been done a lot for planets closer in size to Jupiter, but this is the very first time that this measurement has ever been made for a terrestrial planet around an M dwarf star,” Koll says.

The team also found the planet is tidally locked, meaning one side of it always faces its parent star. The “dayside” is a scorching 770° Celsius (1,410° Fahrenheit), whereas the nightside plummets to as low as -273°C (-460°F).

“The temperature contrast on this planet is about as big as it can possibly be,” Laura Kreidberg, a researcher at the Harvard and Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and lead author of the new study said in a statement. “That matches beautifully with our model of a bare rock with no atmosphere.”

LHS 3844b could be covered in the same cooled volcanic material found in the dark “seas” of the Moon’s surface, called maria.

Now the team wants to apply their technique to other rocky exoplanets. They will also include planets that are further out from their stars and have a better chance of retaining an atmosphere.

“Atmospheres help protect life and shield it from ultraviolet radiation,” Kreidberg says. “I would be thrilled to detect an atmosphere on a planet, even if it’s a little too hot or too cold, because that would tell us, yes, some terrestrial exoplanets can have atmospheres, and probably somewhere out there, there’s going to be one that’s the right temperature, that has been able to keep liquid water.”

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