Yesterday, many of us welcomed 2019 with a brief midnight smooch. But new images taken on New Year’s Day by NASA’s New Horizons spacecraft reveals that, over 4 billion miles from Earth, two icy space rocks may have been locking lips since the earliest days of the Solar System.
Today, NASA’s New Horizons team unveiled a striking set of images of Kuiper Belt object 2014 MU69, beamed back to Earth after the spacecraft’s historic flyby on New Year’s Day. The object, thought to be a 4.6-billion-year-old time capsule from the birth of our solar system, is better known by its nickname, Ultima Thule—Latin for “beyond the known world.” But Ultima Thule is becoming less unknowable by the second.
In these images are the first definitive depictions of the object’s true shape and color: It turns out Ultima Thule is a reddish, pockmarked, two-tiered snowman—a duo of asymmetrically-sized spheres frozen in a permanent crimson kiss. This makes Ultima Thule a contact binary, composed of two once-separate bodies that, long ago, gravitated toward each other until they touched.
If confirmed, this configuration could represent a precious snapshot of planetary formation in action, supporting the idea that the massive, orbiting bodies in our inner solar system assembled in part through the rapid coalescing of pebbles and dust.
“They’re clearly two objects that have come together,” says New Horizons’ Deputy Project Scientist Cathy Olkin. “This is exactly what we need to move the modeling work on planetary formation forward.”
It’s been billions of years since Earth and its planetary brethren first formed—and a lot has changed since. As such, scientists still aren’t entirely sure how the planets of the Solar System got their start.
“Human beings are born, we change over time, and, eventually we die,” says Jason Kalirai, civil space mission area executive at the Johns Hopkins University Applied Physics Laboratory. “Objects in the universe are the same way… they’re dynamic.”
One leading theory is that of pebble accretion, which posits that bits of raw planetary material of all shapes and sizes glommed onto each other until they became singular, gargantuan units. But puzzling through the origins of the Solar System using only the final products, like our own Earth, is like trying to discern a recipe from a loaf of fully baked bread: Many of the components have already been substantially, and often irreversibly, altered by heat and time. The best bet for sussing out the ingredients is sifting through the unbaked scraps left at the bottom of the mixing bowl—the basic building blocks from which the planets may have formed.
That’s where Ultima Thule comes in: It looks to be a partial conglomeration of uncooked space dough—a premature mashup that could have served as the basis for a planet, but didn’t.
“Our solar system is 4 billion years old… so its initial conditions have been kind of washed out,” Kalirai explains. “Ultima Thule is the first object that will shed light on those earliest conditions.”
Ultima Thule lies in the Kuiper Belt, the punishingly cold region of the Solar System past Neptune. Experts believe this celestial body has been quietly orbiting the Sun more or less undisturbed ever since its inception. Though short-period comets (which can also be bilobed) also originate from the Kuiper Belt’s pre-planetary dough, comets get jettisoned out of the Belt and flung closer to the Sun—and these heated encounters fundamentally alter their composition.
Objects like Ultima Thule, on the other hand, remain in the icy outer crust of our disc-like solar system. Ultima Thule is over 40 times farther from the Sun than Earth; this deep in outer space, temperatures clock in around -400 degrees Fahrenheit—and these frigid, Sun-starved conditions can make for fairly pristine preservation.
According to Jeff Moore, New Horizons’ geology and geophysics team lead, Ultima Thule’s two lobes—now named Ultima (the larger) and Thule (the smaller)—might have formed from a throng of small, icy bodies. This “localized swarm,” he says, created two separate orbs, each around 10 miles in diameter. Ultima and Thule then engaged in a slow, romantic waltz, circling each other until, at long last, contact was made. Once engaged, the pair never parted; it appears their union has survived the billions of years since.
Prior to today, images of Ultima Thule were only a handful of pixels across, leaving the object’s true physique ambiguous. It resembled something of a pixelated peanut, or a celestial bowling pin. But now, “that image is so 2018,” Stern quipped during the press conference.
The new images, taken during the New Year’s flyby, are the first to confirm that Ultima Thule’s teeny waistline is more a juncture than an hourglass. If Ultima Thule is indeed the product of a rocky rendezvous, that’s big news: It provides concrete evidence of early interactions between small, icy bodies on their way to bigger things.
“When I first saw the images, I think I probably said ‘wow’ a million times,” says Anne Verbiscer, New Horizons’ assistant project scientist.
Additionally, the New Horizons team can now definitely say that—just as the images taken with the Hubble Space Telescope several years ago tentatively predicted—Ultima Thule’s hue is a toasty brownish-red. On average, the object is about as bright as the darkest spot on Pluto’s surface, Verbiscer says. And it comes with a vivid choker of brightness encircling its slight neck.
Color may seem trivial, but for the New Horizons team, it’s critical information that will help the researchers determine what ices and minerals decorate the object’s surface, says Silvia Protopapa, a co-investigator of the New Horizons Kuiper Belt Extended Mission. Out in the Kuiper Belt, reds may result from the irradiation of ices, but that’s far from the only possibility.
These tantalizing tidbits are only the beginning. According to Stern, the team has far less than one percent of all the data currently onboard New Horizons in hand. The coming weeks will reveal more about the object’s composition and terrain. Ultima Thule’s story is only beginning, but it’s already making history—and back here on Earth, the team can hardly contain their excitement.
“Moments like this are what keep me going,” Verbiscer says. “Those moments when you see an image for the first time. It’s something that, instants before, didn’t exist in our minds—now it does. It’s like, boom, there it is: a whole new world to explore.”
For more on New Horizons and its historic journey through the Solar System, watch “Pluto and Beyond,” premiering tonight at 9 p.m. ET / 8 p.m CT on PBS.