Researchers measure light emitted from Neptune’s atmosphere for the first time


Researchers measure light emitted from Neptune's atmosphere for the first time

UM graduate student Isaac Malsky, a study co-author, ran 3D models of the planet, testing models with and without clouds and haze, to see how these aerosols shape the planet’s thermal structure and help interpret the data. Image credit: NASA/JPL-Caltech/R. Hurt (IPAC).

For more than a decade, astronomers have been trying to get a closer look at GJ 1214b, an exoplanet 40 light-years from Earth. Their biggest obstacle is a thick layer of haze covering the planet, shielding it from the eyes of space telescopes, and hindering efforts to study its atmosphere.

NASA’s new James Webb Space Telescope (JWST) has solved this problem. Infrared technology allows the telescope to see planetary bodies and features that would otherwise be obscured by haze, clouds or space dust, aiding astronomers in their search for habitable planets and early galaxies.

A team of researchers used JWST to monitor GJ 1214b atmospheres It measures the heat it emits while orbiting its host star. The results published in the journal nature On May 10, 2023, it marks the first time anyone has detected light emitted from one of the sub-Neptune exoplanets – a class of planets Which is larger than Earth but smaller than Neptune.

Although GJ 1214b is too hot to live in, researchers have discovered that its atmosphere most likely contains water vapor — perhaps even significant amounts — and consists primarily of molecules heavier than hydrogen. Their findings mark a turning point in the study of sub-Neptunian planets such as GJ 1214b, said Eliza Kimpton, a professor of astronomy at the University of Maryland and lead author of the study.

“I have sought to understand GJ 1214b for more than a decade,” Kempton said. “When we received the data for this paper, we could see the light from the planet completely disappear as it went behind its host star. This hasn’t been seen before for this planet or for any other planet in its class, so JWST is really delivering on its promise.”

new light

Sub-Neptunees are the most common type of planet in the Milky Way, although none are found in our solar system. Despite the hazy atmosphere of GJ 1214b, Kimpton and her colleagues decided that the planet was still their best opportunity to observe Neptune’s subatmosphere because of its bright but small host star.

In their paper, the researchers measured infrared light That emitted GJ 1214b over a period of about 40 hours – the time it takes the planet to orbit its star. As day turns into night, the amount of heat transferred from one side of a planet to the other depends largely on the components of its atmosphere. Known for observing the phase curve, this research method opened a new window into the planet’s atmosphere.

“The JWST operates at longer wavelengths than previous observatories, which gives us access to the heat emitted by the planet and allows us to create a map of the planet’s temperature,” Kempton said. “We finally get GJ 1214b in a new light.”

By measuring motion and temperature variability, the researchers determined that GJ 1214b does not have a hydrogen-dominated atmosphere.

Potential water world?

Astronomers have long been interested in the question of whether GJ 1214b contains water. Previous observations by NASA’s Hubble Space Telescope have suggested that GJ 1214b could be a watery world – a loose term for any planet with a large amount of water.

The latest JWST data revealed traces of water, methane, or a combination of the two. This material corresponds to an accurate absorption of visible light in wavelength range Noted by JWST. More studies will be needed to determine the exact composition of the planet’s atmosphere, but Kempton said the evidence is still consistent with the possibility of significant amounts of water.

“GJ 1214b, based on our observations, could be a watery world,” Kempton said. “We think we’re detecting water vapor, but it’s a challenge because the absorption of water vapor overlaps the absorption of methane, so we can’t say with 100% certainty that we’ve detected Water vapor Not methane. However, we see this evidence in both hemispheres, which increases our confidence that water is indeed there.”

Think about the results

The researchers made another surprising discovery in their study: GJ 1214b is incredibly reflective. The planet wasn’t as hot as expected, which tells the researchers that something in the atmosphere is reflecting the light.

There’s plenty of room for follow-up studies, Kempton said, including studies that take a closer look at the high-altitude aerosols that make up the haze — or possibly clouds — in GJ 1214b’s atmosphere. Previously, researchers thought it might be a dark, soot-like substance that absorbs light. However, the discovery that an exoplanet is a reflection of planets raises new questions.

“Whatever makes the fog or the clouds is not what we would have expected,” Kempton said. “It’s bright and reflective and that’s baffling and surprising.” “This will point us towards a lot of additional studies to try to understand what those risks might be.”

more information:
Eliza Kempton et al, A mineral-rich reflective atmosphere of GJ 1214b from a JWST phase curve, nature (2023). DOI: 10.1038/s41586-023-06159-5.

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