NASA’s Webb Telescope confirms its first exoplanet

Based on new evidence from NASA’s James Webb Space Telescope, this illustration shows that the exoplanet LHS 475 b is rocky and almost exactly the same size as Earth. The planet revolves around its star in just two days, much faster than any other planet in the solar system. The researchers will continue to work this summer, making additional observations with Webb that they hope will allow them to definitively conclude whether the planet has an atmosphere. LHS 475 b is relatively close, 41 light-years away, in the constellation Octans.
Credits: Illustration: NASA, ESA, CSA, L. Hustak (STScI)

Researchers confirmed the finding of an exoplanet, a planet orbiting another star, using NASA’s James Webb Space Telescope for the first time. Formally classified as LHS 475 b, the planet is almost exactly the same size as Earth, clocking in at 99% of our planet’s diameter. The research team is led by Kevin Stevenson and Jacob Lustig-Yaeger, both of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The team chose to observe this target with Webb after carefully reviewing the targets of interest from NASA’s Transiting Exoplanet Survey Satellite (TESS), which hinted at the existence of this planet. Webb’s Near Infrared Spectrograph (NIRSpec) captured the planet easily and clearly with just two observations of its transit. “There is no doubt that the planet is there. Webb’s impeccable data validates this,” said Lustig-Yaeger. “The fact that it is also a small, rocky planet is impressive for the observatory,” Stevenson added.

“These first results from observing a rocky, Earth-sized planet open the door to many future possibilities for studying the atmospheres of rocky planets with Webb,” agreed Mark Clampin, director of the Astrophysics Division at NASA Headquarters. in washington. “Webb is bringing us ever closer to a new understanding of Earth-like worlds outside our solar system, and the mission is just beginning.”

Plot titled “Rocky exoplanet LHS 475 b, Atmosphere Composition, NIRSpec Bright Object Time Series Spectroscopy.”  The plot shows the transmission spectrum of the rocky exoplanet LHS 475 b, imaged using the bright object time series spectroscopy mode of Webb's NIRSpec instrument, with an illustration of the planet and its star in the background.

A flat line like this in a transmission spectrum can be exciting: it could tell us a lot about the planet. The researchers used the James Webb Space Telescope’s Near Infrared Spectrograph (NIRSpec) to observe the exoplanet LHS 475 b on August 31, 2022. As this spectrum shows, Webb did not observe a detectable amount of any element or any molecule. The data (white dots) are consistent with a featureless spectrum, which is representative of a planet with no atmosphere (yellow line). The purple line represents an atmosphere of pure carbon dioxide and is indistinguishable from a flat line at the current level of precision. The green line represents an atmosphere of pure methane, 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); Data 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)

Among all operational telescopes, only Webb is capable of characterizing the atmosphere of Earth-sized exoplanets. The team tried to assess what is in the atmosphere of this planet by analyzing its transmission spectrum. Although the data shows that it is a terrestrial planet the size of Earth, they do not yet know if it has an atmosphere. “The data from the observatory is beautiful,” said Erin May, also of the Johns Hopkins University Applied Physics Laboratory. “The telescope is so sensitive that it can easily detect a variety of molecules, but we cannot yet draw any definitive conclusions about the planet’s atmosphere.”

Although the team cannot conclude about what is present, they can definitely tell what is not present. “There are some terrestrial-type atmospheres that we can rule out,” Lustig-Yaeger explained. “It cannot have a dense methane-dominated atmosphere, similar to that of Saturn’s moon Titan.”

The team also notes that while the planet may not have an atmosphere at all, there are some atmospheric compositions that have not been ruled out, such as an atmosphere of pure carbon dioxide. “Counterintuitively, a 100% carbon dioxide atmosphere is much more compact, so much so that it becomes very difficult to detect,” said Lustig-Yaeger. Even more precise measurements are required for the team to be able to distinguish an atmosphere of pure carbon dioxide from no atmosphere at all. The researchers are scheduled to obtain additional spectra with upcoming observations this summer.

Webb also revealed that the planet is a few hundred degrees warmer than Earth, so if clouds are detected, researchers may conclude that the planet is more like Venus, which has an atmosphere of carbon dioxide. carbon and is perpetually shrouded in thick clouds. “We are at the forefront of the study of small, rocky exoplanets,” said Lustig-Yaeger. “We’ve only just begun to scratch the surface of what their atmospheres might look like.”

The researchers also confirmed that the planet completes one orbit in just two days, information that was revealed almost instantly by Webb’s precise light curve. 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 researchers project it could still have an atmosphere.

Plot titled “Rocky exoplanet LHS 475 b, Transit light curve, NIRSpec Bright Object Time Series Spectroscopy.”  Behind the graphic is an illustration of the planet and its star.

How do researchers detect a distant planet? Observing the changes in light as it orbits its star. A light curve from NASA’s James Webb Space Telescope Near Infrared Spectrograph (NIRSpec) shows the change in brightness of the LHS 475 star system over time as the planet transited its star on August 31. on 2022. LHS 475 b is a rocky, Earth-sized exoplanet orbiting a red dwarf star about 41 light-years away in the constellation Octans. The planet is extremely close to its star, completing one orbit in two Earth days. Confirmation of the planet was made possible by Webb’s data.
Credits: Illustration: NASA, ESA, CSA, L. Hustak (STScI); Data 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 researchers’ findings have opened up the possibilities of identifying Earth-sized planets orbiting smaller red dwarf stars. “Confirmation of this rocky planet highlights the precision of the mission’s instruments,” Stevenson said. “And this is only the first of many discoveries it will make,” Lustig-Yaeger agreed. “With this telescope, rocky exoplanets are the new frontier.”

LHS 475 b is relatively close, just 41 light-years away, in the constellation Octans (Latin for the Octant).

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

The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve the mysteries of our solar system, see beyond distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place in it. Webb is an international program run by NASA with its partners: the European Space Agency (ESA) and the Canadian Space Agency (CSA).

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