Download Astronomy Notes: Planets and Moons

Astronomy Notes: Planets and Moons
This handout outlines the highlights of the planets and moons. But it is not everything in Chapters 39-48. Make
sure you also study the images of the planets and moons for identification on the Final Exam.
MERCURY (Never more than 28° from Sun, 2 hours within sunrise or sunset)
R = 0.4 AU Smooth plains (maria)
No atmosphere except for outgassing of sodium and potassium.
T = 88 days Craters & cratered plains; Temperature: 700 K (Day) , 100 K (Night), Extreme of all planets.
D = 5,000 km Scarps (Cliffs 100s km long)
d=5
Spin-Orbit Lock: 3 Rotations per 2 Revolutions (3:2)
Mercurian Year = 88 days (Earth days), Mercurian Solar Day = 176 days, Mercurian Sidereal Day = 59 days
VENUS
R = 0.7 AU
95% Carbon Dioxide, Circulating Clouds Laced with Sulfuric Acid, "Greenhouse Effect"
T = 225 days
T = 750 K, P = 100 atm, Large valleys, rolling plains, craters, volcanoes (active)
D = 12,000 km Two Main Highlands: Ishtar Terra (North), Aphrodite Terra (South)
d=5
Retrograde Rotation
MARS
R = 1.5 AU
95% Carbon Dioxide, Polar Ice Caps (Carbon Dioxide and some frozen water)
T = 2 years
Channels (water long ago), Craters (old and parts eroded), P = 0.01 atm
D = 6,700 km Volcanoes (largest is Olympus Mons), Canyons – Mariner Valleys (as long as the US)
d=4
Red crust, Dust storms (giving color variation seen from Earth)
Small Moons (2) Phobos & Deimos
JUPITER
R = 5 AU
T = 12 years
D = 140,000 km
d = 1.3
Mostly Hydrogen, Cloud Bands due to Rapid Spin
Zones - bright (rising gas), Belts - dark (falling gas)
Great Red Spot - storm (observed for 350 years)
If Jupiter were 75 times more massive, it would be a star.
The Galilean Moons of Jupiter (Galileo, 1610)
Io, Europa (about the size of our Moon), Ganymede, Callisto (about the size of Mercury)
Io - Active volcanoes, colorful sulfur compounds, molten inside, heating caused by Jovian tidal forces
Europa - Linear markings on icy surface, rocky interior
Ganymede - Scars, craters, and faults, water ice, rock (largest)
Callisto - Heavily cratered, oldest surface, water ice and rock, (impact basin with 10 concentric rings)
SATURN
R = 10 AU
Mostly Hydrogen, Cloud Bands (bland due to lower temperatures than Jupiter)
T = 30 years
Ring System (tilt cycle viewed from Earth is 30 years)
D = 120,000 km Rings - hundreds of thousands of rings or ringlets
d = 0.7
Water-ice particles from grains to boulders, mostly 10-cm balls
Saturn's Rings (Compared to the relative extent of the rings, the rings are relatively flatter than a CD.)
C B A F
Ring Designations, Cassini Division is between B and A
Saturn Radius
R
Encke Division splits the A Ring
|--- Roche Limit = 2.5 Saturn Radii ---|
Pioneer Division between A and F
RING PHENOMENA
Spokes (radial patterns) in major rings come and go (fine dust above the rings held by electrostatic forces).
Braids seen in the F ring (temporarily due to shepherds).
Shepherd moons (Prometheus and Pandora) maintain the F ring. They are about the size of Rhode Island.
- material drifting up is slowed down by the upper Pandora, causing the ring material to fall back into place
- material drifting down is sped up by the lower Prometheus, causing the ring material to rise back into place
Main Saturnian Moons: Mimas, Enceladus (500 km), Tethys (1000 km), Titan (5000 km), Iapetus (1500 km)
Mimas
- Large "Bull's Eye" crater and icy trenches
Enceladus - Craters, smooth regions, linear icy grooves. Craters Aladdin and Ali Baba
Tethys
- Craters with huge icy canyons (Ithaca Chasma)
Titan
- Nitrogen atmosphere (like smog), haze, methane
Iapetus
- Bright icy side and very dark side
Prometheus and Pandora - shepherd moons for the F ring
URANUS (Hydrogen and Helium Atmosphere, Mostly Hydrogen)
R = 19 AU
Blue-green due to methane presence, Ring System (11 Rings)
T = 84 years
Surface appears bland, cold (limited reactions)
D = 52,000 km No internal heat source
d = 1.3
Axis of rotation is nearly in plane of orbit. Retrograde Rotation.
Largest Uranian Moons from Closest to Farthest. Rock and ices, density 1.5. Largest moon is Titania.
Miranda (500 km), Ariel and Umbriel (1000 km), Titania and Oberon (1500 km).
Miranda - undulating cratered plains with chevron marking
Ariel
- brightest and youngest surface, fractures, valleys
Umbriel - uniform, darkest, oldest craters, no valleys
Titania - small craters crossed by deep grooves and valleys
Oberon - many large craters, few with dark floors
NEPTUNE
R = 30 AU
T = 165 years
D = 50,000 km
d = 1.6
Bluish Due to Methane
The farthest planet from the Sun between 1979 and 1999.
High Elongated Clouds
Great Dark Spot (photographed in the late 1980s was gone when Hubble looked in 1994).
Thin Dark Ring System
The Largest Neptunian Moon
Triton (2700 km) - thin nitrogen-methane atmosphere, ice volcanoes
DWARF PLANET PLUTO (Pluto is most similar to other ice-rock objects in the Kuiper Belt.)
R = 40 AU
Thin Methane Atmosphere. Pluto was demoted from planet status in 2006.
T = 250 years Brighter Polar Regions, Darker Equatorial Regions.
D = 2,000 km Temperature (from IRAS): 55 K
d=2
Interior: Rock (75%), Water Ice (25%)
One Moon: Charon - rock and ice with bright southern polar cap
Pluto and Charon are in a kind of super spin-orbit lock.
The same side of Charon faces Pluto and the same side of Pluto faces Charon. They face each other!
(Some astronomers pronounce Charon as “Sharon,” the name of the wife of the discoverer Christy, 1978).
.