The James Webb Space Telescope just identified its first exoplanet

The near-Earth discovery is an 'impressive' find, astronomers say.

By Laura Baisas

Posted on Jan 12, 2023

Exoplanet LHS 475 b and its star detected by the James Webb Space Telescope in an artist's rendition
An illustration of Exoplanet LHS 475 b and its star. NASA, ESA, CSA, L. Hustak (STScI)

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After launching on Christmas Day 2021, the James Webb Space Telescope (JWST) has continued to dazzle us with its data and discoveries. Now, the multi-mirrored space observatory has identified its first new exoplanet named LHS 475 b. At only 41 light years away from Earth in the constellation Octans, the exoplanet is about 99 percent of our world’s diameter.

After reviewing the targets of interest from NASA’s Transiting Exoplanet Survey Satellite, the team from Johns Hopkins University Applied Physics Laboratory (APL) in Maryland honed in on hints of the exoplanet’s existence with JWST. With only two transit observations (when an exoplanet passes in front of its star), JWST’s Near-Infrared Spectrograph (NIRSpec) captured the distant celestial body clearly. “There is no question that it’s there. Webb’s pristine data validate it,” said Jacob Lustig-Yaeger, an astronomer and astrobiologist at APL, in a statement.

[Related: James Webb Space Telescope reconstructed a ‘star party,’ and you’re invited.]

“The fact that it is also a small, rocky planet is impressive for the observatory,” Kevin Stevenson, an astronomer also from APL, added in the statement,

JWST can characterize the atmosphere of exoplanets that are close to Earth’s size. The team tried to assess LHS 475 b’s atmosphere by analyzing its transmission spectrum. According to NASA, “When starlight passes through the atmosphere of a planet some of the light is absorbed by the atmosphere and some is transmitted through it. The dark lines and dim bands of light in a transmission spectrum correspond to atoms and molecules in the planet’s atmosphere. The amount of light that is transmitted also depends on how dense the atmosphere is and how warm it is.”

Transmission spectrum graph from James Webb Space Telescope's first new confirmed exoplanet. Shows waves and dots built from NASA and Johns Hopkins data.
As this transmission spectrum shows, JWST did not observe a detectable quantity of any element or molecule on exoplanet LHS 475 b. The data (white dots) are consistent with a featureless spectrum representative of a planet that has no atmosphere (yellow line). The purple line represents a pure carbon dioxide atmosphere and is indistinguishable from a flat line at the current level of precision. The green line represents a pure methane atmosphere, which is not favored since if methane were present, it would be expected to block more starlight at 3.3 microns. Illustration: NASA, ESA, CSA, L. Hustak (STScI); Science: K. Stevenson, J. Lustig-Yaeger, E. May (Johns Hopkins University Applied Physics Laboratory), G. Fu (Johns Hopkins University), and S. Moran (University of Arizona).

The data shows that the exoplanet is an Earth-sized terrestrial (not water covered) world, but it is not known if it has an atmosphere.

“The observatory’s data are beautiful,” noted Erin May, an astrophysicist at APL, in a statement. “The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet make any definitive conclusions about LHS 475 b’s atmosphere.”

That said, the team can definitely say 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.”

While it is possible that the exoplanet doesn’t have an atmosphere, some environmental conditions haven’t been ruled out. One of those conditions is a pure carbon dioxide atmosphere. “Counterintuitively, a 100-percent carbon dioxide atmosphere is so much more compact that it becomes very challenging to detect,” said Lustig-Yaeger. To distinguish a pure carbon dioxide atmosphere from no atmosphere at all will take even more precise measurements that the team is scheduled to receive this summer.

[Related on PopSci+: There is no Planet B.]

JWST also revealed that LHS 475 b is much warmer than Earth. If clouds are detected, it could be more like Venus, which does have a carbon dioxide atmosphere. It also completes an orbit in just two days, which the JWST’s precise light curve from the telescope’s NIRSpec was able to reveal.

Findings like JWST’s also open up possibilities of pinpointing Earth-sized exoplanets orbiting smaller red dwarf stars. “This confirmation highlights the precision of the mission’s instruments,” said Stevenson.

In addition to LHS 475 b, NASA has confirmed 5,000-plus exoplanets with its many deep-space searching tools. The roster is incredibly diverse, with some looking like Mars’s pebbly terrain and others like Jupiter-esque gas giants. Some of them orbit two stars at once, while others orbit long-dead stars. It is very likely that there are hundreds of billions of exoplanets in the Milky Way galaxy alone. JWST will be able to tell scientists even more about these other worlds.

“We have barely begun scratching the surface of what their atmospheres might be like. And it is only the first of many discoveries that it will make,” stated Lustig-Yaeger. “With this telescope, rocky exoplanets are the new frontier.”

Correction (January 19, 2023): The story initially said that when an exoplanet “transits,” it passes in front of its moon, which was incorrect. It passes in front of its star.