Hubble Space Telescope Detects Water Vapor in Atmosphere of Small Exoplanet

Astronomers utilizing the NASA/ESA Hubble Space Telescope have observed GJ 9827d, the smallest exoplanet known to have water vapor in its atmosphere. With a diameter approximately twice that of Earth, this distant planet could provide insights into the prevalence of water-rich atmospheres around other stars in our galaxy.

Discovery and Characteristics

GJ 9827d, discovered by NASA’s Kepler Space Telescope 2017, completes an orbit around a red dwarf star every 6.2 days. Located 97 light-years away in the constellation Pisces, its compact size makes it a significant candidate for studying water-rich atmospheres beyond our solar system.

Team member Björn Benneke from the Université de Montréal highlights the significance of this discovery: “This would be the first time that we can directly show through an atmospheric detection that these planets with water-rich atmospheres can exist around other stars.” The findings are published in The Astrophysical Journal Letters.

Uncertainties and Potential Scenarios

While detecting water vapor is groundbreaking, uncertainties remain about the composition of GJ 9827d’s atmosphere. The lead author, Pierre-Alexis Roy, notes the ambiguity: “Until now, we had not been able to detect the atmosphere of such a small planet directly.” The planet’s temperature, similar to Venus, is around 425°C, which suggests a potentially inhospitable, steamy world if the atmosphere is predominantly water vapor.

Scientists contemplate two possibilities for GJ 9827d—either it retains a hydrogen-rich envelope with water, resembling a mini-Neptune, or it could be a warmer version of Jupiter’s moon Europa, possibly composed of half water and half rock.

Insights from Hubble’s Observations

The Hubble program observed the planet during 11 transits over three years, utilizing events where the planet crossed in front of its star. This allowed the spectroscopic detection of water molecules in the planet’s atmosphere.

The discovery opens doors for further study, making GJ 9827d a promising target for the upcoming NASA/ESA/CSA James Webb Space Telescope, enabling detailed infrared spectroscopy to explore additional atmospheric molecules.

Read the original artcile on PHYS.

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