Europa is one of 115 moons orbiting Jupiter and one of only four large enough to form a sphere. Each moon has a unique environment from the scorching volcanoes of Io to the frozen water-ice of Europa, Ganymede, and Callisto. Jupiter's tidal forces could cause volcanic activity under the surface and possibly geysers similar to Saturn's moon, Enceladus. Future missions by NASA and ESA in the next 5 years could answer some of these questions and indicate whether life under the surface of Jupiter's icy moons is possible.
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Astro Brief is a podcast collaboration between KSMU, the Missouri Space Grant, and MSU's Department of Physics, Astronomy and Materials Science. Hosted by Dr. Mike Reed, Astro Brief focuses on astronomical events, the field of astronomy, and astronomy-related guests. It airs Thursdays at 9:45 am on KSMU.
Transcript
In this episode, we're going to talk about Europa — a very interesting moon of Jupiter.
Europa is the smallest of the four Galilean moons — so named because Galileo discovered them way back in 1610 — yet Europa is still only slightly smaller than our own moon. The four moons are, from closest to furthest from Jupiter, Io, Europa, Ganymede, and Callisto. And those of you that know your Greek mythology will recognize those names. They were all women seduced by Zeus — the Greek version of the Roman god Jupiter. They are the only moons of Jupiter large enough to be round from their own gravity, and they are all tidally locked — both to Jupiter and to each other.
Europa orbits Jupiter every three and a half Earth days, with Io half that, Ganymede twice that, and Callisto very nearly four times that. Their orbital resonances with each other keep their orbit slightly elliptical, and their proximity to Jupiter's strong gravity means the tidal stresses are huge.
Io — the closest — changes in diameter by a football field every orbit, making it the most volcanically active body in our solar system. The stresses are less at Europa — sort of putting it at the sweet spot for our interest — while Io's extreme volcanism has resulted in the loss of most of its water, Europa has retained a lot of its supply — twice the amount of all the water on Earth.
At Jupiter's distance from our sun, space is very cold, and Europa's average temperature is a freezing minus 260 degrees Fahrenheit on average. Jupiter's tidal stress means Europa does have volcanoes — undersea ones. This gives Europa a very interesting structure. It has a frozen ice crust some five to twenty or more miles thick, but under that, a liquid ocean fifty to one hundred miles deep — kept liquid by volcanoes in Europa's mantle.
The Galileo spacecraft orbited Jupiter from 1995 to 2003 and provided the best pictures of Europa so far. The icy crust has long cracks in it, likely caused by the flowing ocean tides beneath, and the ocean is the real star of the show.
In the depths of Earth's oceans near volcanic vents, there is no sunlight to produce energy. Instead, that is supplied by the vents. Along with energy, there is complex chemistry that is useful to life as gases and elements from inside the crust enrich the local environment. So on Earth, life around vents is abundant and varied.
Could the same be true on Europa? Or Ganymede? Or even Callisto — which also have deep oceans?
The Cassini spacecraft which orbited Saturn passed through water plumes from the moon Enceladus, which has geysers spouting from cracks in its ice crust. Cassini not only measured water, salts and other useful minerals, but also complex organic molecules which could form amino acids or proteins.
So again, the question of whether or not life exists on Europa beneath the ice crust, floating or zooming around in its huge ocean, is an open one. However, it's possible that going into that ocean isn't necessary to find whether or not Europa has life. It's possible Europa also has geysers that occasionally erupt through cracks in its icy crust. Those geysers could deposit that life right onto the surface, stranding it where we could examine it.
In a 2014 paper using Hubble data, Dr. Kurt Rutherford of the Southwest Research Institute and collaborators found evidence for localized water vapor indicative of geysers. However, in a 2026 updated paper with Dr. Rutherford as the second author, they pulled back that assertion. And while not ruling out geysers on Europa, they determined that the Hubble data cannot confirm them. So it remains an open question — and a very important one — as there are two spacecraft zooming towards Jupiter right now to study Europa.
NASA's Europa Clipper will be the first to arrive in April of 2030. It will orbit Jupiter on an elongated orbit that will repeatedly fly it past Europa. Because of Jupiter's strong magnetic field, the radiation environment near Europa is fairly harsh. So the clipper is minimizing its time there while still passing close enough to Europa to study it. ESA's JUICE, or Jupiter Icy Moons Explorer, will arrive in July of 2031. It will spend two and a half years orbiting Jupiter to study the moons and then it will directly orbit Ganymede to study it more closely. Neither mission has a lander, but both have instruments to detect chemical signatures of life-forming materials.
They are merely the first steps of exploring whether deep oceans of moons contain life.