April 2004
Voyage to a Double Planet
By Patrick L. Barry and Dr. Tony Phillips
Download a "nine planets" screensaver for your computer with spectacular photos
of our solar system, and you'll notice that one planet is conspicuously missing:
Pluto. Icy and mysterious, Pluto is the only planet never visited and
photographed by NASA space probes.
In fact, the clearest image we have of Pluto is a tiny, pixelated blob of light
and dark patches taken by the Hubble Space Telescope in 1994. It's tantalizing,
but not much more. Earth-based telescopes have succeeded, however, in
discovering one amazing fact: Pluto is not a lone world, but a double-planet
system. Its companion, measuring about half the size of Pluto itself, is named
Charon.
Work is underway to launch a robotic probe to visit and photograph Pluto and
Charon. The project, called New Horizons, will map both worlds. Sensors will
chart surface minerals and ices, and catalog the gases that make up Pluto's
wispy atmosphere.
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| Artist's idea of the New Horizons spacecraft flying by Pluto and its moon, Charon. (Credit: Dan Durda) |
"It's the second epoch in the exploration of
the planets," says Alan Stern, the principal investigator for New Horizons at
the Southwest Research Institute in Colorado. "We're going to the very edge of
the solar system."
The probe is scheduled to launch in January 2006. Its journey will be a long
one. Pluto is more than 30 times further away from the Sun than Earth is! Even
with a speed boost from a flyby of Jupiter, the probe won't arrive at Pluto
until July 2015. Afterward, the probe will venture on to explore the Kuiper
Belt, a distant "halo" of small, frozen objects surrounding the solar system,
from which comets originate.
Aside from sheer curiosity about these distant worlds, scientists are motivated
by questions about the formation of the solar system. Orbiting in the deep
freeze far from the sun, Pluto and Charon have undergone less change than the
inner planets during the solar system's 4.5 billion year history. These two
worlds will provide a glimpse into the past.
Pluto could also shed light on the origin of our own Moon. Earth, with its
single, large moon, is unusual. The Pluto-Charon system is the only other pair
like it in the solar system. In fact, some astronomers consider Earth and the
Moon to be a double planet, too. So knowing more about Pluto and Charon could
give clues about how the Earth-Moon system formed.
And, of course, the spectacular, up-close photos of Pluto and Charon are going
to look great as a screensaver!
This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.