Comets & Asteroids

Comets • Definition: •  Dirty snowball (rocks & ice)

• Origin: •  Theory #1: During spherical nebular phase, ice

chunks formed in outer part of cloud. •  These became comets in Oort cloud (outside solar

system)

•  Theory #2: Some formed later from plantesimals in outer solar system, now in Kuiper Belt

Wild 2 Comet Stardust NASA mission

Evidence for Comets • Comets can have a short or

long period •  Short: < 200 yrs •  Long: 1 – 30 million years

• Comets can have orbit in the plane of the planets or not. • Composition: Water ice, CO2,

ammonia, methane, rock

Which type of comet are in the Oort cloud? Long or short period?

Parts of a Comet • Comets glow only as they

near the sun (become warm enough to reflect light – they’re too cold to luminesce otherwise)

• Nucleus: solid part, a few km across • Coma: luminous ball

around nucleus •  Tail: dust trail of particles

breaking off comet – points away from the sun

Parts of a Comet

Tails of Comets • Comets have 2 tails •  Dust Tail •  Ion Tail •  Range in size up to 1 AU!

•  Tails always point away from the Sun, due to solar wind

Do Comets Melt? • Estimates are that

comets lose ~0.1% of initial mass each trip around the Sun.

• Particles from comet can continue to orbit even after comet disintegrates

(“Meteor” Showers)

Asteroids • Asteroid belt between Mars and Jupiter

was discovered in 1800, when Ceres was first thought to be a planet. •  After other similar objects in same orbit were

discovered, it was reclassified.

• Asteroids have similar composition to rocky planets •  Origin:

•  Planet that never formed •  Planet that broke apart

Asteroids vs. Meteoroids • Biggest difference is size! •  Usually > 300 m ! asteroid

• Meteor’s name depends on where it is: •  Meteoroid is in space •  Meteor is falling through Earth’s atmosphere •  Meteorite is on the ground.

Asteroid “Ida” and her moon

Asteroids vs. Meteoroids

2018 Meteor Shower Calendar •  January 1st-5th – Quadrantids (peak 1/3)

•  April 22nd-23rd – Lyrids •  May 6th-7th – Eta Aquarids •  July 28th-29th – Delta Aquarids •  August 12th-13th – Perseids

•  October 8th – Draconids •  October 21st-22nd – Orionids •  November 5th-6th – Taurids •  November 17th-18th – Leonids •  December 13th-14th – Geminids •  December 21st-22nd - Ursids