New Horizons closing in for historic flyby of Ultima Thule

An artist’s impression of Ultima Thule and NASA’s New Horizons probe. Image: NASA

NASA’s New Horizons probe is on course and dutifully executing its encounter sequence software as it races toward an action-packed New Year’s Day flyby of Ultima Thule, the most distant solar system body ever targeted for up-close observations.

“Things could not be going better,” Principal Investigator Alan Stern told Astronomy Now on Saturday. “The spacecraft’s in perfect health, the team is assembled and everything is going very, very well. We can’t wait to unwrap Ultima Thule and see what it’s all about.”

Three years and 1.6 billion kilometres (1 billion miles) past Pluto, New Horizons will streak past Ultima Thule, officially known as 2014 MU69, at 5:33 UTC on 1 January, passing within about 3,500 kilometres (2,200 miles) of its as-yet-unseen surface at a velocity of 51,000 kilometres per hour (32,000 mph).

Four hours later, the nuclear-powered spacecraft will will turn back toward Earth and send a status report to waiting scientists and engineers gathered at Johns Hopkins University’s Applied Physics Laboratory near Baltimore, Maryland. A few hours after than, the first high-priority images and other data will begin the 6.6-billion-kilometre (4.1-billion-mile) trip back to Earth, taking six hours and eight minutes to cross the gulf.

The first high-resolution images are expected to be released during a briefing at the Applied Physics Lab on 2 January.

“Across the whole team, people are ready, they’re in the game, we can’t wait to go exploring,” Stern said on 28 December. “It’s been three-and-a-half years (since the Pluto flyby), we’ve worked so hard, people are ready to see that payoff and see what we can learn about the birth of our solar system.”

Scientist do not know what to expect. Ultima Thule, little more than a dim point of light to even the Hubble Space Telescope, is known as a “cold classical” Kuiper Belt body, meaning it has a nearly circular orbit only slightly inclined to the plane of the planets. It is an untouched relic left over from the birth of the solar system 4.6 billion years ago.

Based on occultation observations from Earth, Ultima Thule appears to be an elongated body about 30 kilometres (19 miles) across, possibly a dual-lobed contact binary or two physically separated but gravitationally bound bodies.

In another early mystery, images from New Horizons do not show any discernible changes in reflected light from Ultima Thule. Scientists were expecting variations, which would indicate Ultima’s rate of rotation, but no such changes could be clearly seen within days of the encounter.

Stern said the flyby will put many questions to rest.

“We’re going to find out how this thing is built, how much it’s evolved, what it’s made of, if it has an atmosphere, if it has moons, if it has rings, we’re going to take its temperature, we’re going to measure its radar reflectivity, we’re going to find out if it’s surrounded by a dust cloud left over from formation,” Stern said.

“All that stuff and more, because we’re not just going to take imagery,” he added. “We map its surface, we map it in colour and in addition to that, we map it in stereo so we have topography everywhere. We’ll not just determine its composition, but we map it from place to place to see if it’s the same everywhere or if it’s made up of smaller building blocks.”

Find out more about the New Horizon’s encounter with Ultima Thule in the January issue of Astronomy Now. Get your copy in the shops or order online.