Astronomers Confirms Earth-Sized Planet in the habitable zone of a red dwarf


Astronomers using the NASA/ESA/CSA James Webb Space Telescope have validated the discovery of a warm, 0.99 Earth-radius exoplanet interior to the habitable zone of the red dwarf LHS 475.

LHS 475 is an M3.5-type dwarf star located 41 light-years away in the constellation of Octans.

Also known as Gliese 4102, L 22-69, LTT 7606 or TOI-910, the star is only 28% the size of the Sun.

LHS 475 hosts at least one planet, which was previously classified as a planet candidate by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission.

Named LHS 475b, this planet is 99.1% the size of Earth, and has an orbital period of 2.03 days.

The alien world is likely to be tidally locked, with a permanent dayside facing its host star.

“We selected the LHS 475 system as one of several nearby M-dwarf systems with known or candidate rocky planets,” said Dr. Jacob Lustig-Yaeger, an astronomer at the Johns Hopkins University Applied Physics Laboratory, and his colleagues.

Webb’s Near-Infrared Spectrograph (NIRSpec) captured LHS 475b easily and clearly with only two transit observations.

“There is no question that the planet is there. Webb’s pristine data validate it,” Dr. Lustig-Yaeger said.

“The fact that it is also a small, rocky planet is impressive for the observatory,” added Dr. Kevin Stevenson, also from the Johns Hopkins University Applied Physics Laboratory.

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

“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.”

Among all operating telescopes, only Webb is capable of characterizing the atmospheres of Earth-sized exoplanets.

The astronomers attempted to assess what is in the planet’s atmosphere by analyzing its transmission spectrum.

Although the data show that this is an Earth-sized terrestrial planet, they do not yet know if it has an atmosphere.

“The observatory’s data are beautiful,” said Dr. Erin May, also from 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 make any definitive conclusions about the planet’s atmosphere.”

Although the authors can’t conclude what is present, they can definitely say what is not present.

“There are some terrestrial-type atmospheres that we can rule out. It can’t have a thick methane-dominated atmosphere, similar to that of Saturn’s moon Titan,” Dr. Lustig-Yaeger said.

The researchers also note that while it’s possible the planet has no atmosphere, there are some atmospheric compositions that have not 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 challenging to detect,” Dr. Lustig-Yaeger said.

Webb also revealed that LHS 475b is a few hundred degrees warmer than Earth, so if clouds are detected, it may lead the scientists to conclude that the planet is more like Venus, which has a carbon dioxide atmosphere and is perpetually shrouded in thick clouds.

“We’re at the forefront of studying small, rocky exoplanets. We have barely begun scratching the surface of what their atmospheres might be like,” Dr. Lustig-Yaeger said.


J. Lustig-Yaeger et al. 2023. A JWST transmission spectrum of a nearby Earth-sized exoplanet. Nature Astronomy, in press; arXiv: 2301.04191