A unique planet called GJ 9827 d lies almost 100 lightyears away. It is roughly twice the size of Earth and has an atmosphere primarily composed of water vapor.
Using data from the James Webb Space Telescope, astronomers have discovered a planet like this for the first time. This planet is mainly made of hot water vapor, making it a ‘steam world’ and supportive of life. Despite its unhabitability, astronomers are keen to study its unique atmosphere. Its unique atmosphere provides valuable insights for scientists studying other small planets and their potential to host life.
The team used transmission spectroscopy to determine GJ 9827 d’s atmospheric composition. Most exoplanets have atmospheres enriched in the lightest elements, but GJ 9827 d is the first planet with an atmosphere enriched in heavy molecules.
According to U-M astrophysicist and NASA Sagan Fellow Ryan MacDonald, the broader quest for life attracts many researchers to this field. With the James Webb Space Telescope (JWST), scientists have an exceptional tool for making discoveries.
NASA Sagan Fellow Ryan MacDonald said, “Even with JWST’s early observations in 2022, researchers were uncovering new information about the atmospheres of faraway gas giants.”
Studying the atmospheres of light gases like hydrogen is much easier than examining those with heavier molecules, like the water vapor found on GJ 9827 d.
Now, we are starting to explore what these intriguing worlds—between the sizes of Earth and Neptune—are made of, as we don’t have any similar examples in our solar system. “This is an important step toward detecting atmospheres on potentially habitable exoplanets in the future,” he said.
The U-M team was one of two groups that worked separately to determine what atmospheric composition matched the observed spectrum. At U-M, Raul performed the atmospheric analysis using software created by MacDonald. This process, called atmospheric retrieval, involved Raul creating millions of model atmospheres before focusing on the steam world explanation.
This means Raul was among the first to find direct evidence that steam worlds exist.
“It was a very surreal moment,” said Eshan Raul, now pursuing his doctorate at the University of Wisconsin-Madison. “We were specifically looking for water worlds because we thought they could exist. If these are real, you wonder what else might be out there.”
Journal Reference:
- Caroline Piaulet-Ghorayeb, Björn Benneke, Michael Radica et al. JWST/NIRISS Reveals the Water-rich “Steam World” Atmosphere of GJ 9827 d. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/ad6f00
