PLUTO AND THE KUIPER BELT Beyond Neptune the

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 1990 s 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 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 10 th planet of our solar system. • The detection of this (as yet un-named) object, called (temporarily) UB 313, 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 UB 313, compared to those of Pluto and the giant outer planets. Note, the orbits of Pluto and UB 313, in red, are tilted relative to the plane of the inner giant planet orbits.

KUIPER BELT MEMBERS DISCOVERED TO DATE, COMPARED TO OUR MOON