Water Found in Atmosphere of Neptune-Sized Planet, Trillions of Miles Away

An artist's illustration of HAT-P-11b. Harvard-Smithsonian Center for Astrophysics

By peering throughout the universe with various telescopes, astronomers have found water in many places, such as large gaseous planets the size of Jupiter. But, up until now, they haven't found water on smaller planets, or any approaching the size of our own.

In a study published in the journal Nature, scientists say they detected a "crystal clear" fingerprint of water vapor coming from a planet dubbed HAT-P-11b, nearly 729 trillion miles miles away.

The planet has a mass about 26 times that of Earth, and is about the same size as Neptune. Researchers detected the presence of water by measuring the wavelength of light emitted from HAT-P-11b's atmosphere; water absorbs a specific subset of radiation, which leaves a specific "signature" in the light that passes through it.

"From the strength of the absorption, the authors conclude that the planet's atmosphere has a composition not dissimilar to those of the giant planets of our solar system—mostly hydrogen, with trace amounts of heavier atoms, including oxygen in the form of water vapour," writes astronomer Eliza Kempton, in a Nature commentary accompanying the research.

The results are interesting because water is a precondition for life, but its presence doesn't ensure that life would be found there, the authors write.

The researchers, from the University of Maryland and elsewhere, made the observations and measurements using the Hubble Space Telescope.

Previous attempts to figure out what made up the atmosphere of other planets of this size were foiled, likely by clouds, according to the study. Clouds can mask the presence of materials deeper in a planet's atmosphere, but in the case of this newfound exoplanet, the light made it through.