HW Flashcards
True or false: all Jovian planets have rings and moons
true
Why do moons orbit instead of flying away from their host planet?
gravity ties them to the planet
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?
indigo
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)
shorter, the same
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?
push the Moon into a smaller orbit
Why don’t we see large moons very close to the planets (like inside the Roche limit)?
the difference in gravity between the side near the planet and far from the planet would rip apart a large moon
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
weaker
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?
changing tidal forces
What are planetary rings made of?
millions of little particles each orbiting the planet
Which of the following statements correctly describes the motion of the particles in rings?
Particles in the inner rings orbit the planet at a faster speed than particles in the outer rings
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?
they are made of dark particles and there just aren’t many particles in the rings, either
What is the Roche limit?
how close a moon can get to a planet before being ripped apart by gravity
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?
outside the Roche limit the tidal force is much less and won’t tear apart the moon as it tries to form
True or false: the Moon is the only object that raises a tide on Earth
false
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?
outside Earth’s Roche limit
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?
the Earth has more mass and the water is closer to the center of the Earth than the center of the Moon
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.
the material was outside Earth’s Roche Limit, so it wouldn’t stay as ring particles
