Chapter 11, 12,13Chapter 11, 12,13 Comets, Asteroids, MeteorsComets, Asteroids, Meteors

Minor Body ComparisonsProperty ___Asteroids _________ Comets

Orbit Shape Circular to Highly elliptical elliptical

Size 0.5 km to 625 km Nucleus1 to 10 km

Composition Iron or Rocky Ice and Rock

Named? Named by their Named after theirdiscoverers discoverers

Asteroids• a.k.a Minor Planets

• Belt Asteroids - are those found between the orbits of Mars and Jupiter.

• Trojan Asteroids - share Jupiter's orbit about the Sun

• Apollo Asteroids – have orbits that cross Earth’s orbit

• NEO – Near Earth Objects

Kirkwood Gaps

Asteroids• The are empty regions in the asteroid belt

called Kirkwood Gaps.• (Created by Jupiter’s gravity)

Blink Comparison

Minor Planet

Asteroids• The asteroids are probably fragments of

planetesimals, the bodies from which planets were built.

• Over 100 “new” asteroids are discovered every year.

• There are over 7,000 known asteroids.• Examples:

– Ceres (diameter = 625 miles)

– Gaspra (3 by 12 miles)

– Toutatis (0.5 by 2 miles)

Goldstone Deep Space Communications Complex

Toutatis

• A strange binary asteroid imaged with radar from Earth.

2.5 and 1.6 miles

Gaspra

• The first asteroid to be imaged at close range.

• This was done with the Galileo spacecraft.

12 miles

Ida

• The second asteroid imaged with the Galileo spacecraft.

• It has a moon!

Satellite!

36 x 14 miles

Methilde

• The spacecraft NEAR made a flyby of Mathilde on June 27, 1997.

Vesta

• Vesta has been studied recently with Hubble Space Telescope.

Diameter = 165 miles

Comets• There are two reservoirs for comets

• Kuiper Belt • Oort Cloud

• The solar wind produces two tails on comets: the dust tail and the ion tail.

• Examples: • Halley's Comet• Hale-Bopp• Shoemaker-Levy 9

The Oort Cloud

Structure of a Comet

To Sun

Ion Tail

Dust Tail

Coma

Comet Halley

• It orbits the Sun every 76 years.

• It was imaged in 1986 at close range by Giotto, a European satellite.

Comet Halley 1910

•Pope Callixtus III excommunicated Halley's Comet in 1456

•In 1910, charlatans sold "comet pills"

Comet Nucleus

Hyakutake

Hale-Bopp

Comet West

Comet Shoemaker-Levy 9

Comet Shoemaker-Levy 9

The End.

Comet Shoemaker-Levy 9

• Was shatter by Jupiter’s gravity in 1992.

• All pieces hit Jupiter in the summer of 1994 leaving dark impact scars.

Meteors

• meteoroid - small debris moving though space

• meteorite - space debris found on Earth• Types

• iron meteorites• chondritic meteorites

Iron Meteorites

Chondritic Meteorites

Meteors• Sporadic Meteor

• Random meteors with various compositions

• Bolides• Leave trails (trains) that last for a few minutes

• Sometimes make noise

• Fireball• Sometimes take over half a minute to cross the sky

• Sometimes have magnitudes brighter than Venus

Meteors• How can you determine the composition of

a meteor?• Take its spectra.

• How can you tell how high it vaporizes?• Triangulation from two observers.

Sporadic Meteors

Irons Stony-Irons

Chondrites Carbonaceous Chondrite

Achondrite

Meteors• meteor

• a.k.a. “shooting star”

• A small bit of rock that is heated by friction in the Earth’s atmosphere and gives off light

• meteor shower• Results from the Earth passing though a comet's path

• Can result in 100’s of meteors per minute

• Are named after the radiant constellation

Meteor Shower

The 1833 storm

The Cause of Meteor Showers

P55/Tempel-Tuttle

Earth Impacts and Near Misses

• Arizona Meteor Crater• measures 1 mile across

• from an impact 50,000 years ago

• by a 50 meter meteoroid

• Tunguska Event• in 1908

• an asteroid broke up in our atmosphere

• leveled trees for some 30 kilometers

• Chicxulub Event /cheek-shoo-loob/• 65,000,000 years ago

• 10 kilometer asteroid

• is thought to have caused a mass extinction of dinosaurs

How are asteroids and comets discovered?

• Two pictures are taken of the same region of the sky at different times.

• If any object in the pictures has moved then it could be…

• an asteroid• or comet• or a planet• or a UFO.

How Much Damage?

The End...

Live long and prosper.