NASA's James Webb Space Telescope discovers its first exoplanet

The planet, classified as LHS 475 b, has a diameter 99 percent that of Earth and was found in the constellation Octans.
Deena Theresa
An illustration shows the exoplanet LHS 475 b, almost the exact same size as Earth.
An illustration shows the exoplanet LHS 475 b, almost the exact same size as Earth.

NASA/ESA/CSA 

The James Webb Space Telescope has begun the new year with a bang. It added another extraordinary milestone to its cosmic achievements - peering 41 light years into the cosmos and confirming an exoplanet in the constellation Octans. A first for the telescope, the exoplanet has a diameter 99 percent that of Earth itself and is classified as LHS 475 b.

NASA's Transiting Exoplanet Survey Satellite (TESS) had earlier hinted at the planet's existence. This encouraged the research team led by Kevin Stevenson and Jacob Lustig-Yaeger, both from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, to observe this target with Webb.

Capturing the planet was a cakewalk for Webb's Near-Infrared Spectrograph (NIRSpec) - and it did so with two transit observations.

"There is no question that the planet is there. Webb’s pristine data validate it," Lustig-Yaeger said in a statement. "The fact that it is also a small, rocky planet is impressive for the observatory," Stevenson added.

The planet’s discovery was announced Wednesday at the 241st meeting of the American Astronomical Society in Seattle.

NASA's James Webb Space Telescope discovers its first exoplanet
As this spectrum shows, Webb did not observe a detectable quantity of any element or molecule. The data (white dots) are consistent with a featureless spectrum representative of a planet that has no atmosphere (yellow line).

Does the exoplanet have an atmosphere?

"The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet make any definitive conclusions about the planet’s atmosphere," said Erin May, also of the Johns Hopkins University Applied Physics Laboratory.

Among all operating telescopes, only Webb can characterize the atmospheres of Earth-sized exoplanets. By analyzing its transmission spectrum, the team tried to assess what constituted the planet's atmosphere. However, it is unsure if the planet has an atmosphere even.

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But, the team can conclude what is not present. "There are some terrestrial-type atmospheres that we can rule out," explained Lustig-Yaeger. "It can’t have a thick methane-dominated atmosphere, similar to that of Saturn’s moon Titan."

Webb also detected that the planet is a few hundred degrees warmer than Earth. And so, if clouds are seen, it could be concluded that the planet is similar to Venus, which has a carbon dioxide atmosphere and is shrouded in thick clouds.

NASA's James Webb Space Telescope discovers its first exoplanet
A light curve from NASA’s James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness from the LHS 475 star system over time as the planet transited the star on August 31, 2022.

LHS 475 takes only two days to complete an orbit

The researchers also confirmed that the planet takes only two days to complete an orbit. Though LHS 475 b is closer to its star than any planet in our solar system, its "red dwarf star is less than half the temperature of the Sun", so the researchers think it still could have an atmosphere.

These findings have opened up the possibility of detecting Earth-sized planets orbiting smaller red dwarf stars. "This rocky planet confirmation highlights the precision of the mission’s instruments," Stevenson said. "And it is only the first of many discoveries that it will make." Lustig-Yaeger agreed. "With this telescope, rocky exoplanets are the new frontier."

Mark Clampin, Astrophysics Division director at NASA Headquarters in Washington, said: "Webb is bringing us closer and closer to a new understanding of Earth-like worlds outside our solar system, and the mission is only just getting started."