Out in the icy depths of the solar system, far from the warmth of our star, drifts a tiny frozen world shrouded in perpetual twilight. Officially known as 2104 MU69, astronomers unofficially dubbed the rock Ultima Thule—an ancient moniker used to describe what is "beyond the known world.”
The unassuming orb, nestled among the billions of other small icy bodies in the solar system’s frigid outer rim, is so mysterious that until recently, scientists knew nothing about it. Appearing to us as no more than a speck of light in a vast cosmic sea, MU69 is actually two worlds fused together as one, much like a cosmic snowman. Spanning a mere 20 miles wide, even the most powerful telescopes on Earth cannot resolve it. To find it, astronomers had to rely on the Hubble Space Telescope, which sits above the Earth’s atmosphere—and even then, it appeared only as a faint dot.
2014 MU69 resides in a region of the solar system so remote that no spacecraft had ever ventured there before. This unexplored cosmic wilderness lies out beyond the giant planets, in a region that is vastly more remote than Pluto. Stretching billions of miles in all directions, this chilly expanse is populated by a plethora of objects as old as the solar system itself. Numerous as they are, no Kuiper Belt Object (KBO) had ever been seen up close. That is, until now.
NASA's iconic twin Voyager probes—the New Horizons’ predecessors that trailblazed the region decades ago—might have caught a glimpse of one of these enigmatic KBOs, had they been packing the right instruments, (or if the Kuiper Belt had been discovered yet).
But, on this past New Year’s Eve,NASA’s New Horizons spacecraftwas ready to boldly go.
As part of a daring mission into uncharted space, the robotic explorer hoped to snag some facetime while whizzing by one of these primitive space rocks.
As the final moments of 2018 ticked away, while most of the world rang in the new year by celebrating with friends and family, the biggest New Year’s Eve party in the solar system took place across some four billion miles of space. I, along with several hundred people off all ages, nerded out with some of the greatest minds in science at the Johns Hopkins Applied Physics lab in Maryland. Just 33 minutes after the midnight celebration, a second countdown erupted as a packed room imagined a piano-sized spacecraft flying by a tiny hunk of rock no larger than Washington, D.C. Several hours later cheers erupted as confirmation came that New Horizons had completed its task.
Among the throngs of people in attendance was New Horizons contributing scientist and Queen guitarist Brian May, who debuted a song he wrote about the mission just after midnight. Speaking to a crowd of journalists prior to the flyby, May explained that he was there neither as a tourist, nor as a celebrity. He, like the rest of the team, was there to work. He might be best known for his epic guitar riffs in Bohemian Rhapsody, but May is also an astrophysicist who specializes in stereoscopic imagery.
“I come from a different generation, a generation that didn’t know about the Kuiper Belt; they didn’t know that these objects were out there,” May says.
“These bodies—untouchedandpristine—have beenout there sincethe dawn of thesolar system itself.
There must be so much that can be learned from this.”
Three years ago, May produced incredible stereoscopic images of Pluto, enabling the world to see the dynamic little planet in 3D glory, and hopes to do the same for MU69. As a self-proclaimed stereo evangelist, he believes that 3D is an underappreciated (and underused) art form.
These images are only part of his contribution. Before its debut, May expressed how thrilled he was to collaborate on a song with a world famous scientist and explorer like the mission’s principal investigator, Alan Stern.
May explained that humanity’s innate curiosity was the muse for his song:
I started to get inspired and then it dawned on me that this mission is about human curiosity, about the need of humankind to go out and explore the solar system, and discover what makes the universe tick. It’s something that's been going on since the dawn of time. So, in a sense my song, my track, my anthem became about the human spirit endeavoring to discover the universe.
It was that same endeavoring spirit that enabled New Horizons to get off the ground in the first place. Launched toward the solar system's icy expanse on January 19, 2006, it took the probe nearly a decade to traverse the more than four-billion-mile wide swath of space that lies between Earth and the Plutonian system. But the wait was worth it. On July 14, 2015, the plucky little spacecraft blew minds all around the globe when it beamed back its first images of Pluto and its system of moons.
“Pluto was the most fantastic object I’ve ever seen,” says NASA’s chief scientist Jim Green. (He, like a few other top NASA officials were in attendance at the flyby in an unofficial capacity due to the government shutdown). “It’s smaller than our moon yet it has an atmosphere. It’s a living world, meaning its geology is modifying its surface today. It has nitrogen glaciers that appear to be bubbling. It makes complex chemicals in its atmosphere and then snows them out. I mean, there’s no other body in the solar system that can compare to it,” he gushed. “It’s so unique and so fascinating that it just shocked everyone.”
