Hubble Finds Water Vapor in the Atmosphere of Jupiter's Moon Europa

Using the Hubble Space Telescope an astronomer has detected water vapor in the atmosphere of Jupiter's moon Europa.

Astronomers have long suspected that beneath the icy surface of Europa exists a vast ocean of water. This has led Europa, one of 76 moons around Jupiter, to be considered one of the most likely places in the solar system other than Earth to find life.

The discovery could pave the way for future investigations of Europa, the sixth-largest moon in the solar system, larger than the dwarf planet Pluto, and the Jovian system (Jupiter, its rings and moons) in general. The aim of these missions is to see if life could exist half a billion miles from the sun.

The water vapor discovered is only present in the southern hemisphere of the Jovian moon, with Lorenz Roth, researcher at the KTH Royal Institute of Technology in Stockholm, Lo, finding it only on the side that trails during its orbit around the gas giant.

This asymmetric distribution of water vapor is something that has been predicted by scientists using computer simulations, but this is the first time astronomers have actually spotted this.

Water Vapor Around Europa
An infographic illustrates the discovery of water vapor around Europa. The finding sets the scene for future investigations of the Jovian moon that aims to discover if it could be habitable. Hubble, J. da Silva/ESA

Roth is the author of a paper published in the Geophysical Research Letters that details the observation. The finding follows the discovery of water vapor in the atmosphere of one of Jupiter's other moons, Ganymede.

"The observation of water vapor on Ganymede and on the trailing side of Europa advances our understanding of the atmospheres of icy moons," Roth said in a European Space Agency (ESA) press release. "The detection of a stable H2O abundance on Europa is surprising because the surface temperatures are so low."

In order to discover the water vapor, Roth examined data collected by the Hubble Space Telescope collected in 1999, 2012, 2014, and 2015. The observations were collected using Space Telescope Imaging Spectrograph (STIS).

STIS allows astronomers to assess the chemical elements that make up a planet or a moon's atmosphere. The instrument aboard Hubble has also been used to detect oxygen in Europa's atmosphere.

Water vapor has been detected in Europa's atmosphere before but it was associated with plumes that violently erupt through the Jovian moon's icy shell. This launches water vapor as high as 62 miles into the Europan atmosphere.

This water vapor was labeled "transient" by researchers as it lasted only briefly and was limited to certain areas around Europa.

The observation of water vapor in the trailing atmosphere of Europa appears to be persistent, meaning it is a feature that exists at all times. It is also found in a much wider area than previous observations.

Europa and there other Jupiter's other icy moons will soon be visited ESA's JUpiter ICy moons Explorer (JUICE) mission. JUICE is set to launch in 2022 and it will arrive at Jupiter's system in 2031.

The probe will carry instruments that comprise the most powerful sensing equipment ever sent beyond Mars and the inner planets. In addition to JUICE, NASA's Europa Clipper will visit Europa with the specific aim of searching the moon for signs of life.

"This result lays the groundwork for future science based on upcoming missions to the Jovian moons," Roth concluded. "The more we can understand about these icy moons before spacecraft like JUICE and Europa Clipper arrive, the better use we can make of our limited observing time within the Jovian system."

An image of Jupiter's moon Europa created from multiple images taken by the Galileo spacecraft. The Hubble Space Telescope has observed water vapor around the Jovian moon. JPL-Caltech/SETI Institute/NASA