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Two views of Pluto

Pluto
Pluto was discovered on February 18, 1930, making it the last planet found in our Solar System. Pluto is usually farther from the Sun then any of the nine planets; however, due to the eccentricity of its orbit, it is closer than Neptune for 20 years out of its 249-year orbit. Pluto made its closest approach during 1989 and will remain within the orbit of Neptune until March 14, 1999.
Pluto's orbit is also highly inclined -- tilted 17 degrees to the orbital plane of the other planets. Observations also show that Pluto's spin axis is tipped by 122 degrees. Ground-based observations indicate that Pluto's surface is covered with methane ice and that there is a thin atmosphere that might freeze and fall to the surface as the planet moves away from the Sun. NASA plans to launch a spacecraft, the Pluto Express, in 2001 that will allow scientists to study the planet before its atmosphere freezes.
Pluto has one satellite named Charon [SHAR-on], named after the boatman in Greek mythology who operated the ferry across the River Styx to Pluto's realm in the underworld. Charon was discovered in 1978. Its surface composition seems to be different from Pluto's. The moon appears to be covered with water-ice rather than methane ice. Its orbit is gravitationally locked with Pluto, so both bodies always keep the same hemisphere facing each other. Pluto's and Charon's rotational periods and Charon's orbital period are all 6.3872 Earth days.

      MEAN RADIUS:                     1150 km
      MASS:                            0.0025 (Earth=1)
      DENSITY:                         2.03 (gm/cm)
      GRAVITY:                         ? (Earth=1)
      ORBIT PERIOD:                    247.7 (Earth years)
      ROTATION PERIOD:                 6.39 (Earth days)
      SEMIMAJOR AXIS OF ORBIT:         39.44 au (Earth=1)
      ECCENTRICITY OF ORBIT:           0.248 (Earth=0.017)    
      EQUATORIAL INCLINATION (deg):     122.46 (Earth=23.44) 
      SURFACE PRESSURE:                ~3 microbar  
      AVERAGE TEMPERATURE:             ~50 K
      WIND SPEEDS:                     0-200 m/s

      Atmospheric composition:         Methane (CH4), Nitrogen (N2)

Charon Statistics

Discovered by .................................... J. Christy
Date of discovery ...................................... 1978

Mass (kg) .......................................... 1.77e+21
Mass (Earth = 1) ................................. 2.9618e-04
Equatorial radius (km) .................................. 635
Equatorial radius (Earth = 1) .................... 9.9561e-02
Mean density (gm/cm^3) ................................. 1.83

Mean distance from Pluto (km) ........................ 19,640
Rotational period (days) ............................ 6.38725
Orbital period (days) ............................... 6.38725
Mean orbital velocity (km/sec) ......................... 0.23

Orbital eccentricity ................................... 0.00
Orbital inclination ................................... 98.80°

Escape velocity (km/sec) .............................. 0.610

Visual geometric albedo ................................. 0.5
Magnitude (Vo) ......................................... 16.8