Two Numbers: Pluto Gets Its First Close-Up

Justin Renteria

For those who grew up making Styrofoam models of our solar system with nine planets, Pluto's demotion to dwarf planet in the summer of 2006 came as a cruel blow. But earlier that year, on January 19, NASA launched its New Horizons probe on a path to make the first-ever flyby of Pluto. At the time, the spacecraft, which is roughly the size of a baby grand, broke speed records, leaving the Earth's atmosphere at more than 10 miles per second, according to Jim Green, head of planetary science at NASA.

Despite how fast it was moving, New Horizons still had a long journey ahead. By the time it has its Pluto encounter—expected to be July 14, at 7:49 a.m. EDT—nearly nine and a half years will have elapsed, or 3,462 days. The distance it has traveled, more than 3 billion miles, is the farthest any space probe has ever had to go to reach its primary target.

"Just to get an idea how far Pluto is away," Green explains, if there was a road from Earth to Pluto and you drove a car on it nonstop at 100 mph, "it would take you 4,187 years." If you were to get on a Boeing 747-400 and start flying around the world repeatedly (at an average cruising speed of 565 mph at an altitude of 35,000 feet, and without needing to stop for fuel), you could make your way around about 1,885 times in the 3,462 days that New Horizons will have been on course.

"It's been a mission of delayed gratification," says Hal Weaver, who has been working as a project scientist on the mission since 2003.

"In a sense, it's completing our initial reconnaissance of the solar system, but also beginning a new phase in the exploration of this icy outer solar system," says Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. Pluto may be a "dwarf," but it's one of the largest objects in the Kuiper Belt, which begins near the orbit of Neptune and extends far into space. This outermost part of our solar system is composed of some of its most primitive material, and objects in it can give scientists clues about its formation, says Weaver. At the time of the flyby, Pluto will have an approximate temperature of minus 390 degrees Fahrenheit, he adds. "That's like keeping [it] in a cosmic refrigerator."

New Horizons has instruments that will map the composition of Pluto, take sophisticated measurements of its atmosphere and send back images in high definition and color. At its closest point, New Horizons will pass roughly 7,750 miles from Pluto's surface, Green says. If you were flying above New York City at that distance with New Horizons's imaging capabilities, Weaver says, you'd be able to make out Central Park's individual ponds.

We're at the "frontier of exploration of our solar system," Weaver says. July 14's historic flyby will "transform Pluto and [its largest moon] Charon from these pixelated blobs into real worlds with richness and complexity."