Last Stop in the Solar System
Nine years after leaving Earth, New Horizons sets its sights on Pluto, and whatever lies beyond.
This July, from three billion miles away, a spacecraft will send the first close-ups ever seen of Pluto.
THIS JULY 14,
at around 9 p.m. Eastern time, a burst of radio telemetry will complete a three-billion-mile trek to arrive at one of the huge dish antennas of NASA’S Deep Space Network. The signal will make its way to a command center in Maryland, where planetary scientist Alan Stern will be waiting. If the signal arrives as planned, he will know that the reconnaissance of Pluto he spent the last 25 years working toward has succeeded.
Thirteen hours earlier, the 1,100-pound, grand-piano-size probe called New Horizons will have sped past the dwarf planet and its retinue of moons, gathering close-up images and other data that Stern expects will “rewrite the textbooks.” That is, if New Horizons manages to avoid colliding with particles of dust and ice, which—at a flyby speed of 31,000 mph—could destroy the craft before it has a chance to transmit its findings to Earth. Stern, who is based at the Southwest Research Institute in Boulder, Colorado, says, “That should be a nail-biter.” He says it almost cheerfully, as if he welcomes the ordeal. By now, as the mission’s principal investigator and the driving force behind its creation, Stern is used to tension. Almost everything about getting to Pluto has been a struggle.
Twenty-five years ago, when he began his Pluto quest, planetary scientists were still anticipating the conclusion of the Grand Tour of the outer solar system by the twin Voyager spacecraft, launched in 1977. At one time planners had considered including Pluto on Voyager 1’s itinerary, but instead chose a flight path that would allow close flybys of more alluring targets like Saturn’s moon Titan. And so, after passing Saturn in 1980, Voyager 1 headed off toward interstellar space, and the Grand Tour ended with Voyager 2’s flyby of Neptune in August 1989. Most scientists were untroubled that Pluto had been left out. Not Alan Stern. To him, the exploration of the solar system was unfinished. By the spring of 1989, with a new PH.D. in astrophysics and planetary science, Stern was already thinking about how to get NASA to send a mission to the ninth planet. He started talking up the idea. “I was a young guy,” he recalls, “and senior guys in the field, guys that were in their 50s then, would say to me, ‘Are you kidding me? Everyone will be dead by the time we get there.’ Meaning they would be dead. It’s human nature.”
Stern rallied several young scientists, and even a few older ones, to take up the cause. The idea became even more appealing after Voyager 2’s Neptune flyby, when scientists got their first good look at the icy moon Triton, thought to be a close cousin of Pluto. Voyager’s images revealed weird, contorted terrains and, to everyone’s amazement, geysers of frozen nitrogen. There was reason to think Pluto might be just as strange and exciting.
Discovered in 1930 after a nearly year-long telescopic search by a young observatory assistant named Clyde Tombaugh, Pluto is so faint and so distant—its 248-year orbit averages 3.7 billion