Lesson 12 - Jovian Moons, Rings, & Dwarf Planets

What is the diameter range of small moons, and why are they irregular in shape?

Less than 300km; they have unusual orbits and are irregular due to low gravity

What characteristics define medium-sized moons?

They are 300-1,500km in diameter, usually have circular orbits, and are spherical in shape

What properties do large moons share with medium-sized moons?

They are 1,500km+ in diameter and have similar properties like magnetic fields and tectonic activity

What makes Io colorful and free of impact craters?

Its many volcanoes and sulfurous surface due to thermal energy from internal tidal heating.

What causes Io's significant internal tidal heating?

Its elliptical orbit and orbital resonance with Jupiter.

What is Europa's surface covered with, and what does it suggest about potential life?

It is covered by a subsurface ocean, suggesting the possibility of life.

What causes the fractures on Europa’s icy surface?

Tidal forces from Jupiter and its other moons.

Which is the largest moon in the solar system?

Ganymede.

How are Ganymede and Callisto similar in appearance?

Both are covered with craters and icy surfaces.

What is Titan's atmosphere primarily composed of?

90% nitrogen, along with argon, methane, and ethane.

What makes Titan uninhabitable despite its surface pressure being similar to Earth's?

The lack of oxygen and extremely cold temperature of -180°C.

What geological activity is Enceladus known for?

Geysers that erupt plumes of water vapor, nitrogen, carbon dioxide, and methane.

What is believed to exist beneath Enceladus's icy surface?

A subsurface ocean potentially hosting life.

What makes Miranda stand out among Uranus's moons?

Its tortured surface with craters, cliffs, ridges, and canyons.

Why is Triton known as the "backwards moon"?

Due to its retrograde orbit relative to its revolution.

What unique surface features does Triton have?

A wrinkly "cantaloupe-like" surface of reflective water ice, geysers, and a thin atmosphere.

What are the three distinct ring areas of Saturn called, from outermost to innermost?

The A ring, B ring, and C ring.

What is the difference in the size of ice particles between the A and B rings compared to the C ring?

The A and B rings contain golf ball-sized ice crystals, while the C ring contains boulder-sized chunks of ice.

How thick are Saturn's rings?

They are no thicker than 100 meters, and can be as low as 30 meters thick in many locations.

What is the Encke gap?

A small gap on the outer edge of the A ring.

What causes the Cassini Division, the larger gap separating the A and B rings?

The moon Mimas’s gravity

How were Saturn’s rings formed?

Gravitational forces near Saturn elongate and eventually break apart small moons - the debris is kept in place by shephard moons

Where does the breakup of moons into ring particles occur?

Within the Roche limit, about 144,000 km from Saturn (2.4x Saturn's radius).

What causes ring particles to de-orbit or eject from Saturn's rings?

Atmospheric drag and inter-ring collisions.

How do the rings of Jupiter, Uranus, and Neptune differ from Saturn's rings?

They are thin, dark, and contain varying sizes of particles.

How do shepherd moons like Pandora and Prometheus affect Saturn's rings?

They keep the rings well-defined by their gravitational influence.

What is one of the IAU's criteria for planet status that Kuiper Belt objects do not meet?

Clearing their orbit of debris.

How does Pluto rotate?

Pluto rotates backwards, like Venus and Uranus.

What is the size and mass relationship between Pluto and its largest moon, Charon?

Charon is about half the size of Pluto but 1/10 of the mass.

After whom is Charon named?

The mythical boatman who ferries the dead into the realm of Pluto/Hell.

Describe Charon's orbit in relation to Pluto.

Charon orbits close to Pluto and at its rotation speed, fixing its position in the sky.

How many smaller moons does Pluto have, and what is special about their orbits?

Pluto has 5 smaller moons, with 2 orbiting in a 12:3:2 radius with Charon.

Which three dwarf planets are recognized by the IAU?

Eris, Haumea, and Makemake.