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To Pluto and beyond

The New Horizons mission aims to get a good look at the solar system's most distant reaches.
For more information, contact:
Matt Quandt
Assistant editor
Astronomy magazine
[t] 262.796.8776 x419

January 12, 2006

Astronomy offers publication-quality images below.

WAUKESHA, WI &#151 NASA's New Horizons spacecraft will give the solar system's ninth planet the up-close-and-personal treatment. Its launch window opens Tuesday, January 17, and lasts until February 14. The spacecraft will lift off from the Kennedy Space Center near Cape Canaveral, Florida.

This first-ever mission to Pluto will explore the distant planet, its moon Charon, and the neighboring Kuiper Belt. The New Horizons spacecraft will then travel into deep space on a one-way journey into the cosmos.

Why is the New Horizons mission so important to planetary scientists? "Exploring Pluto and the Kuiper Belt is like conducting an archaeological dig into the history of the outer solar system, a place where we can peek into the ancient era of planetary formation," says Alan Stern, New Horizons principal investigator, of the Southwest Research Institute in Boulder, Colorado.

Astronomy magazine previewed this mission in its annual Explore the universe 2006. For a copy of the six-page article, "First mission to the last planet" by Alan Stern, please contact Matt Quandt:; 262.796.8776.

The mission
The 1,050-pound (476 kilograms), piano-size New Horizons spacecraft will use Jupiter's gravity to slingshot toward the Pluto-Charon system, where it will arrive in mid-2015. For 5 months, New Horizons will study the system's global geology and geomorphology, map both worlds' surface features, compositions, and temperatures, and try to identify their atmospheric structures and compositions. Also on the agenda is an examination of two smaller moons (S/2005 P1 and S/2005 P2) discovered in 2005 by a Hubble Space Telescope team.

The spacecraft's science payload includes infrared and ultraviolet imaging spectrometers, two particle spectrometers, a multicolor camera, a long-range telescopic camera, a space-dust detector, and a radio experiment.

An unusual planet
Pluto is neither a terrestrial planet like Earth nor a gas-giant planet like Jupiter. It lies at an average distance of 39.5 AU (1 AU is the average Earth-Sun distance) &#151 a distance so great not even the Hubble Space Telescope can resolve surface features. Pluto is a small frozen world known as an "ice dwarf." While Pluto's composition remains unknown, its density suggests a combination of 70-percent rock and 30-percent water ice. Bright areas on Pluto's surface indicate the presence of frozen nitrogen, methane, ethane, and carbon monoxide. Dark surface areas are also present, but their makeup is unknown. Surface temperature on the "ice dwarf" ranges between -391° and -346° F (-235° to -210° C).

Pluto's mass, about 0.0021 Earth, and low surface pressure make it likely the planet can't hold much of an atmosphere; however, an ethereal, gaseous mixture of nitrogen, methane, and carbon monoxide may be present above its surface when it is closest to the Sun (perihelion). These gases probably lie frozen throughout much of Pluto's orbit. New Horizons will attempt to measure the escape rate of Pluto's atmosphere directly, which may tell astronomers more about how Earth's atmosphere evolved.

Scientists disagree about Pluto's classification as a planet. Some believe it should be labeled an asteroid, a comet, or a large Kuiper Belt object. Its orbit is inclined 17° above the ecliptic plane and is highly eccentric, or more elliptical than the other planets' orbits. The 2005 discovery of Sedna and other large Kuiper Belt objects poured renewed energy into this ongoing debate.

Mysterious region no more
The Kuiper Belt is a disk-shaped orbital region beyond Neptune at about 30 to 50 AU from the Sun. It's home to a bevy of small objects, possibly planetary debris left over from the solar system's formation.

New Horizons is due to enter the Kuiper Belt by 2016. Cataloging these objects is of the utmost importance because astronomers think they're the main source of comets that occasionally impact Earth, sometimes with catastrophic results. Additionally, the mission will study organic molecules (those containing carbon) to learn more about the evolution of life on Earth.

Fast facts:
  • Spacecraft size &#151 1,050 pounds (476 kilograms), about the size of a piano
  • Distance to Pluto upon New Horizons' arrival &#151 about 33 AU (1 AU is the average Earth-Sun distance); about 3.06 billion miles (4.9 billion km)
  • Arrival at the Pluto-Charon system &#151 mid-2015
  • Pluto's diameter &#151 1,485 miles (2,390 km)
  • Pluto's mass &#151 0.0021 Earth
  • Pluto's orbit around the Sun &#151 248 Earth-years
  • Clyde Tombaugh discovered Pluto in 1930 from Lowell Observatory in Flagstaff, Arizona.
  • First mission to the last planet
    New Horizons' launch window opens January 17. It will be the fastest spacecraft ever launched. It will reach lunar-orbit distance in 9 hours and pass Jupiter in early 2007
    Pluto encounter
    A swing past Jupiter in 2007 will give New Horizons a boost and reduce the probe's travel time to Pluto by several years. About 10 weeks before closest approach, New Horizons' images of Pluto and Charon will be sharper than any from the Hubble Space Telescope.
    Astronomy: Kellie Jaeger
    Also in the sky
    January 15, at 8 A.M. EST, the Moon passes just 4° north of Saturn. The Full Moon appears 1/2° wide, so Saturn will be about 8 Full-Moon widths from the Moon.

    January 17, the Moon is at apogee, its point farthest from Earth (252,205 miles away).


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