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The last image taken of Ultima Thule before New Horizons flew by the rocky body.


Surviving encounter beyond Pluto, NASA probe begins relaying view of Kuiper belt object

LAUREL, MARYLAND—Cheers erupted just after 10:30 a.m. today in a small control room at the Johns Hopkins University Applied Physics Laboratory (APL) here. Alice Bowman, the mission operation manager for NASA’s New Horizons spacecraft, had just announced that the spacecraft had successfully rendezvoused with MU69, a tiny, frigid object on the edge of the solar system, far beyond Pluto. “We’ve just accomplished the most distant flyby,” she said.

Because of transmission delays and the finite speed of radio waves, the triumph occurred last night, at 12:33 a.m., while the team was celebrating the New Year with sparkling wine and a new song from Brian May, the Queen guitarist—and, thanks to his astrophysics degree, a participating scientist on the mission. The 10-hour lag had been a tense wait for some of the team, fretful that their weekslong search for hazards around MU69 (or “Ultima Thule,” its nickname), such as fugitive moons or rings, had missed something before the spacecraft sped past at a distance of some 3500 kilometers. But Alan Stern, a planetary scientist from the Southwest Research Institute in Boulder, Colorado, who is principal investigator for the $800 million mission, which explored Pluto in 2015, said he was confident. “I wasn’t worried about it. Got a nice night’s sleep.”

Finally, after a 4-hour wait for the probe to complete a series of automated observations with its three cameras and six more hours for the transmission to reach Earth from MU69’s location in the distant Kuiper belt, 6.6 billion kilometers from Earth, the first drips of data arrived via NASA’s 70-meter Deep Space Network antenna in Madrid: New Horizons had hurtled past MU69 at 14 kilometers per second and survived. “In lock with telemetry,” Bowman said.

A roll call of the spacecraft’s instruments followed, with each reporting back “green”—healthy. And then came the most important confirmation: The spacecraft’s solid state hard drives were full of new science data, Bowman announced.  “We have a healthy spacecraft.”

A half-hour later, the New Horizons team poured into an APL auditorium to a 5-minute standing ovation and a parade of high-fives from APL staff. “I can’t think a better reason to stay up late and get up early than this,” said APL’s head of space science, Michael Ryschkewitsch. Because of the government shutdown, which includes NASA, the agency’s acting director of planetary science, Lori Glaze, was attending as a private citizen and could not speak in her official role. But, Ryschkewitsch added, “Lori asked me to tell you how proud the agency is.”

With the festivities over and confirmation of the spacecraft’s survival, the real science begins. Unlike every other object previously visited by NASA, including Pluto, MU69 is believed to be unchanged since it formed in its current orbit billions of years ago, granting a window to the solar system’s earliest days. This pristine, primordial history should allow scientists to tease out important clues about the history of the Kuiper belt, the distant and unknown menagerie of objects beyond Neptune, along with insights to the formation and migration of the planets.    

The data will be slow in coming. Given the uncertainty of MU69’s position—it was discovered only 4 years ago and only a fraction of its orbit is known—New Horizons’s first images had to cover a wide field, at low resolution. By this evening, the team should have a 100-pixel image in hand; higher resolutions will follow in the next couple of days, with the best shots not arriving until February. But these first images, Stern added, “will reveal the basic geology and structure for us. We’re going to start writing our first scientific paper next week.” That means some late nights; the team has a meeting scheduled at 10 p.m. tonight.

At a press briefing after confirmation of the flyby’s success, the team released its last view of MU69 before the encounter, taken some 800,000 kilometers away. The image (above) revealed what looked like a peanut or bowling pin, some 32 kilometers long by 16 kilometers wide, with a slight possibility still that MU69 could be a binary object.

The mission had already cleared up one mystery: why the light reflecting off the object does not fluctuate, as might be expected from an irregular spinning body. A series of three approach photos revealed the reason: The rotation axis of MU69 was pointed toward the spacecraft, said Hal Weaver, the mission’s project scientist. “It’s almost like a propeller blade. And that explains everything.” The object makes a full rotation every 15 or 30 hours, he added.

Whatever the return is from its MU69 flyby, Stern hopes its mission isn’t done. The spacecraft is funded through 2021; during much of that time, it will be beaming back data from its flyby. But the spacecraft will scan two dozen other Kuiper belt objects with its modest telescope, in the hopes of extrapolating its findings from MU69 to the broader belt.

The MU69 encounter has also left New Horizons with enough fuel and power to attempt another flyby, albeit one not as close as its pass today, Stern noted last month. “We will be in the Kuiper belt until 2027 or 2028,” he said. While astronomers on Earth would strain to find another target, it’s likely that New Horizons itself could track one down. “There’s plenty of time to think that search through.”

For more on the MU69 flyby and what it could reveal, start here.