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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.
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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Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas flom fledgling stars buried within, was captured by Nasa’s Hubble Space Telelscope in February 2010
Nasa/ESA/STScI
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The first ever selfie taken on an alien planet, captured by Nasa’s Curiosity Rover in the early days of its mission to explore Mars in 2012
Nasa/JPL-Caltech/MSSS
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Death of a star: This image from Nasa’s Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy
Nasa
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Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa’s New Horizons spaceraft at a distance of 4.1 billion miles from Earth
Getty
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An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust
Nasa
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The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth
Getty
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Pluto, as pictured by Nasa’s New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015
Nasa/APL/SwRI
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A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun
Nasa
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Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand
Nasa/JPL/University of Arizona
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Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015
Nasa/Scott Kelly
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Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas flom fledgling stars buried within, was captured by Nasa’s Hubble Space Telelscope in February 2010
Nasa/ESA/STScI
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The first ever selfie taken on an alien planet, captured by Nasa’s Curiosity Rover in the early days of its mission to explore Mars in 2012
Nasa/JPL-Caltech/MSSS
3/10
Death of a star: This image from Nasa’s Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy
Nasa
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Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa’s New Horizons spaceraft at a distance of 4.1 billion miles from Earth
Getty
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An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust
Nasa
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The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth
Getty
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Pluto, as pictured by Nasa’s New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015
Nasa/APL/SwRI
8/10
A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun
Nasa
9/10
Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand
Nasa/JPL/University of Arizona
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Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015
Nasa/Scott Kelly
Since its visit to the object on 1 January 2019, New Horizons has journeyed another 316 million miles beyond Arrokoth, which means sky in the language of the Native American Powhatan people,
The research team is now looking for other potential targets to investigate as it passes through the Kuiper Belt.
“For future missions, we need to be able to send spacecraft to the Kuiper Belt and keep them there,” said David Jewitt of the University of California.
That would allow “these intriguing bodies to be studied in stunning geological and geophysical detail,” he added.
Additional reporting by Associated Press
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