HW

Question 1

True or false: all Jovian planets have rings and moons

Answer 1

true

Question 2

Why do moons orbit instead of flying away from their host planet?

Answer 2

gravity ties them to the planet

Question 3

There are two moons in orbit around two planets; the orbits are both the same size. The moon orbiting planet Indigo takes 2 hours to orbit once. The moon orbiting planet Saffron takes 2 days to orbit once. Which planet has more mass?

Answer 3

indigo

Question 4

These are the orbit sizes of two of Jupiter’s moons: Io orbit semi-major axis 0.002819 AU (1.87 Jupiter’s diameter) Europa orbit semi-major axis 0.004473 AU (2.98 Jupiter’s diameter)

Answer 4

shorter, the same

Question 5

Say you want Earth’s Moon to go through phases in two weeks rather than one month. What should you do to make the Moon orbit Earth faster?

Answer 5

push the Moon into a smaller orbit

Question 6

Why don’t we see large moons very close to the planets (like inside the Roche limit)?

Answer 6

the difference in gravity between the side near the planet and far from the planet would rip apart a large moon

Question 7

A tidal force could arise on a moon because one side is farther from the planet and feels a ____ force of gravity than the near side

Answer 7

weaker

Question 8

We see dramatic evidence of heating on various moons, including volcanoes on Io, a sub-surface ocean on Europa, and geysers on Enceladus. What is responsible for heating these moons?

Answer 8

changing tidal forces

Question 9

What are planetary rings made of?

Answer 9

millions of little particles each orbiting the planet

Question 10

Which of the following statements correctly describes the motion of the particles in rings?

Answer 10

Particles in the inner rings orbit the planet at a faster speed than particles in the outer rings

Question 11

Saturn’s rings are spectacular, but the other jovian planets’ rings are very hard to see. Why are Jupiter’s, Uranus’, and Neptune’s rings so dark?

Answer 11

they are made of dark particles and there just aren’t many particles in the rings, either

Question 12

What is the Roche limit?

Answer 12

how close a moon can get to a planet before being ripped apart by gravity

Question 13

Particles inside a planet’s Roche limit don’t clump and they stay as a ring system, but particles outside of the Roche limit can clump and form a large moon. Why is this?

Answer 13

outside the Roche limit the tidal force is much less and won’t tear apart the moon as it tries to form

Question 14

True or false: the Moon is the only object that raises a tide on Earth

Answer 14

false

Question 15

The Roche limit for a planet is around 2.5x the planet’s radius (or slightly more than the planet’s width). Where is Earth’s Moon?

Answer 15

outside Earth’s Roche limit

Question 16

The Moon can raise tides on Earth but those tides are small, less than a yard tall. That’s not very impressive! Why is the force between the Earth and the water stronger than the force between the Moon and the water?

Answer 16

the Earth has more mass and the water is closer to the center of the Earth than the center of the Moon

Question 17

When Earth was forming it was hit by another small planet, and some material splashed into space from that impact ended up going the right speed to orbit Earth as rings. That material eventually clumped together to become our Moon. Why didn’t this material stay as rings? Hint: consider the size of the Moon’s orbit.

Answer 17

the material was outside Earth’s Roche Limit, so it wouldn’t stay as ring particles