Which galilean moon has volcanic activity

Of the Galilean moons, Callisto is the furthest from Jupiter. Callisto has a very thin atmosphere, is thought to contain an ocean, and is therefore another possible contender for life beyond Earth. Could Jupiter and its icy moons harbour the conditions required for life to exist? Weighing up the evidence on Io, Europa, Ganymede and Callisto.

Is there life on the Galilean moons of Jupiter? A fuller explanation is given in the section on Io. We will see as we move inward to Europa and Io that the role of jovian tides becomes more important for moons close to the planet.

Europa and Io, the inner two Galilean moons, are not icy worlds like most of the moons of the outer planets. With densities and sizes similar to our Moon, they appear to be predominantly rocky objects. How did they fail to acquire a majority share of the ice that must have been plentiful in the outer solar system at the time of their formation?

The most probable cause is Jupiter itself, which was hot enough to radiate a great deal of infrared energy during the first few million years after its formation. This infrared radiation would have heated the disk of material near the planet that would eventually coalesce into the closer moons. Thus, any ice near Jupiter was vaporized, leaving Europa and Io with compositions similar to planets in the inner solar system. Despite its mainly rocky composition, Europa has an ice-covered surface, as astronomers have long known from examining spectra of sunlight reflected from it.

There are very few impact craters in this ice, indicating that the surface of Europa is in a continual state of geological self-renewal. Judging from crater counts, the surface must be no more than a few million years old, and perhaps substantially less. In terms of its ability to erase impact craters, Europa is more geologically active than Earth.

When we look at close-up photos of Europa, we see a strange, complicated surface Figure 3. For the most part, the icy crust is extremely smooth, but it is crisscrossed with cracks and low ridges that often stretch for thousands of kilometers.

Some of these long lines are single, but most are double or multiple, looking rather like the remnants of a colossal freeway system. Figure 3: Evidence for an Ocean on Europa. This view is 70 kilometers wide in its long dimension. Not anchored to solid crust underneath, many of the ice blocks here seem to have slid or rotated from their original positions. Where these ridges intersect, we can see which ones are older and which younger; the younger ones cross over the older ones.

While superficially this system of ridges resembles a giant freeway system on Europa , the ridges are much wider than our freeways and are a natural result of the flexing of the moon.

The area in this picture is only 15 kilometers across. It appears to have formed when viscous icy material was forced up through a long, straight crack in the crust. Note how the young ridge going from top left toward bottom right lies on top of older features, which are themselves on top of even older ones. It is very difficult to make straight lines on a planetary surface. We now know the lines on Mars were optical illusions, but the lines on Europa are real.

These long cracks can form in the icy crust if it is floating without much friction on an ocean of liquid water Figure 4. The close-up Galileo images appear to confirm the existence of a global ocean. In many places, the surface of Europa looks just as we would expect for a thick layer of ice that was broken up into giant icebergs and ice floes and then refrozen in place.

When the ice breaks, water or slush from below may be able to seep up through the cracks and make the ridges and multiple-line features we observe. Many episodes of ice cracking, shifting, rotating, and refreezing are required to explain the complexity we see. The icy crust might vary in thickness from a kilometer or so up to 20 kilometers. If Europa really has a large ocean of liquid water under its ice, then it may be the only place in the solar system, other than Earth, with really large amounts of liquid water.

Hot or at least warm springs might be active there, analogous to those we have discovered in the deep oceans of Earth. The necessary internal heat is generated by tidal heating see the discussion later in this chapter. In this short film, planetary scientist Kevin Hand explains why Europa is so interesting for future exploration. Is it possible that similar ecosystems could exist today under the ice of Europa? Many scientists now think that Europa is the most likely place beyond Earth to find life in the solar system.

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When Io comes back into sunlight, the freezing sulfur dioxide converts to gas once more. Scientists long suspected this phenomenon exists, but it was only after this new study — which saw Io's atmosphere in the dark for the first time — that researchers confirmed it. Io's environment has come under intense scrutiny in recent years as scientists try to explain why the moon has the most active volcanoes in the solar system.

The recent findings involve both observations of the moon and modeling of the interior, which can only be inferred. A study explained why Io's most prolific volcanoes appear to be offset from where scientists expected they would be. While previous models suggested that the zones with the most intense heating would have more active volcanoes, the actual Io had its most active ones farther east.

The study suggests that if there was an ocean mixed with molten and solid rock underneath the moon, the rock portions would rub against each other and create the offset zones scientists observed. However, the existence of a molten ocean came into doubt with a study , which showed that some auroras we can see in Io's atmosphere would have been damped out by an underground ocean.

In other words, we can only see the auroras because the moon likely has no molten ocean, the study concluded.

Insights into Io's surface may also come from a map published by the U. Geological Survey — the first to include the entire surface. The researchers said that volcanic activity would be among the things that could be studied with this map.

The imagery includes observations from the Voyager 1 and Voyager 2 spacecraft, as well as Galileo. While there is no mission specifically planned to look at Io, other missions are now in the vicinity of the moon — such as the aforementioned Juno spacecraft — or will be in future years. Meanwhile, observations continue from the ground; sometimes Io's volcanoes are violent enough to produce spectacular pictures even from so far away.

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