One would think that life half a billion miles from the sun is not a place we call home. But planetary astronomers are very keen to explore Europe in search of life. Europa revolves around a moon that is slightly smaller than Earth’s Jupiter. The icy surface of the moon never gets hotter than minus 260 degrees Fahrenheit F. The temperature is so cold that the water ice is rocky.
However, under the solid icy crust, there can be a global ocean with more water than Earth. And where there is water, there can also be life. Like a leaky garden hose, the ocean spews water vapor into space from geysers penetrating cracks in the surface, as first photographed by Hubble Space Telescope in 2013.
The latest development comes from Hubble observations archived from 1999 to 2015, which showed that water vapor is constantly being replenished across the entire lunar hemisphere. It’s a little vague. However, the atmosphere is only a billionth of the surface pressure of the Earth’s atmosphere.
Water vapor was not directly seen, but the ultraviolet spectroscopic signature of oxygen was measured by Hubble. Oxygen is a component of water. Unlike geysers, this water vapor does not come from Europe, but sunlight causes surface ice to rise. Recently, an atmosphere similar to water vapor was found on Jupiter’s moon Ganymede.
Europe is very exciting as a potential home and destination for life NASAEuropa Clipper and Jupiter Icy Explorer (JUICE) from the European Space Agency – scheduled to launch within a decade.
NASA’s Hubble Space Telescope observations of Jupiter’s icy moon Europa have revealed the presence of persistent water vapor – but mysteriously only in one hemisphere.
Beneath its icy surface, Europe is home to a huge ocean that can provide adequate living conditions. The discovery improves astronomers’ understanding of the icy moons’ atmosphere structure and helps lay the foundation for planned scientific missions to the Jupiter system, in part to investigate whether a living environment half a billion miles from the sun could support it.
Previous observations of water vapor in Europe have been linked to ice-penetrating clouds, as photographed by Hubble in 2013. They are similar to hot springs on Earth, but extend more than 100 miles in altitude. They create temporary points of water vapor in the Moon’s atmosphere, which are only a billionth of the surface pressure of Earth’s atmosphere.
However, the new results show that in Hubble observations from 1999 to 2015, similar amounts of water vapor were distributed over a larger area of Europe. This indicates the existence of a long-term water vapor atmosphere only in the late European hemisphere – the part of the Moon that is always opposite to the direction of its motion in its orbit. The cause of the asymmetry between the anterior and posterior hemispheres is not fully understood.
The discovery was derived from a new analysis of archived Hubble images and spectra using a technique that recently led to the detection of water vapor in the atmosphere of Jupiter’s moon Ganymede by Lorenz Roth of the Royal Institute of Technology, Space and Plasma Physics. , Sweden.
“Observing water vapor at Ganymede and on the later side of Europe improves our understanding of the moon’s icy atmosphere,” Roth said. “However, the discovery of abundant sedimentary water in Europe is somewhat more surprising than the discovery at Ganymede, as the surface temperatures of Europe are lower than those of Ganymede.”
Europa reflects more sunlight than Ganymede, making the surface 60 degrees Fahrenheit cooler than Ganymede. The highest temperature during the day over Europe is 260 degrees Fahrenheit. But even at lower temperatures, new observations indicate that water ice, like Ganymede, sublimates from the surface of Europa, that is, passes directly from solid to vapor without a liquid phase.
To make the discovery, Roth delved into archived Hubble data sets and selected ultraviolet observations of Europe in 1999, 2012, 2014 and 2015 when the moon was in different orbital positions. All of these observations were made using the Space Telescope Imaging Spectroradiometer (STIS). Through STIS’s ultraviolet observations, Roth was able to determine the frequency of oxygen – a component of water – in the European atmosphere, and by interpreting the strength of the emission at different wavelengths, he deduced the presence of water vapor.
This discovery paves the way for in-depth studies of Europe through future investigations, including NASA’s Europa Clipper mission and the European Space Agency’s (ESA) Jupiter Icy Moons Explorer (JUICE). Understanding the formation and evolution of Jupiter and its moons also helps astronomers gain insight into Jupiter-like planets around other stars.
These results have been published in the journal Geophysical Research Letters.
Reference: “A stable H.2O Atmosphere on Europe Trailing Hemisphere from HST Images” by Lorenz Roth, 09/13/2021 Available Geophysical Research Letters.
The Hubble Space Telescope is an international collaboration project between NASA and the European Space Agency (ESA). The telescope is operated by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, is conducting research for Hubble. STScI is operated for NASA by the Consortium of Universities for Research in Astronomy in Washington, DC
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