In July of 2015, the New Horizons space probe will whiz past Pluto, traveling at 40,000 kilometers per hour. For several weeks before and after the close flyby—it’ll pass within 10,000 km above the tiny world’s surface—it will examine Pluto, its moons, and the environment around it.
But this is not an orbiter, or a lander. Pluto is 5 billion kilometers from Earth, and the only way to get a probe there in any decent amount of time was to strip it down as light as possible and fling it as hard as possible, getting it moving so rapidly it could traverse the yawning chasm between us and Pluto as quickly as possible (with a boost from Jupiter along the way).
This is a fast flyby, with no slowing down. Once New Horizons is gone, it’s gone.
Except the solar system hardly ends at Pluto. There’s a vast collection of objects out there in the dark: cold, icy worldlets called Kuiper Belt objects. There are millions of them, relics from the formation of the solar system itself, and largely unchanged for billions of years. Getting a look at one up close is a very tempting goal.
The New Horizons team started a search in 2011 using large ground-based telescopes, and while they found dozens of these KBOs, none was near enough to the probe’s trajectory to investigate. Remember, space is vast and empty—that’s why we call it “space”—and while there may be millions of KBOs, they’re still spread pretty thin out there.
So they turned to Hubble. Narrowing the search but able to detect fainter objects,Hubble was the last hope … and it paid off. They found three potential targets, each over a billion kilometers farther out than Pluto. One, called (for now) PT1 (guess why) should be easy to reach given New Horizons’ present path and fuel supply. Its size is not clear, but based on its brightness and likely surface reflectivity it’s probably more than 30 km (20 miles) in diameter. New Horizons would fly past it in January 2019.