Pluto
Outer World of the Solar System
Feb. 5, 2005, jeb
OUTLINE
Discovery of Pluto
Basic Properties of Pluto
Hubble Space Telescope Images of Pluto
Orbital Properties
Pluto's moon, Charon
Pluto's other properties
Pluto's origin
Future exploration of Pluto
Golden Globe Awards for Pluto
Other Sources on Pluto
Discovery of Pluto in 1930
Percival Lowell
estimated position of ninth planet from deviations in orbits of Uranus and Neptune
Discovered 14 years after Lowell's death very close to Lowell's predicted location by American Clyde Tombaugh
Lowell's calculations now appear to have been incorrect and predicted location was accidentally accurate
Pluto is far too small to have detectable influence on Neptune or Uranus
Pluto is named for the mythical Greek god of the underworld
note 1st two letters of Pluto stand for Percival Lowell
Basic Properties of Pluto
Planet order from Sun
Orbital period
Semi-major axis
Mass
Radius
Density
Rotation Period
Known Moons
Pluto
9
248 years
39.5 AU
0.002 x Earth's mass
0.2 x Earth's radius
2060 kg/m
3
-6.4 days
1
Hubble Space Telescope Images of Pluto
back to outline
Pluto is the only planet that has not been visited by spacecraft
Most revealing images were taken with the Hubble Space Telescope in 1994,
after the mission to repair the optics in 1993
Pluto surface map
Orbital Properties
back to outline
Semi-major axis of 39.5 AU
very faint object
in Earth's sky
highly elongated and tilted orbit
eccentricity of 0.25 (largest in Solar System)
approaches within about 30 AU of Sun (perihelion)
at farthest point, about 50 AU from Sun (aphelion)
inclination of 17
o
to ecliptic (largest in Solar System)
Passes
inside Neptune's orbit
at perihelion
Inside Neptune from 1979 to 1999
making Neptune the most distant planet from the Sun during this period
Locked in 3:2 resonance with Neptune
Will not ever come close enough to Neptune to collide
Pluto's moon,
Charon
back to outline
Discovered
in 1978
named for the mythical boatman who ferried the dead across the river Styx into Hades
HST images
much more distinct than
ground-based observations
Inclined orbit
(118
o
)
orbital period of 6.4 days
NOTE - this is identical to the rotation period of Pluto!
Furthermore, Charon rotates once for each revolution
just as the Earth's Moon does
by chance, a series of
several eclipses
(1985-1991) occurred
provided detailed info on size and orbits of Pluto and Charon
about one-half the radius of Pluto
600 km vs. 1137 km (Pluto)
medium sized moon
most closely matched planet and moon in the Solar System
"double planet"
about one-sixth the mass of Pluto
M
PLUTO
= 0.0021 M
EARTH
Pluto's other properties
back to outline
Radius = 1137 km (more like a
moon
than any other planet)
Density (2060 kg/m
3
) midway between Jovian and Terrestrial
Density similar to Triton (Neptune's moon)
Probably mostly water-ice compostion
Surface temperature of about 50K (solid methane)
Pluto's origin
back to outline
Escaped moon?
Icy asteroid
and Charon?
more icy asteroids beyond Pluto?
Do Triton and Pluto have a similar origin?
They are similar
density, mass, radius
Pluto: 2060 kg/m
3
, 0.002 M
E
, 1137 km
Triton: 2100 kg/m
3
, 0.0035 M
E
, 1350 km
Did both once move in independent orbits around the Sun?
Charon?
Future Exploration of Pluto
back to outline
Pluto is the only planet not explored up close by spacecraft
NASA plans to launch a mission to Pluto-Charon and beyond in 2006.
New Horizons Pluto-Kuiper Belt mission
should arrive at Pluto-Charon in 2015
9 year flight-time
trajectory
compare this to
Voyager
current locations of planets
Golden Globe Awards for
Pluto
back to outline
Largest orbital eccentricity (0.25) of any planet in the Solar System
Largest orbital inclination (17
o
) of any planet in the Solar System
Greatest distance from the Sun of any known planet in the Solar System
Longest orbital period (249 years) of any planet in the Solar System
Lowest surface gravity and escape velocity of any planet in the Solar System
Lowest surface temperature (about 50K) of any planet in the Solar System
Most closely matched planet-moon system in the Solar System ("Double Planet")
Other Sources on Pluto
StarDate Guide to Pluto
Welcome to the Planets - Pluto
Views of the Solar System - Pluto
The Nine Planets - Pluto
back to outline