NASA’s Webb confirms its first exoplanet

The planet is almost exactly the same size as our own.

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Using NASA’s James Webb Space Telescope, scientists confirmed an exoplanet orbiting another star for the first time. The exoplanet LHS 475 b is almost earth-sized and a few hundred degrees warmer than Earth.

Webb also revealed that- if clouds are detected on planets, it may lead to the conclusion that the planet is more like Venus, which has a carbon dioxide atmosphere and is perpetually shrouded in thick clouds. It is relatively close in the constellation Octans at only 41 light-years away.

Scientists decided to look at the targeted planet using Webb after NASA’s Transiting Exoplanet Survey Satellite (TESS) hinted at its existence. Webb’s Near-Infrared Spectrograph (NIRSpec) captured the planet easily and clearly with only two transit observations. The fact that it is also a small, rocky planet is impressive for the observatory.

flat line in a transmission spectrum
A flat line in a transmission spectrum, like this one, can be exciting – it can tell us a lot about the planet. Researchers used NASA’s James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) to observe exoplanet LHS 475 b on August 31, 2022. 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). 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. Credits: 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)

Mark Clampin, Astrophysics Division director at NASA Headquarters in Washington, said, “These first observational results from an Earth-size, rocky planet open the door to many future possibilities for studying rocky planet atmospheres with Webb. 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.”

Jacob Lustig-Yaeger of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said, “Although the team can’t conclude what is present, they can say what is not. There are some terrestrial-type atmospheres that we can rule out. It can’t have a thick methane-dominated atmosphere, similar to Saturn’s moon Titan.”

“There are some atmospheric compositions that have yet to be ruled out, such as a pure carbon dioxide atmosphere. Counterintuitively, a 100% carbon dioxide atmosphere is much more compact and becomes very challenging to detect. Even more precise measurements are required for the team to distinguish a pure carbon dioxide atmosphere from no atmosphere at all. We are scheduled to obtain additional spectra with upcoming observations this summer.”

A light curve from NASA’s James Webb Space Telescope’s Near-Infrared Spectrograph
How do researchers spot a distant planet? By observing the changes in light as it orbits its star. 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 b is a rocky, Earth-sized exoplanet that orbits a red dwarf star roughly 41 light-years away, in the constellation Octans. The planet is extremely close to its star, completing one orbit in two Earth-days. The planet’s confirmation was made possible by Webb’s data. Credits: 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)

Webb’s precise light curve revealed that the planet orbits its star within two days. Although 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 project it still could have an atmosphere.

Kevin Stevenson from Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said“This rocky planet confirmation highlights the precision of the mission’s instruments. 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, Jan. 11, 2023.

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