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What We’ve Learned About Ultima Thule From NASA’s New Horizons Mission

Category: Science & Tech,Space & Cosmos

LAUREL, Md. — A couple of days of before the New Horizons spacecraft made its flyby of a small, icy world far beyond Pluto, scientists working on the mission finally got a picture of the body, nicknamed Ultima Thule, that was more than a single dot. It looked a bit elongated, but that was really all that could be detected from the image.

“I’ve never seen so many people so excited about two pixels,” said S. Alan Stern, the principal investigator of the mission, during a news conference on Monday.

Two days later, the scientists unveiled images from the flyby with some 28,000 pixels. They could finally make out some meaningful details, which could eventually advance scientific understanding of the solar system’s earliest days. At 2 p.m. on Thursday, they will reveal more findings at a news conference, which you can watch on NASA TV, or in the video player below:

Ultima Thule, known also by its official designation of 2014 MU69, turns out to be what planetary scientists call a “contact binary” — two bodies that formed separately and then gently touched and stuck together. It’s a bit more than 21 miles long. To label the two parts, the scientists named the larger one Ultima and the smaller one Thule.

The New Horizons scientists described it as a snowman, but people on Twitter noticed a resemblance to a robot character from recent Star Wars movies.

Planetary scientists are intrigued by the region known as the Kuiper belt — the home of Ultima Thule and other objects — because it is perhaps the only place where some of the solar system’s earliest building blocks are preserved.

The lack of sharp corners and apparently smooth surface of Ultima Thule suggests that it has not changed much in the last 4.5 billion years. What the scientists find there could tell them a lot about how the sun and planets formed.

Images of Ultima Thule taken by the Hubble Space Telescope hinted at a reddish hue.

“Now we can definitively say that Ultima Thule is red,” said Carly Howett, a member of the science team, after New Horizons’ color camera returned its first images.

Ultima Thule’s color is very similar to other similar objects in the Kuiper belt known as the cold classicals, which all seem to be pristine and undisturbed since they formed.

In the past five months, as New Horizons approached Ultima Thule, the spacecraft looked for rhythmic variations in the brightness that would reveals how fast the body was rotating. However, the brightness seemed to remain steady.

They now know that the spacecraft is roughly looking down at one of Ultima Thule’s poles, so that it is mostly the same side of the body that was always facing the spacecraft.

With the world’s two lobes now visible, the mission’s scientists can finally calculate a rotation rate: once every 15 hours, give or take an hour.

The prediction of New Horizons’ closest approach to Ultima Thule was off by only 2 seconds. By contrast, for the spacecraft’s flyby of Pluto in 2015, the prediction was off by about 80 seconds. Even though Ultima Thule is smaller and farther away, the navigators were able to plot a more precise course this time, because in 2017 and 2018, astronomers on the mission team were able to pin down Ultima Thule’s location by observing the object passing in front of a few distant stars.

At closest approach, at two seconds after 12:33 a.m., New Horizons was just under 2,200 miles from Ultima Thule, traveling at 32,290 miles per hour.


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