Exploring Europa presents mysteries
By Amanda Jermyn

Just a little late for Valentineís Day comes the love story of the Greek god Zeus, known to the Romans as Jupiter, and Europa, daughter of the King of Tyre in Phoenicia. According to Greek mythology, Zeus, in the guise of a bull, seduced Europa and carried her off to Crete where she reigned as the island nationís first queen. Perhaps no less intriguing is the story of the planet Jupiterís moon, Europa, named in her honor.

In 1610, using a refracting telescope at the University of Padua, Galileo discovered Europa, as well as Jupiterís three other largest moons, Io, Ganymede and Callisto. All four were named after Zeusís lovers and are known as the Galilean moons.

Just a little smaller than our Moon, Europa is the sixth largest moon in the Solar System and the sixth closest to Jupiter. Comprised mainly of silicate rock, it has an iron core and a thin atmosphere that is mostly oxygen. Its surface is covered by a smooth layer of water ice, somewhere between 6 and 19 miles thick. Crisscrossed with cracks and streaks, the surface is relatively young, with few visible craters.

Europa receives very little heat from the distant Sun, and with a surface temperature of about minus 260 degrees Fahrenheit, seems an unlikely candidate for liquid water, yet below its icy surface there appears to be a salty, liquid water ocean about 60 miles deep. The heat required to maintain this liquid ocean comes mainly from tidal flexing. This occurs when Jupiterís immense gravity pulls with varying strengths on either side of Europa, with more force exerted on the side closest to Jupiter. The tidal flexing that results exerts a squeezing force, causing friction, which generates enough heat within the moon to allow for a liquid ocean. The massive tides within this ocean, generated by Jupiterís gravity, put pressure on Europaís icy crust, causing the cracks and streaks visible on its surface. Europaís ocean is about twice the volume of all the oceans on Earth, and its tidal forces are about 1,000 times as strong as the Moonís effect on Earth.

Europaís liquid ocean, with tidal flexing as a heat source, makes it a prime candidate in the search for extraterrestrial life in the Solar System. Researchers believe life is more likely to arise when water is in contact with rock, and beneath Europaís ocean is a layer of silicate rock. It is thought that life could exist in Europaís ocean in conditions similar to those where various life forms thrive close to hydrothermal vents deep in Earthís oceans.

In December 2013 NASA announced that plumes of water vapor were detected on Europa, similar to those found on Saturnís moon Enceladus. That same month NASA reported it had discovered clay-like minerals, often associated with organic material, on Europaís icy crust, most likely delivered by a collision with a comet or asteroid. Because organic materials are important building blocks of life, this discovery adds to the prospects of finding life on Europa.

Having the right conditions for life does not, of course, mean that life exists on Europa. Most of what we know about this moon comes from the Galileo mission that orbited Jupiter for eight years, starting in 1995, though there were a few flyby missions before it. The next mission to Europa will be the European Space Agencyís Jupiter Icy Moon Explorer (JUICE), due to launch in 2022 and reach Jupiter by 2030. However, so far, no spacecraft has landed on Europa, and none is planned. The depths of her ocean remain a mystery, and our love affair with the quest for extraterrestrial life continues.

Join the Springfield Stars Club on Tuesday, February 25th at 7:30pm at the Springfield Science Museum for a talk by Kevin Collins on designing and building the Arunah Hill Solar Observatory, together with ideas for solar lighting and air-conditioning enhancements. The presentation will include a component of the optics package and photos of the projection device in use at the Transit of Venus. Kevin has a degree in geosciences and is a senior software developer for Environmental Compliance Services, Inc. He is a member of the Amherst Area Amateur Astronomers Association, and a member and graduate of the Star Watch program at Arunah Hill. An avid amateur telescope-maker, he organizes star parties with the Department of Conservation and Recreation throughout the region. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.