Transcript Asteroids Comets and Meteoriods

Remnants of Rock and Ice
• Asteroids
• Meteoroids (meteorites,
meteor)
• Comets
Remnants of the Solar Nebula
•Small bodies remain virtually unchanged since their
formation 4.5 billion years ago
•They carry history of the Solar system in their
compositions, locations, and numbers.
Asteroid means starlike, a rocky leftover
Meteoroid – small rocky material in space Meteor – in
the atmosphere (falling star)
Meteorite – any piece of rock than fell to the ground
from the sky
Comet means hair (Greek), an icy leftover
Asteroids (minor planets)
• Most abundant
between the orbits
of Mars and Jupiter
• Largest is Ceres,
800 km diameter
• Most are much
smaller, irregular
Asteroids
The first asteroid Ceres was discovered by
Piazzi on January 1, 1801 in an attempt to find
the missing planet between Mars and Jupiter
Ceres has a diameter of half of Pluto
There are more than 100,000 asteroids larger
than 1 km in diameter
Asteroid Eros
Asteroids (minor planets)
Evolution of the Belt
Early in the history of the Solar system, the
belt contained enough planetesimals to form
a planet.
Gravitational tugs from Jupiter created the
gaps.
Two stable zones along Jupiter’s orbit host
two families of asteroids (Trojans).
Jupiter’s Trojan Asteroids
Meteorites
Meteorites are pieces of rock that fell
from the sky.
Seen as fireballs (sometimes with sound)
May cause damage, but most fall into
oceans
Meteorites
Meteor showers – result of the Earth’s passing
through a comet orbit
Meteors are single pieces of comet dust
25 million meteoroids enter Earth’s atmosphere
every day
Meteor showers get their names after
constellations from which they appear to radiate
Meteor
Meteor
Showers
(These occur when
earth passes through
cloud of debris along a
comet’s orbit.)
Leonid Meteor Shower
Meteor Trail Recorded During
Leonid Meteor Shower, 1998
Ionized Trail Generation by
Meteor Crossing Eastern US,
1992
The Origin of Meteorites
Primitive meteorites may be either rocky or
carbon-rich
Processed meteorites can be removed from
the surface of a planet by an impact.
There are meteorites from Moon and Mars
found on Earth.
Primitive Meteorites
Processed Meteorites
• Chunks of rock and
ice in highly eccentric
orbits
• Near sun, ice
sublimates to
produce “tail”
• A couple have been
visited by robotic craft
Comets
Comet Structure
Comets are basically dirty snowballs where
ice mixes with rocky dust.
Their mean size is a few kilometers across.
The comet body is called nucleus.
Sublimating ices create coma.
A tail pointing away from the Sun appears.
There are two tails: plasma tail and dust tail.
Nucleus of Comet Borrelli
Comets
Comet Orbits
Comets
Comets contain information about the outer
solar system
Most of them visit the inner part only once, a
few are regular guests
One of the most famous comets is Halley’s comet.
It was discovered by Edmund Halley in 1682. Its
orbital period is 76 years. The last appearance in
1986.
Halley’s Comet
Comet Halley
Comet Hale-Bopp
Comet Hale-Bopp
Sun Grazing Comets
Comet ShoemakerShoemaker-Levy 9
Earth impacts
• Do we ever get hit?
• Yes! The questions are when and
by what?
• Classify events by size
–Small
–Medium
–Large
Impacts
The larger the impactor, the more rare the
impact
In 1908, an unusual explosion occurred in
Siberia.
Meteor crater in Arizona formed 50,000
years ago.
A large impact occurred 65 million years ago
perhaps caused the dinosaur extinction.
Earth impacts: small
• Small: less than 50 m across at top of
atmosphere
– Happening all the time
– Will burn up or break up in the atmosphere
– Most are very tiny (‘pea’ sized)
– Meteors! (“Shooting stars”, “Falling stars”)
• Can see 3 - 5 per hour on a typical night
• 25 million every day!
• 100 tons per day
Earth impacts: medium
• Medium: 50 m - 1 km across at top of
atmosphere
–Only ~ one every century or
millennium
–Causes “severe local damage”
–Two great examples from ‘recent’
history
Earth impacts: medium
• The Tunguska event - Siberia, Russia
–Happened in 1908
–Flattened a forest
–Knocked people over 200 km (140
miles) away
–No crater (exploded just above
ground)
• The impactor?
–A stony meteorite (?) Size: 30 m
across
The Tunguska event
The Tunguska event
Earth impacts: medium
• The Berringer Crater, in Arizona
–Happened 50,000 years ago
–The crater:
• 1,200 m across
• 200 m deep
Earth impacts: medium
• The impactor?
–An iron meteorite
–100 m across (50 m on impact)
–Going 40,000 mph!
–Explosion = 20 million tons of TNT
• A moderate atomic bomb
• 2 Mt. Saint Helens
The Berringer crater, Arizona
Meteor Crater in Arizona
Earth impacts: large
• Large: more than 1 km across at
top of atmosphere
–One every few million years
–Severe global effects
–More than 2 km can cause
mass extinction
–Most recent: 65 million years
ago
Earth impacts: large
• The K/T extinction event
–Some history…
• ‘K/T’ = ‘Cretaceous / Tertiary’
• 60 % of all species on Earth
disappeared, including the
dinosaurs
• One explanation (there are several):
Earth was hit by a large impactor
Earth impacts: large
• The K/T extinction event
–Evidence for an impact:
• Iridium found at that geologic
level
• A crater near the Yucatan, in
Mexico
The K/T
extinction
event
Earth impacts: large
• The K/T extinction event
–The impactor:
• Probably a comet
• Size: ~ 10 km across
• Energy released:
–100 million million tons of TNT
–5 million atomic bombs
–10 million Mt. Saint Helens
How often is there an impacted?
How often do impacts occur?
http://astro1.panet.utoledo.edu/~anatoly/astr1010/materials/324,41,Slide 41
http://campus.pari.edu/sara/arecibo/presentations/fields/294,13,Meteor Trail Recorded During Leonid Meteor Shower,
1998
http://departments.weber.edu/physics/schroeder/astro/lectureslides/356,8,Kuiper Belt objects (other stuff near Pluto)
http://www.phys-astro.sonoma.edu/people/faculty/carico/A100/367,2,Earth impacts