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The Webb Telescope's first confirmed exoplanet is 99 percent the diameter of Earth

LHS 475 b is just 41 light years away.
James Webb Telescope in outer space on orbit of Earth planet. Sci-fi space collage. Astronomy science
Just_Super via Getty Images
Andrew Tarantola
Andrew Tarantola|@terrortola|January 11, 2023 2:34 PM

Having already returned visually stunning and scientifically spectacular results from its first six months in operation, the James Webb Space Telescope has recorded another inaugural milestone: its first exoplanet discovery confirmation. It peered 41 light years into the cosmos and found a planet in the Octans constellation with a diameter 99 percent that of Earth itself — say hello to LHS 475 b.

Specifically a team of astronomers from the Johns Hopkins University Applied Physics Laboratory, led by Kevin Stevenson and Jacob Lustig-Yaeger, first spotted evidence of the candidate exoplanet while digging through data generated from NASA’s Transiting Exoplanet Survey Satellite (TESS). However it was Webb’s Near-Infrared Spectrograph (NIRSpec) that confirmed the planets existence by observing two transits in front of its parent star. “There is no question that the planet is there. Webb’s pristine data validate it,” Lustig-Yaeger declared in a NASA press release

As the space agency notes, among telescopes in operation today (both terrestrial and orbital), only the JWST possesses the resolving capabilities to accurately characterize the atmospheres of Earth-sized exoplanets. The research team is still working to determine what, if any, sort of atmosphere is sitting atop the rocky mass using by analyzing its transmission spectrum

There is a chance that the planet will be devoid of its critical gaseous insulation but at these distances, it could simply be hiding a very small atmo close to the surface. "Counterintuitively, a 100% carbon dioxide atmosphere is so much more compact that it becomes very challenging to detect,” said Lustig-Yaeger. 

They are confident that it does not possess an oppressive atmosphere similar to that of Saturn’s moon Titan, however. “There are some terrestrial-type atmospheres that we can rule out,” he said. “It can’t have a thick methane-dominated atmosphere.” 

That said, the surface of the planet does appear to be around 300 Celsius, several hundred degrees warmer than here on Earth. If cloud cover is discovered in subsequent studies, it could suggest a greenhouse world climate closer to Venus. The researchers have also confirmed that LHS 475 b maintains a tidal-locked orbit with its star of just two days — far too close to attempt with Sol but, because LHS circles a red dwarf that's producing less than half of our sun's energy, can theoretically maintain an atmosphere.

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The Webb Telescope's first confirmed exoplanet is 99 percent the diameter of Earth