Former-planet Pluto is making news again, but this time it’s not because of any controversy over planetary demotion. This little icy body some 2.5 to 4.3 billion miles from Earth will soon be visited by a spacecraft sent from Earth – the first time Pluto, its moons, and its icy neighbors will be studied up close and in detail.
On July 14, NASA mission New Horizons will make a close flyby of Pluto, passing within 6,200 miles of its surface and attempting the first detailed measurements of Pluto and its five known moons. The probe will then move on to explore a few of the many thousands of other similar objects in the solar system’s Kuiper Belt – the disc-shaped region of icy bodies beyond the orbit of Neptune.
While scientifically acceptable names for Pluto are now “Kuiper Belt Object,” “dwarf planet” or “ice dwarf,” its important place in advancing planetary science remains intact. Pluto’s discovery in 1930 by Clyde Tombaugh at Lowell Observatory inspired astronomers to further explore this region of the solar system which, they later found, is buzzing with thousands of icy worlds just like Pluto. The Kuiper Belt, this region of ancient planetary relics, was discovered in 1992 by astronomers David Jewitt and Jane Luu, and extends beyond the orbit of Neptune from about 30 to 55 AU (the distance between the Earth and sun is 1 AU, or about 93 million miles). New Horizons will help find vital clues to the many mysteries surrounding the solar system’s formation approximately 4.56 billion years ago.
The Kuiper Belt is also thought to house an estimated trillion or more short-period comets – those balls of ice and dust that cycle through the inner solar system every 200 years or less – so New Horizons will be the first mission to explore this main repository of primitive objects that continue to dazzle our skies when they pass close to the sun.
New Horizons left Earth on Jan. 19, 2006, at 38,350 mph, making it the fastest launch speed for a spacecraft to date. Comparable in size and shape to a grand piano, the spacecraft is powered by plutonium-238, a radioactive isotope that decays approximately 5 percent every four years, and will power the primary mission through its intended mission duration of 91/2 years. Armed with seven on-board instruments – including optical cameras, dust and radio sensors, plasma detectors and an ultraviolet spectrometer – the mission will map the geology and chemical composition of Pluto and its largest moons, study the atmosphere of Pluto (a thin veil of nitrogen, methane and carbon monoxide derived from its surface ices) and its interaction with solar wind, and search for rings and additional moons of Pluto.
While we can’t yet send humans to deep space, New Horizons carries with it some meaningful proxies. Following the lead of the Pioneer and Voyager probes of the 1970s – missions that carried designed messages from Earth – hitching a ride on New Horizons is a CD-ROM with more than 400,000 names of people who took part in the “Send Your Name to Pluto!” campaign; quarters from the states of Maryland and Florida, where New Horizons was built and launched, respectively; two U.S. flags; and some of the ashes of Pluto discoverer Clyde Tombaugh. These souvenirs from Earth will venture to Pluto, the Kuiper Belt and, eventually, to interstellar space and beyond. Who could be out there to find them?
Rachel Smith is director of the Astronomy & Astrophysics Research Lab and curator of meteorites at the N.C. Museum of Natural Sciences, and an assistant professor of physics and astronomy at Appalachian State University.