James Webb Telescope Confirms the Existence of Its First Exoplanet

The James Webb Space Telescope has added another accomplishment to its already impressive resume: Confirming the existence of an exoplanet.

The $10 billion telescope, which launched in December 2021, certified the discovery of a rocky world known as LHS 475 b, located some 41 light-years away from Earth in the constellation Octans.

LHS 475 b is an exoplanet, meaning it orbits a star other than the sun. Its size is nearly identical to Earth’s, measuring 99 percent of our home planet’s diameter.

Researchers already had a hunch that the planet existed because of past information from NASA’s Transiting Exoplanet Survey Satellite (TESS). Now, thanks to Webb, they know for sure.

“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,” says Mark Clampin, NASA’s astrophysics division director, in a statement.

Webb helped scientists glean additional insights into the exoplanet. They now know that LHS 475 b orbits around its host star—a red dwarf that’s much cooler than the sun—in just two days, making its year much shorter than one on Earth. The far-off world is closer to its host star than any planet in our solar system is to the sun, and it’s a few hundred degrees warmer than the Earth.

To study the toasty exoplanet, scientists used Webb’s Near-Infrared Spectrograph (NIRSpec), which can disperse an object’s light in a wavelength range of 0.6 to 5 microns into a spectrum. Studying the spectrum, in turn, can reveal information about the object’s physical properties.

As the exoplanet twice passed in front of its host star—or, made two so-called transits—Webb’s NIRSpec went to work, “easily and clearly” capturing the spectrum of light that had gone through the planet’s atmosphere, per NASA.

Led by Johns Hopkins University Applied Physics Laboratory (APL) astronomers Kevin Stevenson and Jacob Lustig-Yaeger, a team of researchers analyzed the spectrum in an attempt to determine whether the planet has an atmosphere and, if so, what it is made of. Webb was an ideal tool for the job, as it’s the only operating telescope that can help characterize the atmospheres of Earth-sized exoplanets like this one.

“The observatory’s data are beautiful,” says Erin May, an APL astrophysicist, in the 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 the planet’s atmosphere.”

Though they still don’t know if LHS 475 b has an atmosphere, they can rule out some possibilities. For one, they’ve determined the exoplanet can’t have an atmosphere made predominantly of methane.

It is possible, however, that its atmosphere consists entirely of carbon dioxide.

“Counterintuitively, a 100 percent carbon dioxide atmosphere is so much more compact that it becomes very challenging to detect,” says Lustig-Yaeger in the statement.

The scientists hope to obtain additional data this summer. And, with this successful first exoplanet discovery under its belt, Webb is likely to help make similar revelations in the future.

“With this telescope, rocky exoplanets are the new frontier,” says Lustig-Yaeger in the statement.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.