New Horizons’ path to Ultima Thule clear of hazards

An artist’s impression of NASA’s New Horizons probe racing past Ultima Thule, the first primitive Kuiper Belt body to be visited for a close-up inspection. Image: NASA/JHUAPL/SwRI

Scientists studying images sent back by NASA’s New Horizons spacecraft have found no signs of rings or small moons near Ultima Thule. the probe’s Kuiper Belt target, clearing the robotic explorer to stay on its current course for a New Years Day flyby at a distance of just 3,500 kilometres (2,200 miles).

Mission managers had held open the possibility of a rocket firing to nudge New Horizons to one side if any hazards were found, moving the flyby point three times farther away, but the imagery convinced Principal Investigator Alan Stern the coast is clear.

“The spacecraft is now targeted for the optimal flyby, over three times closer than we flew to Pluto,” Stern said. “Ultima, here we come!”

Given the spacecraft’s speed — about 50,700 kilometres per hour (31,500 mph) — a collision with even a small rock fragment could be fatal. A dozen-member “hazard watch” team used New Horizons’ Long Range Reconnaissance Imager, or LORRI, to scan the area around Ultima Thule looking for any signs of potential trouble.

LORRI was capable of detecting any moons larger than about three kilometres (five miles) across and any reflecting off ring material amounting to just five 10-millionths of the sunlight falling on it. Nothing was found.

“Our team feels like we have been riding along with the spacecraft, as if we were mariners perched on the crow’s nest of a ship, looking out for dangers ahead,” said hazards team lead Mark Showalter. “The team was in complete consensus that the spacecraft should remain on the closer trajectory, and mission leadership adopted our recommendation.”

New Horizons completed a historic flyby of Pluto in July 2015. Now a 1.6 billion kilometres (1 billion miles) past Pluto, New Horizons will race past Ultima Thule at 6:33 GMT on 1 January, the first encounter with a Kuiper Belt body thought to be left over, untouched, since the formation of the solar system 4.6 billion years ago.