Hundreds more images expected of Ultima Thule, 6.5 billion km from Earth

Scientists say NASA's New Horizons spacecraft, as seen from Earth, goes almost directly behind the sun on Friday, so there will be a pause in downloading images of an object known as Ultima Thule in the outer reaches of the solar system.

They held a briefing on Thursday at the Johns Hopkins Applied Physics Laboratory in Maryland to discuss the distant red object, which is 6.5 billion kilometres from Earth.

Alan Stern, New Horizons principle investigator, told reporters radio interference from the sun's outer atmosphere will block transmission of further images, but the link should be restored on Jan. 10.

"And then the data will start to come back down again and begin this long, 20-month period in which we'll be emptying the solid-state recorders of all of the different kinds of data that we've taken, literally hundreds of images and spectra and other data types," Stern said.

Scientists at the briefing said they're still not sure how Ultima Thule, nicknamed the "snowman" formed. They said even Ultima Thule is the informal name for what they know as "Kuiper Belt object 2014 MU69." Ultima is the larger of the two parts, three times the size of the sphere named Thule.

They have deduced that the conjoined bodies were once part of a cloud of smaller, rotating space rocks that eventually bound together into two larger bodies orbiting at a much slower speed.

Scientists have also ascertained the object takes about 15 hours to make a full rotation. If it were spinning fast — say, one rotation every three or four hours — the two spheres would rip apart.

"We're looking for the objects that put the brakes on these objects," New Horizons investigator Mark Showalter said. Finding the moons, which would orbit Ultima Thule up to 800 kilometres from its surface, would also reveal details about the space rock's mass and density.

Ultima Thule is estimated to measure 35 by 15 kilometres and lies in the Kuiper Belt, a doughnut-shaped region beyond Neptune that is home to perhaps trillions of icy objects left over from the formation of our solar system.

In the farthest space probe flyby in history, New Horizons whizzed by Ultima Thule in the early morning of Jan. 1, at speeds of nearly 14 km a second, as several instruments and cameras gathered information.

The spacecraft is now five million kilometres deeper into the Kuiper Belt than Ultima Thule, Stern said on Thursday.

It will take almost two years for all the data to be sent back to Earth, as communications take six hours one way due to the distance of the spacecraft.

At a news conference on Wednesday, the team revealed the first images sent back by New Horizons.

Scientists are studying the object to better understand the solar system's formation.

New Horizons launched in 2006 on a mission to fly by Pluto, which it did on July 4, 2015.

Stern has said that another target in the Kuiper Belt will likely be chosen for another flyby in the upcoming years.