Three years ago, we looked at the first photos of Pluto taken close-up from NASA's New Horizons with admiration. Now the spacecraft is about to re-enter history as it flies to an even more distant world.
Ultima Thule is 1.6 billion kilometers from Pluto in the Kuiper Belt, a space donut of small primitive objects.
No spacecraft has ever explored the world so far from the Sun, said Alan Stern, principal investigator at the Southwestern Research Institute in Boulder, Colorado.
“It took us almost 13 years to travel at this amazing speed, exceeding a million kilometers a day,” said Dr. Stern.
In this case, it is expected that New Horizons will approach Ultima around 4:30 pm (AEDT) on New Year's Day.
What do we know about Ultima Tula?
Ultima thule (ultima thoo-lee) – or 2014 MU69, as it is officially known – was discovered in 2014.
“Ultima is quite mysterious. We know little about its size and shape, ”said Dr. Stern.
What we know so far is its silhouette, captured by telescopes, such as the Hubble Space Telescope, in the form of an ice object passing in front of stars.
“On this basis, we determined that its length is about 30 kilometers, and it has a shape resembling eight,” said Dr. Stern.
This suggests that Ultima Thule can be two objects joined together by a so-called contact binary file, or two objects rotating around each other.
"Since August, we shot Ultima Thule from the spacecraft, but this is just a point in the distance, which is becoming brighter, brighter and brighter."
Since in early December, “New Horizons” discovered their target, extensive searches did not reveal signs of moons, rings, or any dangers near the object.
The first hints of what Ultima Thule actually looks like will begin to appear on December 31, when a piano-sized spacecraft is located further away from the object than the Earth is to the Moon.
Then, on January 1, the New Horizons will approach Ultima at a speed of about 50,000 kilometers per hour, just 3,500 kilometers above the surface – three times closer than it is approaching Pluto.
On board the spacecraft there is a set of seven instruments that will display the composition and topography of the object, measure its temperature, look for signs of the atmosphere.
Traveling at the speed of light, communications from the spacecraft take more than six hours to reach us at about 6 billion kilometers.
“By January 2, we will have detailed images from which we can make maps on the spot, so all this will happen very quickly,” said Dr. Stern.
Why explore the Kuiper Belt?
Ultima Thule is only one of thousands of objects that are called Kuiper Belt, from dwarf planets to comets.
Kuiper belt extends from 4.5 billion kilometers from the Sun (Neptune) to 7.5 billion kilometers from the Sun.
The first small object – 1992 QB1, called Smiley – was discovered in this region in 1992. Since then, more than 2,000 objects have been discovered.
Some of these worlds compete in size with Pluto, but most worlds are from tens to hundreds of kilometers.
“We have a pretty good understanding of these worlds. Many of them have … moons, some even have rings, ”said Dr. Stern.
These little worlds are ancient time capsules left over from the birth of the solar system 4.6 billion years ago.
“We know that Ultima Thule was born at a very great distance from the Sun and has always been in this region of the solar system.”
At this distance, the temperature freezes – almost absolute zero or -273 degrees Celsius.
“These temperatures must remain true to the history of Ultima Thule formation over the course of all these billions of years,” said Dr. Stern.
Flying through the densest part of the region, New Horizons will discover details that could never be imagined in previous missions, such as the Voyager.
Voyager spacecraft made its way above and below the Kuiper belt in the 1990s, but "blissfully unaware" of its existence.
“Travelers did not even look at the Kuiper belt, because they did not know that there was a Kuiper belt,” said Dr. Stern.
"And, of course, by today's standards, they had very primitive equipment based on the technology of the 1970s."
"But never before in New Horizons have any of these objects been studied closely with cameras and spectrometers, as well as with any equipment that we take with us."
What happens outside of Ultima Thule?
According to Dr. Stern, the span will provide enough data that will allow scientists to work over the next year and a half.
But the New Horizons journey doesn't stop at Ultima Thule. The team already has other Kuiper Belt objects.
“The spacecraft is very healthy, it does not use any of its backup systems, and it has the power and fuel to work for another 20 years,” said Dr. Stern.
"New Horizons has a lot of research ahead."
So far, the team is waiting for New Year celebrations.