PLUTO AND THE KUIPER BELT
• Beyond Neptune, the most distant major planet, are a large number
of smaller objects, all of which currently known are smaller than the
smallest major planet, Mercury.
• These objects, which include the first observed and named, Pluto,
also have eccentric orbits in comparison to the inner eight planets.
• Although Pluto was discovered in 1930, no other objects of
comparable size and greater distance were detected until the 1990s
and later.
• Pluto has a very eccentric (and tilted) orbit in comparison to the
inner planets, and in a portion of its orbit, it can be closer to the Sun
than is Neptune.
• Most of the other objects discovered in the Kuiper Belt in recent
years have been smaller in size than Pluto, as well as more distant
from the Sun.
• Most recently, an object has been discovered which is at least equal,
and probably larger, in size than Pluto, and is also the most distant
such object discovered as yet.
PLUTO AND CHARON
• Pluto and its large (relative to Pluto) satellite Charon (on the
average) have been (until recently) the most distant planetary
objects from the Sun.
• Pluto has a highly eccentric orbit; hence it can be, in a small part
of its orbit, closer to the Sun than is Neptune.
• Pluto is similar to Neptune’s largest satellite, Triton, in size and
composition.
• The Pluto system is the only planetary system not yet visited by
spacecraft. However, observations with the Hubble and Spitzer
space telescopes, and new, large ground-based telescopes, have
greatly increased our knowledge in recent years.
• Charon, half the diameter of Pluto, is the largest satellite relative to
the size of its primary, in the solar system.
• Recently, observations with the Hubble Space Telescope have
detected two objects, fainter than Charon, which appear to be
additional satellites of Pluto.
Hubble Space Telescope View of Pluto and Charon
New Satellites of Pluto Discovered by HST
THE NEW HORIZONS MISSION TO PLUTO
• Pluto is the last of the original 9 planets of our solar system which has
not been visited by spacecraft.
• On January 19, 2006 the New Horizons spacecraft was launched by
NASA on a mission which will fly by Jupiter in February, 2007 and
reach Pluto in July, 2015.
• It will also explore Pluto’s satellite Charon, and other members of the
Kuiper Belt zone beyond the orbit of Neptune, to the extent possible.
New Horizons Mission Objectives
 Map surface composition of Pluto and Charon
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Characterize geology and morphology ("the look") of Pluto and Charon
Characterize the neutral atmosphere of Pluto and its escape rate
Search for an atmosphere around Charon
Map surface temperatures on Pluto and Charon
Search for rings and additional satellites around Pluto
Conduct similar investigations of one or more Kuiper Belt Objects
NEW HORIZONS SCIENTIFIC INSTRUMENTS
• ALICE – Ultraviolet Mapping
Spectrometer
• LORRI – Long-Range
Reconnaissance Imager
• RALPH MVIC – Multispectral
Visible Imaging Camera
• RALPH LEISA – Linear Etalon
Imaging Spectral Array
(Infrared Spectrometer)
• REX – Radio Experiment (also
transmits all science data from
the spacecraft)
• SWAP – Solar Wind Analyzer
Around Pluto
• SDC – Student Dust Counter
Artist’s Concept of New Horizons Mission Spacecraft
at Pluto and Charon
THE KUIPER BELT
• The Kuiper belt, named after astronomer Gerard Kuiper, is a
relatively new designation for the region of the outer solar system
beyond the orbit of Neptune (whose largest known member, by this
designation, has (until recently) been Pluto).
• The Kuiper Belt is also believed to be the primary home of most of
the long-period comets.
• In recent years, a significant number of new solar system objects
have been discovered in this region, some at considerably greater
distance than Pluto at its greatest distance from the Sun (but, until
very recently, none as large or larger).
• Two of these, known as Quaoar and (more recently) 2004 DW, are
comparable in size to Pluto’s satellite, Charon.
• The most distant of these, is the object named Sedna, discovered at
a distance of about 13.4 billion km (89 AU), and also comparable in
size to Quaoar, 2004 DW, and Charon.
• Sedna has a highly eccentric orbit, which is estimated to extend
from 76 AU to as far as 950 AU!
MORE KUIPER BELT OBJECTS
• Surveys of the outer part of the solar system, beyond the orbit of
Pluto, have recently found several additional objects
comparable to Sedna in size.
• Most recently, an object apparently larger than Pluto (and much
larger than Sedna) has been found, which would (if verified)
make it the 10th planet of our solar system.
• The detection of this (as yet un-named) object, called
(temporarily) UB313, was made using the ground-based 48-inch
Samuel Oschin telescope at Palomar Observatory.
• The object is 97 times Earth’s distance from the Sun, or more
than twice Pluto’s greatest distance.
• It is likely that, with continuing very deep sky surveys with both
ground-based and space-based telescopes, that more objects of
these types will be discovered.
Orbit of the newly discovered object, 2003 UB313, compared to those of Pluto and
the giant outer planets. Note, the orbits of Pluto and UB313, in red, are tilted relative
to the plane of the inner giant planet orbits.
KUIPER BELT MEMBERS DISCOVERED TO DATE,
COMPARED TO OUR MOON