Europa

Jupiter II

Europa Facts

• Europa is the sixth of Jupiter's known satellites and the fourth largest:
  • distance from Jupiter: 670,900 km
  • diameter: 3138 km
  • mass: 4.80e22 kg
  Europa is the second of the Galilean moons.

• Pronounced "yoo ROH puh".

• Europa was a Phoenician princess abducted to Crete by Zeus, who had assumed the form of a white bull, and by him the mother of Minos.

• Discovered by Galileo and Marius in 1610.

• Europa is slightly smaller than the Moon.

• Europa and Io are somewhat similar in bulk composition to the terrestrial planets: primarily composed of silicate rock. However, Europa's density (2.97 g/cm3, a little less than the Moon's and substantially less than Earth's) indicates the lack of a dense iron core.

• But Europa's surface is not at all like anything in the inner solar system. It is exceedingly smooth: no features more than a few hundred meters high have been seen. The prominent markings seem to be only albedo features.

• There seem to be very few craters on Europa; only three craters larger than 5 km in diameter have been found (picture 3). This would seem to indicate a young and active surface. However, the Voyagers mapped only a fraction of the surface at high resolution. The precise age of Europa's surface is an open question.

• The images of Europa's surface strongly resemble images of sea ice on Earth. It is possible that beneath Europa's surface ice there is a layer of liquid water, perhaps as much as 50 km deep. If so, it would be the only place in the solar system besides Earth where liquid water exists in significant quantities.

• Europa's most striking aspect is a series of dark streaks crisscrossing the entire globe (picture 1, above). They may be due to freezing and expansion of the underlying water layer. But the total area of the streaks is too large for that to be the whole story.

• Recent observations with HST reveal that Europa has a very tenuous atmosphere (1e-11 bar) composed of oxygen. Of the 61 moons in the solar system only three others (Io, Titan and Triton have atmospheres. Unlike the oxygen in Earth's atmosphere, Europa's is almost certainly not of biologic origin. It is most likely generated by sunlight and charged particles hitting Europa's icy surface producing water vapor which is subsequently split into hydrogen and oxygen. The hydrogen escapes leaving the oxygen.

• The Voyagers didn't get a very good look at Europa. But it is a principal focus of the Galileo mission (picture 9).

Pictures

1. (above) Europa in Color 112k gif; 54k jpg

2. Europa South Pole 70k gif; 36k jpg

3. Europa close up 593k gif

4. Europa from a distance 39k gif

5. Europa with Narrow Angle Camera (Blue filter) 350k gif
6. Europa with Narrow Angle Camera (Violet filter) 430k gif
7. Europa with Narrow Angle Camera (Violet filter) 205k gif

8. Another view of Europa 27k jpg

9. Galileo's first view of Europa 82k jpg (caption)

More about Europa

• from LANL
• from JPL
• speculation about life on Europa

Open Issues

• How thick is the surface ice? Is there liquid water below?
• What are the surface streaks? How were they formed?
• Why is the surface so smooth?
• Is Europa being heated by tidal friction like Io? How much? Is there any volcanism, perhaps hidden beneath the ice?
• The possible presence of liquid water and volcanism on Europa puts it on my list of possible life-bearing bodies, though, of course, the probability is very low.

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