Hubble Discovery: Water Vapor Found in Atmosphere of Smallest Known Exoplanet

The Hubble Space Telescope was able to observe the smallest planet beyond the solar system and found that it has water vapor in its atmosphere. This finding is considered a landmark discovery that brings the field of astronomy closer to characterizing worlds that are like Earth.

Smallest Known Exoplanet

Planet GJ 9827d has roughly double Earth's diameter. It orbits a red dwarf star that is roughly 97 light-years away from the Pisces constellation.

The team behind the novel discovery is looking into two different scenarios. These scenarios are that the planet could be a mini-Neptune with a water-laced and hydrogen-rich atmosphere and that the planet could be a warmer version of the Europa moon of Jupiter. Europa has twice as much as Earth's water beneath the crust.

Bjorn Benneke, a co-leader of the study from the Universite de Montreal, explains that the exoplanet could be half rock and half water. Benneke adds that a lot of water vapor could be present over a smaller and rocky body.

Benneke adds that until now, they were not able to directly detect such a small planet's atmosphere, further noting that they are getting the regime slowly.

Water Vapor Found in Tiny Exoplanet Atmosphere

In a span of three years, Hubble observed the planet in 11 transients, which are events in which it crossed at the front of its star. During these events, starlight is filtered through the atmosphere of the planet and allows astronomers to make use of the instruments of Hubble to analyze wavelengths, or color patterns, which shed light on water molecules' nature.

Even if the small exoplanet had an atmosphere rich in water, its Venus-like temperature of 425 degrees Celsius would make it a steamy world incapable of habitation.

Nevertheless, the water vapor discovery made by Hubble serves as a step closer to studying the exoplanet and other similar worlds.

Laura Kreidberg, a co-leader of the study from the Max Planck Institute for Astronomy, explains that water on a planet of this size is considered a "landmark discovery" that pushes them closer to characterizing worlds that are like the Earth.

Benneke also explains that this is the first time that they could directly reveal through atmospheric detection that planets that have atmospheres rich in water could exist around other stars. This is a crucial step when it comes to determining the diversity and prevalence of atmospheres on planets that are rocky.

The findings were included in the "Water Absorption in the Transmission Spectrum of the Water World Candidate GJ 9827 d" study.

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