How James Webb peers into the atmospheres of far-off exoplanets

We’re entering a latest period of exoplanet astronomy, with a recent announcement that the James Webb Space Telescope has detected its first exoplanet. The promise of Webb is that it can have the ability to not only spot exoplanets but additionally study their atmospheres, which might mark a significant step forward in exoplanet science.

Studying exoplanets is incredibly difficult because they’re generally far too far-off and too small to be observed directly. Very occasionally, a telescope is in a position to directly image an exoplanet, but more often than not researchers must infer that a planet is present by taking a look at the star around which it orbits. There are several methods for detecting planets based on their effects on a star, but one of the crucial commonly used is the transit method, during which a telescope observes a star and appears for a really small dip in brightness which happens when a planet passes between the star and us. That is the strategy Webb used to detect its first exoplanet, named LHS 475 b.

Based on latest evidence from the NASA/ESA/CSA James Webb Space Telescope, this illustration shows the exoplanet LHS 475 b. It’s rocky and almost precisely the identical size as Earth. The planet whips around its star in only two days, far faster than any planet within the Solar System. NASA, ESA, CSA, L. Hustak (STScI)

The large aim, though, is for Webb to detect exoplanet atmospheres. The researchers were in a position to gather some data on the newly detected planet’s atmosphere and to rule out some possibilities, but they aren’t yet in a position to determine the precise composition of its atmosphere. That’s because as difficult as it might be to detect an exoplanet, studying its atmosphere is even harder.

The way in which Webb does that is by utilizing a way called transit spectroscopy. Like using the transit method to detect an exoplanet, studying its atmosphere also relies on the planet passing in front of its star (called a transit). When the planet is in front of the star, a small amount of sunshine coming from the star will go through the planet’s atmosphere. If scientists can hone in on that light and split it into different wavelengths, they’ll see which wavelengths are missing — indicating which wavelengths have been absorbed by something within the atmosphere. We all know what chemicals absorb at which wavelengths, so this information can show what the atmosphere consists of.

Nonetheless, attempting to piece together information from a transmission spectrum is complicated as the share of sunshine being blocked is so low, at around 0.1% of the star’s brightness. And keep in mind, this can be a star situated 41 light-years away. In case you have a look at the transmission spectrum of the recently detected planet, shown below, you possibly can see the information points in white.

This transmission spectrum of the rocky exoplanet LHS 475 b was captured by Webb’s NIRSpec instrument on August 31, 2022. This transmission spectrum of the rocky exoplanet LHS 475 b was captured by Webb’s NIRSpec instrument on August 31, 2022. A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere because it moves in front of the star to the unfiltered starlight detected when the planet is beside the star. Each of the 56 data points on this graph represents the quantity of sunshine that the planet blocks from the star at a special wavelength of sunshine. ILLUSTRATION: NASA, ESA, CSA, Leah Hustak (STScI) SCIENCE: Kevin B. Stevenson (APL), Jacob A. Lustig-Yaeger (APL), Erin M. May (APL), Guangwei Fu (JHU), Sarah E. Moran (University of Arizona)

The coloured lines are possible models of what the atmosphere could possibly be like, and the researchers search for the road with the most effective fit. On this case, you possibly can see that the methane atmosphere, shown in green, clearly isn’t correct, in order that’s how the researchers know the planet doesn’t have a methane atmosphere. Nevertheless it could haven’t any atmosphere (shown in yellow, labeled as featureless) or a carbon dioxide atmosphere. There isn’t enough data to say definitively, though the researchers plan to make more observations with Webb later this yr which should give them more data.

Though we are able to’t make certain concerning the atmosphere of this exoplanet yet, this research shows how Webb should have the ability to research exoplanet atmospheres someday soon. “We’re on the forefront of studying small, rocky exoplanets,” said lead researcher Jacob Lustig-Yaeger of the Johns Hopkins University Applied Physics Laboratory in an announcement. “We’ve got barely begun scratching the surface of what their atmospheres is perhaps like.”

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