Astronomy Ch. 9 - Asteroids, Comets and Dwarf Planets (Nov. 16)
- Solar System has many objects smaller than the major planets:
- asteroids = minor planets
- dwarf planets (since 2006)
What are Asteroids?
- “aster” = star + “oid” = body - an object that looks like a star, but it orbits the Sun
- Largest (known) = 1000 km in diameter
- Smallest detectable ≈ 100 m
- More than 400,000 catalogued asteroids, but many more have been detected
- Probably more than 1 million asteroids larger than 1 km
Where are the Asteroids?
- Almost all have nearly circular orbits between Mars and Jupiter = “asteroid belt”
- these orbits show the strong inﬂuence of Jupiter’s powerful gravity
- A few orbit with Jupiter, ahead or following in its orbit - captured by Jupiter + Sun
What are Meteoroids?
- Tiny asteroids, too small to detect at a distance - sizes are m, cm, mm, ... dust
- Some meteoroids (speed ≈ 30 km/s) hit Earth’s atmosphere, heat up (friction), give off
a ﬂash of light as they disintegrate
▯ = meteor or shooting star
- Any remnant large enough to survive and reach the ground = meteorite = sample of
solar system matter
Families of Meteorites
- “Primitive” meteorites - the matter is just clumped together - no signs of having been
- “Processed” meteorites - the matter has been heated - has been hot enough to melt
into pure metal, mostly iron
What are Comets?
- Comet = hairy star
- Orbits are very elliptical - comets move from near the Sun out to the edge of the Solar
- Mostly “ice” = frozen water + frozen gases + small amount of dust/grit/sand/pebbles
mixed into the ice = like a dirty snowball
- Comet approaches the Sun - heats up
- Note: comets are evaporating
▯ → the comets we see near the Sun cannot survive this loss of material for billions
▯ of years Where do Comets Live?
- Comets break all the “rules”
- Orbits are very elliptical → come from the outer Solar System where it is very
cold, where they live most of the time (Kepler