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THE KUIPER
BELT IS REAL
EXPLORING BEYOND NEPTUNE
IN CONTEXT
KEY ASTRONOMERS
David Jewitt (1958–)
Jane Luu (1963–)BEFORE
1930 American astronomer
Clyde Tombaugh discovers Pluto
orbiting beyond Neptune. It is
initially identified as the ninth
planet but is later reclassified.1943 Kenneth Edgeworth
suggests that Pluto is just
one of many objects in the
outer solar system.1950 Fred Whipple describes
the icy nature of comets as
“d i r t y snowba l l s.”AFTER
2003 Sedna is discovered
orbiting 76 AU−1,000 AU from
the sun, beyond the outer edge
of the Kuiper belt.2005 Eris is seen in the disk
beyond the Kuiper belt.2008 Two Kuiper Belt Objects
are classified as dwarf planets
along with Eris, Pluto, and Ceres.I
n 1950, Dutch astronomer Jan
Oort proposed that a spherical
shell of potential comets
surrounds the solar system half a
light-year away. The so-called Oort
cloud was the source of long-period
comets, which took millennia to
orbit the sun. But the source of
the short-period comets that orbit
the sun every few centuries must
be nearer. In 1943, Irish scientist
Kenneth Edgeworth speculated
that the comet reservoir was abelt beyond Neptune. But the
Dutch−American astronomer
Gerard Kuiper argued in 1951 that,
although there was once such a
belt, it would have been scattered
away by the gravity of the outer
planets. It was a puzzle, and comet
nuclei that far away would be too
faint for even the best telescopes.
In the 1980s, sensitive new CCD
(charge-coupled device) detectors
became available. With these,
astronomers at last had a chanceThe outer solar system contains the
leftover material from the formation of the planets.Some of the material travels
from the edge of the solar
system in the form of
long-period comets.Short-period comets
must come from a
nearer source.The Kuiper belt, a theoretical reservoir of icy bodies beyond the
orbit of Neptune, could be the source of short-period comets.