LAUREL, Md. — NASA’s New Horizons spacecraft, which flew past Pluto in 2015, will zip past another icy world nicknamed Ultima Thule on New Year’s Day, gathering information on what is believed to be a pristine fragment from the earliest days of the solar system. It will be the most distant object ever visited by a spacecraft.
As 2019 dawns on the East Coast of the United States, New Horizons will pass within about 2,200 miles of Ultima Thule, speeding at 31,500 m.p.h.
“It’s on course, it’s healthy, it’s conducting observations as we speak and it’s going to arrive on time,” said S. Alan Stern, the principal investigator for the mission, during a news conference on Monday afternoon.
How do I watch the flyby?
Though it is a NASA spacecraft, the New Horizons mission is operated by the Johns Hopkins Applied Physics Laboratory in Maryland. Coverage of the flyby will be broadcast on the lab’s website and YouTube channel as well as NASA TV. On Twitter, updates will appear on @NewHorizons2015, the account maintained by Dr. Stern, and on NASA’s @NASANewHorizons account. Or watch the countdown to the flyby in the video player below:
While the scientists will celebrate the moment of flyby as if it were New Year’s, they will have no idea how the mission is actually going at that point. The spacecraft, busy making its science observations, will not turn to send a message back to Earth until a few hours later. Then it will take six hours for that radio signal, traveling at the speed of light, to reach Earth.
Tell me about this small frozen world
Based on suggestions from the public, the New Horizons team chose a nickname for the world: Ultima Thule, which means “distant places beyond the known world.” Officially, it is 2014 MU69, a catalog designation assigned by the International Astronomical Union’s Minor Planet Center. The “2014” refers to the year it was discovered, the result of a careful scan of the night sky by the Hubble Space Telescope for targets that New Horizons might be able to fly by after its Pluto encounter.
No telescope on Earth has been able to clearly spot MU69. Even sharp-eyed Hubble can make out only a dot of light. Scientists estimate that it is 12 to 22 miles wide, and that it is dark, reflecting about 10 percent of the light that hits it.
Four billion miles from the sun, MU69 is a billion miles farther out than Pluto, part of the ring of icy worlds beyond Neptune known as the Kuiper belt. Its orbit, nearly circular, suggests that it has been undisturbed since the birth of the solar system 4.5 billion years ago.
Why do planetary scientists care about this small thing 4 billion miles from the sun?
Every time a spacecraft visits an asteroid or a comet, planetary scientists talk about how it is a precious time capsule from the solar system’s baby days when the planets were forming. That is true, but especially true for Ultima Thule.
Asteroids around the solar system have collided with each other and broken apart. Comets partially vaporize each time they pass close to the sun. But Ultima Thule may have instead been in a deep freeze the whole time, perhaps essentially pristine since it formed 4.5 billion years ago.
Will there be pictures of Ultima Thule?
New Horizons has been taking pictures for months, but for most of that time Ultima Thule has been little more than a dot in any of these images. A picture shown during a Monday news conference offered hints at the shape of the object.
“We know it’s not round,” said John Spencer, the mission’s deputy project scientist.
At a news conference on Tuesday morning after the flyby, the scientists expect to release a picture taken before the flyby. Ultima Thule is expected to be a mere six pixels wide in that picture — enough to get a rough idea of its shape but not much more.
The first set of images captured by New Horizons during the flyby should be back on Earth by Tuesday evening, and those are to be shown at news conferences describing the science results on Wednesday and Thursday.
But when the pictures come, they could be striking — in case you forgot what kind of pictures New Horizons took when it flew past Pluto, here are some highlights of its findings.
Isn’t NASA closed?
Yes, NASA is one of the agencies affected by the partial federal government shutdown, and most NASA employees are currently furloughed. However, missions in space, including New Horizons, are considered essential activities. (It would be a shame if NASA had to throw away spacecraft costing hundreds of millions of dollars.)
NASA will not be issuing news releases, but the Johns Hopkins Applied Physics Laboratory public affairs staff will get the news out, and on Friday, NASA Administrator Jim Bridenstine indicated that the agency would continue providing information on New Horizons as well as Osiris-Rex, a mission that is exploring a near-earth asteroid, Bennu.
What happens after the flyby?
Because New Horizons is so far away, its radio signal is weak, and the data will trickle back over the next 20 months. At the same time, it will make observations of other objects in the Kuiper belt to compare with Ultima Thule.
The spacecraft has enough propellant left to possibly head to a third target, but that depends on whether there is anything close enough along its path. Astronomers, busy with Ultima Thule, have yet to start that new search.
Beyond that, New Horizons will continue heading out of the solar system. Powered by a plutonium power source, it will take data and communicate home with Earth for perhaps another 20 years, headed out of the solar system. However, it is not moving quite as fast as the Voyager 1 and Voyager 2 spacecraft that have now both entered interstellar space, so it is unclear whether New Horizons will make a similar crossing before its power runs out.