Evidence of Europa Plume Found in Old Galileo Data

A team of scientists scouring 21 year old data from NASA’s Galileo probe has found evidence further supporting the idea that Jupiter’s moon Europa ejects plumes of material into space from a liquid ocean under its icy crust.  Until now, only images from the Hubble Space Telescope have hinted at these geysers, though the mere possibility that they exist has fueled intense interest in sending probes there to investigate.

Life as we know it requires liquid water, so any discovery of liquid water in the solar system opens the potential for finding other life, though the expectation in our neighborhood is that it is microbial, not intelligent.

For decades, Mars was considered the most likely place to have provided an environment suitable for life in its past, at least, but more recent revelations that some moons of planets in the outer solar system may have oceans under icy crusts have redirected attention to these “ocean worlds.”

Jupiter’s moon Europa is one candidate.  NASA’s Galileo probe orbited Jupiter from 1995-2003 and made 11 passes of Europa, coming as close as 125 miles (200 kilometers) on December 16, 1997.  At the time, nothing was known about the possibility of plumes erupting through fissures in Europa’s icy crust.

Strange readings detected by the spacecraft’s magnetometer and an instrument that detects charged particles (a Plasma Wave Spectrometer) on that day almost 21 years ago were set aside as something that simply was not understood according to Margaret Kivelson, a space physicist at the University of California at Los Angeles (UCLA).  She was the principal investigator (PI) for the Galileo magnetometer and spoke at a briefing today on the results of the new analysis.

The decision to take a second look was prompted by two recent developments.  In 2012, the first of several images were made by the Hubble Space Telescope that suggested that a plume of material had been ejected into space from Europa.  Then, NASA’s Cassini probe in orbit around Saturn detected plumes from Saturn’s moon Enceladus, another ocean world.

Xianzhe Jia, a space physicist at the University of Michigan, created new 3D computer models to look at the old Galileo data with insight gained from Cassini’s observations of Enceladus and the Hubble data.  That research led to the conclusion that Galileo may well have flown through a plume.  The results were published today in Nature Astronomy.

The findings are not definitive, however.  That requires further study and thanks to Rep. John Culberson (R-TX), chairman of the Commerce-Justice-Science (CJS) subcommittee of the House Appropriations Committee, NASA is building a spacecraft to do just that — Europa Clipper.  He is convinced there is life on Europa and is determined to give NASA the money it needs to send probes there to find it.  He wants NASA to send not only Clipper, which will orbit Jupiter and made 44 flybys of Europa, but also a lander.  He put into law that NASA must launch Clipper in 2022 and the lander in 2024, both on NASA’s new Space Launch System (SLS).  SLS can send the probes directly to Jupiter instead of requiring gravity-assists from other planets, significantly shortening the trip time.

Jia, who is lead author of the Nature Astronomy article published today, is a co-investigator for two of the instruments on Clipper. Kivelson also is a co-investigator.

Last Wednesday, Culberson’s subcommittee marked up the FY2019 CJS bill, which funds NASA, and he excitedly told his appropriations committee colleagues — and therefore the public — about the new findings at the markup.  Unfortunately, the Nature Astronomy article was embargoed until this morning, so he jumped the gun, to the journal’s dismay.  However, it may have given the journal more visibility than it would have gotten otherwise.

As approved at subcommittee level, the bill provides $545 million for Clipper and $195 million for the lander.  That is more than twice what NASA requested for Clipper ($265 million) and it requested no funding for the lander, which it is not planning to build despite Culberson’s direction.  It had not been planning to build Clipper either, however, and its FY2019 budget request does not support Culberson’s insistence that it be launched in 2022 on SLS. It is concerned that funding the Europa missions will mean cutbacks to others, but Congress has been very generous to NASA’s planetary science program recently.

The full committee will mark up the bill on Thursday.

NASA currently has another spacecraft, Juno, in orbit around Jupiter, but it is not designed to study Europa.  The European Space Agency (ESA) plans to launch its Jupiter ICy Moons Explorer (JUICE) in 2022, with arrival in 2029.  It will study Jupiter and three of its moons: Ganymede, Callisto, and Europa.  Its focus is Jupiter and Ganymede, however, and will make only two flybys of Europa.

Jupiter has 69 moons.  Europa, Ganymede, Callisto and Io were the first four to be discovered by Galileo Galilei in 1610 and thus are called the Galilean moons.