The most distant object ever explored by spacecraft is helping scientists to understand how planets are formed.
Arrokoth, a cold, ultrared rock of frozen methane more than four billion miles from Earth, possesses a distinctive shape that has been compared to a potato or a snowman.
However observations by the New Horizons spacecraft during its close encounter with the 22-mile long object last year have revealed that it was created by the merger of two separate bodies 4.5 billion years ago.
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These two objects formed close together and at low velocity from a cloud of solid particles in the primordial solar nebula, orbited each other, and then gently combined, according to analysis by the Nasa mission team.
“Just as fossils tell us how species evolved on Earth, planetesimals tell us how planets formed in space,” said William McKinnon, a New Horizons co-investigator from Washington University in St Louis.
“Arrokoth looks the way it does not because it formed through violent collisions, but in more of an intricate dance, in which its component objects slowly orbited each other before coming together.”
The team’s findings were reported at the annual meeting of the American Association for the Advancement of Science on Thursday and in three separate papers in the journal Science.
“Arrokoth is the most distant, most primitive and most pristine object ever explored by spacecraft, so we knew it would have a unique story to tell,” said New Horizons investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado.
“It’s teaching us how planetesimals formed, and we believe the result marks a significant advance in understanding overall planetesimal and planet formation.”
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