Pluto

PlutoDiameter

0.18DE

Rotation Period 6 days 9 hours

Orbital Period 250 years

Distance from Sun 39.44AU

Orbit Eccentricity 0.25

Tilt 118 degrees

Temperature

possibly –228C to -238C

Atmosphere

probably N, CO and methane – when not frozen

Gravity

0.069g

Moons

1

Visits

none

Pluto and Charon

Pluto's eccentric orbit intersects Neptune's orbit, so sometimes is closer to the sun than Neptune

Pluto has an atmosphere when it is close to the sun, which then freezes as the planet moves away from the sun

Charon discovered in 1978 (diameter 1200 km, about half the size of Pluto)

Pluto is in a 3:2 orbit resonance with Neptune

The Outer Solar System – The Kuiper belt

An asteroid belt beyond the orbit of Neptune between 30-100 AU, consisting of icey bodies more like comets than asteroids

Red Orbits = PlutinosBlue Orbits = Classical Kuiper Belt ObjectsBlack Orbits = SKBOs

Also the Centaur group (Chiron etc) of asteroids that lie beyond the orbit of Saturn may also be Kuiper belt objects

Quaoar – The Largest Kuiper Belt Object

Discovered June 4 2002, by Michael Brown and Chadwick Trujillo

(California Institute of Technology)

Comets

Comets are essentially dirty lumps of ice that melt as their highly eccentric orbits take them closer to the sun.

The melting process creates geysers of carbon dioxide and water vapour that forms a kind of atmosphere called a coma around the comet's nucleus

Two tails trail beyond the comet in its orbit – one tail consists of dust and points away from the comet's direction of motion the other tail consists of ionised plasma that points away from the sun

The Giotto probe

Launched in 1985 by ESA to study Comet Halley on its last close

encounter with Earth (next time will be

2061)

(above) Nucleus of Comet Wild 2 as observed by the Stardust probe

(right) Nucleus of Comet Halley as

observed by the Giotto probe

There are two types of Comets

Periodic comets reach perihelion roughly every 100 years, and are thought to originate in the Kuiper belt

disc (e.g. Halle-Bopp, Halley's Comet)

Long period comets have aphelia of 50,000 AU and are thought to originate in the theorised Oort Cloud of comets – they have only ever been observed once (e.g. Hyakutake).

High and random orbital inclinations suggest the Oort cloud is a large shell rather than a disc.

Meteor Showers

Meteor showers are regular annual events caused by the Earth passes through a patch of its orbit where a periodic comet has left behind a dust trail

These dust particles burn up in the Earth's atmosphere leaving behind bright trails that light up the sky

All meteor trails in the sky appear to originate from a single radiant.

The largest meteoroids will survive the passage through the Earth's atmosphere and land on the surface as a meteorite.

Like asteroids, some meteorites are Iron based, others are just rocks