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posted by Fnord666 on Wednesday July 04 2018, @10:48PM   Printer-friendly
from the queue-the-uranus-jokes-in-5,4,3,2,1 dept.

Many asteroids might be remnants of 5 destroyed worlds, scientists say

For years, asteroids were thought of as the leftovers of planet formation - chunks of material that never quite made it to planet size and that were drawn into the crowded belt of rocky remnants that circles the sun between Mars and Jupiter.

But according to a study published Monday in the journal Nature Astronomy, these were once pieces of worlds, too. A vast majority of the half-million bodies in the inner asteroid belt may in fact be shrapnel from as few as five parent bodies called "planetesimals," scientists say. But the tangled orbits of those lost worlds meant they were doomed to collide, producing fragments that also collided, producing still more fragments in a cataclysmic cascade that's been going on for more than 4 billion years.

The finding doesn't only illuminate a "mystery" of the asteroid belt, said Katherine Kretke, a planetary scientist at the Southwest Research Institute who was not involved in the study. It could also help resolve a debate about the formation of the eight planets - including Earth. "I find it really exciting that we can look back in time and potentially see evidence of what were the building blocks that built up our solar system," she said. "If we can turn back the clock and see the asteroid belt was made by these big planetesimals, that really is telling us something quite definitive about the circumstances that formed our own planet."

[...] Scientists have previously known that roughly half of inner-belt asteroids belong to five "families." But Dermott and his colleagues say their analysis suggests that number is as high as 85 percent.

Another ancient collision is suspected of causing the unusual tilt and low temperature of Uranus:

Uranus was hit by a massive object roughly twice the size of Earth that caused the planet to tilt and could explain its freezing temperatures, according to new research. Astronomers at Durham University led an international team of experts to investigate how Uranus came to be tilted on its side and what consequences a giant impact would have had on the planet's evolution. The team ran the first high-resolution computer simulations of different massive collisions with the ice giant to try to work out how the planet evolved.

The research confirms a previous study that said Uranus' tilted position was caused by a collision with a massive object – most likely a young proto-planet made of rock and ice - during the formation of the solar system about 4 billion years ago. The simulations also suggested that debris from the impactor could form a thin shell near the edge of the planet's ice layer and trap the heat emanating from Uranus' core. The trapping of this internal heat could in part help explain Uranus' extremely cold temperature of the planet's outer atmosphere (-216 degrees Celsius, -357 degrees Fahrenheit), the researchers said.

Also at University of Florida.

The common origin of family and non-family asteroids (DOI: 10.1038/s41550-018-0482-4) (DX)

Consequences of Giant Impacts on Early Uranus for Rotation, Internal Structure, Debris, and Atmospheric Erosion (DOI: 10.3847/1538-4357/aac725) (DX)


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  • (Score: 2) by frojack on Thursday July 05 2018, @01:27AM (3 children)

    by frojack (1554) on Thursday July 05 2018, @01:27AM (#702787) Journal

    How could they know that?
    Maybe 3. Maybe 6?

    After all, after the first collision the ability to differentiate fragments becomes highly suspect, as contents are mixed, trajectories are suppositions, and the current asteroids have been churned by any number of other secondary collisions. Further, the shrapnel would coalesce over time only to be hit again.

    Its like they started with the intent to find the fewest possible contributors to these "Families of asteroids", rather than the the conventional theory of lots of leftovers, or a single shattered planet.

    But the "Famlies" are themselves merely probabilities dreamed up by Hirayama 1n 1918, using nothing more than the crude photos of the day, and no computational power.

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  • (Score: 2) by fyngyrz on Thursday July 05 2018, @02:08AM (1 child)

    by fyngyrz (6567) on Thursday July 05 2018, @02:08AM (#702794) Journal

    Yeah, and they got the planet count wrong, too. They used the pop-culture 8 instead of the actual 9.

    But don't worry, Pluto doesn't care. It's a planet no matter what those IAU revisionists want to call it this week. :)

  • (Score: 1, Offtopic) by Runaway1956 on Thursday July 05 2018, @07:39AM

    by Runaway1956 (2926) Subscriber Badge on Thursday July 05 2018, @07:39AM (#702897) Journal

    But, but, but - after you've got your degree, you can do guesswork forever, and the rabble has to accept it as fact.

    First family comes from the larger body's surface. Second family comes from the larger body's core. Third family comes from the smaller body. Fourth family is the leftovers that everyone else was guessing at. And, the fifth family is just some crap that got caught in the asteroid's general orbit. And, the sixth family, that hasn't been mentioned, is the remainder of whatever hit Uranus.

    See, anyone can play guess the origin of crap, you don't even need a degree!