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Planetary News: New Horizons (2005)

New Horizons Gearing Up for Epic Voyage to Pluto

by Amir Alexander

February 18, 2005:
Ever since it was discovered 75 years ago, Pluto has been in the habit of posing many more questions than it answered. First seen in the night sky as a faint point moving slowly among the constellations, it remained exactly that for decades – a single point of light. Even the strongest telescopes could not resolve Pluto into an elegant planetary disk like the rest of the planets, and so, although scientists had many questions about Pluto, few answers were forthcoming. By the 1970s observational technology had advanced to the point that the single point was resolved into two points, and so we learned that Pluto had a moon. Finally, over the past decade, the Hubble Space Telescope has taken pictures of Pluto far superior to anything available before, showing a surface with varying shades of color. And yet, Pluto remains a mystery. What it is composed of? What are its surface features? What kind of atmosphere does it possess? Scientists just don’t know.

New Horizons during Assembly
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New Horizons during Assembly
The spacecraft being assembled at Johns Hopkins University's Applied Physics Laboratory on January 29, 2005. Credit: JHUAPL/SWRI

This unfortunate situation, however, may soon change because Pluto, the last planet not yet visited by a human-made spacecraft, will finally get a visitor. New Horizons, the spacecraft built to explore Pluto and Kuiper Belt, is now in its final stages of assembly at Johns Hopkins University’s Applied Physics Laboratory in Maryland. “The spacecraft assembly is scheduled to be completed late in March” said S. Alan Stern, the mission’s Principal Investigator. The next stage, he added, is a long series of functional and environmental tests, checking whether the spacecraft is ready for its epic journey.

The day when New Horizons is sent on its way to the outer reaches of the Solar System will be the culmination of over 15 years of effort for Stern and others. Since 1989 he has been involved in no less than five different Pluto missions, four of which were cancelled before they ever got off the drawing board. Finally, in 2001, NASA selected Stern’s New Horizons mission from among several competing proposals, and work on the project has been ongoing ever since. Repeatedly over the past five years the mission was threatened with cancellation. Time after time The Planetary Society stepped in, mobilizing tens of thousands of people in petitions and letter-writing campaigns to Congress, demanding that the mission be preserved. Together, we succeeded, and New Horizons is now on the final stretch to its scheduled launch.

New Horizons
Click to enlarge >
New Horizons
Artist's conception of the New Horizons spacecraft at Pluto and Charon. Created: 2004. Credit: JHUAPL / SwRI

If all goes as planned, New Horizons will launch early in 2006. Depending on the exact launch date, the spacecraft may or may not pick up a gravity assist from Jupiter, which would make a difference of several years in the length of its trip. At the earliest New Horizons will reach Pluto in 2015, but the trip could potentially take up to four years longer. If the launch is put off to the next window of opportunity in 2007, the spacecraft could reach Pluto as late as 2020. Once it reaches its destination New Horizon’s first priority is to conduct a detailed survey of Pluto and Charon. If its fuel reserves hold it will then move on to investigate other objects in the Kuiper Belt.

To Stern, the importance of Pluto and the Kuiper Belt today has to do with our understanding of the basic architecture of the Solar System. “We are familiar with two classes of planets,” he explained, “the rocky planets of the inner Solar System, and the gas giants beyond them. And then there is Pluto, which doesn’t fit in either category.” Pluto, Stern suggests, is just the first recognized member of a third category of planets, which he refers to as “icy dwarfs.” Based on the density of objects in the Kuiper Belt, Stern suggests that there could be as many as 10,000 planetary bodies in the Solar System. Out of these, he estimates, the icy dwarfs are by far the most numerous. “Pluto was once viewed as a misfit in the Solar System,” said Stern. “Today we realize it was just the tip of the iceberg.”

"I want to know what Pluto is like," said Stern, and the only way to find out is to go there. Traveling to Pluto and the Kuiper Belt, Stern explains, is also a voyage in time to the very beginning of the Solar System. Whereas all matter closer to the Sun was radically transformed by heat and radiation, the debris field that is the Kuiper Belt has remained much as it was. “It is the only pace where the material was left in cold storage” said Stern. By visiting this primordial region, planetary scientists believe they will learn a great deal about the fomation of the planets and the origins and history of the Solar System.

With questions of the fundamental architecture of the Solar System, its origins and its history hanging in the balance, it is hardly surprising that the National Academies of Science placed the exploration of Pluto and the Kuiper Belt among its highest research priorities for the coming decade. 75 years after its discovery as a faint dot in the night sky, Pluto is the focus of scientific attention like never before.