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Astrophysics

Atmospheric retrieval evidence for water isotopologue HDO on exoplanet WASP-39b

Fabian Gruebel, Karan Molaverdikhani

Featured August 5, 2026

Original Paper

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Simply

Scientists used the powerful James Webb Space Telescope to find heavy water (HDO) on a distant planet, WASP-39 b, showing it has much more heavy hydrogen than our own gas giants, which tells us about its birth story.

In depth
This study provides the first detection of deuterated water (HDO) in an exoplanet's atmosphere, WASP-39 b, using James Webb Space Telescope data. By employing an atmospheric retrieval framework, the authors determined the planet's water deuterium-to-hydrogen (D/H) ratio, which is significantly higher than Solar System gas giants, offering new insights into its formation or atmospheric evolution.

Key Takeaways

  • 1
    The paper presents the first atmospheric retrieval evidence for deuterated water (HDO) on an exoplanet, WASP-39 b, utilizing JWST observations.
  • 2
    The inferred deuterium-to-hydrogen (D/H) ratio in WASP-39 b's water is substantially higher than Solar System gas giants, suggesting unique formation pathways or atmospheric escape processes.
  • 3
    This detection, achieved through a Bayesian atmospheric retrieval framework, establishes a new method for tracing the chemical history and origin of exoplanetary water.

Conceptual Flow

HIGH LEVEL
1
Methodology: How was it done?

Scientists used a computer model to guess what the planet's air is made of, then checked if their guess matched the light signals from the telescope.

Telescope Light Data
Planet Air Model
Compare & Adjust
Best Fit Air Recipe
2
Results: What did they find?

They found a special kind of water on the planet, and it has a lot more heavy hydrogen than expected, like water from very old space clouds or rocky planets.

Planet's Water
Measure Heavy Hydrogen
High Heavy Hydrogen Ratio

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