A
Hubble space telescope picture of Pluto and it's moon Charon
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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 orbits the Sun
at mean distance of 5,913,520,000km, and 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. |
