NASA’s Hubble Space Telescope spectroscopically detected water vapor over the frigid south pole of Jupiter’s satellite Europa, providing the first strong evidence of water plumes erupting off the moon’s surface. This is an artist’s concept of a plume of water vapor thought to be ejected off the frigid, icy surface of Jupiter’s moon Europa, located about 500 million miles (800 million kilometers) from the sun. Courtesy of NASA/ESA/K. Retherford/SWRI. Previous findings from other sources point to the existence of an ocean under Europa’s icy crust. If confirmed as water plumes, the vapor would show that this underground ocean has easy access to the surface — at least sometimes. If the finding is supported by additional observations, it would make Europa the second moon in the solar system known to have water vapor plumes. The discovery could also have future implications of Europa’s potential habitability. “By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa,” said Lorenz Roth of Southwest Research Institute in San Antonio, Texas. “If those plumes are connected with the subsurface water ocean we are confident exists under Europa’s crust, then this means that future investigations can directly investigate the chemical makeup of Europa’s potentially habitable environment without drilling through layers of ice. And that is tremendously exciting.” Roth and colleagues used images taken by the Hubble Space Telescope in November and December 2012, as well as older images of Europa, to identify surpluses of hydrogen and oxygen in two distinct regions of the moon’s southern hemisphere. These surpluses can be observed for just a small window — approximately seven hours at a time, according to the researchers. They suggest that the surpluses are actually 124.27-mile-high (200 km) plumes of water vapor. Jupiter and its satellite Europa with bright UV signal from the newly discovered south polar water vapor plumes. Courtesy of Lorenz Roth, Southwest Research Institute/USGS. The imaging spectrograph detected faint UV light from an aurora, powered by Jupiter’s intense magnetic field, near the moon’s south pole. Atomic oxygen and hydrogen produce a variable auroral glow and leave a telltale sign that they are products of water molecules being broken apart by electrons along magnetic field lines. “We pushed Hubble to its limits to see this very faint emission,” said Joachim Saur of the University of Cologne in Germany, principal investigator of the Hubble observation campaign. “These could be stealth plumes, because they might be tenuous and difficult to observe in the visible light.” The plumes are present when Europa is near the apocenter of its orbit, or farthest from Jupiter, and they vanish when the moon is close to the pericenter, or very near its planet, they say, suggesting that tidal acceleration plays a primary role in the phenomenon of plume spouting (it opens surface cracks). This graphic shows the location of water vapor detected over Europa’s south pole, providing the first strong evidence of water plumes erupting off Europa’s surface. NASA’s Hubble Space Telescope didn’t photograph plumes, but spectroscopically detected auroral emissions from oxygen and hydrogen. Courtesy of NASA, ESA and L. Roth, Southwest Research Institute and University of Cologne, Germany. Based on their observations, the researchers suggest that Europa’s plumes may be similar to those of one of Saturn’s moons, Enceladus, with high-pressure vapor emissions escaping from very narrow cracks. The research appears in the Dec. 12 issue of Science Express; Roth is lead author and Saur co-author. The work was reported last week at the meeting of the American Geophysical Union in San Francisco. For more information, visit: www.nasa.gov/content/goddard/hubble-europa-water-vapor or www.nasa.gov/hubble