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ASTR 1345: Chapter 9 Vegabonds of the Solar System
Composition of Comets
|
- ice
- dust
- rock
- frozen gasses
- dry ice (C02) |
Sublimation of Comets
|
frozen material and ice directly changes into gas from solid state without becoming a liquid
|
|
|
A = hydrogen envelope
B = tail
C = coma
D = nucleus |
Hydrogen Envelope
|
sparse envelope released by breakup of molecules (such as H20)
- not seen in visible light
- millions of km in length |
Dust Tail
|
blown off the nucleus by Sun's radiation pressure
- made of dust particles
- broad, diffuse and curved |
Ion Tail
|
blown off by the solar wind (ionized particles from sun)
- made of plasma
- mostly straight |
Both Ion Tail and Dust Tail can reach ____
|
1 AU (108 km)
|
Coma |
dense sphere of material evaporated hen the comet reaches the inner solar system
- 100,000 km across |
Nucleus |
relatively stable and solid (dirty snowball)
- mixed dust/ice
- H20, methane, amonia, C02
- 10 km across |
Space crafts that visited Halley's Comet (1986)
|
- Vega 2 (soviet space craft)
- Giotto (european space craft) |
Nucleus of Halley's Comet (1986)
|
irregular
- size: 15 x 10 km
- very dark
- several jets streaming out form coma and tail |
Spacecraft that landed on Comet 67P/Churyumov-Gerasimenko
|
Philae from Rosetta spacecraft (Nov 12th, 2014)
|
Comets orbits are ___
|
highly elliptical
|
Comets orbits extend ___
|
far beyond Pluto
- as far as 50,000 AU |
Comets orbits tend to be ____
|
inclined relative to the ecliptic
|
In all cases, comet tails are ___
|
directed away from Sun by solar wind
|
Ion Tails vs. Dust Tails
|
differ in shape because of the different responses of gas and dust to the forces acting on them
|
Ion Tail (Type 1)
|
pushed rapidly, straight back by solar wind
- straight tail |
Dust Tail (Type 2)
|
gently pushed back by solar radiation
- dust particles left behind are in longer orbits
- curved tail |
Oort Cloud
|
long-period comets
- hundred of thousands, some even million of years long orbit
- all inclinations, all orientations, both pro and retrograde (never come anywhere near Sun)
- occasionally pulled into inner solar system due to gravitational tug by nearby star |
Kuiper Belt
|
short-period comets
- less than 200 years
- prograde orbits laying close to ecliptic
- circular orbits (between 30-100 AU) |
Meteoroid Swarm
|
formed each time a comet rounds the Sun, some cometary material becomes dislodged (30 tons per second if comet is within an AU from Sun)
|
Micro-meteoroids
|
over course of time, the swarm gradually disperses along orbit, and become more or less smoothly spread all the way around parent comet's orbit following the same path -> these small objects are micrometeoroids
|
Meteor Shower
|
if Earth's orbit happens to intersect the orbit of a young cluster of meteoroids
|
Do Comets always have a tail?
|
No |
Where do Comets belong?
|
Our solar system
|
Away from the Sun, Comets are made up of ___
|
just a nucleus
|
Nucleus of Halley's Comet is not ____; looks like ____
|
not spherical; looks like a rock
|
Halley's Comet orbit is ___ around the Sun
|
76 years
|
Rosetta Spacecraft launched in ___
|
2004 |
Philae Lander landed on surface of ___
|
Comet P67
|
The tail of a comet becomes longer when ___
|
closer to the Sun
|
The tail always points ___
|
away from the Sun
|
(Venus) Continents defined by ___
|
eleveation
|