The New Horizons leader on how the mission succeeded, what the distant planet revealed, and where the probe is going next.
Laurel, Md. Pluto is alive—and no one knows why.
On Tuesday the New Horizons spacecraft, having traveled three billion miles since 2006, darted past this orb of rock and ice, gathering data and taking photographs. The first high-resolution shots beamed home showed mountains of water ice roughly the size of the Rockies, and a smooth area without impact craters.
That indicates the section of the planet’s surface is young, renewed and reformed by geological activity. “The solar system, meaning also Pluto, is four and a half billion years old,” Alan Stern, the scientist in charge of the mission, tells me during a Thursday interview. “Already—and this is loose, we can do better later—we can show that surface is less than 100 million years old.”
But geological processes require heat, and therein lies the riddle. “There’s no really good model for how these small planets can have their engines running after four billion years. As planets get smaller, the ratio of surface area compared to their mass goes up. That means that they can’t trap the heat inside very long. They cool off.”
He gestures to the paper cup of coffee on the table in front of him. A small cup of coffee will go cold faster than a large one; a large cup of coffee will go cold faster than a big pot. The point is that without an outside source of energy, such as tidal forces from a nearby gas giant, a planet like Pluto, which is one-sixth the size of our moon and circles the outer reaches of our solar system, should be long dead.