When it comes to New Year’s Eve parties, a gathering of astrophysicists may not be what you associate with a wild time. But as 2018 wound down Monday night, a large group of giddy scientists, their families and friends had a lot to be excited about at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
Just after the new year arrived on the East Coast (about 35 minutes before midnight in Chicago), came the main event that had brought together the scientific revelers at the unlikely party site. It was the moment that NASA’s New Horizons spacecraft reached its closest approach to Ultima Thule, the farthest object ever to be explored.
Alan Stern, the principal investigator of the New Horizons mission and his colleagues cheered the moment not really certain that it had gone off as planned. But on Tuesday, Stern issued the good news: “We’re here to tell you that last night overnight the United States spacecraft New Horizons conducted the farthest exploration in the history of humankind and did so spectacularly.”
At a distance of 4 billion miles and rapidly increasing, information from New Horizons to Earth takes about six hours to arrive and when it does it’s being received at a rate of 1 to 2 kilobytes per second. The spacecraft has seven instruments that will be transmitting quite a bit of data for years to come. But what astronomers and fans of space exploration wanted to know before anything else was what the tiny Kuiper Belt object looked like. On Wednesday, NASA revealed the first detailed image of Ultima Thule taken when New Horizons was about 17,000 miles away from the rocky surface.
“This object that we flew by, a billion miles beyond Pluto … is a contact binary,” explains Stern. “There are two lobes, one is about three times larger than the other. They seemed to have formed nearby and then, through some gravitational process, came together to where they appear stuck together. We’re not sure if that’s gravity or mechanical forces holding them together.”
The voyage to Ultima Thule began in 2006 with the launch of NASA’s New Horizons spacecraft. At the time, the mission’s main objective was to explore Pluto for the first time ever, which it did in July 2015. As New Horizons travelled to Pluto, scientists began searching for another object for New Horizons to explore in what’s called the Kuiper Belt. That search required a fine-tuned look into the distant solar system where scientists know that countless objects left over from the formation of the sun and planets 4.5 billion years ago reside in a frigid and dimly lit cosmic landscape.
It was on June 26, 2014 that astrophysicists using the Hubble Space Telescope discovered the object that carries the official designation of 2014 MU69. New Horizon’s flight team dubbed it Ultima Thule, an ancient Latin phrase meaning “beyond the borders of the known world.” Finding Ultima Thule was an achievement in itself given the object’s distance and tiny size. Stern points out that, at 21 miles long, Ultima Thule is smaller than the city of Chicago. But the most important feature was that Ultima Thule was in New Horizons’ flight path as it travels out of the solar system. Getting the spacecraft to it, however, had its challenges.
“This was a tough, tough assignment,” Stern said. “We didn’t understand the hazard environment, the navigational challenges were severe, the lighting levels are lower than at Pluto, the communications times are longer.” Mission scientists could overcome some of the issues confronting them but others required a degree of luck, such as not encountering space dust which could fatally damage New Horizons. In the end, the voyage went off without a hitch. At its closest point, the spacecraft got to within 2,200 miles of Ultima Thule’s surface. Just what was gleaned about the tiny Kuiper Belt object will take years to sort out.
“We have less than 1 percent of the data on the ground,” Stern said. “We’re still awaiting high-resolution imagery, good information about the composition of Ultima Thule, data about any atmosphere it might have [and] its temperature.” The most detailed imagery of Ultima Thule, which will be 25 times sharper than the preliminary photos, are expected to arrive in February.
New Horizons still has plenty of life left in its instruments and radioisotope power system. In the absence of any calamity, it will eventually become the fifth spacecraft to depart the solar system and begin a voyage among the stars of the Milky Way. But scientists hope New Horizons can maneuver one more flyby before sailing into the infinite. “We haven’t started looking yet,” Stern said. “I wanted my team to pay attention to getting this right before we go after the next shiny thing. We actually won’t search for a new target for a year or possibly two and then we have to write a proposal to NASA to carry on the mission for a longer period of time. And if that’s approved then we’ll go about the search.”
But if another distant object isn’t in New Horizons’ future, the data it sends back from Ultima Thule will keep scientists very occupied for a long time. And the tiny spacecraft that could, just might reveal some long-hidden secrets about how the sun, planets, moons, asteroids—and even the life on Earth—came to be.