Scientists: Impacts on rubble-pile asteroid are different than on planets
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Using data collected by OSIRIS-REx at the asteriod Bennu, scientists have determined that the ejecta from impacts on a rubble-pile asteroid behaves in a very different manner than on planets with higher gravity.
Instead of flying away at about the same speed as the impactor and escaping into space, as expected in the weak gravity, the material is lifted up at a very slow speed, falls back down, and then rolls downhill like a landslide. The graphic to the right from the press release, reduced and enhanced to post here, illustrates what the scientists think happened when one of Bennu’s larger craters was created.
[M]ost of that material, called ejecta, returned to the surface and slid down the face of the asteroid, starting a wide avalanche that slowly rolled toward Bennu’s equator. Perry said the only way this could happen on a small object like Bennu, which is less than 500 meters (1,640 feet) in diameter and has low gravity, is if the dust had low or next to no cohesion.
“Because Bennu is so small, its escape velocity is less than a few tenths of a mile per hour, so any particle ejected faster than that would leave the surface,” he said. “These slow speeds are possible only if Bennu’s surface is weaker than we thought, even weaker than very loose, dry sand. This extremely low surface strength also means material on a slope is easily disturbed, and that’s what led to the landslide.”
In other words, the low cohesion prevents the impact’s energy from being transferred efficiently to the asteroid’s particles. They move, but only slowly, and thus end up sliding away more or less along the asteroid’s surface.
This discovery helps explain how these rubble-pile asteroids accumulate material, despite their low gravity.
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Click for full image.
Using data collected by OSIRIS-REx at the asteriod Bennu, scientists have determined that the ejecta from impacts on a rubble-pile asteroid behaves in a very different manner than on planets with higher gravity.
Instead of flying away at about the same speed as the impactor and escaping into space, as expected in the weak gravity, the material is lifted up at a very slow speed, falls back down, and then rolls downhill like a landslide. The graphic to the right from the press release, reduced and enhanced to post here, illustrates what the scientists think happened when one of Bennu’s larger craters was created.
[M]ost of that material, called ejecta, returned to the surface and slid down the face of the asteroid, starting a wide avalanche that slowly rolled toward Bennu’s equator. Perry said the only way this could happen on a small object like Bennu, which is less than 500 meters (1,640 feet) in diameter and has low gravity, is if the dust had low or next to no cohesion.
“Because Bennu is so small, its escape velocity is less than a few tenths of a mile per hour, so any particle ejected faster than that would leave the surface,” he said. “These slow speeds are possible only if Bennu’s surface is weaker than we thought, even weaker than very loose, dry sand. This extremely low surface strength also means material on a slope is easily disturbed, and that’s what led to the landslide.”
In other words, the low cohesion prevents the impact’s energy from being transferred efficiently to the asteroid’s particles. They move, but only slowly, and thus end up sliding away more or less along the asteroid’s surface.
This discovery helps explain how these rubble-pile asteroids accumulate material, despite their low gravity.
Readers!
Every February I run a fund-raising drive during my birthday month. This year I celebrate my 72nd birthday, and hope and plan to continue writing and posting on Behind the Black for as long as I am able.
I hope my readers will support this effort. As I did in my November fund-raising drive, I am offering autographed copies of my books for large donations. Donate $250 and you can have a choice of the hardback of either Genesis: the Story of Apollo 8 or Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space. Donate $200 and you can get an autographed paperback copy of either.
Please consider supporting my work here at Behind the Black. My analysis of space, politics, and culture, taken from the perspective of an historian, is almost always on the money and ahead of the game. For example, in 2020 I correctly predicted that the COVID panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Every one of those 2020 conclusions has turned out right.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
You can support me either by giving a one-time contribution or a regular subscription. There are four ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation or subscription:
4. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above.
This is hard to fathom, if the impactor’s energy is not transferred into the asteroid, then how does it slow down? Is there an exit crater on the other side? The rubble pile has low gravity and ridiculously low escape velocity, yet most of the ejecta has ludicrously low velocity and remains? I always ASSumed the rubble pile bodies formed by relatively low velocity accretion and probably by accreting other rubble piles. But who knows. Let’s repeat deep impact on one.
Anyway, what we all want to know, and the reason for the missions- what does it look like when a rubble pile slams into the Earth?
A giant shotgun filled with phosphorus/Dragon’s Breath. Lots of airbursts. A nuke stand-off detonated with the fireball as wide as the impactor on contact may give a cupping shove. A penetration might give you a “fuzzy torus” where the energy rolls back onto itself-beware the blob!
So, the material is akin to dust on this planet Question Mark
Is it possible that the asteroid will “eat” the impactor and then “ring” until it dissipates the excess energy?
Try dropping a ball bearing into a bowl of jello, a bowl of sand and onto a piece of sand stone. Jello is a better analogy than sand because there is some cohesive gravity on a rubble pile but there is nothing cohesive in a bowl of sand. Maybe a bowl of wet sand is more appropriate?
Rubble piles will probably be much easier to mine for minerals though!
“Rubble piles will probably be much easier to mine for minerals though!”
Just need a space-rated vacuum truck. Managing the waste stream might be more difficult than the actual mining.
John asked: “what does it look like when a rubble pile slams into the Earth?”
Scott Manley asked the same question a couple of years ago:
https://www.youtube.com/watch?v=7OSvtznJYuI (12 minutes: “What Would Happen If Asteroid Bennu Hit Earth?”)
It might be harder to mine…I have heard it described as being like those ball pits.
Think of The Blob—made of dirt.
Now an iron slug you can anchor to with cables—and cut into a bola with cables. At a certain distance—the inner faces of the two bola-bergs give you artificial gravity.
You won’t be in danger of being absorbed in space quicksand. These things are ochre jellies of the solar system.
Maybe you just park your spaceship and use an electromagnet to pull out any rocks that are iron rich? The difficulty of mining a solid rock is dealing with torque in a near zero-g environment. Any form of rotating head to drill or cut becomes unwieldy. It will also consume enormous amounts of energy to do any form of cutting or drilling. Not to mention you will be generating a lot of debris that is hazardous for navigation. In this situation you gather up all the richest pieces that have already been broken down for you and you haul them off to your space station or higher gravity processing plant.