JWST Spots a Nearby Super-Earth That Could Look Like the Moon or Mercury
The exoplanet LHS 3844 b is a rocky world orbiting a cool red dwarf located 48.5 light years away. With a radius 30% larger and a mass more than twice that of Earth, it officially fits the description of a Super-Earth, according to NASA. But new research suggests it’s more like Mercury or the Moon than our home planet.
A study recently published in the journal Natural astronomy used evidence collected from the James Webb Space Telescope (JWST) to determine the surface composition of LHS 3844 b.
“Thanks to the incredible sensitivity of JWST, we can detect light coming directly from the surface of this distant rocky planet,” Laura Kreidberg, director of the Max Planck Institute for Astronomy in Germany, said in a statement. “We see a dark, hot, barren rock, devoid of any atmosphere.”
Learn more: When searching for life on exoplanets, the absence of its signs is only a starting point
A planet similar to the Moon
Data collected from JWST show the hot-side infrared spectrum of LHS 3844 b derived from the brightness contrast with its host star in ppm (parts per million = 0.0001%) at different wavelengths.
(Image credit: Sebastian Zieba et al./MPIA)
To find out exactly how similar LHS 3844 b is to Earth, astronomers used JWST technology which can provide clues about the composition of a planet’s surface. Specifically, the team used the Mid-Infrared Instrument (MIRI), which measures the absorption and emission of light and radiation in the mid-infrared section of the electromagnetic spectrum.
Rather than observing the planet directly, the researchers measured changes in brightness levels relative to its host star. An additional data point, collected from observations made by the Spitzer Space Telescope, was also included. These measurements were then compared to models in the RELAB spectral database to determine what type of surface could produce the observed spectrum.
The results suggest that the exoplanet is more like Mercury, or even the Moon, than our home planet. Its surface is likely made of basalt or mantle rock—materials containing high concentrations of magnesium, iron, and a magnesium-iron silicate called olivine—rather than a silicate-rich crust like Earth. It is also possible that the surface is composed of crushed materials, such as rocks or gravel, resulting from spatial weathering. Devoid of an atmosphere, LHS 3844 b would be and still is particularly vulnerable.
“It turns out that these processes don’t just slowly dissolve hard rocks into regolith, a layer of fine grains or powder found on the moon,” Sebastian Zieba of the Harvard & Smithsonian Center for Astrophysics, who led the research, said in a press release. “They also darken the layer by adding iron and carbon, making the regolith properties more consistent with observations.”
Young and strong versus old and powdery
The team identified two possible scenarios that could result in a “very dark and featureless surface” of the planet. The first is a young exterior made of solid rock that has not yet been pulverized by space weather. The second is an old powdery surface damaged by space weather, similar to the Moon.
The researchers point out that a younger surface would imply ongoing geological activity, such as volcanism. However, there is no evidence of volcanic outgassing that could produce carbon dioxide and sulfur dioxide. They nevertheless call for more observations to provide more clarity.
What else do we know about LHS 3844 b?
Researchers announced the discovery of LHS 3844 b in 2019. Unlike Earth, the exoplanet has an extremely fast orbit. The distance separating it from its host star is equivalent to only three stellar diameters, and it makes the round trip in just 11 hours.
This is the same time it takes to rotate around its axis, explain the authors of the study. This means that one side of the planet experiences a permanent day with average temperatures of 1,340°F (725°C), while the other side experiences constant darkness. The measurements used in the study were obtained from the day side of LHS 3844 b.
Learn more: 5 of the strangest and most dangerous exoplanets ever discovered
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