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Webb Finds Water Vapor, But From a Rocky Planet or Its Star?

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May 01, 2023 10:00AM (EDT)Release ID: 2023-120
Occupying the left two-thirds of the image is a foreground planet mostly in shadow. On the right side, a tan crescent shows subtle surface features. A thin, tenuous blue atmosphere lines the planet’s limb. On the right, a small red globe represents a red dwarf star. Its surface is mottled with small, dark spots resembling sunspots. Both planet and star are on a mostly black background speckled with hundreds of faint, distant stars.

Summary

More observations will be needed to determine if exoplanet GJ 486 b has an atmosphere.

GJ 486 b is about 30% larger than the Earth and three times as massive, which means it is a rocky world with stronger gravity than Earth. It orbits a red dwarf star in just under 1.5 Earth days. It is too close to its star to be within the habitable zone, with a surface temperature of about 800 degrees Fahrenheit. And yet, Webb observations show hints of water vapor.

The water vapor could be from an atmosphere enveloping the planet, in which case it would need to be continually replenished due to losses from stellar irradiation. But an equally likely possibility is that the water vapor is actually from the outer layer of the planet’s cool host star. Additional Webb observations will help answer the question: Can a rocky planet maintain, or reestablish, an atmosphere in the harsh environment near a red dwarf star?

Full Article

The most common stars in the universe are red dwarf stars, which means that rocky exoplanets are most likely to be found orbiting such a star. Red dwarf stars are cool, so a planet has to hug it in a tight orbit to stay warm enough to potentially host liquid water (meaning it lies in the habitable zone). Such stars are also active, particularly when they are young, releasing ultraviolet and X-ray radiation that could destroy planetary atmospheres. As a result, one important open question in astronomy is whether a rocky planet could maintain, or reestablish, an atmosphere in such a harsh environment. ...

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