James Webb telescope detects ammonia in atmosphere of exoplanet HATS-6b

September 27, 2026 at 06:06 PM2 min

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Astronomers using the James Webb Space Telescope detected water, methane, and ammonia in the atmosphere of HATS-6b, a gas giant 500 light-years from Earth. The planet's temperature appears to be around 120°C, far below the predicted 425°C. The findings, published in the Astronomical Journal, raise questions about how gas giants form around small M-dwarf stars.

Key Facts

The James Webb Space Telescope detected water, methane, and ammonia in the atmosphere of HATS-6b, a gas giant 500 light-years from Earth.
HATS-6b orbits an M-dwarf star every three days and is roughly the size of Jupiter.
Preliminary analysis suggests the planet's temperature is about 120°C, compared with the predicted 425°C.
The ammonia detection is only the second time the molecule has been found on a distant world using transmission spectroscopy.
The findings were published in the Astronomical Journal by a team led by the University of Maryland.

Atmospheric Composition

Using the James Webb Space Telescope, a team led by the University of Maryland detected water, methane, and ammonia in the atmosphere of HATS-6b. The ammonia was identified through transmission spectroscopy, which observes starlight passing through the planet's atmosphere during transit. This marks only the second detection of ammonia on a distant world using this method. Nitrogen-bearing molecules like ammonia are more common on cooler planets, supporting the idea that worlds around M-dwarfs form a chemically distinct population.

Temperature Anomaly

Standard calculations predicted HATS-6b would be heated to 425°C due to its proximity to its star. Preliminary analyses by the researchers instead indicate a temperature closer to 120°C. If the planet is indeed that cool, something must be reflecting a large amount of starlight back into space before it can heat the atmosphere. The most likely explanation is dense clouds and haze enveloping the planet, similar to Venus.

Formation Puzzle

HATS-6b is roughly the size of Jupiter and completes an orbit every three days around an M-dwarf star. Theory suggests such small stars lack enough material or time to create planets of this size. Lead author Giannina Guzman Caloca said the existence of HATS-6b is interesting because, based on available data, it should not be possible. Astronomers know of only about 40 such anomalous planets, and HATS-6b is one of seven being studied under the GEMS program.