James Webb discovers exoplanet with helium tail

Observations with the James Webb Space Telescope have revealed a strange world that refutes ideas about the chemistry of the atmosphere, and is also a tail formed as a result of escape helium.

One of the first signs of scientific power James Webb occurred last summer when he focused on the passage of an exoplanet the size of Jupiter and the mass of Saturn called ShAP-P-18b.

astronomical surprises

A team led by Guangwei Fu (Johns Hopkins University) detected several molecules in the planet’s upper atmosphere using the Near Infrared Imaging Instrument and Slitless Spectrograph (NIRISS), but what they didn’t find was more surprising.

The first of these surprises was the takeover by the firm heliumbut not around the planet: instead, their results show that ShAP-P-18b dragging a weak tail helium which escapes. Similar features have been observed on other planets, but this one was so subtle that ground-based observatories did not notice it.

The second surprise concerned a molecule not displaced from the planet, and perhaps not at all. One of the main motives to focus on ShAP-P-18b it is its position in the corner of the parameter space that is extremely useful for modellers working on the methane puzzle.

paradigm shift

Hot planets with surface temperatures above 726 °C are not expected to release methane into their atmospheres, as thermodynamics favor other species under these extreme conditions. However, simple models suggest that any world colder than this should show signs of absorption caused by methane molecules in the upper atmosphere intercepting photons at a certain wavelength.

However, oddly enough, this prediction did not come true in previous studies. When searching for several planets that should contain methane, none were found. This contradiction required further analysis: were the assumptions of the models incorrect or was there something strange in the first worlds studied? At an equilibrium temperature of 526°C, ShAP-P-18b it was the perfect target to help move the needle one way or the other.

Fu and colleagues, who published their study in Letters from an astrophysical journal, did not definitively detect methane, delving into the puzzle of model mismatch. Models assuming the atmosphere is in chemical equilibrium failed to reproduce the combination of non-methane and da-water observed in the data, suggesting additional mechanisms to remove the expected gas. And more surprisingly, other models that did not assume equilibrium also did not choose to include methane in the final fit rather than exclude it entirely. (Europe Press)

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