Transcript File - Astronomy, Incorporated

Definition
1. Small, rocky objects orbiting Sun
2. Undifferentiated “Minor Planets”
a. Eccentric orbits between M & J
b. MAsteroid Belt = 1/10th MMoon
3. Largest (& most spherical): CERES
th
(1/10,000 ME / < 600 miles wide)
A.
1. Titius-Bode “Law” - prediction
2. Piazzi- Ceres (1801) at 2.8 AU
3. Today > 100,000 known
4. Asteroid Belt
a. Home to most (2.1 - 3.3 AU)
b. Prograde orbits
1. C-type / Carbonaceous aster.
a. Darkest, most carbon
b. Primitive material
c. Includes 75% of all asteroids
2. S-type / Silicate asteroids
a. Rocky material (“stony”)
b. 15% of all asteroids
3. M-type asteroids
a. Large fraction of
iron/nickel
b. ~ 10% of all
asteroids
c. $$ Future mining ?
d. Planetary
Resources
(platinum/palladium)
4. Sizes of 50,000 + asteroids known
a. 99% of > 60 miles wide found
b. +90% of > 6 miles wide found
c. 86% of > 1 Km wide found
d. 10% of > 100 m wide found
e. < 1% of < 30 m wide found
5. Larger asteroids more spherical
1.Vesta #3 ~ 340 miles wide
a.Only one w/ ancient volcanism
b. Basaltic meteoroids chipped off
Vesta, hit Earth
c. DAWN spacecraft (August ‘11)
2. Galileo close-ups in early ‘90s
a. Ida (38 miles wide) / Gaspra
b. Ida has small moon - Dactyl
Vesta, 2011
(DAWN Spacecraft
from 3,000 miles)
1.Renamed NEAR-Shoemaker
2. Visited porous Mathilde (‘97)
(Very low density - “rubble pile”)
3. Orbit around EROS (2000)
a. 3 miles up- high res. pics 1 yr
b. Landed ‘01 w/o landing gear!
c. Still sent radio for 16 days
1. Eccentricities
> .4
2. Apollo asteroids
(Mars -Amors)
3. 1200 known
PHA’s - 1284
4. 300 potentially hazardous
a. >150 m across, 5 million miles
b. Icarus-Close to Sun, us, in ‘68
c. ‘72 – Great Daylight Fireball
Wyoming
d. ‘04 – 2 close calls (4,000 miles)
e. ‘08 – Sudan (1st ever impact
predicted in advance)
f. About 40 per decade get “close”
(within ~6 million miles)
g. ~ 3 strike per million yrs. (1km)
i. Obliterate 60 mile wide area
ii. 100x energy of all nukes
iii. Species extinctions..
h. Apophis (2029, 2036 - 1000 ft. wide)
G. Options
1. Attach a “solar sail”
2. Attach thrusters
3. Gravity “tractor”
4. Nudge it with a nuke
(detonate to the side)
5. Blow it up (probably not a good idea)
1.Several hundred Trojan asteroids orbit
the Sun with Jupiter (2 are comets)
2. Found at
Lagrange points
- Joseph
Lagrange (1772)
a. 5 pts. in sync with a
planet
b. Trojans only found at
L4 and L5 pts. - 600 in
front of & behind
Jupiter
c. Asteroids also found
at L pts. For Venus,
Earth, Mars
A. Basics
1. “Dirty Snowballs” (Whipple)
many AU’s from the Sun
2. Only reflect light
3.Tail only develops close to Sun
1.Nucleus - main body
of comet
a. Only part for most
of its orbit
b. Few miles wide
c. Only seen by space
probes
d. Contains most of the comet’s mass
2. Coma - gaseous halo
a. As comet approaches Sun, ice
sublimates into a gas
b.Up to 60,000 miles wide (Sat.!)
c. Brightest part
3. Hydrogen envelope - stretched
millions of miles by solar wind
a. Longest near Sun- up to 1 AU
b. Ion tail
i. Charged particles
ii. Straight, glowing, bluish tint
iii. Affected most by solar wind
c. Dust tails -curved by gravity
d. Tails always pt. away from Sun!

http://www.windows.ucar.edu/tour/link=/comets/
comet_model_interactive.html
Hale-Bopp ‘97
Light show!
Comet P17 Holmes - 2007
1.
Comets may break up close to Sun
or plunge into the Sun
a. Home to short period (~ 200 yrs.)
comets- don’t orbit far beyond Neptune
b. Usually prograde, fairly flat orbits
c. Comets may be “kicked” into eccentric
orbits by collision or pull of Jovian planets
a.Vast spherical region (random
orbits) around s. syst. ~100,000 AU
b. Home of trillions of long-period
(millions of yrs) cometary nuclei
c.Total mass ~ mass inner planets
d. Passing stars may deflect them
1. Edmund Halley (1705) predicted its return
a. 76 yr. period
b. 1682 comet came back in 1758
c. Recorded back to 240 B.C.
2. History
a. Came close in 1910
b. Mark Twain
c. Bayeux Tapestry (1066)
a. Soviet Vega 2 thru coma
b. Italian Giotto
i. 600 km from nucleus
ii. Dark, potato-shaped nucleus
iii. Sunlit-side jets cause rotation of
nucleus and orbit irregularities
Hartley 2
1.
2.
3.
4.
5.
Nucleus split ‘92
Hit 60 km/s in ‘94
Earth-size fireballs
Energy = 1 billion
nuclear bombs
Dark spots for days
on Jupiter
F. Physical properties of comets
1. ~ Mass of small asteroid- 3x faster
2. 30 tons/sec lost near Sun
(Halley’s - 5000 orbits/40,000 yrs.)
3. Nuclei: 100 kg/m3 gas/dust/ice
4. Dust mixed w/ CH4, NH3, CO2
Definitions
1.Meteoroids: Space rock <100m
2.Meteor: Streak of light due to
atm. friction from asteroid, comet
3.Meteorites: Any debris that
reaches the ground (~ 4000 /yr)
A.
1972 Grand Teton
RUSSIA 2-15-13
The truth comes out…
1. Comets lose particles near Sun
2. Micrometeoroids spread out over
entire path of comet
3.Denser areas: Meteoroid swarms
4. Earth goes thru path once or
twice each yr.- meteor shower
Ex/ Perseid (Aug.) Leonid (Nov.)
Geminid (Dec.)
Leonid Meteor
Shower
1. Early solar system bombarded
2. Some from belt / others from
Mars or the Moon (not Venus)
3. ~ 1 m wide / 1 ton survive entry
4. Earth has 100 craters > .1 km, best
viewed in satellite photos
(170 known impact sites)
Egypt
(Crater Discovered in 2010)
Meteor Crater in 3-D
5. Tunguska
Event- 1908
a. ~ 30 m meteoroid exploded miles
above ground in Siberia
b. Energy of a
10-megaton
nuke
1. Micros: Low density (750)
2. Meteorites - up to 5000 kg/m3
3. Most rocky, some iron/nickel
4. Almost all are
very old
(~ 4.5 billion yrs. old)
Chelyabinsk Meteor (2013)
Chelyabinsk Impact Site (2013)
Chelyabinsk Meteorite (2013)