New Horizons revealed Pluto as a mysterious world, with icy mountains and very smooth plains.


Three years ago, when the New Horizons spacecraft sped toward Pluto on July 4th and began sending humans their first clear images of the tiny world at the end of the Solar System, it all seemed preordained.

Of course NASA would fund and build a spacecraft to complete its initial survey of the Solar System and visit the only “planet” found by an American. (For the purposes of this article, we will set aside the debate over Pluto’s planethood.) But as ever in spaceflight, the end result almost invariably looks far simpler and smoother to the casual observer than the messy reality experienced by those actually doing it.

For example, anyone tuning in to watch a spacewalk on NASA TV will see splendid views of Earth in the background as two astronauts float around holding funny tools, slowly unscrewing this, or installing that. It all looks so easy. Yet those six or seven hours in space represent the culmination of years of training, and the EVA activity itself is as physically punishing for the astronauts in their bulky spacesuits as running a marathon.

Today, we can hardly think about Pluto and its moons without conjuring in our minds the iconic image of the reddish, brownish world that resembles nothing so much as a heart. The reality, however, is that we almost didn’t get these images of Sputnik Planitia or Pluto’s ghostly atmosphere. Rather, it seems a miracle that we did.

This is the essence of the new book Chasing New Horizons, written by the principal investigator of the New Horizons mission to Pluto, Alan Stern, and his co-author David Grinspoon. The story of how New Horizons came to be is easily as compelling as the breathtaking imagery and discoveries it made.

Voyager and Pluto

NASA could have spied Pluto decades ago with the most iconic planetary science missions of all time, the Voyagers. Although the trajectory of Voyager 2 did not bring it near Pluto’s orbit, the Voyager 1 spacecraft could have reached the tiny world five years after its 1980 flyby of Saturn.

Mission scientists faced a dilemma: visit Titan or Pluto. They could either execute a maneuver immediately after passing Saturn that would bring the spacecraft near Titan; or they could skip a close Titan flyby, maneuver toward Pluto, and roll their dice on Voyager surviving for five more years. Ultimately Titan, with its tantalizingly thick atmosphere, won out. Few regret that decision today.

After the Voyagers, NASA was eager to send dedicated probes back to Jupiter and Saturn to better explore those complex worlds and their dozens of intriguing moons that the Voyagers had observed. These became the Galileo and Cassini probes. But Stern, a graduate student in the late 1980s, began to wonder why NASA wasn’t going to finish its exploration of the Solar System by sending a probe to Pluto.

He soon found (or arm twisted) a few scientific allies to join him in this cause—up-and-coming planetary scientists such as Fran Bagenal. As a first step, they decided to convene a session at the American Geophysical Union meeting in 1989. This would begin the process of building a consensus in the scientific community for such a mission.

Just before the meeting, Stern went to visit with Geoff Briggs, who then directed Solar System exploration for the space agency, at NASA Headquarters. In the book, Stern recalls telling Briggs, “With Voyager winding down, why don’t we complete the job of exploring the Solar System? Would you fund a study of how to do a mission to Pluto?”

Briggs was immediately enthusiastic. “You know, no one’s ever asked me about that before. It’s a wonderful idea, we should do that.” This would be the last real bit of enthusiasm Stern heard from NASA for a long time.




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