Water Vapor Confirmed on Jupiter Moon

November 19, 2019, 12:24 PM HST (Updated November 19, 2019, 12:24 PM)
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PC: NASA

Europa, a moon orbiting Jupiter, may be capable of supporting life based on its newly discovered properties.

Forty years ago, a Voyager spacecraft snapped the first closeup images of Europa, one of Jupiter’s 79 moons, according to a press release from W.M. Keck Observatory.

These revealed brownish cracks slicing the moon’s icy surface, which give Europa the look of a veiny eyeball. Missions to the outer solar system in the decades since have amassed enough additional information about Europa to make it a high-priority target of investigation in NASA’s search for life.

What makes this moon so alluring is the possibility that it may possess all of the ingredients necessary for life, the release continued. Scientists have evidence that one of these ingredients, liquid water, is present under the icy surface and may sometimes erupt into space in huge geysers.

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But no one has been able to confirm the presence of water in these plumes by directly measuring the water molecule itself. Now, an international research team led out of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has detected the water vapor for the first time above Europa’s surface. The team measured the vapor by peering at Europa through W. M. Keck Observatory in Hawai‘i, one of the world’s largest telescopes, the release continued.

Confirming that water vapor is present above Europa helps scientists better understand the inner workings of the moon. For example, it helps support an idea, of which scientists are confident, that there’s a liquid water ocean, possibly twice as big as Earth’s, sloshing beneath this moon’s miles-thick ice shell.

Another source of water for the plumes, some scientists suspect, could be shallow reservoirs of melted water ice not far below Europa’s surface. It’s also possible that Jupiter’s strong radiation field is stripping water particles from Europa’s ice shell, though the recent investigation argued against this mechanism as the source of the observed water.

“Essential chemical elements — carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur — and sources of energy, two of three requirements for life, are found all over the solar system. But the third, liquid water, is somewhat hard to find beyond Earth,” said Lucas Paganini, a NASA planetary scientist who led the water detection investigation. “While scientists have not yet detected liquid water directly, we’ve found the next best thing: Water in vapor form.”

In a study published Tuesday in the journal Nature Astronomy, Paganini and his team reported that they detected enough water releasing from Europa (5,202 pounds per second) to fill an Olympic-size swimming pool within minutes. Yet, the scientists also found that the water appears infrequently, at least in amounts large enough to detect from Earth.

“For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method,” Paganini said.

Paganini’s team detected the faint yet distinct signal of water vapor just once throughout 17 nights of observations between 2016 and 2017. Looking at the moon from Keck Observatory, the scientists saw water molecules at Europa’s leading hemisphere, or the side of the moon that’s always facing in the direction of the moon’s orbit around Jupiter. Europa, like Earth’s moon, is gravitationally locked to its host planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction.

They used Keck Observatory’s Near-Infrared Spectrograph, which measures the chemical composition of planetary atmospheres through the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light as they interact with solar radiation.

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