Earth-sized exoplanet found to have no atmospherePeter Brown | August 20, 2019
Scientists have been hunting for Earth-like planets for years, hoping to discover an atmosphere similar to Earth's atmosphere or one close enough to maybe support life, and, in 2018, they thought they had with the discovery of a planet called LHS 3844b. However, researchers have found that LHS 3844b is not at all what they first thought.
First discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS), LHS 3844b measured 1.3 times larger than Earth. The planet, which resides just 49 light-years from Earth, orbits a small, cool M-dwarf star in just 11 hours — one of the fastest known orbiting exoplanets. Atmospheres have been previously detected on planets much larger than Earth including Jupiter and Neptune, but these are made primarily of ice and gas.
However, researchers have discovered that LHS 3844b does not have, as they first thought, a thick Venus-like atmosphere or a thin, Earth-like atmosphere. Instead, they discovered that LHS 3844b has a similar atmosphere to Mercury — a barren rock. If an atmosphere ever existed, it was destroyed in the early planet’s formation by its star’s radiation.
“We basically found a hot planet with no gases around it,” said 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.”
It is unlikely given these conditions that any type of life could be supported there because the lack of an atmosphere would instantly cook off any organisms on the planet’s surface.
Scientists did not expect to find a planet hospitable for life. Instead, they were attempting to determine whether the category of planets surrounding smaller stars had atmospheres or not. LHS 3844b was the first crop of extrasolar worlds confirmed by TESS, which monitors thousands of the closest, brightest stars for orbiting planets.
How they found out
LHS 3844b is a tidally locked planet, meaning that it has a permanent dayside and night side, the same way that Earth’s moon always faces the same way to Earth. If an atmosphere were to exist, it would circulate the heat emitted by both the day and night sides around the entire planet. In the absence of an atmosphere, the dayside would be considerably hotter than the night side.
As the planet orbits its star, various faces of the planet are visible. As the planet comes out from behind the star, the planet’s dayside is exposed. When it circles in front of the star, the planet’s night side is exposed.
Researchers determined that they could measure the heat given off by the planet’s various faces during its orbit, distinguishing between the dayside and the night side to determine whether the planet had an atmosphere.
The team then used NASA’s Spitzer Space Telescope, which measures infrared radiation or heat, to capture 100 hours of LHS 3844b orbits. From these measurements, researchers calculated the dayside temperature to be 1,000 kelvins (1,340° F) and the night temperature drops to as low as 0 kelvins (-460° F).