For ancient explorers, "ultima thule" or the farthest region was what lay on the northernmost edges of maps beyond the boundaries of the known world.
So when NASA selected a target for their New Horizons probe, that was further than anything that had been researched so far, Ultima Thule seemed to be a fitting nickname. The far-away space rock is a resident of the Kuiper Belt, the debris ring that surrounds the icy outer reaches of the solar system.
Ultima Thule is so weak and so far away that scientists are not even sure what it looks like. Some of their only information about size and shape came from coordinated observations last summer when astronomers surveyed the shadow she passed in front of a star.
New Horizons will fly past its target shortly after midnight on January 1
"This is just a raw exploration," said Alan Stern, a scientist at the Southwest Research Institute and director of the mission.
"No one has ever seen an object of a Kuiper Belt as anything other than a point of light – no one has ever seen an object frozen to near absolute zero – there are many ideas and each one could be wrong."  He took a breath. "We'll find out Tuesday."
NASA celebrates the record-breaking meeting at the perhaps nerdy New Year Party of the Solar System.
At the Johns Hopkins University Applied Physics Laboratory (APL), which builds and operates the spacecraft, scientists will count to 12:33 Eastern Time (05:33 UTC) at the time of closest approach from New Horizons , Meet again 10 hours later to see the first signals of the Vorbeistroms on their screens. (It takes more than six hours for the light from Ultima Thule to reach Earth.)
NASA's acclaimed social media operation was a victim of partial government shutdown, temporarily restored to cover the event. The countdown, signal capture and subsequent news conferences will be streamed live on NASA TV and YouTube.
Alice Bowman, mission operations manager for New Horizons at APL, said the spaceship had entered "encounter mode" on Wednesday. This configuration restricts the spacecraft's communication with the Earth and commands it to solve all technical problems on its own and then return to science.
Although the thrill for engineers is a thrill, the encounter mode makes New Horizons take full advantage of its short time near Ultima Thule.
"Because this is a flyby, we only have one chance to get it right," said Bowman.
Above:  above: ] Our best view yet of Ultima Thule (between the yellow crosshairs). The image on the right has been enlarged and the background stars have been removed from the image.
New Horizons left Earth in January 2006. It was the first mission to explore the farthest part of the solar system.
Nine years and 3.5 billion miles later, it was the first close-up of Pluto that revealed a complex and colorful world full of methane mountains and a huge, heart-shaped nitrogen plane.
After passing by, Stern and his colleagues began to search for a new target in the Kuiper belt, which extends from the edge of Neptune's orbit to a distance of about 5 billion miles from the Sun.
Until the 1990s nobody knew what was hiding where sunlight was 0.05 percent as weak as it is on Earth. The Kuiper Belt is believed to contain millions of icy objects, unused planetary building blocks left over from the earliest days of the solar system.
These bodies are time capsules that have been frozen for 4.6 billion years. According to NASA, Ultima Thule is probably the most primitive planet object ever explored.
The object of the Kuiper Belt was discovered in 2014 with the Hubble Space Telescope. Subsequent observations indicate that it is small – no more than 20 miles wide – and how a peanut is shaped
Astronomers believe it is a contact binary consisting of two touching objects or even a binary system in which orbiting two objects.
The encounter with Ultima Thule will be short and technically demanding – even more so than New Horizons & # 39; s flyby of Pluto. While Pluto is about the size of the United States, Ultima could fit on Washington DC. This means New Horizons needs to get closer to the space rock to investigate, and the encounter will be over much quicker.
One day before the next approach, Ultima Thule takes only two pixels in images taken by New Horizons. Camera screen. As New Horizons speeds through space at 9 miles per second, it will take less than a day to turn Ultima Thule back into a spot in the rearview mirror.
The performance of New Horizons suggests, however, that she is ready for the challenge, Stern said. Saturday measurements showed that the spacecraft was within 20 miles of Ultima Thule's intended flyby distance and that the time of the encounter will be within 2 seconds of what was expected.
"We meet with something that's covered in a mountain of black velvet in almost pitch-dark conditions, and we scream for perfection within  seconds of [..]," Stern said. "It could not be better."
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