New Horizons spacecraft 'alters theory of planet formation'

[muriel_volestrangler]

The established view is that material violently crashed together to form ever larger clumps until they became worlds.

New results suggest the process was less catastrophic - with matter gently clumping together instead.
...
The claim arises from detailed study of an object in the outer reaches of the Solar System. Named Arrokoth, the object is more than six billion km from the Sun in a region called the Kuiper belt. It is a pristine remnant of planet formation in action as the Solar System formed 4.6 billion years ago, with two bodies combining to form a larger one.

Scientists obtained high-resolution pictures of Arrokoth when Nasa's New Horizons spacecraft flew close to it just over a year ago. It gave scientists their first opportunity to test which of the two competing theories was correct: did its components crash together or was there gentle contact?

https://www.bbc.co.uk/news/science-environment-51295365

Arrokoth’s position in the Kuiper belt marks what was once the fringes of the cloud of dust and gas, known as the solar nebula, that surrounded the newly formed sun. In this region, planetary development was arrested at an early stage because of the lower density of material available. Exploring these frozen wastelands allows scientists to peer back in time to an epoch when the seeds of today’s planets were being sown.
...
For decades, scientists have wrestled with two competing scenarios for how planetary formation kicked off. In the first, known as hierarchical accretion, small grains and pebbles zipped around occasionally bashing into each other with enough force to stick, making bigger and bigger objects. Gradually, over millions of years, planets accumulated matter though random, forceful collisions.

Under a second scenario, known as cloud collapse, certain regions of the nebula had a higher density of particles and these clumps were drawn towards each other, until they spontaneously gravitationally collapsed. Collisions were gentle and the planets were “born big”, with objects tens or hundreds of miles in diameter emerging within hundreds of years.

Arrokoth’s appearance and composition provide compelling evidence in support of the cloud collapse theory. “The imagery shows no signs of violence, no fractures, the two lobes don’t looks smashed together,” said Stern, who is based at Southwest Research Institute in Boulder, Colorado.

https://www.theguardian.com/science/2020/feb/13/not-just-a-space-potato-nasa-unveils-astonishing-details-of-most-distant-object-ever-visited-arrokoth

Lucky they picked the the object formerly known as Ultima Thule as the follow-up project for New Horizons.

[PJMcK]

1. Fascinating, as all discoveries are

Thanks for the post, muriel.

Have a heart!

[Princess Turandot]

2. From the article. Bill McKinnon: "Not just a space potato"

A great line.

Lucky indeed! It took the New Horizons team several years of looking for an object that NH could reach (location and fuel-wise), before they found Ultima Thule. And it turned out to be a bonanza.