Using the powerful James Webb Space Telescope, astronomers have detected a water-rich atmosphere on GJ 9827 d, a small exoplanet located 98 light-years away. With a unique composition of heavier molecules such as water vapor, this discovery marks the first detection of a dense, water-rich atmosphere on a smaller exoplanet.
Webb Telescope Unveils Water-Rich Atmosphere on GJ 9827 d, a Potential Steam World
Astronomers have discovered a water-rich atmosphere on exoplanet GJ 9827 d, located 98 light-years away in the constellation Pisces. Using the James Webb Space Telescope (JWST), researchers identified a high concentration of water vapor on this small planet, which is about twice the size of Earth.
The study, led by Caroline Piaulet-Ghorayeb from the Université de Montréal's Trottier Institute for Research on Exoplanets (IREx) and published in Astrophysical Journal Letters, marks a major advancement in studying smaller exoplanets, positioning GJ 9827 d as a potential “steam world” and offering new insights into planetary atmospheres.
Unveiling a Unique Atmosphere on GJ 9827 d
One of the most exciting aspects of the James Webb Telescope's discovery is the unique atmospheric composition of GJ 9827 d. Unlike the hydrogen-dominated atmospheres typically found on gas giants and mini-Neptunes, GJ 9827 d features a denser atmosphere rich in heavier molecules, most notably water vapor. This discovery is a significant deviation from the trend observed in other exoplanets and has prompted scientists to label it a “steam world.”
Using transmission spectroscopy, the team was able to analyze light as it passed through the exoplanet’s atmosphere during its transit in front of its star. The data from both JWST and HST was combined to confirm the presence of water vapor and rule out the possibility of contamination from the star. Piaulet-Ghorayeb explained, “For now, all the planets we’ve detected that have atmospheres are giant planets, or at best mini-Neptunes. These planets have atmospheres made up mostly of hydrogen, making them more similar to gas giants in the Solar System than to terrestrial planets like Earth."
The findings suggest that GJ 9827 d could possess one of two atmospheric types: either a cloudy, hydrogen-dominated atmosphere with traces of water, or, more likely, a dense, water-vapor-rich atmosphere in a gaseous or steam-like state due to its proximity to its host star. The discovery marks the first time an atmosphere on a smaller planet has been found to contain heavy molecules, setting GJ 9827 d apart from previous exoplanet discoveries.
Challenges Overcome in Studying Smaller Planets
The successful observation of a water-rich atmosphere on GJ 9827 d highlights the groundbreaking capabilities of the James Webb Space Telescope in studying smaller, more elusive planets. Prior to this discovery, most exoplanet atmospheric research focused on gas giants and mini-Neptunes due to their larger size and hydrogen-rich atmospheres, which are easier to detect. Smaller planets, especially those near Earth-size, typically have thin atmospheres, making them difficult to observe with existing technology.
Using JWST’s NIRISS, the team observed GJ 9827 d as it transited its host star, capturing light as it passed through the planet’s atmosphere. By combining these findings with prior Hubble observations, the research team was able to confidently distinguish between different types of atmospheres. This detection of water vapor provides solid evidence that small planets can possess dense atmospheres dominated by heavier elements.
While GJ 9827 d is located too close to its star for conditions that could support life—its surface temperatures are estimated at 350°C—the discovery of such a steam world is a significant advancement in our understanding of planetary systems. As Piaulet-Ghorayeb stated, "This detection supports the idea that other small, rocky exoplanets may also have such atmospheres, paving the way for further exploration and the eventual study of potentially habitable worlds."
A New Chapter in the Search for Life
The detection of a water-rich atmosphere on GJ 9827 d is an important milestone in the study of smaller exoplanets, offering hope that other rocky planets may also have atmospheres conducive to life. Although GJ 9827 d itself is not a candidate for habitability due to its extreme temperatures, the planet's dense, water-vapor-filled atmosphere adds to the growing body of knowledge about planetary formation and composition.
Astronomers are optimistic that future JWST observations will uncover more details about GJ 9827 d’s atmosphere and potentially reveal new characteristics that could provide deeper insights into the nature of steam worlds. The ability to study such atmospheres on smaller planets is crucial in refining the search for Earth-like planets that could support life.
This discovery also showcases the incredible capabilities of the James Webb Space Telescope, which is enabling scientists to explore smaller exoplanets with greater precision than ever before. As the quest to understand distant worlds continues, the detection of atmospheres on planets like GJ 9827 d could play a pivotal role in identifying potential candidates for future exploration and, ultimately, the search for extraterrestrial life.