Three years ago, we stared in awe at the first close-up of Pluto captured by NASA's New Horizons spacecraft. Now the spacecraft is set to make history again while flying by a world even farther away.
Ultima Thule is located 1.6 billion kilometers outside of Pluto in the Kuiper Belt – a cosmic donut of small primitive objects.
No spacecraft has ever explored the world so far from the Sun, said Alan Stern, the mission's principal investigator at the Southwest Research Institute in Boulder, Colorado.
"We need almost 13 years to get there traveling at an incredible speed of more than one million kilometers per day," said Dr. Stern.
At that level, Cakrawala Baru is expected to enlarge Ultima around 16:30 (AEDT) on New Year's Day.
What do we know about Ultima Thule?
Ultima Thule (ultima thoo-lee) – or MU69 2014 as officially known – was discovered in 2014.
"Ultima is very mysterious. We don't know much about its size and shape," said Dr. Stern.
What we know so far is from the silhouettes captured by telescopes such as the Hubble Space Telescope when cold objects pass in front of stars.
"From there we determine the length of about 30 kilometers, and the shape is a bit like the number eight," said Dr. Stern.
This shows Ulule Thule can be two interconnected objects, known as binary contacts, or two objects that orbit each other.
"We have taken pictures of Ultima Thule since August from above the spacecraft, but only one point in the distance has grown brighter and brighter and brighter."
When New Horizons reached its target in early December, extensive search found no moon signs, rings, or any danger near the object.
The first clue about what Ultima Thule will actually look like will begin to appear on December 31, when a piano-sized spacecraft is still far from the object of the Earth to the moon.
Then on January 1, New Horizons will enlarge Ultima around 50,000 kilometers per hour, only 3,500 kilometers above the surface – three times closer than its approach to Pluto.
Above the spaceship is a set of seven instruments that will map the composition and topography of an object, take its temperature, look for signs of the atmosphere.
Traveling at the speed of light, messages from spacecraft take more than six hours to make 6 billion kilometers back to us.
"On January 2 we will have detailed images that we can map from above so that this will all happen very quickly," said Dr. Stern.
Why explore the Kuiper Belt?
Ultima Thule is just one of thousands of objects that call home Kuiper Belts, ranging from dwarf planets to comets.
The Kuiper Belt extends from about 4.5 billion kilometers from the Sun (Neptune) to 7.5 billion kilometers from the Sun.
The first small object – 1992 QB1 nicknamed "Smiley" – was discovered in this region in 1992. Since then more than 2,000 objects have been found.
Some of these worlds rival Pluto in size, but most of the world is only tens to hundreds of kilometers in diameter.
"We have a pretty good understanding of this world. Many of them have … months, some even have rings," said Dr. Stern.
This small world is an ancient time capsule left from the birth of the solar system 4.6 billion years ago.
"We know that Ultima Thule was born at a great distance from the Sun and is always in the region of the solar system."
At that distance the temperature freezes – almost absolute zero or -273 degrees C.
"That temperature must keep Ultima Thule's record of formation very faithfully for billions of years," said Dr. Stern.
Flying through the densest parts of the region, New Horizons will pick up details that had never been imagined by previous missions like Voyager.
The Voyager spacecraft made their way above and below the Kuiper Belt in the 1990s, but were "very unaware" of its existence.
"Voyagers don't even see the Kuiper Belt because they don't know there is a Kuiper Belt to look at," said Dr. Stern.
"And of course they have, according to current standards, very primitive instrumentation based on 1970s technology."
"But there has never been in New Horizons these objects studied closely with cameras and spectrometers and whatever equipment we carry."
What happened outside of Ultima Thule?
Flying will produce enough data that will keep scientists busy for the next one and a half years, said Dr. Stern.
But the New Horizons trip does not stop at Ultima Thule. The team already has other Kuiper Belt objects in view.
"Spacecraft are very healthy, don't use any backup systems and have the energy and fuel to operate for almost 20 years," said Dr. Stern.
"There is a lot of future exploration for New Horizons."
For now, the team is waiting to celebrate on New Year's Day.