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Lecture 30 - Galilean Moons cont.

Terms in this set (28)

How does the surface of Callisto erode away?
Surface erodes away with bombardment of radiation
What causes the loss of water ice on Callisto?
Ionized radiation
What do cross-cutting relationships give us information about?
Cross-cutting relationships give us information about the sequence of events
Ganymede is the only moon in the solar system known to possess its own ...? Which other moon might have one as well?
Ganymede is the only moon in the solar system known to possess its own internally-generated magnetic field, although Europa might have a weak field as well.
How is Ganymede's magnetic field generated? What is this similar to?
Ganymede's magnetic field is thought to be generated by convection in its molten iron core, just as Earth's magnetic field is generated.
What did the Galileo spacecraft discover about Ganymede? What does the combination of these discoveries result in?
The Galileo spacecraft discovered that Ganymede not only has a magnetic field, it also has a very tenuous atmosphere composed of oxygen. In fact, the combination of a magnetic field and an atmosphere results in aurora on Ganymede.
Why is our atmosphere rich in oxygen?
On Earth, our atmosphere is rich in oxygen due to photosynthesis.
Is there life on Ganymede? How is oxygen released on Ganymede? What happens to the hydrogen?
No. On Ganymede, oxygen is released from the surface by the photolysis of water: 2H2O => 2H2 + O2. The hydrogen escapes into space, but the oxygen escapes more slowly, resulting in a very thin atmosphere.
What kind of structure does Ganymede have? How do we know? What is it made of?
In addition to having a fully differentiated structure (evidence for this comes from Ganymede's low moment of inertia), Ganymede may also have a liquid ocean of salt water ~200 km below the surface, sandwiched between layers of ice. (Ice-liquid-ice)
Liquid water is what kind of insulator? Does it ?conduct electricity well? What about salt water?
Liquid water is an electrical insulator (doesn't conduct electricity very well)
Salt water is a better conductor of electricity
Why do we think that Ganymede is going through a sea of electrical currents?
Ganymede is going through a sea of electrical currents - if it was completely solid then the currents would interact with it in a different way. A portion of it can conduct electricity well so we think it is salt water layer because we need something that conducts underneath the surface in order for these electric currents.
What are many large icy moons thought to have?
Many large icy moons are thought to potentially have layers of liquid water trapped between layers of ice.
What are several of the Galilean moons thought to have? Which ones? Why do we think this?
Several of the Galilean moons (Europa, Ganymede, and possibly even Callisto) are thought to have a layer of liquid water at various depths beneath the surface. This is because liquid water is denser than water ice at low pressures, but less dense at higher pressures.
Water ice has many different forms or crystal structures depending on...?
Water ice has many different forms or crystal structures depending on pressure and temperature.
Which is denser: Ganymede, Europa or Callisto? What does this suggest about its composition?
Europa is denser than Ganymede and Calisto (2.99 g/cm3), suggesting it is made primarily of rock rather than ice.
What is the surface of Europa like? What do the complex terrains suggest?
It has an icy surface that is only lightly cratered and which is covered with a very complex network of cracks, ridges, and grooves. Young (sparsely cratered), complex terrains suggest Europa's surface may have been reworked by cryovolcansim or by tectonic processes.
Have we found definitive evidence for active cryovolcanism on Europa?
Definitive evidence for active cryovolcanism on Europa has not yet been found, but a number of structures certainly look "suspicious", such as the blister-like features.
What warms Europa's interior? What might it's icy crust be hiding?
Europa's proximity to Jupiter and gravitational interaction with the other Galilean satellites results in tidal heating, which warms Europa's interior. Europa's icy crust may be quite thin and hide an ocean of liquid water several hundred km thick.
Two different models for the internal structure of Europa?
Most scientists believe Europa has an ocean of liquid water beneath a hard icy crust that is a few kilometers up to ~30 km thick. However, it is possible that the interior of Europa is warm enough to soften the ice below the surface, but not cause it to melt. Solid-state convection of soft ice could produce the grooved features observed at the surface.
What do some portions of Europa's crust resemble?
Some portions of Europa's crust resemble icebergs embedded in a frozen sea.
Scientists think there is liquid water beneath the surface ice layer on Europa, but how do we detect something we cannot see? What does the magnetic moment of Europa require? Does the magnetic moment support the existence of liquid water?
One way of probing the interior of these moons is to measure how they interact with Jupiter's magnetic field. The magnetic moment of Europa requires that the planet contain a layer of electrically conductive material below the surface. Ice is a poor conductor of electricity, but salt water is a good conductor, so Europa's magnetic moment supports the existence of a liquid water layer. Evidence is based on the electromagnetic currents happening on the surface.
Why do we care so much about whether Europa has a hidden ocean?
On Earth, deep-sea hydrothermal vents team with life, and may have been home to the earliest life forms. Could similar vents beneath Europa's icy crust provide a habitat for life?
What might future missions to Europa use? How are these missions developed and tested?
Future missions may use cryobots to melt through Europa's outer ice layer and explore the ocean beneath. The technology for these missions can be developed and tested in sub-glacial Antacrtic lakes such as Lake Vostok.
How could we look for life on Europa?
In the future, we may develop probes that can melt or drill through the icy crust, and submersibles that can explore Europa's ocean. However, for now, Europa's surface may provide the clues we need.
What do the grooves on Europa mark?
The grooves on Europa mark areas where warm ice that forms at the top of Europa's ocean pushes up to the surface. If life exists in the ocean, this ice could contain chemical clues (e.g., complex organic molecules) to its existence. A sample return mission could help answer this question.
What kind of atmosphere does Europa have? What is this kind of atmosphere primarily composed of? What similarities do we see between Ganymede and Europa?
Europa has a very tenuous atmosphere. As we saw for Ganymede, this atmosphere is primarily composed of oxygen, and can be detected by oxygen fluorescence. Just as for Ganymede, the oxygen atmosphere is not evidence for biological processes.
Is the oxygen in the atmospheres of Ganymede and Europa evidence for biological processes?
No, however, the breakdown of water due to intense radiation produces the oxygen.
What are the surfaces of Galilean moons influenced by?
The surfaces of all the Galilean moons are strongly influenced by the constant bombardment of high energy radiation and ionized particles produced by Jupiters monster magnetic field.
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