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Solar System Debris:Comets and Asteroids

● Primarily found in two zones in the solar system.

The AsteroidBelt (rocky, between Jupiter and Mars)

The Edgeworth/Kuiper Belt (beyond Neptune) and Oort Cloud (way out there) – sources of comets (icy)

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Solar System Debris:Comets and Asteroids

● Why do these things exist?.... Solar system formation is a messy process.

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Solar System Debris: Comets ● Beyond the orbit of Neptune material was sparse and

planetary accumulation times were very slow. – Some icy planetesimals remain. Some were ejected to great

distances by encounters with the giant planets.

– Occasionally one has an orbit modified so that it falls into the inner Solar System. Warmed by the Sun, ices sublimate away and dust is released making a “comet”.

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Comets● Comets originate in the “Oort Cloud” and the

Edgeworth/Kuiper belt.– Collisions and gravitational tugs can send them falling into the

inner solar system.

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Cometary Orbits● Since comets can fall into the inner solar system from great

distances, many have highly eccentric elliptical orbits outside the plane of the planetary orbits.

6What Happens When You Heat Upan Icy Asteroid

● Note that the ices involved include CO2 and ammonia in addition to water vapor.

7What Happens When You Heat Upan Icy Asteroid

● Gasses and debris stream away from the evaporating nucleus.

Comet Hartley 2 observed by the (recycled) Deep Impact spacecraft.

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Cometary Nuclei● Cometary nuclei are basically “dirty snowballs” a few kilometers in

size.– Although small, this lump of ices (water, carbon dioxide, ammonia, ...) is

the source of all of the interesting phenomena.

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Cometary Nuclei● Comets are basically “dirty snowballs” a few kilometers in

size.– When close to the Sun, volatile ices such as CO2 and water

sublimate and create jets of gas and dust.

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Comets● Comets are basically “dirty snowballs” a few kilometers in size.

– During the brief time they are close to the Sun, water, CO2 and other ices are vaporized and create a cloud of gas and dust around the tiny nucleus.

– Pushed away from the Sun by the solar wind and sunlight, this tenuous debris can stretch a distance equal to the diameter of the Earth's orbit.

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Cometary Nuclei● Comets are basically “dirty snowballs” a few kilometers in

size.– When close to the Sun, volatile ices such as CO2 and water

sublimate and create jets of gas and dust.

The Nucleus of Comet Halley with “jets”

Jets and rotation combined

Sunlight and solar wind push back a tail

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Cometary Tails● Gases and dust vented by the nucleus get pushed back by

the pressure of sunlight and solar wind.– Comet tails point away from the Sun

The Nucleus of Comet Halley with “jets”

Jets and rotation combined

Sunlight and solar wind push back a tail

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Cometary Tails● Comets have two tails

– A gas tail pushed directly away from the Sun by solar wind and sunlight

– A dust tail also pushed away from the Sun, but with some memory of the comet's path.

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Cometary Tails● Comets are basically “dirty snowballs” a few kilometers in

size.– Comets have two tails

● A gas tail pushed directly away from the Sun by solar wind and sunlight● A dust tail also pushed away from the Sun, but with some memory of

the comet's path.

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Cometary Tails● Comets have two tails

– A gas tail pushed directly away from the Sun by solar wind and sunlight

– A dust tail also pushed away from the Sun, but with some memory of the comet's path.

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Cometary Tails● Comets are basically “dirty snowballs” a few kilometers in

size.– Comets have two tails

● A gas tail pushed directly away from the Sun by solar wind and sunlight● A dust tail also pushed away from the Sun, but with some memory of

the comet's path.

STEREO mission

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Notable Cometary Exploration Missions

● Giotto and Vega missions to Halley's comet– European and Soviet missions providing the first closeup look at a

cometary nucleus (1986).

● Stardust (afterlife in progress)– Fly through a cometary coma, collect material and return it to

Earth!

● Deep Impact (afterlife in progress)– Formation fly two spacecraft. Fly one, about the size and mass of

a washing machine into the comet while the other one collects data.

● Rosetta (in progress)– Formation fly with a comet and monitor its activity.

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Stardust

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Stardust

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Stardust

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Stardust

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Deep Impact● Launch a pair of spacecraft. Have one observe while the

other (about the size of a washing machine) impacts the comet.

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Deep Impact● Launch a pair of spacecraft. Have one observe while the

other (about the size of a washing machine) impacts the comet.

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Deep Impact● Launch a pair of spacecraft. Have one observe while the

other (about the size of a washing machine) impacts the comet.

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Deep Impact● Launch a pair of spacecraft. Have one observe while the

other (about the size of a washing machine) impacts the comet.

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Deep Impact/Stardust-NExT● Re-visit the comet using the Stardust spacecraft and look for

changes after six years.

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Deep Impact/Stardust-NExT● Re-visit the comet using the Stardust spacecraft and look for

changes after six years.

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Deep Impact/Stardust-NExT● Re-visit the comet using the Stardust spacecraft and look for

changes after six years.

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Meteor Showers● Comets are messy objects and spread debris around their orbits

– If the Earth intersects this debris trail we experience a meteor shower.

– Since the intersection point is a fixed location in the Earth's orbit, the shower associated with a given comet will occur annually on the same date.

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Meteor Showers● Prominent Reliable Showers

– Perseids – Aug 11 - 13

– Geminids - December 12-14● These showers produce 50-100 meteors per hour.

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Watching a Meteor Shower● Two required items – a lawn chair and patience

– Expect to see a meteor a minute at best.

– Know your radiant (if the constellation is not up you can't see the shower).

– Moonlight is a killer. Some years are “off” years for the best showers.

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Meteor Showers● When a meteor shower occurs the meteors all appear to originate

(radiate) from the same point in the sky (known as the “radiant”)– The shower is named after the constellation that contains the radiant.

– A shower can only be observed when it's radiant is above the horizon.● Perseids after 1 a.m.; Geminids after 10 p.m.

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Meteor Showers● The illusion of a radiant is the effect of perspective. All meteors

are moving through the atmosphere on parallel paths.

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Meteor Showers● The illusion of a radiant is the effect of perspective. All meteors

are moving through the atmosphere on parallel paths.

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Meteor Storms– Occasionally the Earth moves through a dense clump of cometary

debris.

http://www.astro.virginia.edu/class/skrutskie/images/leo_1499_double.mpg