Presentation on theme: "Remnants of Rock and Ice Asteroids Meteoroids (meteorites, meteor) Comets."— Presentation transcript:
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
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 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 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.
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 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 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 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
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
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
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