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New Horizons' Alan Stern
New Horizons principal investigator Alan Stern, a planetary scientist at the Southwest Research Institute, stands alongside a scale model of the New Horizons spacecraft after a briefing on the Ultima Thule flyby. (GeekWire Photo / Alan Boyle)

LAUREL, Md. — The sleeping bags are rolled out and the videos are cued up for a New Year’s celebration of cosmic proportions here at Johns Hopkins University’s Applied Physics Laboratory, but the star of the show is still a mystery.

That’ll change once NASA’s New Horizons spacecraft flies past an icy object more than 4 billion miles from Earth, known as 2014 MU69 or Ultima Thule. The piano-sized probe is due to make its closest approach at 12:33 a.m. ET on New Year’s Day (9:33 p.m. PT Monday), nearly 13 years after New Horizons’ launch and three and a half years after it flew past Pluto.

Mission managers say it’s all systems go for history’s farthest-out close encounter with a celestial body.

“We are ready to science the heck out of Ultima Thule,” the mission’s principal investigator, Alan Stern, told reporters today at a pre-flyby briefing.

Ultima Thule, pronounced “Ultima Too-Lee,” gets its nickname from a Latin phrase designating a place beyond the known world. A few basic facts about Ultima Thule, such as its size (about 20 miles wide) and its brightness (darker than Pluto), are known. But there’s much more that’s unknown, including its shape and its composition.

“We’ve never, in the history of spaceflight, gone to a target that we knew less about,” Stern said.

Astronomers didn’t even know Ultima Thule existed when New Horizons was launched on its way to Pluto in 2006. The science team first spotted it in 2014, during a Hubble Space Telescope survey aimed at identifying objects to target after the Pluto flyby in 2015.

Almost a year after the Pluto flyby, NASA approved a mission extension targeting Ultima Thule, a billion miles farther out.

“This is probably the perfect object to go to after Pluto,” said Marc Buie, a member of the science team from the Southwest Research Institute, which is also Stern’s home institution.

Unlike Pluto, Ultima Thule lies within a disk of icy material that lies along the solar system’s main plane, stretching far beyond the orbit of Neptune in a region known as the Kuiper Belt. Such objects are classified as “cold classicals,” and are thought to have been little changed since the beginnings of the solar system more than 4.5 billion years ago.

Ultima Thule will be the first cold classical seen up close. “It’s probably the most primitive object ever encountered by a spacecraft. … Because of that, it lends mystery to the story, because we have no analog for it,” said Hal Weaver, mission project scientist at APL.

Based on two rounds of observations made when Ultima Thule moved in front of distant stars — rare events known as occultations — astronomers have surmised that the mini-world is elongated, and may consist of two or three blobs of ice and rock that came to be stuck together. But during the buildup to this week’s flyby, the New Horizons team saw none of the telltale signs they thought would reveal Ultima’s rate of rotation.

Ultima’s shape, composition and rotation are among the mysteries that should be revealed when New Horizons flies past, coming as close as 2,200 miles at a relative speed of 32,000 mph. Seven scientific instruments — including imagers and spectrometers, plus a solar wind detector, a radio experiment and a dust counter — will be gathering readings.

But scientists won’t get those readings immediately. Because of the spacecraft’s cost-saving design, it can’t collect data and send data simultaneously. And when it does send data, the transmission rate will be a glacial 1,000 bits per second, with signal reception delayed by more than 6 hours due to the finite speed of light.

Today the probe sent back batches of pre-flyby data, including pictures that showed Ultima Thule as little more than a blip on the screen. Scientists also fine-tuned the spacecraft’s flyby schedule to start collecting data two seconds later than previously planned.

Hal Weaver
New Horizons project scientist Hal Weaver uses his wallet to demonstrate how the spacecraft will try to determine Ultima Thule’s shape. (GeekWire Photo / Alan Boyle)

APL will host a New Year’s flyby party on Monday night. Highlights include the midnight debut of a song written for the occasion by British astrophysicist Brian May, who’s better known as the lead guitarist of the rock band Queen. An official observance of the flyby will follow half an hour later.

The first post-flyby data transmission won’t include any pictures at all. Instead, it’ll be a 15-minute “Phone Home” transmission confirming that the spacecraft survived the encounter. That signal is scheduled to come in after 10 a.m. ET (7 a.m. PT) on New Year’s Day, with a news conference to follow at 11:30 a.m. ET (8:30 a.m. PT).

Follow-up transmissions should provide a 100-pixel-wide image of Ultima Thule for release on Wednesday, and a 200-pixel-wide image on Thursday.

Monitoring spacecraft operations, and interpreting the science data, could be a nearly 24/7 task over the next few days. Mission operations manager Alice Bowman said some team members have already laid out sleeping bags, mattresses and pillows at JHU APL to hunker down for the marathon.

“We even had a gentleman who brought his tent and set it up in his office,” she said.

The show will go on even though NASA is one of the agencies affected by the partial government shutdown. Some team members from NASA, including Jeff Moore and Dale Cruikshank from Ames Research Center in California, had to get special dispensation to participate in this week’s activities. “We both spent the day filling out paperwork and dealing with the system,” Moore recalled.

Others from NASA, deemed less essential, are having to miss out. Even high-ranking NASA executives are supposed to hold off from participating in their official capacity, although Stern said they’re welcome to attend the festivities as private citizens.

NASA TV will provide video coverage on the air and online, and the space agency’s social-media accounts on Twitter and Facebook will be updated for the flyby. Websites and social media that aren’t directly controlled by NASA, ranging from JHU APL’s New Horizons website and YouTube channel to the @JHUAPL and @NewHorizons2015 Twitter accounts, will be on the job as well.

Check APL’s website for “where to watch” information and the latest schedule.

This week may mark the climax of the Ultima Thule campaign, but it’s by no means the end of the New Horizons mission. Because of the spacecraft’s transmission limitations, it’s expected to take 20 months or so to send back more than 6 gigabytes worth of data from the flyby.

By then, Stern and his colleagues are hoping to spot yet another flyby target deeper in the Kuiper Belt. It helps that New Horizons is powered by a long-lasting, plutonium-fueled generator, with extra reserves of propellant for its navigational thrusters.

“All I can really say now is that we’re going to use every tool in the book,” Stern said. “We’ve got about 10 years till we leave the Kuiper Belt, so I’m not worried about a time crunch. And since the spacecraft’s operating so well, and it has power and fuel to do this, I’m relatively optimistic.”

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