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 leftoverMeteoroid – small rocky material in space Meteor – in the atmosphere (falling star)Meteorite – any piece of rock than fell to the ground from the skyComet 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 BeltEarly 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

MeteoritesMeteor 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

Comets• Chunks of rock and ice in highly eccentric orbits

• Near sun, ice sublimates to produce “tail”

• A couple have been visited by robotic craft

Comet StructureComets 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

CometsComets 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 Shoemaker-Shoemaker-Levy 9

Earth impacts

• Do we ever get hit?• Yes! The questions are when and by

what?• Classify events by size

–Small–Medium–Large

ImpactsThe 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/Textinctionevent

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