New Horizons heads for flyby of space rock 4bn miles from Earth
A Nasa probe will perform the most distant flyby in history in the early hours of New Year’s Day when it barrels past a space rock called Ultima Thule on the outer edge of the solar system.
Unless gremlins intervene, the New Horizons spacecraft will zoom by the cosmic body at 5.33am GMT and snap thousands of photographs of the dark, icy body as it speeds on into the void.
Ultima Thule lies 4bn miles from Earth in the Kuiper belt, a band of dwarf planets, space rocks and icy debris left over from the formation of the solar system 4.6bn years ago.
New Horizons is so distant that mission scientists have no way of helping out if any last-minute glitches arise. Instead, any final troubleshooting must be handled by the probe’s onboard software.
“It’s a once-in-a-lifetime opportunity,” said Hal Weaver, a research professor at Johns Hopkins University in Maryland and a project scientist on the New Horizons mission. “This is another great step in the exploration of our solar system.”
In 2015, New Horizons flew past Pluto and captured a stunning series of photographs of the dwarf planet’s surface. The images revealed Pluto to be a world where nitrogen mountains tower above the ground and volcanoes erupt ice into a thin hydrocarbon atmosphere.
After the Pluto encounter, Alan Stern, the principal investigator on New Horizons, asked Brian May, the Queen guitarist and astrophysicist, if he would compose a track to celebrate the Ultima Thule flyby.
“I did scratch my head for a while,” said May. “The name is quite hard to conjure with. But then it came to me that this is about man’s desire to reach out into the universe and explore, and see things that have never been seen before.”
The New Horizons track, May’s first solo single for two decades, includes a message from Stephen Hawking and will be premiered at the New Horizons control centre at Johns Hopkins University shortly before the flyby.
“It’s been very exciting. I feel like I’m on that thing,” May said. “To me, it’s about the human spirit and reaching out to discover where we are and why we are here.”
In what promises to be the briefest of cosmic encounters, New Horizons will hurtle past the 20-mile-long Ultima Thule at 31,500mph and get as close as 2,200 miles. Once the probe has gathered all the information it can, it will beam images back to Earth. Even travelling at the speed of light, the data will take six hours to reach home.
In recent weeks, scientists on the New Horizons team have scoured pictures from the spacecraft’s Long Range Reconnaissance Imager (Lorri) for signs of trouble ahead. At such speed, a particle the size of a grain of rice could knock out the spacecraft.
“We’ve looked pretty hard for hazards and we haven’t seen anything to be concerned about, so we are sticking with our primary trajectory,” said Weaver. If the team had spotted dust rings around Ultima Thule, the spacecraft would have been nudged on to a more cautious trajectory that would have taken it further from its target.
Mission controllers will not know if the flyby has gone well until engineering data from the probe is beamed back after it has passed Ultima Thule. The probe’s software should respond to most glitches, such as an instrument suddenly drawing too much current or an incoming cosmic ray upsetting the computer.
Little is known about Ultima Thule, or MU69, to use its official name. But based on preliminary observations, scientists think it may resemble a giant peanut with two large lobes fused together. The dark rock may contain frozen carbon monoxide, carbon dioxide, molecular nitrogen and methane, which may be exposed by impact craters on the surface.
While some comets that streak through the solar system are thought to have originated in the Kuiper belt, those as distant as Ultima Thule have remained on the outer edges of the solar system since birth. For this reason, it is thought that objects such as Ultima Thule, the so-called cold classical Kuiper belt objects, look the same today as they did at the dawn of the solar system.
“We’ve never explored a body as primordial or as far away from the sun as Ultima Thule,” said Mohamed Ramy El Maarry, a New Horizons science team collaborator and lecturer at Birkbeck, University of London. “This gives us a chance to look at what comets are like before they enter the inner solar system. They’ve been in deep freeze since they formed 4.6bn years ago.”
He added: “What’s really exciting is we expect to see surprises. We are really looking at the basic ingredients of the solar system. This can tell us a lot about the building blocks of the solar system, about the conditions when the solar system formed, and about other solar systems as well.”
The first images to be beamed home from Ultima Thule will be small and grainy, but a day or two after the encounter, Nasa hopes to have more impressive pictures from the probe. “This is the first time we’ll fly past a cold classical Kuiper belt object and really see what it looks like,” said Weaver. “We’re taking our first steps into this whole new zone of the solar system. We’re on our way.”