The Outer Planets. The Moon. The Origin of the Moon The Outer Planet Family. Lecture 34. Chapter 16.9 16.16. Summary of Terrestrial Planets. All the planets are relatively small (diameter < 13,000 km) Composition: rocks and metals (mean densities 3-5 g/cm 3 ) Density of water is 1 g/cm 3
All the planets are relatively small (diameter < 13,000 km)
Composition: rocks and metals (mean densities 3-5 g/cm3) Density of water is 1 g/cm3
The planets are closely spaced (mean distance between them is 0.4 A.U.)
1 Astronomical Unit (A.U.) is the mean distance between the Sun and the Earth – 150 million kilometers
The outermost planet, Mars, is located 1.5 A.U. from the Sun
The Moon is the largest satellite of a planet in the inner solar system.
The mean distance from the Earth is 384,000 km.
Diameter 3476 km (27% of the Earth’s diameter)
Mass is 1/81 of the Earth’s mass
Average density is 3.3 g/cm3 (60% of the Earth’s)
Why is there a large gap between the two families of planets?
What did cause the differences in the structures, compositions, and surroundings of the two families?
No solid surfaces
Content: Almost entirely H and He + trace amounts of methane (CH4), ammonia (NH3), and H20.
Jupiter’s weather occurs in troposphere where clouds can be formed of ammonia crystals and other compounds
There are more than 100 known moons orbiting Jovian planets (J-52, S-30, U-21, N-11)
Three main groups of jovian moons:
Small moons - less than 300 km in diameter
Medium-size - 300-1500 km
Large - more than 1500 km
Medium and large moons have circular orbits that lie close to the equatorial planes of their parent planets
Pre-visit expectations: cold and geologically dead
Voyager missions: the moons are active!
Four Galilean moons: Io, Europa, Ganymede, Callisto
Io has many volcanoes and no impact craters
Europa – no craters, fractured surface, icebergs
Ganymede – grooves on surface, magnetic field
Callisto – a heavily cratered iceball
Eruptions erased all Io’s impact craters.
Io has an additional heating source – tidal heating
Tidal heating is due to the Io’s orbit ellipticity.
Io is continuously flexed by Jupiter.
Source of the orbit ellipticity – orbital resonances
Periodical lining up of the three closest satellites of Jupiter (Io – 4 orbits, Europa – 2 orbits, Ganymede – 1 orbit)
Two of Saturn’s rings can be seen from Earth
In fact, there are as high as 100,000 individual rings and gaps
Rings and gaps are caused by grouping of particles at some orbital distances which are being forced out at others.
Gaps can be created by gap moons located within rings. They clear up gaps around their orbits.
The Earth’s Moon seems to be a result of a collision with a large proto-planet (Mars size)
Jovian planets are dynamic worlds with rapid winds, huge storms, strong magnetic fields, and interiors where common materials strangely behave.
Jovian moons are geologically active because of their ice compositions.
Ring systems were formed from small moons.