Occasionally comets or minor planets collide with larger objects like the earth
Small Bodies of the Solar System
- Asteroids: within the orbit of Jupiter
- Centaurs: Between Jupiter and Neptune
- Kuiper Belt Objects (KBO’s): Beyond Neptune
- Scattered Disk: Extreme KBO’s
- Comets: Icy bodies with elongated orbits
- Meteoroids: Small objects
- Meteors: vaporize in Earth’s atmosphere
- Meteorites: survive to reach surface
The Bode-Titius Law
The planets have fairly regular spacings
Start with 0, 3, 6, 12, 24, 48, 96, 192, 384, 788
Add 4: 4, 7, 10, 16, 28, 52, 100, 196, 388, 792
Divide by 10: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10 …
Matches distances of planets in A.U.
What’s at 2.8?
First Asteroid Discovered, 1801
Neptune,discovered in 1846, matched the predicted 38.8 value poorly (30.1)
Pluto didn’t match at all (39.5 versus 79.2)
Coincidence?
Or is the Bode-Titius pattern due to the influence of Jupiter and planetary clearing?
Other Hypothetical Planets
Vulcan
Hypothetical planet within the orbit of Mercury
Some asteroids and many comets cross the orbit of Mercury, but nothing is known to orbit entirely within the orbit of Mercury
Planet X
Hypothetical massive outer planet beyond Neptune
Nemesis
Hypothetical dwarf star companion to Sun
The Asteroid Belt, 2001
The Asteroid Belt, 2010
Asteroid Discoveries
|
Asteroids
|
Year
|
|
1
|
1801
|
|
100
|
1867
|
|
500
|
1902
|
|
1,000
|
1921
|
|
2,000
|
1942
|
|
5,000
|
1972
|
|
10,000
|
1981
|
|
20,000
|
1993
|
|
50,000
|
1999
|
|
100,000
|
2000
|
|
200,000
|
2003
|
2010 SEPT. 2
535789 Minor planets catalogued
251651 Officially numbered
16154 Named
How We Study Them
Spacecraft
Ground-Based and Hubble Imaging
Radar Imaging
Spacecraft Images
951 Gaspra (15 km)
243 Ida (40 km) and Dactyl
253 Mathilde (50 km)
Three Asteroids Compared
433 Eros (20 km)
Eros
Eros
Asteroid Itokawa
Spacecraft Shadow
Earth-Based Optical Imaging
4 Vesta (500 km)
Ceres and Vesta
Radar Imaging
Double Asteroids
Comets
Types of Comets
Short Period (<200 years)
Record reobserved comet is Comet Ikeya-Zhang (1661-2002)
Long Period (>200 years)
Hale-Bopp (2400 years)
Need a source very far away
Oort Cloud
Too little material very far from the Sun
Flung out by planetary encounters
Where Comets Come From
Ice and Frozen Gases
Outer Solar System (Kuiper Belt)
Planetary Encounters perturb Orbits
Diverted inward to become short-period
Diverted outward to Oort Cloud
Creation of Long Period Comet
Capture of Short Period Comet
Anatomy of a Comet
Comet McNaught 2008
Comet McNaught 2008
Record-Breaking Hale-Bopp
Most-observed comet in history
Discovered the furthest from the Sun
Largest cometary nucleus known
Visible to the naked eye for 18 months – twice the previous record
Brighter than magnitude 0 for eight weeks, longer than any other comet in the last thousand years.
Comet Hale-Bopp 1997
Halley’s Comet
Comet Holmes 2007
Comet Borelly
Comet Tempel I
The Deep Impact Mission
A Comet Hits The Sun
Meteoroids
Meteoroid – Small object orbiting Sun
Meteor – Meteoroid that becomes incandescent from friction with atmosphere
Bolide or Fireball – Exceptionally brilliant meteor
In impact studies, “bolide” often used for an impacting meteoroid prior to impact
Meteorite – A meteoroid that reaches the surface
Micrometeorite – microscopic meteoroid
Bolide
Meteor Showers
Earth passes through streams of orbiting debris
Many linked to orbits of known comets
Occur predictably
Perseids: August
Orionids: October (Halley’s Comet)
Leonids, November
No known falls
Generally 20 or so per hour, rarely 1000’s
Appear to radiate from one point in sky
A Meteor Shower
Radiant
Meteorites
Stony (95%)
Chondrites: Pellet-like texture
Carbonaceous Chondrites: Most similar to the Sun (minus gases), planetary raw material
Achondrites: Basalt
Stony-Iron (1%)
Nickel-Iron (4%)
Kamacite (>6% Ni) and Taenite (>25% Ni)
Texture revealed by etching
Finding Meteorites
Finds versus Falls
Fall: Observed to fall, then recovered
Find: Identified long after fall
Stony Meteorites weather and are hard to tell from natural rocks
Iron meteorites are more easily recognized
Prime Scientific Collecting Localities
Antarctica
Deserts
Meteorite
Peekskill, NY 1992
Chondrite
Stony-Iron Meteorite
Iron Meteorite
Meteo-Wrongs
- Meteorites Never:
- Have internal cavities
- Have layers
- Have veins
- Flatten on impact
- Mold around objects
- Almost never light in color outside
- If you “think” it’s magnetic, it’s not magnetic
Nope
Nope
Nope
Nope
Nope
Nope
Nope
Tektites
Very silica-rich, water poor glassy rocks
Terrestrial vs. Extraterrestrial origin?
Volcanic vs. Impact origin?
Problems:
Odd chemistry
If terrestrial, why are they spread so widely?
If extraterrestrial, why are they so localized?
Now considered impact glass
Atmospheric shock wave evacuates atmosphere
Tektites
Zodiacal Dust
Speaking of Zodiacal Bands….
Chancellor Brian May, CBE
(Liverpool John Moores University)
Take-Away Points
Small objects in the solar system are leftovers that never accreted into planets
Minor planets mostly orbit between Mars and Jupiter
Comets formed in the outer solar system and were flung outward by close encounters with other planets
Comets can be trapped in the inner solar system by planetary encounters
The head and tail of a comet glow from sunlight shining on gases evaporated from the comet
Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets
Occasionally comets or minor planets collide with larger objects like the earth
Return to Bosnia index
Return to Professor Dutch's home page
Forward to Next Page
Back to Previous Page
Created 23 Apr 1997 Last Update
15 January 2020
Not an Official U.S. Army Site