NASA's New Horizons probe, which completed an unprecedented flyby of Pluto in July, has a new destination: a 30-mile-wide chunk of ice known as 2014 MU69 that orbits nearly a billion miles farther out.
Scientists have always planned for the spacecraft to visit to another Kuiper belt object (KBO) — one of the thousand or so pieces of rock and ice that orbit the sun in a cloud beyond Neptune. Today, NASA announced that New Horizons scientists selected 2014 MU69 instead of the other destination in consideration, a similar KBO called 2014 PN70.
NASA still has to officially approve this secondary mission, but all indications are that it will. If everything goes to plan, the spacecraft should reach this distant destination in January 2019.
Why New Horizons is going to visit a Kuiper belt object
Many of us imagine Pluto to be at the outer edge of the solar system. But in reality, it's just one of the largest of thousands of Kuiper belt objects. And from the start, NASA planned for New Horizons to fly by another one of these after Pluto: It was sent off with enough fuel to do so, and for the past year, scientists have been using the Hubble Space Telescope to spot potential targets.
Why visit two Kuiper belt objects? Mainly because we know so little about the Kuiper belt as a whole — and because the composition of these KBOs might tell us a lot about the original formation of the whole solar system.
KBOs were formed about 4.6 billion years ago, when Earth and the other planets were created, as well. But for unknown reasons, as Earth continued to grow larger, Pluto stopped growing and was flung outward, perhaps along with many other Kuiper belt objects.
That means that their contents could serve as a sort of frozen time capsule of the early solar system. We've now studied some of the smallest ones (comets, which have extremely elliptical orbits that occasionally bring them closer to Earth) and one of the largest ones (Pluto). Visiting a midsize object like 2014 MU69, New Horizons principal investigator Alan Stern told me before the Pluto flyby, "will really help us connect the dots."
To get there, mission scientists will direct New Horizons to fire its thrusters in October, to slightly alter its trajectory and set it on the proper course. When it flies by the KBO in 2019, it'll take photos and collect other sorts of scientific data to beam back to Earth. After that, New Horizons will keep on flying — but with no subsequent destinations planned, it'll just travel alone, advancing toward the outer reaches of the solar system until its power runs out sometime in the 2030s.