A NASA probe is racing toward a historic New Year's Day flight of the farthest planetary object ever studied, a frozen relic of the initial solar system called Ultima Thule.
The New Horizons unmanned spacecraft is ready to zoom in at 12:33 p.m. on Jan. 1, at a distance of only 3,500 km (2,200 miles) from Ultima Thule.
That is more than three times closer than New Horizons reached Pluto when it was closed by the dwarf planet in 2015.
So what is this strange object, which has the name of a mythical island from the far north of medieval literature and has its own rock anthem played by Queen guitarist Brian May?
"This is actually the most primitive object ever found by a spacecraft," said Hal Weaver, a project scientist at the Johns Hopkins Applied Physics Laboratory.
Relatively small, scientists are not sure about its exact size.
But they believe it is about 100 times smaller than Pluto, which measures nearly 2,400 kilometers in diameter.
Ultima Thule is also in a frozen area of space, suggesting that it can remain well preserved.
"It really is a relic of the formation of the solar system," Weaver said.
Ultima Thule is in the Kuiper Belt, a vast cosmic disk reminiscent of the days when the planets first formed. Astronomers sometimes call it the "attic" of the solar system.
Scientists did not even know that the Kuiper belt existed until the 1990s.
The Kuiper belt begins about 4.8 billion kilometers (3 billion miles) beyond the Sun, beyond the orbit of Neptune, which is the farthest planet from the Sun.
"It is filled with billions of comets, millions of objects like Ultima, which are called planetesimals, the building blocks from which the planets were formed, and a handful of continent-sized dwarf planets like Pluto," said Alan. Stern, principal investigator at New Horizons. "It is important to us in planetary science because this region of the solar system, being so far from the Sun, preserves the original conditions of four and a half billion years ago. So when we fly through the Ultima, we can see how things were in the beginning. "
The New Horizons spacecraft is accelerating through space at 51,500 km (32,000 miles) per hour, traveling nearly a million miles a day.
At this rate, if you reach a fragment as small as a rice ball, the spacecraft could be destroyed instantly.
"We do not want that to happen," Stern said.
If the New Horizon survives this overflight, it will do so while furiously taking hundreds of photos of Ultima Thule, hoping to reveal its form and geology for the first time.
New Horizons sent back impressive images of Pluto – including a heart shape never seen before on its surface – in 2015.
This time, "in the closest approximation, we will try to imagine Ultima in three times the resolution we had for Pluto," said Stern.
But the fly-by "requires extremely accurate navigation".
"Much more accurate than we've tried before. We can do it and maybe not, "Stern said.
Ultima Thule was first discovered by the Hubble Space Telescope in 2014.
Scientists have discovered in 2017 that Ultima Thule is not spherical, but possibly elongated in shape. It may even be two objects.
It does not project the repeated pulsating light that scientists expect to see from a rotating cosmic object, raising intriguing questions. Could it be surrounded by cosmic dust? Involved by many tiny moons? Oriented in such a way that your pole is facing the approaching spacecraft?
NASA expects the flyby to reveal the answers.
The first images are expected for the night of January 1, with the release scheduled for January 2.
More, higher resolution shots should follow.
Although no live image is possible from this distance, NASA plans to broadcast on-line during the flight by featuring an animated video and music by Queen Brian May's guitarist who is a graduate of astrophysics and is launching a musical tribute to accompany the event .
"I was inspired by the idea that this is the furthest Man's Hand has ever achieved," May said.
And Stern hopes this is not the end of New Horizons, which was launched in 2006 and is plutonium-powered.
"We are hoping to hunt another KPO (Kuiper Belt Object) by making an even more distant flyby in the 2020s," Stern said.