For the New Horizons spacecraft mission scientists, it has been a whirlwind week of discoveries and new views of the Kuiper Belt object Ultima Thule — including the first 3D image of the object on Thursday.
That pace is about to change.
On Friday, the spacecraft will go almost directly behind the sun from the perspective of Earth, which will cause radio interference. That means no data can return to Earth until January 10. So expect a quiet period, followed by new images and exciting insights in about two weeks.
The New Horizons spacecraft, which performed a flyby of Pluto in 2015, passed Ultima Thule on New Year’s Day. This flyby is the first exploration of a small Kuiper Belt object up close — and it’s the most primitive world ever observed by a spacecraft. The object is so old and pristine that it’s essentially like going back in time to the beginning of our solar system.
“The first exploration of a small Kuiper Belt object and the most distant exploration of any world in history is now history, but almost all of the data analysis lies in the future,” Alan Stern, principal mission investigator at the Southwest Research Institute, said at a news conference.
Although we’ve seen images depicting the 4.5 billion-year-old object as a red “space snowman” and revealing that it’s two objects held together by gravity, there’s so much more to come. In fact, it will take 20 months for the scientists to downlink all of the images and data New Horizons collected about Ultima Thule.
“Those of us on the science team can’t wait to begin to start digging into that treasure trove,” Stern said.
Where’s New Horizons?
But what about the spacecraft itself? It went hurtling past Ultima Thule at 32,000 miles per hour, and mission scientists didn’t tell it to slam on the brakes. New Horizons is now about 3 million miles deeper into the Kuiper Belt than Ultima Thule.
The Kuiper Belt is the edge of our solar system, part of the original disk from which the sun and planets formed.
After conducting the last observations of Ultima Thule by essentially watching it in the rearview mirror, New Horizons has received a new set of commands from the scientists. Now, it will observe the deeper environment of the Kuiper Belt and look at other Kuiper Belt objects in the distance. Although it won’t come as close to those objects as it did Ultima Thule, the images will still have better resolution than the Hubble Space Telescope. Those observations will continue into next year.
New Horizons flew three times closer to Ultima than it did to Pluto, coming within 2,200 miles of it and providing a better look at the surface. After the quick flyby, New Horizons will continue on through the Kuiper Belt with other planned observations of more objects — but the mission scientists said this is the highlight.
On Thursday, the researchers said they believe that about a dozen other objects in Kuiper Belt are contact binarys, or two separate objects joined together, like Ultima Thule.
What did we learn today?
The mission scientists have been working around the clock this week to translate data into the very first findings and observations to share with the public. On Thursday, they shared more details.
Although they have been searching for evidence of rings or moons around Ultima Thule, none is apparent in the images that have come back. That rules out rings and moons larger than 1 mile in diameter. But the possibility hasn’t been ruled out.
The mission scientists believe that 4.5 billion years ago, a rotating cloud of small, icy bodies coalesced. Eventually, these two bodies remained, slowly spiraling closer until they touched, forming Ultima Thule. Gravity is holding them together.
This means we’re truly seeing one of the first planetesimals, or objects that went on to form planets.
When the two bodies that make up Ultima Thule first came together, they were probably rotating much more quickly than the single object is today. So how did they slow down? A moon, or multiple moons, would help put the brakes on, said Mark Showalter, mission co-investigator.
If they were to find a moon, it would probably be about a mile across and about 500 miles from Ultima Thule itself. More images could help the scientists determine if one is present.
The scientists also haven’t found evidence of an atmosphere — not that they expected one. But more data from New Horizons flyby as it looked back at Ultima Thule could be interesting. That view would allow sunlight to reveal any atmospheric halo, dust or plasma present around the object.
The dark red color of the object has been determined to be similar to worlds like it in the Kuiper Belt. But the two objects that make up Ultima Thule are also nearly identical in color, meaning they formed in close proximity at the same time under the same conditions.
Based on current images, there appear to be ridges on the object, but the topography will be much more clear when new images arrive in the coming weeks.