Webb discovers its 1st exoplanet

Webb discovers its 1st exoplanet: Illustration of a planet and its star on a black background. The rocky planet is large, foreground, in the center. And the star is smaller, in the background.
Artist’s concept of the new exoplanet discovered by Webb. It’s been labeled LHS 475 b. Image via ESA/ NASA/ CSA/ L. Hustak (STScI).

Originally posted by the European Space Agency on January 11, 2022. Edits by EarthSky.

Webb discovers its 1st exoplanet

More news from the American Astronomical Society meeting, happening this week in Seattle. Astronomers said yesterday (January 11, 2023) that – for the first time – they’ve confirmed an exoplanet, a planet orbiting a distant star, using the Webb space telescope. The mighty telescope went into orbit and began operating in 2022. The planet has been labeled LHS 475 b. It’s thought to be rocky and Earth-sized (99% of Earth’s diameter). The planet whips around its star in just 2 days, far faster than any planet in our solar system. It’s only 41 light-years away, in the direction of the south polar constellation Octans the Octant.

Kevin Stevenson and Jacob Lustig-Yaeger, both of the Johns Hopkins University Applied Physics Laboratory, led the research team. The team chose to observe this target with Webb after carefully reviewing data from NASA’s Transiting Exoplanet Survey Satellite (TESS) which hinted at the planet’s existence. Webb’s Near-Infrared Spectrograph (NIRSpec) captured the planet easily and clearly with only two transit observations. Lustig-Yaeger said in a statement:

There is no question that the planet is there. Webb’s pristine data validate it. The fact that it is also a small, rocky planet is impressive for the observatory.

Mark Clampin, Astrophysics Division director at NASA Headquarters in Washington, agreed, saying:

These first observational results from an Earth-sized, rocky planet open the door to many future possibilities for studying rocky planet atmospheres with Webb … And the mission is only just getting started.

Planet on the background, to the right. Graphic on the top with different measurements and timings.
How do researchers spot a distant planet? By observing the changes in light as it orbits its star. A light curve from the NASA/ ESA/ CSA 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. The graphic shows the change in relative brightness of the star-planet system spanning 3 hours. The spectrum shows that the brightness of the system remains steady until the planet begins to transit the star. It then decreases, representing when the planet is directly in front of the star. The brightness increases again when the planet is no longer blocking the star, at which point it levels out. Image via NASA/ ESA/ CSA/ L. Hustak et al.

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What makes Webb so powerful

Among all operating telescopes, only Webb is capable of characterizing the atmospheres of Earth-sized exoplanets. The team 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. Erin May, also of Johns Hopkins, said:

The observatory’s data are beautiful. The telescope is so sensitive that it can easily detect a range of molecules. But we can’t yet draw any definitive conclusions about the planet’s atmosphere.

Although the team can’t conclude what is present, they can definitely say what is not present. Lustig-Yaeger said:

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.

The team also notes 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. Lustig-Yaeger explained:

Counterintuitively, a 100% carbon dioxide atmosphere is so much more compact that it 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. The researchers are scheduled to obtain additional spectra with further observations this summer.

Maybe more like Venus?

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, which has a carbon dioxide atmosphere and is perpetually shrouded in thick cloud. Lustig-Yaeger said:

We’re at the forefront of studying small, rocky exoplanets. We have barely begun scratching the surface of what their atmospheres might be like.

The researchers also confirmed that the planet completes an orbit in just two days, information that was almost instantaneously revealed 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 our sun, so the researchers project it still could support an atmosphere.

The researchers’ findings have opened up the possibility of pinpointing Earth-sized planets orbiting smaller red dwarf stars. Lustig-Yaeger agreed, saying:

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.

With this telescope, rocky exoplanets are the new frontier.

Bottom line: Webb discovers its first exoplanet! And – speaking this week at the American Astronomical Society meeting in Seattle – astronomers are excited.


January 12, 2023

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