Although signatures in Hubble images from 2012, 2014, and 2016 seem to indicate the presence of plumes of water emerging from the surface of Europa (Jupiter’s icy satellite with an internal ocean), these data were still subject to uncertainty, even controversy, being at the global level. the limit of the space telescope’s sensitivity. Today a reanalysis of the survey data Galileo which flew by Europa in 1997 at just under 200 km altitude, provide additional, independent evidence for the existence of such plumes of water vapor, like the one Cassini discovered in 2005 on Enceladus.
It is from the measurements of the magnetic field and plasma waves recorded by Galileo during its close flyby of Europa on December 16, 1997 (flyby E12) that Xianzhe Jia (University of Michigan) and his colleagues arrive at this conclusion. During this flyby at 196 km from the surface of the icy satellite, the probe’s magnetometer recorded a rotation of the magnetic field on a scale of 1000 km, associated with a drop in its amplitude of more than 200 nT. At the same time, the instrument Plasma wave spectrometer a brief but substantial increase in plasma density was recorded, resulting in intense and very localized emission. At the time, planetary scientists had noticed these anomalies but had not explained them, leaving them aside.
With Hubble’s ultraviolet images appearing to show something emerging from Europa’s surface, the idea came to Margaret Kivelson, who had conducted the magnetometer measurements in 1997, to combine these data from more than 20 years ago with the knowledge of recent Hubble data. With information about the size of a plume and its approximate location based on space telescope images, Xianzhe Jia, Margaret Kivelson, Krishan Khurana and William Kurth were able to deduce how long it should have taken Galileo cross such a plume and connect these data with the anomalies detected in 1997. The researchers show in the article published in Astronomy of nature today that the position, duration, and variations of the magnetic field, as well as the variation of the plasma waves, are all consistent with an interaction of Jupiter’s plasma with Europa, but only if a water plume with the inferred characteristics is present in the Hubble images at the same time as the thermally anomaly regions of Europa’s surface. These beautiful results therefore provide strong and independent evidence for the presence of water plumes on Europa.
As in the case of Enceladus, it is very tempting to analyze on site what is the exact composition of these water plumes coming directly from the ocean below. The European investigation JUICE (Explorer of Jupiter’s Icy Moons) which should be launched in 2022 to reach the Jovian world in 2032 will make two close flybys of Europa at less than 400 km before going on to explore Ganymede and Callisto in 2032. It is the Americans at NASA who have seized this new study with great communication reinforcements today to further sell their mission Europe Clipperwhich will be able to explore Europa in detail, with no fewer than 45 close flybys, including 40 within 400 km of its surface, and many over hotspots identified by Hubble.
Needless to say, the most optimistic (or dreamers) are already talking about the future discovery of signs of life. Let’s just say that Europa, with a protected and probably warm liquid ocean, offers favorable conditions for the arrangement of complex organic molecules, probably like Enceladus and other small worlds yet to be discovered.
Source
Evidence for a Plume on Europa from Galileo’s Magnetic Wave and Plasma Signatures
Xianzhe Jia, Margaret G. Kivelson, Krishan K. Khurana, and William S. Kurth
Astronomy of Nature (May 14, 2018)
Illustrations
1) Europa imaged by the Galileo probe (NASA/JPL-Caltech)
2) Artist’s impression of Galileo’s magnetic field measurements revealing the presence of water plumes (NASA/JPL-Caltech/Univ. of Michigan)
3) Composite image showing signs of plumes from the Hubble telescope in December 2012 (NASA/ESA/L. Roth/SWRI/University of Cologne)