Pluto, which is only about two-thirds the size of our moon, is a cold,
dark and frozen place. Relatively little is known about this tiny planet with
the strange orbit. Its composition is presumed to be rock and ice, with a
thin atmosphere of nitrogen, carbon monoxide and methane. The Hubble
Space Telescope has produced only fuzzy images (above) of the distant
Pluto's 248-year orbit is off-center in relation to the sun, which causes
the planet to cross the orbital path of Neptune. From 1979 until early
1999, Pluto had been the eighth planet from the sun. Then, on February
11, 1999, it crossed Neptune's path and once again became the solar
system's most distant planet. It will remain the ninth planet for 228
Pluto's orbit is inclined, or tilted, 17.1 degrees from the ecliptic -- the
plane that Earth orbits in. Except for Mercury's inclination of 7 degrees,
all the other planets orbit more closely to the ecliptic.
Interestingly, a similar thing happens with Jupiter's moons: Many orbit
on the ecliptic, but some are inclined from that plane.
Did you wonder: Will Pluto and Neptune ever collide? They won't,
because their orbits are so different. Pluto intersects the solar system's
ecliptic, or orbital plane, twice as its orbit brings it "above," then "below"
that plane where most of the other planets' revolve -- including Neptune.
And, though they are neighbors Pluto and Neptune are always more than
a billion miles apart.
Is it a planet at all?
Some astronomers think Pluto may have wandered into the system of
planets from a more distant region known as the Kuiper belt -- a region
beyond the orbit of Pluto thought to contain Pluto-like objects and
comets that orbit the sun in a plane similar to the planets of the solar
If that's the case, Pluto is not a planet at all, but is probably more like
a large asteroid or comet. Some have also suggested that it may have
once been a moon of Neptune and escaped.
The International Astronomical Union, the organization responsible for
classifying planets, gives these reasons for questioning Pluto's status as a
· All the other planets in the outer solar system are gaseous, giant
planets whereas Pluto is a small solid object
· Pluto is smaller than any other planet by more than a factor of 2.
· Pluto's orbit is by far the most inclined with respect to the plane
of the solar system, and also the most eccentric, with only the
eccentricity of Mercury's orbit even coming close
· Pluto's orbit is the only planetary orbit which crosses that of
another planet (during 1999 Pluto will again cross Neptune's orbit,
thus regaining its status as the most distant planet)
· Pluto's satellite, Charon, is larger in proportion to its planet than
any other satellite in the solar system.
Pluto has one moon, Charon, which was discovered in 1978. The
satellite may be a chunk that broke off Pluto in a collision with another
PLUTO: HADES IN ANCIENT MYTH, ROMAN GOD OF THE
Pluto was not discovered until 1930, by amateur American
astronomer Clyde Tombaugh. Since Tombaugh's death in 1997, many
astronomers have increasingly urged the International Astronomical
Union, which names celestial objects, to strip Pluto of its status as a
After a news report generated a flurry of irate e-mails about the
possible change, officials assured the world that Pluto would remain a
planet. But it will also likely become the first in a new class of celestial
object known as a TNO, or Trans-Neptunian Object. It seems Pluto may
then have a sort of dual citizenship.