On New Year's Day, scientists flew NASA's nuclear-powered New Horizons probe past a mysterious, mountain-sized object.
The space rock is known formally as (486958) 2014 MU69, though it's more commonly referred to as "Ultima Thule".
It's located more than 4 billion miles (6 billion kilometres) from Earth and 1 billion miles (2 billion kilometres) beyond Pluto, making MU69 the farthest object humanity has ever explored up close.
New Horizons recorded hundreds of photos in a highly choreographed flyby at 32,200 miles per hour (52,000 kilometres per hour); it came within about 2,200 miles (3,500 kilometres) of MU69.
On Wednesday, researchers giddily revealed the first photographic spoils of their unprecedented mission.
"It's a snowman," Alan Stern, who leads the New Horizons mission, said of the object's shape during a press conference on Wednesday.
Stern explained that MU69 appears to be what's technically called a contact binary, or "two completely separate objects now joined together."
(NASA)
Jeff Moore, a geologist and co-investigator on the New Horizons mission, said during the briefing that the two lobes of MU69 likely smooshed together at few miles per hour, or "the speed at which you might park your car."
"If you had a collision with another car at those speeds, you might not even fill out the insurance forms," he added.
(NASA)
The scientists also referred to MU69 as a bi-lobate (or two-lobed) comet that has never journeyed near the sun. They are currently called the larger lobe "Ultima" and the smaller lobe "Thule."
MU69 is so distant, cold, and relatively unchanged – each lobe is surprisingly round – that Moore said it's likely "the most primitive object that has yet been seen by any spacecraft."
"What we think we're looking at is the end product of a process which probably took place in only a few hundred thousand or few million years – the very beginning of the formation of the Solar System," he added.
No one knew what MU69 looked like until this week. Fuzzy images captured before the flyby led some scientists to guess it was an elongated object, shaped like a bowling pin or peanut, or two objects caught in tight orbit with each other.
The first low-resolution pictures beamed to Earth from New Horizons show MU69 is one object formed from two separate ones and has reddish colouring. Scientists compared the hue with that of Pluto's moon, Charon.
A comparison of Pluto's moon, Charon, and 2014 MU69. (NASA)
"We can definitely say Ultima Thule is red," Carly Howett, a co-investigator of the New Horizons mission, said during the briefing.
Howett noted that the red colour likely comes from billions of years' worth of radiation that has pummelled organic compounds on MU69's surface, turning them into chemicals called tholins.
New Horizons team members are expecting to get the highest-resolution colour photos in February, Stern previously told Business Insider. He also said the team would start writing its first scientific paper (based on the data it already has) next week.
"This is going to revolutionise our knowledge of planetary science," Stern said.
A low-resolution colour image of MU69 (left), a high-resolution black-and-white image (center), and a merged version to show the object's colour (right). (NASA/JHUAPL/SwRI)
An unprecedented bonus mission beyond Pluto
The mission to fly past MU69 was as surprising as it was ambitious.
When NASA launched New Horizons toward Pluto in 2006, nobody knew MU69 existed. There wasn't even a reliable way to detect the object until astronauts plugged an upgraded camera into the Hubble Space Telescope in 2009.
The Kuiper Belt with New Horizons' flight path, Pluto, and Ultima Thule (or 2014 MU69).(NASA/JHUAPL/SwRI/Alex Parker)
New Horizons achieved the first-ever visit to Pluto in July 2015. Once the probe finished that main mission, it coasted farther into a zone called the Kuiper Belt.
In this cold and icy region, sunlight is about as weak as the light from a full moon on Earth. Frozen leftovers of the solar system's formation, called Kuiper Belt objects (KBOs), lurk in vast numbers.
Pluto is one of them, but MU69 is the most pristine yet encountered. It might have been a comet with a brilliant tail, had it been tossed toward the sun, but instead it has stayed in its distant, freezing-cold orbit for billions of years.
"Any time we see comets, we have to remember that they're post-toasties; they have been fired, crackled, and crunched by the sun. They're badly damaged examples of former Kuiper Belt objects," Moore said. "Being able to go out and see a pristine Kuiper Belt object tells us now that, indeed, contact binaries really do form – and maybe when we see comets, we're looking at smaller versions of very badly damaged contact binaries."
