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  • Writer's pictureStephen Strum

Ultima Thule!

Updated: Feb 16, 2019

Two images of Ultima Thule taken 38 minutes apart showing the rotation of the Kuiper Belt object. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The New Horizons spacecraft, which brought us spectacular images of Pluto a few years ago, passed by another Kuiper Belt object on New Year's Eve, an object named Ultima Thule. The first images are now coming in, but high-resolution imagery, which should be about five times more detailed than what is currently available, likely won't be downloaded from New Horizons until February. The great distance between Earth and the New Horizons spacecraft combined with the 15-watt transmitter on the spacecraft result in slow data transmission rates. The highest resolution data will be transmitted after more critical science data is downloaded during the next month. Even so, we can already learn a great deal about Ultima Thule. In the animated gif above, two images taken 38 minutes apart are flashed back and forth to show the rotation rate. The second of the two images resolves more surface detail because it was captured at a distance of 17,000 miles while the first image was taken at a distance of 38,000 miles. The closest approach of New Horizons to Ultima Thule was only 2,200 miles and the higher resolution images taken at that time should prove to be spectacular. The animation shows that the object is rotating in a clockwise direction at a relatively rapid rate.

A low resolution color image of Ultima Thule is combined with a medium resolution black and white image to produce a moderately detailed color image.

These first images show that Ultima Thule is a contact binary, an object created from two objects that were slowly orbiting around each other and gradually spiraled in closer until they ground themselves together. The mass of the object is not high enough for the resulting gravitational force to pull the combined object into a circular shape. While the BB-8 shaped object looks unusual, objects of this shape are likely quite common in the Kuiper Belt. We will learn more about the composition of Ultima Thule in the coming months, possibly including the mass and amount of rock and ice contained in the object. However, the mass of Ultima Thule can only be determined with any accuracy if there is another small body in orbit around the object. Since Ultima Thule is small, and the New Horizons craft passing a couple thousand miles away at closest approach, the spacecraft wasn't influenced enough by the gravity of Ultima Thule to determine the object mass. If another small object is seen in orbit around Ultima Thule, then the mass can be estimated from the gravitational effects on that orbiting object.

Ultima Thule is also a type of Kuiper Belt object known as a "cold classical". These are interesting objects because their relatively circular orbit in the same plane as the planets of the solar system indicate that they haven't been disturbed much by other objects since they formed 4.6 billion years ago. Since Ultima Thule is such a pristine and primitive object, it should help us learn more about the solar nebula from which the solar system developed.

In another month or two we will get to see imagery five times more detailed than this image.

New Horizons has proven to be an amazing spacecraft and will continue to stream back data collected during the flyby for several months.

Check here for the latest Ultima Thule images from New Horizons as they are downloaded and processed:

You can read more about the New Horizons mission in the book I have linked to below:

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