Pluto was discovered on February 18, 1930, making it the last planet found in our Solar System.

    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.

    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.

Pluto's Moon

    Charon was discovered in 1978.

    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 Statistics
Discovered by -------------------------------------------------------- Clyde W. Tombaugh
Date of discovery ----------------------------------------------------- February 18, 1930
Mass (kg) ------------------------------------------------------------ 1.29 x 10²²
Mass (Earth = 1) ----------------------------------------------------- 2.1586 x10^-3
Equatorial radius (km) ------------------------------------------------ 1,160
Equatorial radius (Earth = 1) ------------------------------------------ 0.18188
Mean density (gm/cm³) ----------------------------------------------- 2.05
Mean distance from the Sun (km) ------------------------------------- 5,913,520,000
Mean distance from the Sun (Earth = 1) ------------------------------- 39.5294
Rotational period (days) ----------------------------------------------- -6.3872
Orbital period (years) -------------------------------------------------- 248.54
Mean orbital velocity (km/sec) ----------------------------------------- 4.74
Orbital eccentricity ----------------------------------------------------- 0.2482
Tilt of axis (degrees) ---------------------------------------------------- 122.52
Orbital inclination (degrees) --------------------------------------------- 17.148
Equatorial surface gravity (m/sec²) --------------------------------------- 0.4
Equatorial escape velocity (km/sec) -------------------------------------- 1.22
Visual geometric albedo -------------------------------------------------- 0.3
Magnitude (Vo) ---------------------------------------------------------- 15.12
Atmospheric composition ------------------------------------------------- Methane, Nitrogen 0.3 .
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• Summarised  information (Word 97 document)
• Information extracted from Britannica 97