From the American Geophysical Union and the “Pluto is still denied planetary status” department comes this idea:
WASHINGTON, DC — Scientists suggest in a new study the existence of a planetary object called a “synestia,” a huge, spinning, donut-shaped mass of hot, vaporized rock, formed as planet-sized objects smash into each other.
Credit: Simon Lock and Sarah Stewart.
At one point early in its history, Earth was likely a synestia, said Sarah Stewart, a planetary scientist at the University of California Davis and co-author of the new study in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union.
Stewart and Simon Lock, a graduate student at Harvard University in Cambridge, Massachusetts and lead author of the new study, explore how planets can form from a series of giant impacts. Current theories of planet formation hold that rocky planets such as Earth, Mars and Venus formed early in the solar system when smaller objects smashed into each other.
These collisions were so violent that the resulting bodies melted and partially vaporized, eventually cooling and solidifying to the nearly spherical planets we know today.
Lock and Stewart are particularly interested in collisions between spinning objects. A rotating object has angular momentum, which must be conserved in a collision. Think of a skater spinning on ice: if she extends her arms, she slows her rate of spin. To spin faster, she holds her arms close by her side, but her angular momentum stays constant.
Now consider two skaters turning on ice: if they catch hold of each other, the angular momentum of each skater adds together so that their total angular momentum stays the same.
In the new study, Lock and Stewart modeled what happens when the “ice skaters” are Earth-sized rocky planets colliding with other large objects with both high energy and high angular momentum.
“We looked at the statistics of giant impacts, and we found that they can form a completely new structure,” Stewart said.
Lock and Stewart found that over a range of high temperatures and high angular momenta, planet-sized bodies could form a new, much larger structure, an indented disk rather like a red blood cell or a donut with the center filled in. The object is mostly vaporized rock, with no solid or liquid surface.
They have dubbed the new object a “synestia,” from “syn-,” “together” and “Estia,” Greek goddess of architecture and structures.
The key to synestia formation is that some of the structure’s material goes into orbit. In a spinning, solid sphere, every point from the core to the surface is rotating at the same rate. But in a giant impact, the material of the planet can become molten or gaseous and expands in volume. If it gets big enough and is moving fast enough, parts of the object pass the velocity needed to keep a satellite in orbit, and that’s when it forms a huge, disc-shaped synestia, according to the new study.
Previous theories had suggested that giant impacts might cause planets to form a disk of solid or molten material surrounding the planet. But for the same mass of planet, a synestia would be much larger than a solid planet with a disk.
Most planets likely experience collisions that could form a synestia at some point during their formation, Stewart said. For an object like Earth, the synestia would not last very long – perhaps a hundred years – before it lost enough heat to condense back into a solid object. But synestia formed from larger or hotter objects such as gas giant planets or stars could potentially last much longer, she said.
The synestia structure also suggests new ways to think about lunar formation. The moon is remarkably like Earth in composition, and most current theories about how the moon formed involve a giant impact that threw material into orbit. But such an impact could have instead formed a synestia from which the Earth and Moon both condensed, Stewart said.
No one has yet observed a synestia directly, but they might be found in other solar systems once astronomers start looking for them alongside rocky planets and gas giants, she said.
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This research article is open access for 30 days. A PDF copy of the article can be downloaded at the following link: http://onlinelibrary.wiley.com/doi/10.1002/2016JE005239/pdf.
Angular momentum could also cancel between objects depending upon their spin directions and angle of impact. There are a semi infinite number of potential combinations of these factors so how do these “researchers” come up with their theoretical results?
They could call it a Larry Niven.
Another theory has the Earth heated by a decay of radioactive elements. We know a precious little about the topmost 10 kilometers of the crust and almost nothing about the remaining 6,360 km to the center. A great playground for a general speculation.
If anything CAN happen, it WILL happen.
I’m having a little trouble with the conception of how a synestia would work.
A disk/ring of debris is one thing, as the range of velocity from inner edge to outer edge varies consistently to remain in orbit. But it seems to me the upper and lower boundaries of a synestia would either rip it apart very quickly or there has to be something strange going on.
The upper and lower boundary orbital velocities are surely radically different to what it required to orbit with the central plane of the debris? Unless there is some internal synestia force operating to force the upper and lower boundary debris (& of course everything above and below the ‘ecliptic’ of the debris) to travel in lockstep with the central plane velocity, that non-central plane debris would assume radically different velocity.
They appear to need something akin to the invention of Dark Matter, which supposedly causes the disks of galaxies to travel in non-Kepler fashion – so we’d have something causing galactic disks to be unusual, then planetary orbits which are ‘normal’ and then another ‘unusual version at a single planet scale.
Or do I have my head off the planet? 😀
And what happens to all the angular momentum in the synestia as it collapses into a solid planet again? Surely the planet would be spinning like a top?
MarkMcD, interesting thoughts.
I was also curious about these two statements:
“If it gets big enough and is moving fast enough, parts of the object pass the velocity needed to keep a satellite in orbit, and that’s when it forms a huge, disc-shaped synestia, according to the new study.”
This isn’t quite clear, but they seem to be suggesting that parts of the object will exceed escape velocity? If that is true, what would cause those parts to stay around? Once you’ve exceeded escape velocity, presumably you will continue on the same trajectory (unless otherwise disturbed), heading ever farther away from the initial collision point . . .
Or maybe they aren’t talking about escape velocity at all and are just saying the particles will orbit farther out than our current satellites? But in that case in order to remain in orbit those farther particles would have to move slower than the closer particles, not faster . . .
In any case, it seems poorly worded.
Also:
“Most planets likely experience collisions that could form a synestia at some point during their formation, Stewart said. For an object like Earth, the synestia would not last very long – perhaps a hundred years – before it lost enough heat to condense back into a solid object.”
Why would losing heat cause orbiting debris to condense back into a solid object? Is there any evidence that, say, the rings of Saturn are condensing back into a single object? The observational evidence we have for Saturn’s rings seems to suggest that larger objects are breaking up into smaller ones, not the other way around . . .
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I’m probably missing something obvious here, but just a couple of questions that come immediately to mind.
We are not certain about birthplace of the human race, let alone planets, solar systems or galaxies.
“Europe was the birthplace of mankind, not Africa, scientists find”
http://www.telegraph.co.uk/science/2017/05/22/europe-birthplace-mankind-not-africa-scientists-find/
Other apes besides hominids have convergently evolved molars like our ancestors’, to include Gigantopithecus, a ten foot-tall, ground dwelling orangutan. Until fossils of this ape’s feet and other post-cranial anatomical features are found, this conclusion is tentative at best.
As one wag joked, “I’d rather be African than Bulgarian”. Regardless of where the first hominid evolved, we’re still ultimately African great apes.
But there is no reason why our ancestors couldn’t have traveled between Europe and Africa in the late Miocene and early Pliocene Epochs. They did in the prior Oligocene. Orangutans evolved in Asia earlier in the Miocene, as shown by Ramapithecus (Sivapithecus) of India c. 12 Ma and Gigantopithecus in China and SE Asia c. 9 Ma until only 100 Ka.
Paper grabbed for later reading in detail. But I hope it does not have the assertion made in this post!
Angular momentums (like any momentums) are additive – but not always (actually, very infrequently) with the same sign.
Ice dancers know this one quite well. Watch any pair do a “romantic” piece, and you’ll probably see them rotating in opposite directions until they grab hold of each other, and “discover” their love. Slowly rotating around their now common center to display their expressions to the audience around the rink. (They could stop dead, too – but that is usually not part of the routines.)
About Earth’s core temperature… Anyone but me thinking P = U * I ?