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Space Beyond Pluto - 02 Jan 2019

This image made available by NASA on shows images with separate color and detail information, and a composited image of both, showing Ultima Thule, about 1 billion miles beyond Pluto. The New Horizons spacecraft encountered it on Tuesday, Jan. 1.

The new year came in with a bang as the New Horizons spacecraft flew by the snowman-like icy body nicknamed Ultima Thule. This is the most distant exploration of any world in history. Scientists will need to wait 20 months to receive the several gigabytes of data collected from the flyby, since it is being transmitted at a rate of only about 1,000 bit per second. Nevertheless, scientists have already learned a lot about it, as summarized below.

What do we call it?

Ultima Thule was discovered on June 26, 2014 by astronomers (led by former Lowell Observatory scientist Marc Buie) using the Hubble Space Telescope. This culminated the search for a Kuiper belt object — icy bodies that inhabit the outer solar system in a disc known as the Kuiper belt — that the New Horizons spacecraft could fly by after its successful passing of Pluto in 2015. The scientists cataloged the body as (486958) 2014 MU69, a precise enough name but pretty clunky and uninspiring.

When New Horizons team members designated this body as the target for the spacecraft flyby, they realized a simpler nickname was in order. They chose Ultima Thule after considering multiple possibilities. This term dates back hundreds of years to classical times and means “beyond the borders of the known world.”

The name caused some consternation in the public because it has been used by Nazis in relation to their Aryan race creation myth. On Jan. 2, New Horizons boss Alan Stern addressed the issue: “The term ‘Ultima Thule,’ which is very old — many centuries old, possibly over a thousand years old — is a wonderful meme for exploration, and that’s why we chose it. Just because some bad guys liked that term, we’re not going to let them hijack it.”

Eventually the issue will be a moot point because Ultima Thule will receive an official name. Once all the data comes back from the flyby and scientists can fairly comprehensively characterize the object, they will formally propose a name to the International Astronomical Union, the official naming body for astronomical objects.

As an aside, Ultima Thule was discovered eight years after New Horizons was launched. The flyby marks the first time a spacecraft flew by an object that was not even discovered yet when the spacecraft launched.

What are Ultima Thule’s characteristics?

Scientists describe Ultima Thule as a bi-lobate contact binary, a solar system body consisting of two roughly spherical bodies pulled together by gravity until they touch. In this case, the larger part (nicknamed Ultima by the New Horizons team), measures 12 miles in diameter while the smaller one (nicknamed Thule) is nine miles across. The bonded pair rotates on its axis every 15 hours and revolves the Sun once every 300 years or so.

Like parts of the surfaces of Pluto and its moon Charon, Ultima Thule is red. This discoloration is probably caused by intense deep-space radiation.

Ultima Thule’s surface appears to be only moderately cratered. The Sun from Ultima Thule would appear 1,900 fainter than from Earth, making for a pretty dark setting. So far, the New Horizons data has not revealed any moons or atmosphere, though this could change as the trickles in.

How did it form?

Ultima Thule probably originated as two bodies that formed out of a rotating cloud of small, icy debris some 4.5 billion years ago, during the early days of the solar system. Over time they slowly spiraled in to each other until they came in contact. The speed of impact had to have been slow enough — maybe just a few miles per hour — that the bodies didn’t demolish each other.

Scientists consider the pair planetesimals, the building blocks of the planets. They thus serve as time machines, as it were, revealing conditions of the early solar system.

Considering only about 1 percent of the data from the New Horizons flyby of Ultima Thule has been received and analyzed, astronomers feel pretty good about what they’ve already been able to explain. Stay tuned for more scientific results in the coming months. In the meantime, you can read about the New Horizons flyby event in Laurel, Maryland, in an upcoming story in the Daily Sun.

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