Heavy water detected in the atmosphere of exoplanet WASP-39 b

Star system: WASP-39 | Distance from the Sun: 702 light years

The atmosphere of the hot Jupiter exoplanet WASP-39b contains detectable amounts of deuterated water, also known as heavy water. This molecule, denoted as HDO, consists of one hydrogen atom, one oxygen atom, and one deuterium atom—a heavier isotope of hydrogen containing an extra neutron. This finding provides critical insight into the chemical history and evolution of this distant planet, which is located 702 light-years from our Sun.

The research identified a deuterium-to-hydrogen ratio in water of approximately 4.0 times 10 to the power of negative three. This value was determined by analyzing high-precision transmission spectra collected by the James Webb Space Telescope. Transmission spectroscopy works by observing the light of the host star as it filters through the planet's atmosphere during a transit, allowing specific chemical fingerprints to be identified based on how they absorb different wavelengths of light.

This deuterium-to-hydrogen ratio is significantly higher than that observed in our own solar system's gas giants, such as Jupiter or Saturn. The enrichment suggests that WASP-39b may have formed from water-rich materials gathered far from its star, or that the planet's atmosphere has undergone intense chemical processing, such as atmospheric escape or photochemical reactions, which preferentially removed lighter hydrogen atoms over time.

Key findings
- Evidence of heavy water (HDO) identified in the atmosphere of WASP-39b.
- Measured deuterium-to-hydrogen ratio in water is 4.0 (+1.3/-1.1) times 10 to the power of negative three.
- Observed ratio exceeds values typically found in solar system gas giants.
- Potential evidence of formation processes involving water-rich material or atmospheric chemical evolution.

Scientific study

Atmospheric retrieval evidence for water isotopologue HDO on exoplanet WASP-39b (external link)