On Tuesday, the first image of the Kuiper Belt object Ultima Thule taken by the New Horizons spacecraft revealed a bowling pin. On Wednesday, more distinct and color images revealed a snowman.
Mission scientists said the first science data transmitted back from New Horizons has shown Ultima Thule to actually be two separate objects joined together, making it the first contact binary to be explored by a spacecraft.
The object has two lobes, with the larger one now taking the name Ultima and the smaller becoming Thule.
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 Kuiper Belt is the edge of our solar system, part of the original disk from which the sun and planets formed.
The new color image also revealed it to be definitively red, like the top of Pluto’s moon Charon. This is consistent with other irradiated objects that are in the Kuiper Belt, Carly Howett, mission co-investigator at the Southwest Research Institute, said Wednesday.
Images also revealed that the two lobes have a mottled appearance. Though they do not appear to have impact craters, there could be hills and ridges, with the neck connecting the two lobes being one of the steepest slopes.
However, more will be revealed as more data comes in. This first data is a result from New Horizons approaching Ultima Thule with the sun behind the spacecraft, making it hard to see whether there are craters.
So how did Ultima Thule form? 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.
“It’s a time machine to time zero,” said Jeff Moore, the mission’s geophysics lead investigator from NASA Ames.
A 15-hour rotation rate has also been established for Ultima Thule. The object itself is as dark as potting soil, said Cathy Olkin, deputy project scientist from the Southwest Research Institute. The brightest areas on the surface of Ultima Thule reflect only about 13% of the sunlight that reaches it – an incredibly small amount, given that it’s 4 billion miles from the sun.
All of this information came from “far less than 1% of the data on New Horizons that has reached the ground,” said Alan Stern, mission principal investigator at the Southwest Research Institute.
Stereo analysis and subsequent imaging will be available Thursday.
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.