November 21 st November 23rd 2012
Astronomy Lecture Notes
Jupiter’s moon Europa: fresh surface of Ice w/ cracks
o Tidally heated water below the ice.
Ganymede: surface has two ages.
Callisto: dark, cratered, old surface.
Distance from Jupiter Systematic change.
Saturn’s moon Titan: dense atmosphere of N2 w/ lakes of methane and
Medium-sized moons have surprising geology.
All Jovian planets have rings.
Saturn’s rings = not solid but consist of billions of objects from 10M to dust
size in orbits.
Composition of the Rings:
Use Kirchhoff’s 3 law again:
o Observe the spectrum of sunlight reflected by rings compare
spectrum coming from sun any extra absorption = due to rings
match to samples of Earth.
Conclusion: rings are mostly chunks of ice
Dust and Rocks
What causes the Rings?
All Jovian planets have large families of moons (small/medium) made of
rocks and ice.
These satellites = crowded together.
Because ice is brittle and fragile the satellites fragment when they collide.
Jovian planets have powerful gravities.
Tides pull apart the fragments into rings.
Chapter 9: Asteroids. Comets & Dwarf Planets:
Solar Systems smaller objects are different that major planets:
o Asteroids minor planets.
o Dwarf Planets (2006)
What are Asteroids?
- “Aster” = star; “oid” = body – an object that looks like a star but it orbits the sun.
Largest = now known = 1000 km in diameter
Smallest detectable = 100 m.
More than 40,000 cataloged asteroids but many more detected.
Probably more than 1 mill.
What are the asteroids?
Most asteroids orbit between Mars + Jupiter “asteroid belt” November 21 st November 23rd 2012
Astronomy Lecture Notes
o Jupiter’s powerful gravity controls the spacing.
Some asteroids that are in Jupiter’s orbit
o Located ahead of and following Jupiter’s orbit.
o These are captured by gravity of Jupiter and Sun.
Some asteroids have elliptical orbits
o Orbit close to sun and beyond Jupiter.
What are Meteoroids?
Meteoroids are tiny asteroids, too small to detect beyond Earth size = m =
Meteoroids travel at 30 km like Earth.
If one hits Earth’s atmosphere:
o Heats up from frication.
o It gives off light that disintegrates called a meteor of shooting star.
- If it is large enough to survive and reach the ground it is called at meteorites =
sample of solar system matter that comes to us.
Two Families of Meteorites:
“Primitive” meteorites – the matter is just clumped together.
No signs of having reacted.
“Processed” meteorites – the matter has been heated – has been not enough
to melt the pure metal, mostly iron.
The distinctive pattern required gradual cooling over million of years inside a large
asteroids that broke apart.
What are comets?
Means “hairy star”.
Orbits = elliptical – going from near the sun out to the edge of the solar
Comets are “dirty snowballs” mostly of “ice” = frozen water and gases + small
amount of dust, grit, sand and pebbles.
As comet nears the sun, it heats u