Those four moons are likely about the same age as the rest of the solar system — about 4. Each planet in the inner solar system is less dense than their inner neighbor — Mars is less dense than Earth, which is less dense than Venus, which is less dense than Mercury.
The Galilean moons follow the same principle, being less dense the farther they are from Jupiter. The reduced density at greater distances is likely due to temperature: denser, rocky, and metal material condenses out first, close to Jupiter or the Sun, while lighter-weight icy material only condenses out at larger distances where it is colder.
Distance from Jupiter also determines how much tidal heating the Galilean satellites experience — Io, closest to Jupiter, is heated so much that it is the most volcanically active body in the solar system, and it likely long ago drove off any water it had when it formed. Europa has a layer of ice and water on top of a rocky and metal interior, while Ganymede and Callisto actually have higher proportions of water ice and so lower densities.
Like our planet, Europa is thought to have an iron core, a rocky mantle, and an ocean of salty water. While evidence for an internal ocean is strong, its presence awaits confirmation by a future mission.
All along Europa's many fractures, and in splotchy patterns across its surface, is a reddish-brown material whose composition is not known for certain, but likely contains salts and sulfur compounds that have been mixed with the water ice and modified by radiation. This surface composition may hold clues to the moon's potential as a habitable world.
Some of these fractures have built up into ridges hundreds of meters tall, while others appear to have pulled apart into wide bands of multiple parallel fractures. Galileo also found regions called "chaos terrain," where broken, blocky landscapes were covered in mysterious reddish material. In , scientists studying Galileo data proposed that chaos terrains could be places where the surface collapsed above lens-shaped lakes embedded within the ice. Europa has only a tenuous atmosphere of oxygen, but in , NASA announced that researchers using the Hubble Space Telescope found evidence that Europa might be actively venting water into space.
This would mean the moon is geologically active in the present day. One of the most important measurements made by the Galileo mission showed how Jupiter's magnetic field was disrupted in the space around Europa. The measurement strongly implied that a special type of magnetic field is being created induced within Europa by a deep layer of some electrically conductive fluid beneath the surface.
Based on Europa's icy composition, scientists think the most likely material to create this magnetic signature is a global ocean of salty water, and this magnetic field result is still the best evidence we have for the existence of an ocean on Europa.
Resource Packages. A 3D model of Jupiter's moon Europa, an icy moon with a hidden subsurface ocean. A 3D model of Europa Clipper, a future mission to Jupiter's ocean moon. The effect is more than just a cool visual. The surface of Jupiter's moon Europa features a widely varied landscape, including ridges, bands, small rounded domes and disrupted spaces that geologists call "chaos terrain.
Scientists discovered that the yellow color visible on portions of the surface of Europa is actually sodium chloride, a compound known on Earth as table salt, which is also the principal component of sea salt.
Table Salt Compound Spotted on Europa. Europa's Ocean Ascending. PDT 1 p. The Europa Clipper project team continues to grow as we move into more detailed design of the equipment, and it is gratifying to see such a geographically distributed team work well together.
The Sextant: Europa Clipper Newsletter. Juno Observes Jupiter, Io and Europa. A mission to examine the habitability of Jupiter's ocean-bearing moon Europa is taking one step closer to the launchpad, with the recent completion of a major NASA review. A new NASA study modeling conditions in the ocean of Jupiter's moon Europa suggests that the necessary balance of chemical energy for life could exist there, even if the moon lacks volcanic hydrothermal activity.
Two powerful science investigations will help unravel the mystery of whether Jupiter's icy moon Europa might have the right conditions for life, when a new NASA mission heads there sometime in the s.
Ice, liquid water and NASA's Galileo spacecraft today successfully made its closest-ever flyby of Jupiter's icy moon Europa, marking the start of an extended mission.
Europa's Surface Ice. Remote Probe. When Galileo Galilei discovered Europa in , he could only imagine whether the Jovian satellite contained life. But recent scientific discoveries suggest that Europa could possibly be an abode for life. At one time, scientists believed that a solid layer of ice covered Europa's frigid surface.
Later, photographs taken by the Galileo space probe, which is in orbit around Jupiter, revealed that the white, icy landscape is striated by spindly, rust-colored fissures, with relatively few crater impacts. The lack of craters and the surface ice cracks some of which are more than nine miles wide indicate that something is constantly fracturing and replacing the ice. Probably an ocean below. Could an Europan ocean contain living things?
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