But exploring Pluto wasn’t something NASA was always sure it wanted to do. The notion of a “grand tour” of the outer planets first emerged in the 1960’s. Many scoffed at the idea as It was an incredibly ambitious undertaking, especially at a time when the apex of interplanetary exploration was Mariner 4’s grainy photos of Mars. That changed when NASA’s Jet Propulsion Laboratory realized that in the late 1970s, the positions of the planets would align themselves in such a way that a spacecraft could use the planets’ own gravity to slingshot from one to the next, gaining enough velocity to visit all four outer planets within a decade—an opportunity that only came around every 175 years. Unfortunately, this grand tour didn’t include a stop at Pluto.
Stern, who was born at the dawn of the space age in 1957, knew he was destined to explore space from day one. His pursuit of that dream eventually led him to the Southwest Research Institute where he’d one day lead the voyage to Pluto and beyond.
Earning his PhD at the same time as Voyager wrapped its reconnaissance of the giant planets, Stern said he knew then that Pluto was an incredibly fascinating target, but because Voyager’s planned trajectory didn’t cross paths with it, it seemed out of reach.
“At the time we knewnothingabout Pluto,much likewhat we knowabout Ultima Thule,”
Stern explained that three years ago, the Pluto encounter—New Horizons’ primary mission—was the first opportunity in a generation to really see a new planetary system up close for the first time. “There hadn’t been anything like this in a very long time, and now we’re doing it again,” he said.
For decades, Pluto was the mystery planet, the misfit of the solar system that had been stripped of its planethood and tossed aside. But this classification conundrum only stirred Pluto’s popularity. Pluto was often thought of as the outpost to the stars, a seemingly lifeless world akin to the king of the underworld it was named for. And yet there was also hunger to know more. Not just from scientists like Stern, but also from the general public.
That, in conjunction with the growing belief that there was a third section of the solar system beyond Neptune, helped motivate a mission to Pluto. (Although it wasn’t officially discovered until 1992, people were searching for the Kuiper Belt as early as the 1980s). Stern describes this third zone of our solar system as a scientific treasure trove. Because it’s so far from the sun, it’s incredibly cold. As such, it’s where the best data is preserved about the formation era of the solar system—particularly the planets.
“We have primordial planetary bodies in essentially a mummified form, preserved in a crypt created by the cold temperatures,” Stern explained. “It’s a perfect place for what I call an archaeological dig into the history of our solar system and planet formation.”
The Kuiper Belt is full of cosmic debris leftover after the planets formed some 4.6 billion years ago, and objects like 2014 MU69 are the building blocks of the planets. “It’s an opportunity to learn about the material planets were made out of and to look at the seeds of planetary formation,” says Stern.
Thanks to the region’s frigid temperatures (which hover around absolute zero), KBOs are like perfectly preserved cosmic time capsules, making them enticing destinations for astronomers. Using its onboard cameras, New Horizons will provide the first close-up look at such a pristine building block of the solar system—a feat that’s never been done before.
Green, who was part of the Voyager team, says the flyby of Pluto and subsequently Ultima Thule are revolutionary. Just as Voyager spurred other missions to Jupiter and Saturn, New Horizons proves there is far more to be learned about the Kuiper Belt. “There are so many interesting objects there; we really need to explore it more,” he says. “This is a realm where that material is starting to coalesce into larger objects over time. It’s a new regime.”
NASA's plan to visit MU69 is more than a simple flyby mission, it's an archaeological expedition on a cosmic scale. “This is the most distant exploration of any world in history. It’s the most distant exploration on the books. No one is planning anything else like this,” Stern says.
“We are theLewis andClarkof our era.”
Preliminary images of this pristine body show it’s a contact binary composed of two lobes, nearly spherical in shape, which provide insight into its formation. A few hundred years after the birth of the solar system, a bunch of tiny pebbles swirled around in a cosmic dance, coalescing as time went on.
Eventually they formedtwo larger lobesthat twirledcloserand closeruntil theygently kissed,
The object appears red in color, a trait consistent with other primitive bodies in the solar system. The ruddy hue is thought to come from carbon-containing compounds (called tholins) which form when exotic ices—usually composed of nitrogen and methane—are blasted by high-energy particles from the sun.
These first few images are just the beginning; it will take nearly two years to download the wealth of data stored onboard New Horizons. As our robotic emissary continues on its path out of the Kuiper Belt, Stern and his colleagues will search for its next target—one even further from the sun and perhaps, even more mysterious.