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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.

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Remnants of Rock and Ice


Meteoroids (meteorites, meteor)


remnants of the solar nebula
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 spaceMeteor – in the atmosphere(falling star)

Meteorite – any piece of rock than fell to the ground from the sky

Comet meanshair(Greek), an icy leftover

asteroids minor planets
Asteroids (minor planets)
  • Most abundant between the orbits of Mars and Jupiter
  • Largest is Ceres, 800 km diameter
  • Most are much smaller, irregular

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

evolution of the belt
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).


Meteorites are pieces of rock that fell from the sky.

Seen as fireballs (sometimes with sound)

May cause damage, but most fall into oceans


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 showers
Meteor Showers

(These occur when earth passes through cloud of debris along a comet’s orbit.)

the origin of meteorites
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.

  • 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 structure
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.


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.

earth impacts
Earth impacts
  • Do we ever get hit?
  • Yes! The questions are when and by what?
  • Classify events by size
    • Small
    • Medium
    • Large

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
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
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 medium1
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
earth impacts medium2
Earth impacts: medium
  • The Berringer Crater, in Arizona
    • Happened 50,000 years ago
    • The crater:
      • 1,200 m across
      • 200 m deep
earth impacts medium3
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
earth impacts large
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 large1
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 large2
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
earth impacts large3
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
slide49,41,Slide 41,13,Meteor Trail Recorded During Leonid Meteor Shower, 1998,8,Kuiper Belt objects (other stuff near Pluto),2,Earth impacts