NASA’s James Webb telescope discovers its first Earth-sized exoplanet

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The James Webb Space Telescope has discovered its first new exoplanet, an Earth-sized rocky planet called LHS 475 b. The planet, which is only 41 light-years away, orbits very closely around a small, faint star, completing a full orbit in just two days.

The discovery, presented at the American Astronomical Society (AAS) meeting on Wednesday, Jan. 11, is notable because most exoplanets discovered are typically large gas giants, similar to Jupiter. It is more difficult for most telescopes to detect Earth-like planets because they are much smaller, less than a tenth of their diameter.

The planet orbits very closely around a small, faint star

Previous research with NASA’s Transiting Exoplanet Survey Satellite, another space telescope launched in 2018 specifically to search for exoplanets, had shown that there may be a planetary candidate in this system. JWST was able to confirm the presence of the planet based on observations in August and September 2022.

The fact that JWST has been able to detect this planet indicates that it will be able to identify more Earth-like planets in the future. And even more than that, it should be able to detect their atmospheres – something other telescopes can’t do with planets this size.

The ultimate goal of much current exoplanet research is to understand the atmospheres around exoplanets. To better understand whether certain planets are habitable, astronomers need to study their atmospheres, as this can greatly influence factors such as surface temperature.

“In the coming years, and eventually decades, the search for life on exoplanets will fundamentally depend on the detailed characterization of exoplanet atmospheres,” lead researcher Jacob Lustig-Yaeger of the Johns Hopkins University Applied Physics Laboratory said at the AAS meeting. “And the first step on this journey is simply detecting the presence of exoplanet atmospheres.”

“The search for life on exoplanets will fundamentally depend on the detailed characterization of exoplanet atmospheres.”

While JWST should be able to detect exoplanet atmospheres, the task remains a challenge. Exoplanets are much smaller than stars and emit much less light, so they are rarely directly detected. Instead, astronomers study host stars and look for slight anomalies in their brightness or motion that indicate the presence of a planet orbiting them.

Given these conditions, JWST will probably only be able to detect atmospheres from rocky planets orbiting very small stars called red dwarfs, Lustig-Yaeger explains. In some ways, that’s good for hunting habitable planets, since these rocky worlds are similar in size to Earth. However, these types of planets orbit much closer to their stars than Earth does around the sun, and are therefore much hotter. When a planet gets this close to its host star, its atmosphere can be wiped out by the heat and radiation from the star.

In the case of the recently discovered exoplanet LHS 475 b, JWST observed two transits (where the planet passes in front of its host star, causing a temporary and very small dip in the star’s brightness), both of which confirmed that the planet was present and enabled the team to work out its radius.

They also used a method called transmission spectroscopy to look at the atmosphere, and while they couldn’t confirm exactly what the atmosphere was, they were able to rule out several options. The findings show that the planet does not have a hydrogen-dominated atmosphere like Jupiter or an atmosphere of pure methane. It could possibly have a thick carbon dioxide atmosphere like Venus, or it could have no atmosphere at all – having had its atmosphere stripped away by its star.

“The data from the observatory is wonderful.”

“The data from the observatory is beautiful,” fellow researcher Erin May said in a statement. “The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet draw any firm conclusions about the planet’s atmosphere.”

The research team has planned another observation of the planet this summer using JWST, which should help them learn more. And the research shows how powerful JWST is as a tool for learning more about exoplanets: “Even though we do not detect an atmosphere in this case, our measurements meet the sensitivity requirements to detect the atmospheres of Earth-sized planets. . So it’s a really exciting time,” said Lustig-Yaeger. “We’re just beginning to scratch the surface of what’s possible with JWST.”

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