The unprecedented data acquired by New Horizons will likely reveal new clues about how the solar system evolved to form planets like Earth.
"Ultima is the first thing we've been to that is not big enough to have a geological engine like a planet, and also something that's never been warmed greatly by the sun," Stern previously told Business Insider. "It's like a time capsule from 4.5 billion years ago. That's what makes it so special."
He compared the flyby to an archaeological dig in Egypt.
"It's like the first time someone opened up the pharaoh's tomb and went inside, and you see what the culture was like 1,000 years ago," he said. "Except this is exploring the dawn of the solar system."
Another analogy: Stern said he thinks of MU69 as a "planetary embryo" since it's a building block of larger planets that never became one.
"In that sense, it's like a paleontologist finding the fossilized embryo of a dinosaur," Stern said. "It has a very special value."
The long wait for more unprecedented data
A photo of 2014 MU69, taken by NASA's New Horizons probe just 30 minutes before its closest approach on January 1, 2019. At left is a raw spacecraft image, and at right is a sharpened version. (NASA/JHUAPL/SwRI)
As with New Horizons' flyby of Pluto several years ago, researchers on the mission must now play a waiting game for more images and scientific data.
According to Stern, the first pictures New Horizons captured during the flyby each took two hours to transmit. Each bit of data, moving at the speed of light as radio waves, then took about six hours to reach antennas on Earth.
Although the first images are now public, they are low-resolution versions. It will take much longer to receive the most detailed, full-resolution images because of physical limitations of the New Horizons spacecraft and its location. In fact, it may take 20 months to download all of the probe's data.
Part of the reason it will take so long is because the output of the spacecraft's radio antenna is now about 15 watts – or one-quarter of a standard light bulb's power – and it's broadcasting from 4 billion miles away.
"What is striking home with me is that we can build a spacecraft on Earth, and we send it out billions of miles away from Earth, and it sends us back all this wonderful data that we get to look at and learn more about our world, our solar system," Alice Bowman, the New Horizons mission operations manager, said during a press conference on Tuesday.
'10,000 times harder than reaching Pluto'
This flyby was dramatically more difficult to pull off than New Horizons' Pluto visit, Stern said.
"Rendezvousing with something the size of a large, filthy mountain covered in dirt, a billion miles away from Pluto, and honing in on it is about 10,000 times harder than reaching Pluto," Stern previously told Business Insider. "That's because it's about 10,000 times smaller. The achievement of getting to it is unbelievable."
Pinpointing exactly where MU69 would be in space when New Horizons could fly near it required a "two and a half week odyssey" of telescopic observations around the world, mission scientist Simon Porter said on Twitter.
To see MU69 block the light of a distant star – a way to confirm the space rock's precise orbit – the researchers had to fly an aeroplane-mounted telescope called SOFIA and deploy dozens of telescopes in Argentina.
The New Horizons team is already plotting and scheming to make a flyby of an even more distant object.
"New Horizons is a very healthy spacecraft. In fact, all of the systems on board are redundant, and we're not using any of the backup systems because we haven't had any systems failures in 13 years of flight," Stern told Business Insider during Wednesday's press conference.
The probe's power supply – a system that converts the heat emitted by decaying plutonium-238 into electricity – has about 15 to 20 years of life left in it. Stern said this could power all of the spacecraft's electronics out to a distance of about 10 billion miles, or about 2.5 times its current distance.
Where the team might go next is still up in the air.
"I can't give you the answer today because we don't know," Stern said. "We've been very careful, during this period of three years, where we were planning every detail of this flyby, to stay focused on that – and not get distracted by the next shiny thing, if you know what I mean."
He added that by the summer of 2020, the team will make a formal pitch to NASA to look for another object to fly past, perhaps at the very edge of the Kuiper Belt (and a decade from now).
"There's plenty of time to go find other targets – if we're in the position of having a still-healthy spacecraft and an accepted proposal," Stern said.
This article was originally published by Business Insider.
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