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Life on Europa, Part 1

Transcript & real audio of Karl Kruszelnicki's Great Moments in Science program. Life on Europa, Part 1

Oceans are wonderful places. In fact, according to John R. Delaney, an oceanographer at the University of Washington "An ocean is the womb of a planet". An ocean is where life starts. The last time we discovered an ocean was 500 years ago, when Balboa supposedly discovered the Pacific Ocean. But scientists think that they might have discovered another ocean, of water, on one of the moons of Jupiter - and that ocean might mean Life. Jupiter is the biggest planet in the Solar System, and has some 16 moons looping around it. By itself, it accounts for 90% of the mass of all the planets and moons in our Solar System. Jupiter has a gravitational field about 300 times stronger than that of the planet Earth.

The innermost moon of Jupiter, Io, has a slightly elliptical (or egg-shaped) orbit around Jupiter. The combination of Jupiter's enormous gravity, and this elliptical orbit, means that during each orbit, the surface of Io actually pumps up and down by about 50 metres. This enormous flexing generates heat, called "Tidal Heating". On Io, this heat is so great that the little moon is continually erupting with volcanoes of molten sulphur.

Jupiter's second moon, Europa

The next moon out, Europa, has the same kind of tidal heating, but to a lesser degree. It seems to have volcanoes of molten ice - either icy slush, or later. Europa, which takes 3.6 days to orbit Jupiter, is the moon that might have oceans of liquid water - thanks to this tidal heating. Now the three inner moons of Jupiter are locked in a strange cosmic gravitational dance.

To get a feel for this dance, look at our Moon. As the Moon goes around the Earth, it drags the water with it, which gives us the tides. These tides create friction on the floor of the ocean, and so as time goes by, the Earth spins a little more slowly. Energy is transferred from the Earth to the Moon, and so the Moon moves a little further away. The Moon is moving away from the Earth at about 4 metres per century. Jupiter and its three inner moons have a similar cosmic dance, but one which is far more elegant and ornate.

In the beginning of the Solar System, soon after Jupiter and its moons popped into existence, all these moons moved independently of each other. Over a few hundred million years, Jupiter transferred some of its energy to Io, which began to slowly spiral outwards (just like the Moon moves away from the Earth).

Io kept on moving out, until it ran into the gravitational pull of the next moon out, Europa. Now the gravitational pull of Europa is tiny - less than one 10,000-thousandth of the pull of Jupiter. But it was enough to lock the orbits of the two moons together. Every time Europa makes one complete loop around Jupiter, Io makes two. Every 1.8 days, Io comes just underneath Europa. Europa gives Io a little pull, which keeps their orbits in that 2-to-1 relationship. This pull also shoves both Io and Europa into more elliptical orbits. This means they get more tidal heating, as their crusts move up and down.

Io and Europa were now locked together as a pair, and they were still robbing rotational energy from Jupiter. So, as a pair, they kept on spiralling out, moving slowly away from Jupiter.

After about a billion years, they were far enough out from Jupiter to be pulled by the third moon of Jupiter, Ganymede. Soon Ganymede joined the gravitational dance. So now when Ganymede goes around Jupiter once, Europa goes twice and Io goes around four times. In another five or ten billion years or so, the three moons will have moved out enough to get Callisto,the fourth moon of Jupiter, to join in this cosmic dance.

We didn't know much about Europa until 1977, when the Voyager 1 and Voyager 2 spacecraft zipped past Jupiter. They didn't get really close to Europa, so the photos don't show much detail. The moon Europa is just a little bit smaller than our own Moon. But the photos do show that the surface of Europa seems to be entirely cracked ice. Europa looks like a strange fractured egg shell, or a cracked billiard ball. Its surface is covered with strange lines, up to 3,000 kilometres long, and up to 70 kilometres wide. Most of these strange lines were straight, but some of them were jagged or curved, and they all cross each other every which way.

Image of Europa

A view of the Conamara Chaos region on Jupiter's moon Europa showing cliffs along the edges of high-standing ice plates. This image covers an area approximately 1.5 kilometers by 4 kilometers.

Our next big jump in knowledge happened after December 7, 1995, when the Galileo spacecraft arrived at Jupiter after a six-year trip. Next time, I'll talk about the strange ocean of water, that seems to be under the ice of Europa.....

Other images and data from Galileo can be found on the Galileo mission home page.

Life On Europa Part 2

Tags: astronomy-space

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Published 05 November 2001

© 2015 Karl S. Kruszelnicki Pty Ltd