Date post: | 22-Jan-2016 |
Category: |
Documents |
Upload: | nasir-prickett |
View: | 223 times |
Download: | 0 times |
1155
CometsComets
Fire and Ice
1515
GoalsGoals
• What are comets?• How are they different from asteroids?• What are meteor showers?• How are they different from typical
meteors?
1515
Comets – Hale Bopp
Copyright – Tyler Nordgren
Copyright – Tyler Nordgren
Copyright – John Glerason
1515
Comets
Copyright – Ray Gralak
Copyright – Michael Jager
Copyright – Stefan Seip
1515
Comet Facts
• Formed beyond the frostline, comets are icy counterparts to asteroids.
• “Dirty snowballs” = the nucleus• Most comets do not have tails.• Most comets remain perpetually frozen
in the outer solar system. Only a few enter the inner solar system, where they can grow tails.
1515
Copyright – Tyler Nordgren
1515
Concept Test
• Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude? a. It has been on its current orbit for only a
very short time compared to the age of our solar system.
b. It has a coma and tail during most of each orbit.
c. It came from the Oort cloud.d. It came from the Kuiper belt.e. None of the above.
1515
1515
Concept Test
• Why are comets icier than asteroids?a. Asteroids were once as icy but the solar
wind blasted it awayb. Planetesimals that formed closer to the
Sun contained fewer icesc. The sun’s gravity attracts dense objects
mored. Comets and asteroids formed in the same
region but asteroids were flung outwarde. Comets are not icier: comets are actually
less icy on average
1515
Comet Motion
1515
Concept Test
• Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different? a. It would not have an ion tail.b. It would not have a nucleus.c. It would not have a coma.d. It would be much brighter in appearance. e. It would not have a dust tail.
1515
Comet DisintigrationSW3 - HST
1515
Comets eject small particles that follow the comet around in its orbit and cause meteor showers when Earth crosses the comet’s orbit.
1515
Meteors in a shower appear to emanate from the same area of sky because of Earth’s motion through space
1515Copyright – Fred Bruenjes
1515
Kuiper belt:On orderly orbits from 30-100 AU in disk of solar system
Oort cloud:On random orbits extending to about 50,000 AU
Only a tiny number of comets enter the inner solar system - most stay far from the Sun
1515
Sedna
1515
How did they get there?
• Kuiper belt comets formed in the Kuiper belt: flat plane, aligned with the plane of planetary orbits, orbiting in the same direction as the planets.
• Oort cloud comets were once closer to the Sun, but they were kicked out there by gravitational interactions with jovian planets: spherical distribution, orbits in any direction.
1515
Concept Test
• Oort cloud comet orbits are ‘random’ compared to Kuiper Belt comets because…a. The comets have collided so frequently their orbits
became randomizedb. They formed from the collapsing cloud before it
formed an organized diskc. They were ejected by the jovian planets onto
random orbitsd. Orbital resonances with nearby stars randomized
the orbitse. None of the above: Kuiper Belt comets have more
random orbits
1515
Halley Borrelly Wild 2
• Mesas• “Craters” (circular depressions)• “Smooth” terrain as sources of jets• Pinnacles• Dark Spots; Bright Spots (small albedo features)• Sharp Edges
Each nucleus had some (but not all!) of these:
1515
Deep Impact
• NASA mission to impact comet nucleus.• Use spectroscopy to determine
composition of nucleus.
Deep Impact movies
1515
What the Impactor saw
A’Hearn et al 2005
1515A’Hearn et al 2005
Geology of the Geology of the surfacesurface
• Circular “craters”: due to impacts? Like Wild 2? Unlike Borrelly.
• Cliffs, mesas: like Borrelly, maybe like Wild 2.
• Smooth and rough terrains, like Borrelly.
• Fairly uniform reflectivity, like Wild 2, unlike Borrelly.
1515
1515
Homework #20Homework #20
• Due Friday 21-Nov:• Read Bennett 12.4• Do 13, 33, 34• What is the Torino Scale?