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Solar System Debris
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Keys to Our Origin
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Feb 21, 2005, jeb
PRELIMINARY
Over a hundred-thousand rocky objects concentrated in the
Asteroid belt
- Quite eccentric orbits (not circular)
- largest: Ceres
- 940 km diameter
- 1/10,000 MEarth
- Total mass of all asteroids is about 10% MMoon
- therefore, they are a small fraction of the Solar System
- All but one in prograde orbits
- Why is there an Asteroid belt?
- Theories
- fragments of a planet that broke up long ago?
- rocks that never managed to accumulate
- Researchers favor 2.
- Jupiter's gravity continuously disturbs these chuncks of matter, preventing
them from accumulating
Types of Asteroids
- C-type
- carbonaceous(largely carbon, dark)
- 75% of the asteroids
- outer orbits
- very old (4.6 billion years)
- S-type
- silicate(largely silcon, light)
- 15% of the asteroids
- inner orbits
- M-type
- nickel-iron
- about 10% of the asteroids
Earth and Mars Crossing Asteroids
- A few dozen crossing asteroids have been discovered
- all the Earth crossing asteroids will eventually collide with the Earth
- about 3 every million years
-
Apollo asteroids
- Earth crossing with semi-major axis greater than 1 AU
- Aten asteroids
- Earth crossing with semi-major axis less than 1 AU
-
Amor asteroids
Orbital Resonances of Asteroids
Close-up Views of Asteroids
- Galileo (on journey to Jupiter)
- visit to
Gaspra
- S-type
- maximum diameter of 20 km
- about 200 million years old
- fragment of larger object
- visit to Ida
- S-type
- maximum diameter of 60 km
- about 1 billion years old
- fragment of larger object
- tiny moon: Dactyl (1.5 km across)
-
NEAR-Shoemaker (Near Earth Asteroid Rendezvous) -
official web site
-
spacecraft
misson to rendezvous with asteroid
Eros
- launched February 17, 1996
- planned Eros rendezvous in early 1999
- passed by
Mathilde on June 27, 1997
- C-type
- low density of 1400 kg/m3
- missed planned rendezvous with EROS in January, 1999, when spacecraft engine mis-fired
- but obtained initial up close data
- Eros is S-type
- Eros is a bit smaller then thought(33 km x 13 km x 13 km)
- Twice the size of Manhattan
- density is 2700 kg/m3
- appears homogeneous, not porous as Matilde
- NEAR-Shoemaker
in orbit around Eros since February 14, 2000
- orbit Eros for a year and do detailed study
- being a minor body, Eros has little gravity
- 200 pound person would weigh 2 ounces
- escape velocity is 0.01 km/sec (22 miles/hour)
-
crater densities indicated Eros is old, like Ida and Matilde, but
unlike Gaspra
-
5 km flyby on October 20, 2000
- landed on Eros, February 12, 2001
Collisions with Earth
- Icy matter in
highly elliptical orbit
- left-over material, unchanged since the formation of the Solar System
- as they near the Sun
- heat up and emit radiation
- develop tail
Comet
Structure
- Nucleus - few km in diameter
- Density : 100 kg/m3
- Evaporation Rate: 10 tons/ second near the Sun
- Lifetime: about 5000 orbits or about 400,000 years for Halley's Comet (in other words - short on cosmological scale)
- Coma- evaporated gas and dust forms halo around nucleus as comet approaches the Sun
- Hydrogen envelope
- Tail
Two sets of orbits
- short-period comets:
- long-period comets:
- from
Oort Cloud
- orbits of 100,000 AU in diameter
- surrounds Sun in all directions
Halley's Comet
- Probably the most famous comet
- In 1705, Edmund Halley predicted that this comet would reappear in 1758
- Halley died in 1742, and his comet appeared right on schedule in 1758
-
period of 76 years
- recorded every passage since 240 BC
- last visit in 1986
- met by armada of spacecraft in 1986
- USSR, Japan, Western European
-
Vega 2
and
Giotto resolved Halley's nucleus
- advanced understanding of
Halley's nucleus
- 30 tons of material lost every second the comet spends near the Sun
- related studies of Comet Linear shows Comet Flare-up.
Cometary Impact on Jupiter in 1994
- Comet Shoemaker-Levy crashed into the surface of Jupiter in July, 1994
- Comet was discovered in March, 1993
- How did Comet get this way?
- July, 1992 passed within Roche Limit of Jupiter -> broke apart
- Series of impacts
- interesting comparison
tables
Comets of 1996/1997
-
Hyakutake
- in January of 1996, an amateur comet astronomer in Japan discovered this comet
with a pair of binoculars
-
the orbit was predicted to pass 0.1 AU from Earth
- a spectacularly bright, naked eye image was predicted, and observers were
not disappointed
- Hyakutake turned out to be the brightest comet in 20 years
-
Hale-Bopp
- discovered in July, 1995
- simultaneously by Alan Hale in New Mexico and Thomas Bopp in Arizona
- Comet Hale-Bopp was visible to naked eye in the 1997
- Perihelion on April 1, 1997
- period is about 4000 years
- One of the brightest comets of the 20th century
- passed 1.3 AU from Earth (compared to 0.1 for Hyakutake), but still was brighter
Stardust Mission
- Mission launched in February, 1999 to collect cometary
material and return it to Earth
- Passed through tail of Comet Wild-2 in January, 2004
- Onboard foam-like gel will collect comet debris
- Returns to Earth in January, 2006
Terminology
-
Meteoroid - chunk of debris before entering Earth's atmosphere
-
Meteor -
bright streak in the sky caused by piece of debris
- Meteorite - a piece of a meteoroid that survives and lands on Earth
-
Meteoroid swarm - fragments from comet that follow same orbit
-
Meteor shower - event where frequent meteors can be seen
Cometary Fragments
- smaller meteoroids are rocky remains of broken up comets
- certain meteor showers are regular and (fairly)
predictable events
- named for "radiant", or constellation from which they
appear
to come.
Stray Asteroids
- larger meteoroids (more than a few centimeters) are generally
from the asteroid belt
- these objects are responsible for most cratering in the inner Solar System
- massive meteoroids
(more than a ton and a meter across)
- can make it to the surface of the Earth
- Earth is scarred with nearly 100 craters larger than 0.1 km in diameter
-
Major collisions of large meteoroids with the Earth occur every
few hundred-thousand years
-
Demise of the dinosaurs 65,000,000 years ago?
Meteorite Properties
-
Fairly dense: up to 5000 kg/m3 (like asteroids)
- Most have
rocky composition
- Some are composed mostly of
iron and nickel
- Some show geologic history
- indicating strong heating sometime in their past, perhaps when they
were liberated from a larger body
- Most are very old (4.4 - 4.6 billion yrs)
Lunar and Martian Meteorites on Earth
-
Over 30 meteorites
have been established as having come to Earth from Mars or the Moon
- typically billion year old
-
Several are from the Moon
Conclusion
- Someday,
perhaps in a thousand years,
perhaps in a million,
perhaps sooner
One of these large objects will strike the Earth and life will be significantly affected
Remember the Dinosaurs!
Asteroids
Comets
Meteors
