The most distant object that NASA has ever investigated up close, 2014 MU69, orbits near the edge of the solar system, well beyond Pluto. Because of the desolate conditions out there, it’s remained virtually unchanged since the beginning of the solar system. Less than five years ago, astronomers didn’t even know it existed. Now they know what it looks like, thanks to images captured by a passing spacecraft.
The New Horizons spacecraft arrived at 2014 MU69—4 billion miles away from Earth—on New Year’s Eve, snapped hundreds of photographs, and then continued on, headed even deeper into space. On Wednesday, NASA released the first set of photographs.
Seen from Earth, 2014 MU69 looks like a tiny speck of light. Up close, it resembles, delightfully, a snowman.
2014 MU69 is so far away, details like this could never come into focus from Earth.“There’s no way to make anything like this, this type of observation, without having a spacecraft there,” Cathy Olkin, the deputy project scientist, told reporters at a press conference on Wednesday.
In 2015, New Horizons flew past Pluto and revealed a stunning icy world with towering mountains, smooth plains, and a feathery atmosphere. The probe had enough fuel to keep going after the encounter, and 2014 MU69 turned out to be along its path.
Nicknamed Ultima Thule, Latin for “beyond the known world,” the object is a contact binary, a cosmic configuration in which two separate objects become joined together. “They obviously came together at such a gentle speed—maybe a mile an hour, or a few miles an hour,” said Jeff Moore, the head of the geology team for New Horizons. “They really are sort of resting on each other.”
The snowman description is fitting for the conditions in the Kuiper Belt, where frozen bits and pieces left over from the formation of the solar system 4.6 billion years ago abound, receiving very little sunlight. It’s an incredibly cold place: The surface temperature of Pluto, the largest object in the region, is nearly –400 degrees Fahrenheit. If you could somehow build Frosty the Snowman out there, he’d last forever.
Unlike typical snowmen, Ultima Thule is red, roasted and darkened over time by cosmic radiation. Below, the photo on the right is a composite image from two of the three cameras aboard New Horizons. (The color looks more like iced coffee with a little half-and-half to me, but by planetary-science measures, it’s red.)
There’s more than one kind of ice in the universe, and the flyby data haven’t yet revealed the composition of Ultima Thule. The object may be made of water ice, nitrogen ice, or methane ice.
Ultima Thule is frozen another way—in time. The frigidness of the Kuiper Belt has kept Ultima Thule in pristine shape. The New Horizons data will describe the very material that shaped Earth and the other planets, and scientists hope the spacecraft’s scientific instruments collected some new information about this chapter in our cosmic history.
The newly released images are the first of many still to come. These were taken about a half hour before New Horizons made its closest approach to Ultima Thule, and at a moment when sunlight struck the object head-on. As the spacecraft flew past, the illumination shifted, and shadows emerged. It’s these shadows, scientists say, that will soon reveal whether Ultima Thule has hills, ridges, or craters.
It takes some time for data from New Horizons to reach Earth from a distance of 4 billion miles. Scientists will reveal the best, highest-resolution photographs in the coming weeks and months.
An uncomfortable question, unrelated to the science, hovered over the New Horizons team’s presentation on Wednesday. On Tuesday night, a Newsweek story from March prompted discussion on social media about NASA’s decision to use the name Ultima Thule, which arose out of a public naming contest. The term was coined more than 2,000 years ago by the Roman poet Virgil and has appeared frequently in literature as a descriptor for distant, mythical lands. Newsweek pointed out that the term was also adopted by the Nazi party as the name of a mythical Aryan homeland.
NASA officials were aware of this historical usage when they chose Ultima Thule and decided its ancient meaning outweighed the troubling connotations. “I think New Horizons is an example, one of the best examples, in our time of raw exploration, and the term Ultima Thule—which is very old, many centuries old, possibly over 1,000 years old—is a wonderful meme for exploration,” Alan Stern, the lead investigator of the New Horizons mission, said in response to a question from a reporter. “And that’s why we chose it. And I would say that just because some bad guys once liked the term, we’re not going to let them hijack it.”
But this shadow couldn’t dampen the jubilance in the room as the scientists shared the shape of their new discovery. To anyone used to the smooth, rounded architecture of planets and moons, this distant world might look funky. But the solar system is flush with oddly shaped clumps that don’t fit into neat schemes.
Billions of years ago, some of the material hurtling around the sun began to collide together. The gentler collisions allowed clumps of material to grow with each merger. Small clumps led to big clumps, and if they grew large enough, gravity tugged at their edges and collapsed them into spheres. Ultima Thule, about the size of a city, is too small for this effect.
“Most of the small bodies in the solar system are highly elongated,” Hal Weaver, the New Horizons project scientist, explained recently. “They just don’t have enough mass to form themselves into a perfect sphere.”
New Horizons is now headed deeper into the Kuiper Belt. The spacecraft left Earth in 2006 and, despite a few malfunctions along the way, remains healthy. Stern predicts it could keep going for another 15 to 20 years and plans to submit a new exploration proposal to NASA leadership. With Ultima Thule in the rearview, the spacecraft may set its sights on another target, prepared to extend humanity’s reach into the cosmos even further.