Thus, said William B. McKinnon, Ph.D., professor of earth and planetary sciences in Arts & Sciences, there is a real urgency behind the proposed New Horizons mission to Pluto and the Kuiper Belt.

Photo by David Kilper

William B. McKinnon, Ph.D., professor of earth and planetary sciences in Arts & Sciences, is a team member of New Horizons, a group proposing a mission to Pluto and the nearby Kuiper Belt. "The New Horizons mission is the Lewis and Clark beyond Neptune," McKinnon says.

McKinnon is a team member of New Horizons, led by the Southwest Research Institute (SWRI) in San Antonio and the Johns Hopkins Applied Physics Laboratory, with the involvement of many other universities and research institutions. The principal investigator of the collaborative effort is Alan Stern, Ph.D., of the SWRI.

New Horizons recently entered its NASA-funded final design stage, after winning two rounds of proposals to NASA for a "Pluto-Kuiper Belt Mission," which would explore the smallest planet in the solar system, Pluto; its moon, Charon; and the Kuiper Belt, a mysterious conglomeration of ice-rock bodies beyond the orbit of Neptune.

Launch is proposed for 2006, with a flyby of Jupiter in 2007, Pluto and Charon in 2015, and a tour through the Kuiper Belt lasting until 2026. Data collected from the mission should provide basic information on the geology, chemistry, interior structures and atmospheres of these celestial bodies.

Pluto remains the only planet in our solar system not to be visited by spacecraft.

"The New Horizons mission is the Lewis and Clark beyond Neptune," said McKinnon, a well-known researcher of the outer solar system and one of more than 20 Pluto and Kuiper Belt experts on the New Horizons team. McKinnon will be analyzing the data-stream from the spacecraft to help plan the necessary encounters with Jupiter, Pluto, Charon, and the Kuiper Belt.

The mission plans to take advantage of Jupiter's position in the solar system.

"Jupiter is cycling by Pluto right now," McKinnon said. "By launching at the right time, we can get a gravity assist from Jupiter and get to Pluto with a total travel time of nine-and-a-half years. We also get some great science at Jupiter, for which we otherwise have no planned future missions."

The gravity boost reduces the flight time, and also the cost of the mission, as NASA can launch a smaller spacecraft that requires less fuel.

But what's the hurry?

When astronomer Clyde Tombaugh first discovered Pluto as a spot of light on his photographic plates in 1930, the planet was gradually moving closer to the sun along its 248-year elliptical orbit.

"The discovery of Pluto was a nice historical accident," McKinnon said. "Despite its long, eccentric orbit, the planet was relatively close during the early stages of investigation."

Pluto drew nearer until it reached perihelion -- the point in its orbit at which it is closest to the sun -- in 1989. The planet is now retreating from the sun, influencing future investigations in several ways.

Pluto cools off as it recedes from the sun, and scientists anticipate that its nitrogen atmosphere will freeze and fall to the planet's surface. New Horizons scientists hope to study the precise composition and structure of Pluto's atmosphere before it freezes out completely and disappears for more than a century.

Scientists also want to map the surfaces of Pluto and Charon. Because both bodies nearly rotate on their sides (compared with the Earth), seasons are extreme and the poles of both bodies endure decades-long and geographically extensive polar nights.

Pluto and Charon presently are moving from southern hemisphere autumn into winter, and as they move farther away from the sun, the areas of polar darkness get larger and hide more of the surface from direct study.

Contemporary knowledge of Pluto and the Kuiper Belt comes from the Hubble Space Telescope and various ground-based telescopes. Pluto appears as little more than a tiny spot of light to these high-powered instruments. The New Horizons mission intends to provide the clarity these instruments lack.

The mission will focus on the basic geology of Pluto, Charon and the Kuiper Belt.

"We will be studying a kind of wonderland of strange and exotic worlds, none of which have been seen up close," McKinnon said.

Composition, structure, atmospheres, radio occultations and solar-wind interactions will be studied.

Scientists also will count the number of craters present on the surfaces of these bodies. Counting craters will help scientists see the "flux" of smaller objects that once rattled and still are rattling around deep in our solar system.

"Some of these (objects) are destined to approach the Earth as comets, so understanding their home base, so to speak, is important," McKinnon said.

Pluto is the smallest and perhaps most controversial planet in the solar system. Pluto is approximately two-thirds the size of Earth's moon, and its surface is covered with nitrogen ice, with smaller amounts of carbon monoxide and methane ice, as well as dark, reddish (probably organic) matter.

Charon is about half the size of Pluto and shows evidence of a surface dominated by water ice.

Kuiper Belt Objects (KBOs) have different colors; scientists have observed both spectrally gray and red bodies. They also exhibit different compositions; data show the presence of water ice and dark (probably organic) materials.

More than 500 KBOs have been discovered to date, but researchers expect to find thousands before the New Horizons mission gets to the Kuiper Belt.

"Pluto and Charon are, technically speaking, part of the Kuiper Belt (being the largest known bodies there)," McKinnon says, "and New Horizons represents our first exploration of the third major region of the solar system, after the terrestrial planets and the gas giants."

As the final design for the Pluto-Kuiper Belt Mission nears conclusion, its future remains in question. NASA funded the project design to this point, but President Bush's new budget does not allot money for missions to the outer solar system.