New Horizons is on its way to its next frontier.

On Wednesday afternoon, the instrument-packed spacecraft fired its thrusters in the last of four maneuvers steering it toward an object a billion miles past Pluto. New Horizons has been speeding into the fringes of the solar system since passing Pluto this summer, and scientists have directed it to shift its trajectory gradually over the past week and a half.


"It's a very small nudge," said Mark Holdridge, a scientist at the Johns Hopkins Applied Physics Laboratory who managed New Horizons' encounter with Pluto. The Hopkins lab handles the mission for NASA.

However small, that nudge makes a bonus mission possible for New Horizons, though it has not been fully planned or approved. The mission plan is due in 2016 and, if approved, it would begin in 2017.

"We knew if we didn't maneuver now, our option space would shrink," said Holdridge, referring to the range of possible targets New Horizons could reach. "The longer we waited, the greater the maneuver size would be."

The baby grand piano-sized spacecraft was scheduled to burn its hydrazine thrusters for about 20 minutes starting at 1:45 p.m. Wednesday. It has made three similar burns, the longest for about 30 minutes, since Oct. 23.

The objective is not to significantly speed New Horizons' 32,000-mph clip, increasing it by only about 100 mph. And it isn't changing its direction much, either — at least not immediately.

Across hundreds of millions of miles and over the next three years, though, the nudge will push the spacecraft significantly closer than it would otherwise be to an object known as 2014 MU69.

"If you add 50 meters per second, times the number of seconds in three years, it's a pretty great distance off to the side," Holdridge said.

New Horizons spent nearly a decade traveling 3 billion miles to Pluto, making its historic flyby and capturing detailed images and scientific observations of the dwarf planet in July. But 2014 MU69 is about a billion miles farther, within the Kuiper Belt, a swarm of icy comets and asteroids at the edge of the solar system.

The Hopkins lab scientists expect New Horizons to pass even closer to 2014 MU69 than it did to Pluto — it came within 7,800 miles at its closest approach to the dwarf planet July 14 — but more thruster burns could be required. The next opportunity to adjust the spacecraft's course won't come until July, Holdridge said.

Observations of the Kuiper Belt object ultimately could illuminate scientists' understanding of the early solar system, which formed 4.6 billion years ago. Because they are so far from the sun's heat, such objects are thought to be in a state similar to what they were when the planets first formed.

In the meantime, Hopkins scientists continue to download and analyze data from the Pluto encounter. Recent revelations have included images of Pluto's largest moon, Charon, depicting a mountainous and colorful surface; a blue haze and evidence of water ice on Pluto; and images of the last of Pluto's moons, tiny Kerberos.