Download Comets and KBOs

Astronomy 241: Foundations of Astrophysics I
17. Comets & KBOs
Comets are icy
objects which fall
into the inner
solar system.
Warmed by the
Sun, they may
develop long tails.
un
To
S
Comets
Com
Mot et’s
ion
Comet Halley
At other times, a comet is an inert lump of ice & dust.
Comet Nuclei
Asteroids and comets to scale
Deep Impact: the Nucleus of Tempel 1
Evidence of Cometary Ice
Analysis of collision
debris suggests Tempel
formed ~ 30 AU from
the Sun.
Tempel Alive With Light
Comets and Meteor Showers
Comets shed dust, sand and
gravel which slowly spread
out as they move along the
comet’s orbit.
If the Earth encounters one
of these trails, we get a
meteor shower.
Meteor Showers
Comet Encke
Overview: Structure
100 AU
S
20,000 AU
5 AU
Inner system:
terrestrial planets,
asteroids.
Outer system:
giant planets and
moons, “KBOs”.
Oort Cloud:
comets.
Largest Known Kuiper Belt Objects (and Satellites)
Wikipedia: Kuiper Belt
KBO Orbits
Classical: outside
Neptune’s orbit
Resonant: like
Pluto’s orbit
Scattered: highly
elliptical
Plan View of the Solar System
Pluto’s Orbit
Pluto’s orbit is highly tilted
(inclination i = 17°) to the
rest of the solar system.
Wikipedia: Pluto
Pluto is in a 3:2 resonance
with Neptune. This is
stable since Pluto avoids
Neptune.
Pluto’s Orbit
Orbital Populations
Resonant KBOs
(plutinos) avoid
Neptune’s influence.
KBOs above
this line cross
Neptune’s orbit
3:2
Scattered KBOs which
cross Neptune’s orbit
are easily perturbed.
The Resonant KBOs
These scattered KBOs may become comets.
Pluto and Charon
Double planet; many small moons;
possibly formed by giant impact
(similar to Earth-Moon system).
• orbit mass: MPluto = 0.002 ME
3
density:
~
2
g/cm
•
rd rock, 2/3rd ice
composition:
1/3
•
• thin atmosphere: N2, CH4, CO
Pluto has probably differentiated;
Charon is too small to melt itself.
Hubble Maps Pluto