Scientists Publish First Findings From Ultima Thule Flyby

Published: Thursday, May 16, 2019 - 3:07pm
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ASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute, National Optical Astronomy Observatory
The most detailed images of Ultima Thule — obtained just minutes before the spacecraft's closest approach at 12:33 a.m. EST on Jan. 1 — have a resolution of about 110 feet (33 meters) per pixel.

In January, NASA's New Horizons probe began sending observations from the most distant object ever visited by a spacecraft. Now the team is reporting what that data tells them — and what it doesn't.

The findings appear in the journal Science.

To co-author Tod Lauer of the National Optical Astronomy Observatory in Tucson, 2014 MU69 (informally known as "Ultima Thule") brings to mind a fat hamburger patty stuck to a meatball.

"It's a little bit lumpy, it's thick, like a good burger you get at a nice restaurant," Lauer said. "Not something thin and smashed up like a fast food place."

Figuring out the forces at play in the slow-motion collision that united these objects is one of many challengs facing the team as it grapples with data slowly trickling in from the probe.

Like Pluto, Ultima Thule lies in the Kuiper belt beyond Neptune, a doughnut-shaped region made up of hundreds of thousands of objects — many of them leftover "building supplies" from the birth of the solar system.

Following its successfully Pluto flyby, New Horizons zipped past Ultima Thule, which measures around 20 miles long, at more than 31,000 miles per hour and a distance of around 2,000 miles.

Before that, scientists knew only a few sketchy details about the object, such as its orbit, its ruddy color and its size.

Now, up close, the object's primeval character becomes clear.

"One of the things we can see is very small cratering on the object. And that's important, because it's been sitting there in the environment of the Kuiper belt, the outer section of our solar system, basically unaltered since our solar system was formed," Lauer said.

That means the reddish-brown object could be the 4.5 billion-year-old time capsule scientists were hoping for.

Unfortunately, because Ultima Thule lacks a satellite to tug on it gravitationally, scientists cannot draw strong conclusions about the object's mass or density — and, therefore, its likely makeup.

"It's yielding its secrets very grudgingly. We have to kind of work at it. You know, it doesn't have a list of ingredients printed there with our cameras that we can have a look at," Lauer said.

As for how its two halves came together, only a gentle mutual orbit, shrinking at something like walking speed, could explain Ultima Thule's lack of lack of distortion and fracturing.

But Lauer said the physical properties necessary to explain that gentle smoosh, and the current rotation rate, only deepen the mystery of the object's makeup.

"However the objects are made, they're very, very fluffy, maybe twice the density of Styrofoam or something. Not ice, which, you know, would be very, very dense," Lauer said. 

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