It was a New Year’s Eve like no other. First of all, the big celebration started a half hour after midnight. Children were waving mini-flags, surrounded by throngs of giddy planetary scientists. And four billion miles away, one billion miles past Pluto, the New Horizons spacecraft was flying past an enigmatic object called 2014 MU69–better known by its nickname, Ultima Thule.
When radio signals from New Horizons finally reached Earth the next morning, they revealed that the mission was a smashing success. The first images of MU69 showed that it is a double-lobed object, apparently created from the delicate joining of two primitive planetary building blocks, or planetessimals. It was everything the mission scientists had hoped for. The only thing that felt off about the triumphant event was the object’s name: not only because some people objected to the Nazi mythology attached to Ultima Thule, but because of the name’s literal meaning of “beyond the known world.”
The moment that New Horizons reported back, MU69 became part of the known world. The probe had lived up to its name, pushing back the horizon of human understanding, so that it can be pushed back farther, again and again, in the future. There is no final frontier anywhere in sight, and that is what truly made the New Year’s encounter so exciting.
Novelists have “It was a dark and stormy night.” For planetary scientists, the equivalent cliche is, “We expect to be surprised.” The story of every new space mission seems to begin that way. No matter how intensely researchers study some solar-system object, no matter how they muster the best resources available on Earth, they are inevitably caught off-guard when they get to study it up close for the first time. And no matter how worn and familiar that cliche may sound, it also rings true every time. Nature’s creativity surpasses human imagination, time after time.
Even by those standards, the flight of the New Horizons probe past Ultima Thule tonight is something special. In the words of Alan Stern, the mission’s principle investigator and spiritual leader, “We’ve never, in the history of spaceflight, gone to a target we know less about.” It’s a type of object never seen up close before, a small (30 kilometers wide) member of the Kuiper Belt. Even more exciting, it belongs to the so-called “cold classical” region of the Kuiper Belt, meaning that it probably has remained largely unchanged for more than 4 billion years, frozen in deep storage 6.5 billion kilometers from the Sun.
Will it look battered from ancient collisions? Will it be covered with organic molecules from the early solar system? Will it resemble Pluto’s moons, or look like a fresh comet, or like something else entirely? Nobody knows.
On July 14, 2015, the New Horizons spacecraft swept past Pluto, returning eye-popping images of the dwarf planet and its huge (relatively speaking) moon, Charon. At the time, the best existing images of Pluto showed nothing more than an enigmatic blur. New Horizons revealed a world of astonishing diversity: organics-coated dark patches, ice mountains, nitrogen glaciers, and methane snows, all in a state of astonishing activity considering the temperatures there are only about 40 degrees above absolute zero.
The scientific bonanza from the Pluto flyby was sweet vindication for Alan Stern, principal investigator on New Horizons. Stern spent decades fighting to make a Pluto mission happen, persisting long after it seemed like a hopeless cause. Teaming up with writer and astrobiologist David Grinspoon, Stern tells the full, thorny story in his engaging new book Chasing New Horizons: Inside the Epic First Mission to Pluto. It’s a a tale about space science, yes, but it’s also a reminder of what can happen when you refuse to let dreams die.