From NASA Spitzer space telescope has provided new insights into a rocky exoplanet that may be very similar to the planet Mercury or Earth’s Moon. Orbiting an M-type dwarf star 48.6 light-years from Earth in the constellation Indus, LHS 3844b is 1.3 times the mass of our planet, probably airless and covered in plains of lava that resemble maria. lunar.
With the number of exoplanets now found in the thousands and many more expected to be discovered, counting one more is getting a bit old, but newer space and ground-based telescopes allow astronomers to not only confirm the existence of exoplanets, but also tell us something about its nature.
LHS 3844b was found in 2018 by NASA’s Transiting Exoplanet Satellite Survey (TESS) mission measuring the dip in the light curve of its parent star as the planet passed in front of it. That’s good enough for catalogs, but when the Spitzer infrared telescope was turned on on the exoplanet, things got a little more interesting.
For one thing, its parent star is of a type that is not only the most common and longest-lived in the Milky Way galaxy, but is also home to a large percentage of exoplanets. LHS 3844b orbits its star in a “year” that lasts only 11 hours at such a close distance that NASA says it is tidally locked and shows only one face to its star, just as the Moon does to Earth.
It is also so close that the day side has a surface temperature of 1,410 ° F (770 ° C). That’s very useful because M-type stars tend to be not only small, but also on the cool side, so the infrared light that LHS 3844b radiates can be seen directly by Spitzer. Not only that, but the telescope can see with enough resolution to differentiate between the day and night sides.
According to NASA, the research team found that the night side is very cold. This means that there is probably little or no atmosphere. Otherwise, storms would arise and the winds would blow to the dark and cold side and heat it up. In the case of the LHS 3844b, it matches computer models of the type of temperature profile you would expect in an airless world. As for what happened to the atmosphere, that’s another question.
“We have a lot of theories about how planetary atmospheres around M dwarfs fare, but we haven’t been able to study them empirically,” says Laura Kreidberg, a researcher at the Center for Astrophysics at Harvard and the Smithsonian. “Now, with LHS 3844b, we have a terrestrial planet outside our solar system where for the first time we can determine observationally that there is no atmosphere.”
The basic mechanism is that M dwarfs emit high levels of ultraviolet radiation, as well as frequent solar flares, which can strip the atmosphere of worlds that are not very massive or are shielded by powerful magnetic fields. The Spitzer data indicates that although an atmosphere could exist under very peculiar circumstances, the most likely conclusion is that the planet has very little air, if any.
In addition to this, the light from LHS 3844b shows that it is quite dark, suggesting that its surface is similar to the Moon, with large lava fields that have cooled to basalt. As to whether the planet is typical of those orbiting M-type stars, that remains to be seen.
“I’m still hopeful that other planets around M dwarfs can maintain their atmospheres,” says Kreidberg. “The terrestrial planets in our solar system are enormously diverse, and I hope the same is true for exoplanet systems.”
The research was published in Nature.