NASC 1100 - The University of Toledo

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Transcript NASC 1100 - The University of Toledo

Lecture 34
The Outer Planets. The Moon.
Chapter 16.9  16.16
• The Origin of the Moon
• The Outer Planet Family
Summary of Terrestrial Planets
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
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)
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Hypotheses of the Moon’s origin:
Forming together with Earth and splitting
Captured by the Earth fully formed
Double-planet
Collision
What Do We Need to Learn?
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?
Jovian Planets: Basics
• Distance: 5-30 AU
– Much farther from Sun than terrestrial planets
– Much colder (100-50 K)
• Mass: 10-100 Earth masses
– Much more massive than terrestrial planets
• Jupiter & Saturn are similar
– Size (about 10 Earth diameters)
– Composition: mostly hydrogen and helium
• Uranus & Neptune are similar
– Smaller than Jupiter & Saturn
– Less hydrogen and helium
Basic Parameters
Planet
Jupiter
Dist.
A.U.
5.20
Mass
MEarth
317
Radius
REarth
11.2
Density Composition
g/cm3
1.33
H, He
Saturn
9.53
90
9.4
0.70
H, He
Uranus
19.2
14
4.11
1.32
Neptune 30.1
17
3.92
1.64
H compounds
rock, H, He
H compounds
rock, H, He
Appearance
• Jovian planets show “banded” appearance
– due to atmosphere
– we see only cloud tops
• Rotation quite fast (hours)
– Jupiter: 10 hrs
– Saturn: 11 hrs
– Uranus: 17 hrs
– Neptune: 16 hrs
Clouds
• Clouds on Jupiter & Saturn
composed of ammonia ice (NH3)
• different colors due to differing cloud composition
Saturn’s clouds deeper; less visible
• Clouds on Uranus & Neptune
– composed of methane (CH4)
• produces blue-green color
Planet Interiors
Jupiter
Planet Density
Jovian Planet Atmospheres
No solid surfaces
Jupiter atmosphere
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
The Great Red Spot
Jovian Planet Moons
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
Jupiter Moons
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
Io
Eruptions erased
all Io’s impact
craters.
Reasons for Geological Activity
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)
Tidal Heating
Rings and Gaps
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.
Rings of Saturn
Telescopic view
Rings of Saturn (Voyager image)
Rings of Saturn (close up)
Summary of Jovian Planets
• Jovian planets larger, more massive than terrestrial
• Composition:
– mostly hydrogen (H) and helium (He)
– dominated by hydrogen
– also large amounts of ices (water, ammonia,
methane)
• Why So Large?
– basic reason is distance from sun
• cooler temps allowed ices (volatiles) to freeze
Role of Volatiles
• Inner solar system is hot:
–volatiles are gaseous; not available for planet core formation
–planet cores
• only rock (no ice)
• smaller, less massive (1 earth mass)
• Outer solar system is cold:
– volatiles are solid; available for planet core formation
– planet cores
• both rock and ice
• bigger, more massive (10 earth masses)
• Massive cores have larger gravity; can capture gas
– Jovian planets have massive atmospheres (lots of H and He)
– Terrestrial planets have minimal atmosphere (little H and He)
Summary
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.