Pluto
Mass (kg)............................................1.29 x 10^22
Diameter (km)........................................2300
Mean density (kg/m^3) ...............................2030
Escape velocity (m/sec)..............................1100
Average distance from Sun (AU).......................39.53
Rotation period (length of day in Earth days)........6.39
Revolution period (length of year in Earth years)....247.7
Obliquity (tilt of axis in degrees)..................122.5
Orbit inclination (degrees)..........................17.15
Orbit eccentricity (deviation from circular).........0.248
Mean temperature (K).................................37
Visual geometric albedo (reflectivity)...............about 0.5
Atmospheric components...............................perhaps
methane and
nitrogen
Surface materials....................................perhaps
methane ice
Clearest View
This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope. The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 4.4 billion km (2.6 billion mi) from Earth. Hubble's corrected optics show the two objects as clearly separate and sharp disks. This has allowed astronomers to measure (to within about 1 percent) Pluto's diameter of 2320 km (1440 mi) and Charon's diameter of 1270 km (790 mi). The Hubble observations show that Charon is bluer than Pluto. This means that both worlds have different surface composition and structure. A bright highlight on Pluto suggests it has a smoothly reflecting surface layer.
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