- In just a few weeks time tiny Pluto will
regain its crown as the most distant planet orbiting the Sun. Soon afterwards
however it may lose its planetary status forever.
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- Pluto revolves around the Sun every 248
years in a highly elliptical path. This means that for a few years every
orbit it comes closer to the Sun than Neptune, the next most distant planet.
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- That will end at 11.22 GMT on February
11th when it will cross Neptune's path and once again become the solar
system's most distant planet.
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- It will be 220 years before it again
comes closer than Neptune. But long before that it may have been demoted
from its status as a planet.
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- Depending upon an email vote among astronomers
our solar system may soon have eight instead of nine planets as all the
textbooks say.
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- Always strange
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- Discovered in 1930 Pluto almost defies
classification, there is no other body quite like it. It is only two-thirds
the diameter of our Moon and it has a relatively large companion Charon,
discovered in 1978.
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- Charon may have been born through a head-on
collision between Pluto and another large ice body, in much the same way
as the Earth-Moon system is believed to have formed.
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- According to computer models, some of
the debris from this giant impact on Pluto went into orbit around Pluto
and coalesced to form Charon.
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- Made of a mixture of rock and ice Pluto
has always been an oddity. It neither qualifies as an Earth-like or a gas
giant planet.
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- Very little is known about its surface.
Images taken by the powerful Hubble Space Telescope show only fuzzy details.
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- Experts disagree about what it is, but
a growing number say that if it was discovered now, it would never even
occur to them to call it a proper planet.
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- It may be the last survivor of a lost
population of ice dwarfs that inhabited the primeval solar system. It may
even be an escaped satellite of Neptune.
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- Last to be visited
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- Pluto's significance in the solar system
has been a point of contention since soon after it was discovered in 1930
by Clyde Tombaugh, an astronomer at the Lowell Observatory in Arizona.
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- Since Tombaugh's death in 1997 pressure
has grown for the International Astronomical Union, the international authority
for naming celestial bodies, to take a tough line on Pluto.
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- The latest blow came in 1995 with the
discovery of the first object in the so-called Kuiper Belt. Since then
about 60 more objects, made of rock and ice and a few hundred km in size,
have been found in the solar systems cold outer reaches.
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- Pluto remains the only major body in
the solar system not to have been visited by a spacecraft.
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- Plans are being drawn up for a mission
called the Pluto-Kuiper Express that would fly past Pluto after having
spent over ten years getting there.
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- One of the reasons scientists want to
see it at close quarters is that despite its small size and remote location,
Pluto undergoes dramatic seasonal changes.
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- As Pluto recedes from the Sun, much of
its atmosphere is believed to freeze out onto the surface. This explains
the observation of fresh white ice on its surface.
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