James Webb Confirms Its First Exoplanet

The James Webb Space Telescope (JWST) has recently confirmed the presence of an exoplanet, a planet that orbits another star other than the Sun. What was classified as LHS 475 b, the planet is almost the same size as our own, clocking in at 99% of Earth’s diameter.

The research team is led by Kevin Stevenson and Jacob Lustig-Yaeger, both from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. The team chose to observe this target with Webb after carefully examining data from NASA’s Transiting Exoplanet Survey Satellite (TESS) which indicated the planet’s existence.

Webb’s Near-Infrared Spectrograph (NIRSpec) captured the planet clearly with only two transit observations. “There is no question that the planet is there. Webb’s fresh data validates it,” said Lustig-Yaeger. “The fact that it is also a small, rocky planet is impressive for the observatory,” Stevenson added.

“These first observational results from an Earth-sized, rocky planet open the door to many future possibilities for studying rocky planet atmospheres with Webb,” agreed Mark Clampin, Astrophysics Division director at NASA Headquarters in Washington. “Webb is bringing us closer and closer to a new understanding of Earth-like worlds outside the Solar System, and the mission is only just getting started.”

Among all operational telescopes, Webb is currently the only one capable of distinguishing the atmospheres of Earth-sized exoplanets. The team attempted to assess what is in the planet’s atmosphere by analyzing its transmission spectrum, as besides its similarities with Earth in size, it’s still unknown if it has an atmosphere.

“The observatory’s data are beautiful,” said Erin May, also of the Johns Hopkins University Applied Physics Laboratory. “The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet draw definitive conclusions about the planet’s atmosphere”, she explained in an ESA briefing.

Although it is unknown what can be found on said planet, it is easy to say what is not present. Lustig-Yaeger explains: “There is some terrestrial-type atmosphere that we can rule out. (...) It can’t have a thick methane-dominated atmosphere, similar to Saturn’s moon Titan.”

The team also notes that while the planet may have no atmosphere, some atmospheric compositions haven’t been ruled out, such as a pure carbon dioxide atmosphere. “Counterintuitively, a 100% carbon dioxide atmosphere is so much more compact that it becomes very difficult to detect,” said Lustig-Yaeger. Better measurements are needed for the team to characterise a pure carbon dioxide atmosphere from a no atmosphere at all. The researchers are scheduled to obtain additional spectra with further observations this summer.

Webb also revealed that the planet is a few hundred degrees warmer than Earth, so if clouds are detected it may lead the researchers to conclude that the planet is more like Venus, our neighbouring planet, which has a carbon dioxide atmosphere and is perpetually shrouded in thick clouds.

The researchers have also confirmed that the planet completes an orbit in just two days, information that was almost instantaneously revealed by Webb’s precise light curve. The discovered exoplanet is relatively close to home, as LHS 475 b is located 41 light-years away from the Solar System, deep in the constellation Octans. Although LHS 475 b is closer to its star than any planet in the Solar System, its red dwarf star is less than half the temperature of the Sun, and as such, researchers estimate that it could support an atmosphere.

The researchers’ discoveries have opened up the possibility of pinpointing 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.”

The team’s results were presented at a press conference of the American Astronomical Society (AAS) on Wednesday, January 11, 2023.