Recent observations of Europa by the NASA/ESA Hubble Space Telescope have uncovered a plume of material erupting from the moon’s surface at precisely the same location as a similar apparent plume seen in 2014. The Hubble images bolster evidence that the plumes are a real phenomenon, flaring up intermittently in the same region on the icy moon.
Hubble captured additional evidence of water vapor plumes on Jupiter’s icy moon Europa; the probable plumes appear to be repeating in the same location and correspond with a relatively warm region on Europa’s surface observed by the Galileo spacecraft. Image credit: NASA / JPL-Caltech.
In the most recent observation, on February 22, 2016, Hubble uncovered a dark patch, silhouetted against Jupiter and protruding slightly off the surface at Europa’s equatorial region.
The dark feature is not only in the same location but is also similar in appearance to the one seen in a previous study of Europa, taken March 17, 2014.
The newly imaged plume rises about 62 miles (100 km) above Europa’s surface, while the one observed in 2014 was estimated to be about 30 miles (50 km) high.
These composite images show a suspected plume of material erupting two years apart from the same location on Europa. Both plumes, photographed in UV light, were seen in silhouette as the moon passed in front of Jupiter. The image was taken February 22, 2016. The plume in the image at left, observed by Hubble on March 17, 2014, originates from the same location. The snapshot of Europa, superimposed on the Hubble image, was assembled from data from NASA’s Galileo mission to Jupiter. Image credit: NASA / ESA / W. Sparks, STScI / USGS Astrogeology Science Center.
Both correspond to the location of an unusually warm region that contains features that appear to be cracks in the moon’s icy crust, seen in the 1990s by NASA’s Galileo spacecraft.
Dr. William Sparks, a researcher at the Space Telescope Science Institute, and co-authors speculate that this could be evidence of water erupting from the moon’s interior.
“After Hubble imaged this new plume-like feature on Europa, we looked at that location on the Galileo thermal map. We discovered that Europa’s plume candidate is sitting right on the thermal anomaly,” said Dr. Sparks, who is the lead author of the paper reporting the results in the Astrophysical Journal Letters.
The green oval highlights the plumes Hubble observed on Europa. The area also corresponds to a warm region on Europa’s surface. The map is based on observations by the Galileo spacecraft. Image credit: NASA / ESA / STScI / USGS.
If the plumes and the warm spot are linked, it could mean water being vented from beneath the moon’s icy crust is warming the surrounding surface, according to the team.
Another idea is that water ejected by the plume falls onto the surface as a fine mist, changing the structure of the surface grains and allowing them to retain heat longer than the surrounding landscape.
Artistic representation of Europa in cross-section showing processes from the seafloor to the surface. Boxes indicate potentially habitable sites such as hydrothermal vents, and regions on and within the ice shell that could harbor biosignatures. This diagram shows an integrated perspective pf how the seafloor, ocean, and ice shell could yield biosignatures detectable on the surface by a landed spacecraft. Image credit: K.P. Hand et al / NASA.
For both the 2014 and 2016 observations, Dr. Sparks and his colleagues used Hubble’s Space Telescope Imaging Spectrograph (STIS) to spot the plumes in UV light. As Europa passes in front of Jupiter, any atmospheric features around the edge of the moon block some of Jupiter’s light, allowing the instrument to see the features in silhouette.
The researchers are continuing to use Hubble to monitor Europa for additional examples of plume candidates and hope to determine the frequency with which they appear.
They said the findings are laying the groundwork for NASA’s Europa Clipper mission, which is planned for launch in the 2020s.
“If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them,” said Dr. Jim Green, Director of Planetary Science at NASA Headquarters.
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W.B. Sparks et al. 2017. Active Cryovolcanism on Europa? ApJL 839, L18; doi: 10.3847/2041-8213/aa67f8
