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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