New Horizons: Ultima Thule 'a time machine' to early Solar System

[nitpicker]

https://www.bbc.com/news/science-environment-47621019

New Horizons: Ultima Thule 'a time machine' to early Solar System

By Paul Rincon
Science editor, BBC News website, The Woodlands, Texas

19 March 2019

Scientists are getting closer to understanding how the distant object known as Ultima Thule came to be.

Nasa's New Horizons spacecraft flew by the 35km-long world on 1 January at a distance of 3,500km.

It's made up of two distinct pieces that once orbited each other before colliding at a gentle speed, team members told a major US conference.

The scientists may also be close to understanding why it's flattened like a pancake, rather than spherical.

Researchers are excited because the object gives us a unique window into the formation of the Solar System, some 4.5 billion years ago.

Ultima (the larger lobe) and its counterpart, Thule, are primordial building blocks from a time when smaller objects called planetesimals were merging to form the planets we know today.

"We have never seen a pristine binary like this anywhere in the Solar System," said Prof Alan Stern, the mission's principal investigator from the Southwest Research Institute in San Antonio, Texas.

"We have seen bi-lobe comets, but we were never sure when we were looking at those whether it was something that was born with that shape or evolved to that shape.

"Theoretical models of planetesimal and planet formation predicted that objects like this should be out there. And the very first Kuiper Belt planetesimal that we visit turns out to be one of them... you can't get luckier than that. Unless they're very common."
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