4/27/09:

v Regions of debris:

Ø Astroid belt 2-5 AU

§ Stony and Metalic

Ø Kuiper belt 30-50 AU

§ Icy

Ø Oort Cloud 1000’s AU- 100,000 AU

§ Icy

v Nearest star is Alpha Centorie at 200,000-300,000 AU

v Comets:

Ø Only called comets when they are close to the sun.

Ø They leave behind dust particles.

§ When earth crosses a comet’s orbit it causes a meteor shower.

· Meteors: particles that burn up inside earth’s atmosphere.

· Meteorites: particles in space that land on the earth.

Ø Dirty snow balls that sometimes crash into the sun.

v Asteroids

Ø Small

Ø Ceres is about 100,000km in size and is the largest asteroid

§ It is the only spherical asteroid because gravity was enough to change its shape

Ø Toutakus isn’t spherical

Ø Dactyl has a satelight

v Kiper belt:

Ø Key because comets come from here.

4/29/09:

v Kirkwood gaps: Gaps in the asteroid belt caused by resonances.

Ø Resonances: period of inner object to the period of outer object in some fraction.

v Kuiper belt:

Ø Plane that was formed by left over debris.

v Oort Cloud is spherical

Ø Know its there by studying the orbits of non-returning objects.

Ø Not a lot of stuff out there.

Ø Didn’t form in place

§ As the Jovian planets formed, some pieces were kicked out to the oort cloud due to gravity.

v Impacts:

Ø 1994 a comet smacked into Jupiter.

§ Made people aware things could hit earth like that

Ø There are asteroids big enough that can hit earth and cause mass extinction, but they are rare and only occur about every 100 million years.

§ The last one to hit was 65 million years ago. It is attributed to the extinction of the dinosaurs.

Ø In 1908 a large asteroid hit in Siberia and leveled trees for several miles.

Ø Things hit earth often, but they aren’t very large.

4/30/09:

v Trans Neptunian objects:

Ø Larger ones have been dubbed “dwarf planets”

Ø ~1000km

Ø Pluto

§ Was originally thought to be a terrestrial like planet that was calculated to be bigger than the earth

§ However, the moon is actually bigger than it.

§ In 1980’s, telescopes had changed the prediction of its size

§ 1990’s people had discovered other big objects in the Kuiper belt.

§ Has a few satellites, one decent sized one.

Ø Eris

§ Actually bigger than Pluto

Ø There are small debris objects orbiting the sun between Saturn and Neptune’s orbit.

Ø A lot of tiny objects out there that if you paste them all together they would amount to nothing.

Ø Nemesis Hypothesis: a planet that had an orbit perpendicular to the elliptical plane, so you wouldn’t know that it was out there, but causes disruptions in the Oort cloud and leads to mass extinctions.

§ Unlikely due to how it formed a weird orbit.

v Science is easy to generalize

v Nature is quantitative