LHS 3844b, a 1.3-Earth-radii terrestrial world in an 11-hour orbit around the small nearby star LHS 3844, very likely has little to no atmosphere and could be covered in the same cooled volcanic material that comprises the dark lunar regions known as mare, according to new research.
An artist’s conception of the Earth-sized exoplanet LHS 3844b which orbits a small star 49 light-years from Earth. Image credit: NASA / JPL-Caltech / R. Hurt, IPAC.
Discovered in 2018 by NASA’s TESS mission, LHS 3844b is located about 49 light-years from Earth.
The planet has a radius 1.3 times that of Earth and orbits a small, cool type of star called an M dwarf (red dwarf).
LHS 3844b is most likely ‘tidally locked’ with one side of the planet permanently facing the star. The star-facing side, or dayside, is about 1,410 degrees Fahrenheit (770 degrees Celsius).
TESS found LHS 3844b via the transit method, which detects when the observed light from the parent star dims as its orbiting exoplanet crosses the line-of-sight between the star and Earth.
During follow-up observations, the IRAC camera aboard NASA’s Spitzer Space Telescope was able to detect infrared light from the surface of LHS 3844b.
By measuring the temperature difference between the planet’s hot and cold sides, astronomers concluded that there is a negligible amount of heat being transferred between the two.
If an atmosphere were present, hot air on the dayside would naturally expand, generating winds that would transfer heat around the planet.
“The temperature contrast on this planet is about as big as it can possibly be. That matches beautifully with our model of a bare rock with no atmosphere,” said lead author Dr. Laura Kreidberg, a researcher at the Harvard & Smithsonian Center for Astrophysics.
The Spitzer observations rule out an atmosphere with more than 10 times the pressure of Earth’s (measured in units called bars, Earth’s atmospheric pressure at sea level is about 1 bar).
An atmosphere between 1 and 10 bars on LHS 3844b was almost entirely ruled out, although there’s a slim chance it could exist if the stellar and planetary properties were to meet some very specific and unlikely criteria.
“We’ve got lots of theories about how planetary atmospheres fare around M dwarfs, but we haven’t been able to study them empirically,” Dr. Kreidberg said.
“Now, with LHS 3844b, we have a terrestrial planet outside our Solar System where for the first time we can determine observationally that an atmosphere is not present.”
The study was published online this week in the journal Nature.
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Laura Kreidberg et al. Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b. Nature, published online August 19, 2019; doi: 10.1038/s41586-019-1497-4
