Way out yonder
4 billion miles from Earth
As Earthlings marked the start of a new year, one of the most distant spacecraft successfully explored the farthest and most primitive objects that humans have ever seen.
Nasa received confirmation yesterday that its New Horizons probe survived its encounter 6.4 billion km from Earth with Ultima Thule, a rocky relic from the solar system’s infancy whose name means “beyond the borders of the known world”.
The rendezvous, at 6.33pm Tuesday NZ time occurred in the Kuiper belt, a halo of icy bodies so far from Earth it takes more than six hours for signals to travel at the speed of light to reach the Earth.
But just after 4.30am yesterday NZT, at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, mission operations manager Alice Bowman turned to her colleagues with a wide grin.
The probe’s systems were working. Its cameras and recorder were pointed in the right direction.
“We have a healthy spacecraft,” Bowman announced.
“We have just completed the most distant fly-by. We are ready for Ultima Thule science transmission — science to help us understand the origins of our solar system.”
At mission control, and in an APL auditorium where the rest of the science team were watching, people jumped from their seats and burst into cheers. The borders of the known world had expanded just a little bit more.
“I don’t know about you, but I’m really liking 2019 so far,” said the mission’s principal investigator, Alan Stern.
Although coincidental, the timing of New Horizons’ encounter — in the early hours of a new year — is “auspicious”, Stern said.
At a moment when humanity marks the passage of time, looking forward and thinking back, New Horizons is doing the same.
At 6.4 billion km from Earth, Ultima Thule is the farthest celestial body scientists have viewed up close; it is a door to future exploration in a region that is almost entirely unknown. But it is also a window to the past — a time capsule from the era when the planets formed, which
might contain clues about how Earth came to be.
Scientists are analysing early data collected just before the moment of closest approach. An image taken from 800,000km away from Ultima Thule showed a blurry bowling pin-shaped body about 30km across.
Until New Horizons’ fly-by, no person had ever seen a Kuiper belt object as anything but a pinpoint of light in the distance.
By today, the scientists at APL will have received their first highresolution images of the distant rock, revealing whether it has craters, and whether it is one long object or comprises two small bodies orbiting each other.
As for answers to other questions about the Kuiper belt object, Stern advised patience. “This mission has always been about delayed gratification,” he said. “It took us 12 years to sell the spacecraft, five years to build it, 13 years to get here.”
It will take as long as 20 months for scientists to download and process all the data collected during that brief encounter.
But the resulting science will be worth the wait, project scientist Hal Weaver said. “Ultima Thule will be turned into a real world.”
New Horizons was the first mission dedicated to exploring the outermost edges of the solar system. In 2015, it took the first close-up photos of Pluto, revealing a complex and colourful world mottled with methane mountains and a vast, heart-shaped nitrogen ice plain.
When the mission was first conceived in the early 1990s, no one knew what lay beyond the distant dwarf planet. But in the intervening decades, scientists discovered that the Kuiper belt — which extends from Neptune’s orbit to 8 billion km from the sun — is home to millions of small and icy objects.
Out there, where sunlight is 0.05 per cent as strong as it is on Earth and temperatures are near absolute zero (-273.15C), primitive bodies like Ultima Thule have existed in a “deep freeze” since they first formed.
The Kuiper belt object, whose official name is 2014 MU69, was discovered five years ago during a sky-wide search for potential New Horizons targets after the probe left Pluto. But Ultima Thule is so dim and so distant that even the most powerful telescopes could barely make it out. Before yesterday, some of the only information about its size and shape came from co-ordinated observations last year, when astronomers measured the shadow Ultima Thule cast as it passed in front of a star.
The encounter was riddled with uncertainties, making it among the more difficult feats Nasa has attempted. Ultima Thule is 1 per cent the size of Pluto, and New Horizons had to get four times closer to capture an image of it. At the moment of closest approach, the spacecraft was moving at a breathtaking 51,500km/h.
If its cameras were even slightly off track, or if scientists’ projections about Ultima Thule’s trajectory were just a little bit wrong, the probe might fail to capture useful information about its target.
Every image sent back from New Horizons is the most distant photograph ever taken. Each manoeuvre is further than anything Nasa has done before.
We have just completed the most distant fly-by. We are ready for Ultima Thule science transmission — science to help us understand the origins of our solar system. Alice Bowman