The space flyby of the most distant object ever seen up close by humanity has sent back new images of Ultima Thule, a comet belt inhabitant leftover from the early solar system.
NASA's New Horizons spacecraft flew past the tiny frozen world called 2014 MU69, or Ultima Thule, early on Tuesday morning. Only 22 miles wide at most, Ultima Thule spins in the comet belt some 4 billion miles from the sun.
"What this spacecraft and this team has accomplished is unprecedented," mission principal investigator Alan Stern of the Southwest Research Institute (SwRI) said in a briefing on the 32,000 mph flyby.
The new images reveal Ultima Thule is the first "contact binary" ever seen up close in the comet belt, a double-lobed comet built of two snowballs gently wedded together that rotates once every 15 hours. "That bowling pin is gone. It's a snowman!" Stern said.
A signal from the probe takes more than 6 hours to return to Earth, necessitating a slow return of images from the flyby. High-resolution pictures are expected in February, and they should answer questions about how comets first formed some 4.5 billion years ago, whether in dramatic collisions or as loose collections of icy bodies.
The double-lobed shape of Ultima Thule argues for slow agglomerations of icy objects as the construction method for the earliest building blocks of planets, rather than violent smashups, said mission scientist Jeff Moore of NASA's Ames Research Center.
"We can say Ultima Thule is red," said SwRI mission scientist Carly Howett. However, the team has not seen any craters in the tiny world yet.
On Thursday, New Horizons scientists released an updated stereo view of Ultima Thule meant for viewing with 3-D glasses, as well as a short video clip showing its rotational motion as seen from the spacecraft. The team is already looking for another such object to flyby in coming years, according to Stern, with plenty of fuel left to the mission.
Images and comments from Thursday's New Horizons news conference were added to this post.
This post has been updated with comments from Jeff Moore.