Transcript: Tidal heating is another consequence of gravity acting on moons of planets. The tidal force is the differential force or stretching force on a moon orbiting a planet. Tidal force increases with increasing moon size and decreasing distance from the planet. If the tidal force is too large, the moon will be disrupted, but even a moderate tidal force is enough to cause heating of a moon. Basically the stretching force, in particular in an elliptical orbit where the stretching...

Transcript: The composition of the atmosphere of any planet depends on three things. The first is the chemical composition of the material available to form an atmosphere. This is the original hydrogen and helium of the solar nebula plus trace elements combined with the amount of gas that outgases from the interior of the planet though it evolution. Second is the mass of the planet which dictates its surface gravity, and third is the temperature of the planet determined by its distance...

Transcript: How large does a chunk of rock have to be to be called by a moon or a satellite? There is no simple answer to this question; it's largely a matter of definition. However, in general objects that are less than 10 kilometers across are too small to be called moons. Deimos, Mars' smaller of the two moons, is slightly larger than this number. All the moons between 10 and 100 kilometers in the solar system typically have names, and above 1,000 kilometers the moons are distinctive...

Transcript: How large does a chunk of rock have to be to be called by a moon or a satellite? There is no simple answer to this question; it's largely a matter of definition. However, in general objects that are less than 10 kilometers across are too small to be called moons. Deimos, Mars' smaller of the two moons, is slightly larger than this number. All the moons between 10 and 100 kilometers in the solar system typically have names, and above 1,000 kilometers the moons are distinctive...

Transcript: Each planet in the solar system is surrounded by an imaginary spherical region called the sphere of gravitational influence. For any object, such as a moon or ring particle situated within this sphere, the motions are dictated by the planet. Beyond this sphere the motions are dictated by the Sun. Thus, a moon placed just outside the sphere of gravitational influence of Jupiter would gradually drift apart from Jupiter and would move into a different orbit of the Sun. In a...

Transcript: Is there something that sets the maximum size of the moon of a planet? The answer to this question complex, but one part of the answer is Roche's limit. The tidal force on a moon increases both with the size of the moon and it's proximity to the planet. Thus, a moon that is large and close to a planet will have a large tidal force, and at some point that tidal force will disrupt the solid material and break apart the moon leading perhaps to a ring system. Thus, moons that are...

Transcript: All ring systems in the solar system have outer edges that are somewhere between 1.8 and 2.5 times the planet radius from the center of the planet. What is particular about this ratio and how does it arise? The answer was derived in the mid-nineteenth century by the French mathematician Edward Roche. He calculated that the edge of planetary rings is defined by tidal forces. If we consider the gravity force between particles composing a planetary ring, the Roche limit, as it's...

Transcript: Gravity keeps planets in their orbit of the Sun and keeps moons in their orbit of the planets. There is a second type of force that is important, however, in the solar system, tidal force. A tidal force is caused by the difference between the gravity force on one side of an object and the other side. It's essentially a stretching force. The size of a tidal force depends on the ratio between the front to back distance, or diameter, of an object like a moon or a planet and its...

Transcript: Resonance is a phenomenon that’s common to all vibrations and waves. It’s a situation where a vibration, a wave, or an oscillation caused by one object induces a vibration, a wave, or an oscillation in another object. Obvious example of resonance is the fact that soldiers must break step when they walk across a bridge in case the pattern of their marching motion corresponds to a natural frequency of the bridge, in which case the marching adds energy to the bridge motion which...

Transcript: The rings of Saturn are spectacular and highly complex. The Voyager space probes showed the existence of thousands of individual ringlets, with the widest gap being Cassini's division, which was discovered in the seventeenth century. The particle sizes within the rings range from golf ball size up to about the size of a house. Larger blocks of material are broken down by collisions. The material is mostly made of frozen ices rather than dark, rocky material, so the rings are...

Transcript: Where did the rings of the giant planets come from? Interplanetary debris has rained down upon the giant planets and the moons of the giant planets since the formation of the solar system four and a half billion years ago. Some of the giant planets undoubtedly accreted a ring of debris material early in their history, yet more of the material must have come from impacts of interplanetary debris on the inner moons of the planets themselves. Some of these impacts sandblasted the...