Europa:
An "Icy Cueball" of a Moon
- About the same size as earth's moon.
- It is the second closest of these four to the planet.
- Very smooth surface criss-crossed by long streaks.
- Average distance from Jupiter is 671,000 km.
- Rotation on axis is 3.6 days (Earth time).
- Diameter is 3,130 km, or about 1,946 miles (slightly smaller than our moon).
- Fourth largest satellite to Jupiter.
- Surface composition mostly of water determined by Earthbound astronomers prior to 1979.
- Brighter surface richer in ice than other Jovian satellites.
- It's nearly featureless surface revealed by Voyager missions.
- Faint surface markings and virtually no impact craters.
- Markings appear as pale tan streaks with almost no relief.
- Darkness of streaks only 10% more than surface,
- Streaks barely visible; photos returned processed for contrast.
- Resemble Percival Lowell's Martian "canals."
- Streaks appear to be broad, shallow valleys with straight of curved paths across the plains of Europa.
- They are about 5 to 70 kilometers (3 to 43 miles) across and as long as 3,000 kilometers (1,860 miles).
- Brighter central strips appear on some, resembling flat valley floors.
- Scientific study suggests these "valleys" can be no more than a few hundred meters deep.
- Europa's surface is essentially ice.
- The mean density of the interior is much greater than that of ice.
- It is about that of silicate rocks, such as volcanic lavas on Earth or the moon.
- Also indicates that Europa is composed mostly of rock.
- Only a layer of ice covers the surface.
- Ice may be as much as 100 km or 62 miles thick.
- Large craters are absent from Europa's surface.
- Only three craters are larger than 20 km or 12 miles across mapped.
- Surface apparently does not date back to the era of intense cratering
(4 to 4.5 billion years ago during planet formation).
- Icy surface area believed to be less than 1 billion years old.
- Shares similarities with Ganymede and
Callisto:
- Probably formed from a mixture of icy and rocky dust.
- Probably formed in the cold, primordial cloud of debris orbiting newly formed Jupiter.
- Europa received more heat, from two sources:
- Radiant heat came from nearby proto-Jupiter.
- Additional heat came from tidal flexing - the mechanism that causes the volcanoes on Io.
- The heat melted portions of Europa's interior.
- Watery "lava" erupted and coated the surface.
- Calculations indicate that under current conditions, tidal heating may maintain a melted layer of liquid water under the surface ice.
- This creates a sort of buried ocean.
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