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