22.2 Comets and Kuiper Belt Objects

Roxanne Ryan

Overview

• Comets– Dynamics of tail– Composition

• Oort Cloud• Kuiper Belt

Model of a Comet

• 1950 -Fred Whipple proposed a model which explained most physical characteristics.

Nucleus Tails Coma Halo

Dynamics of Comet Tails

• Two distinct tails– Dust tail- created by radiation pressure on freed

dust grains– Ion tail – interaction of ions in the comet with

solar wind and suns magnetic field.• Tails are always directed away from the sun.

Composition of Comets

• Dust tails are white or yellowish due to light scattering off the particles.

Composition of Comets

• The ion tail is blue because it is rich in CO+ ions which absorb and reradiate photons at wavelengths near 420 nm

Robotic Exploration of Comets

• In March 1986 Whipple’s “dirty-snowball” model was confirmed.

• July 4, 2004 Deep Impact sent a impactor into Comet Temple 1, allowing scientist to study interior.

• Comets density is roughly that of powder snow ~600 kg/m3.

Where do Comets come From?

• Two types of comets:– Short period: periods of less than 200 year and

are found near the ecliptic– Long period: periods greater than 200 years and

seemingly random orbits

Kuiper Belt

• Located 30 – 50 AU from the sun • First proposed around 1950• The first KBO was discovered in 1992• By 2006 over 900 had been discovered

Classes of Kuiper Belt Object’s

Classical KBO’s– 30 – 50 AU from the sun– Orbital inclination of less

than 30˚– Semi-major axis 42-48 AU

Classes of Kuiper Belt Object’s

Scattered KBO’s– Much higher eccentricity– Greater orbital inclination – Perihelion ~ 35 AU– Source of short period

comets

Classes of Kuiper Belt Object’s

Resonant KBO’s– KBO’s that are in orbital

resonance with Neptune– Resonant Kbo’s with the

same 3:2 resonance as Pluto and Charon are called Plutinos

Oort Cloud

• In 1950 Jan Oort proposed that long period comets originate in a distant distribution of cometary nuclei.

• Has never been observed, but it’s existence is certain.

Oort Cloud

• 3,000-100,00 AU from the sun

• 1012 -1013 bodies• Total mass

~ 100 solar masses

22.2 Comets and Kuiper Belt Objects

Roxanne Ryan