Lesson 8a

Moons, Asteroids and Rings

Europa

• These interactions also keep Europa in a slight elliptical orbit as well.

• But since Europa is farther from Jupiter the effect is not as strong as on Io.

Europa’s interior

Possible volcanic vents on beneath Europa

Possible Life?

New theory on Europa ice flows

• http://www.youtube.com/watch?v=7vAUMS6VtXo&feature=related

Orbits of all of Jupiter’s moons

What do you think about the origin of most of Jupiter’s moons?

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1 2 3 4

25% 25%25%25%1. Co-accretion origin2. Fission origin3. Capture origin4. Giant impact origin

What do you think about the origin of most of Jupiter’s moons?

Asteroid Belt

Lagrangian Points

Asteroids

Asteroids

Eros

Ida & Dactyl

Dawn mission to Vesta (current)

Phobos – Martian Moon

Deimos – Martian moon

• What is the likely origin of the moons of Mars?

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1 2 3 4

25% 25%25%25%1. Fission2. Co-accretion3. Capture4. Giant impact

Russian probe Phobos-Grunt.

• Probe stuck in Earth’s orbit.• Would have landed on Phobos and returned

to Earth, soil and rock samples.

• If Phobos is chemically similar to Mars, then it could be the Phobos and Demos originated as shot out debris from a Martian impact.

• Phobos orbits Mars every 11 hours.• Demos orbits Mars every 30 hours.• Mars rotates on its axis every ~ 25 hours.

• In the next 50 million years, Phobos will crash into Mars.

Earth and the Moon

• Why will Phobos crash into Mars?

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1 2 3

33% 33%33%1. Phobos is too close and Mars

gravity will pull it in.2. Phobos is orbiting faster than Mars

spins. Mars is slowing it up.3. Demos is pulling on Phobos

causing it to fall into Mars

Effect of sub-synchronous orbit.

Phobos is speedingUp Mars rotation, and Mars is slowing up Phobos’sOrbital speed.

• What does this 3:1 represent?

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1 2 3 4

25% 25%25%25%1. Jupiter is 3 times farther from the Sun than the gap is.

2. Jupiter completes 3 orbits for every 1 gap orbit.3. The gap is 3 times closer to the Sun than Jupiter4. The gap completes 3 orbits for every 1 of

Jupiter’s orbits.

Keplers 3rd law relates period to semi-major axis

• Kirkwood gap with resonance 3:1.• Semi-major axis is a = 2.5 AU.

P2 = a3 P = (2.53)0.5 = 3.95 yearsJupiter has a = 5.2 AU. PJ = (5.23)0.5 = 11.85 years.

11.85/3.95 = 3 This is the 3:1 resonance

Eris

Kuiper belt and scattered disk

The Planets• Currently there is little evidence that the

planets in the Solar System are in any type of resonance orbit.

• Example:• Jupiter orbital period = 11.86 years• Saturn orbital period = 29.46 years 29.46/11.86 = 2.48 Close to a 2:5 resonance• But this wasn’t always the case.

• It has been shown with theoretical modeling that Saturn likely formed much closer to Jupiter.

• Also Uranus and Neptune were within 15 AU of the Sun originally. Now they are at 19 AU and 30 AU.

• Some models suggest that Neptune actually formed closer to the Sun than Uranus.

• When Jupiter and Saturn formed they were very close to 1:2 resonance orbit

The giant planets and Kuiper belt objects.

• Jupiter and Saturn exchanged angular momentum and finally Saturn reached a resonance 1:2 orbit with Jupiter.

• When this happened in a very short period of time the combined effects of the two enormous planets was to move Uranus and Neptune outward.

• Their motion also effect Saturn, like-wise moved outward.

A model of planetary migration

Other models of this migration

The effect of this migration

• Jupiter moved inward in its orbit. It is thought that this is what allowed it to capture some of its moons and as it moved into the asteroid belt, it picked up the Trojan asteroids in its lagrange points.

• Neptune moved rapidly outward. Its elliptical orbit settled down to circular by exchanging angular momentum with the Kuiper objects.

New evidence published this year

• Gravity models using just the four gas giant planets is not able to produce the orbits we see today.

• Early on in the solar system it is thought that this extra planet was sped up by interactions and flung out of the solar system.

• Many of the Kuiper objects were moved outward onto highly eccentric orbits. Some inhabited a large region around the Solar System called the Oort cloud. These are seen today as comets when they near the Sun.

• Others were sent down to the center of the solar system where they collided with the Sun and the terrestrial planets.

• This time is called the “Late Heavy Bombardment” around 4 billion years ago.

• It is thought that the large impacts that made the Lunar Maria came from this event.

• Also Hellas crater on Mars.• Also the axis tilts of Saturn, Uranus and

Neptune probably occurred because of this migration.

• It is thought that the large impacts that made the Lunar Maria came from this event.

• Also Hellas crater on Mars.• Also the axis tilts of Saturn, Uranus and

Neptune probably occurred because of this migration

• After the Jupiter-Saturn 1:2 resonance event, the Solar System settled into the configuration seen today.

New evidence published in 2011• Gravity models using just the four gas giant

planets are not able to produce the orbits we see today.

• By adding an additional Neptune-size planet the orbits of the current gas-giants are correct.

• Early on in the solar system it is thought that this extra planet was sped up by interactions and flung out of the solar system.