Scientists Say 'Rubble Pile' Asteroids are Surprisingly Hard to Kill
Rubble pile asteroids are more common and durable than previously thought, according to new research. The scientists behind the study say this could pose a problem for planetary defense measures. But there may be reason for optimism, given recent insights gleaned from NASA's successful DART mission to deflect an asteroid.
Once just a hypothesis, rubble pile asteroids appear to be a common fixture of the solar system, as evidenced by missions to asteroids Itokawa, Ryugu, Bennu, and Dimorphos, the latter asteroid not yet officially confirmed as such but very likely is. As the name suggests, rubble pile asteroids are loosely bound conglomerations of rock and dust held together by exceptionally weak gravity. And by weak, I mean weak; the forces involved at the surface are comparable to the weight imposed by a couple of pieces of paper held in your hand.
[...] The researchers analyzed dust particles brought back to Earth in 2010 by the Japanese Space Agency's Hayabusa 1 probe, which extracted surface samples from the near-Earth asteroid Itokawa five years earlier. [...]
Or as Jourdan explained in a Curtin press release: "In short, we found that Itokawa is like a giant space cushion, and very hard to destroy." And because rubble pile asteroids are hard to destroy, the solar system is likely chock full of them.
Space Dust Reveals Earth-killer Asteroids Hard to Destroy
Good luck blowing up a pile of rubble:
An asteroid named Itokawa that's been identified as potentially hazardous to Earth would be difficult to destroy, according to new research analyzing dust particles collected from the ancient rock.
Measuring 330 metres across, Itokawa is the first-ever asteroid to be sampled in a space mission. Japan's Aerospace Exploration Agency launched its Hayabusa 1 probe in 2003 to study Itokawa, and managed to return about a milligram of stuff taken from the asteroid's surface to Earth seven years later.
Now, an international team of researchers led by Curtin University, Australia, has studied three dust particles from the sample to estimate Itokawa's age and disposition. Argon dating revealed the asteroid is older than 4.2 billion years, and has been described as having a cushion-like structure. The team discovered Itokawa is older and tougher than previously thought.
[...] "Now that we have found they can survive in the solar system for almost its entire history, they must be more abundant in the asteroid belt than previously thought, so there is more chance that if a big asteroid is hurtling toward Earth, it will be a rubble pile," said Nick Timms, co-author of the paper and geology professor also from Curtin University.
[...] "The good news is that we can also use this information to our advantage – if an asteroid is detected too late for a kinetic push, we can then potentially use a more aggressive approach like using the shockwave of a close-by nuclear blast to push a rubble-pile asteroid off course without destroying it," he said.
Journal Reference:
Fred Jourdan, Nicholas E. Timms, Tomoki Nakamura, et al., Rubble pile asteroids are forever, PNAS, 120, 2022. (DOI: https://doi.org/10.1073/pnas.2214353120)
(Score: 5, Insightful) by Beryllium Sphere (r) on Monday January 30, @03:25AM (8 children)
Switch paradigms when thinking about space. Why destroy something when the most minor deflection is enough to make it miss? Imagine how little force it would take to ruin the aim of someone planning a thousand yard rifle shot. Then remember that in order to cause damage the asteroid has to hit its target from millions of miles away.
https://b612foundation.org/the-effect-of-warning-time-on-the-deflection-of-earth-impacting-asteroids/ [b612foundation.org]
The necessary delta-Vs with good warning time are measured in centimeters per second.
A gentle push over months will do the job completely.
(Score: 1, Insightful) by Anonymous Coward on Monday January 30, @04:23AM (1 child)
Your idea is right, but you have to know about it first. That's not so easy all the time.
(Score: 1, Informative) by Anonymous Coward on Monday January 30, @05:14AM
Fortunately, the danger is proportional to size and the larger they are, the easier they are to detect. If the asteroids are composed of a lot of loose gravel or sand-sized particles that's good too when it comes to moving them. With enough lead time, we should be able to station a solar powered robot on the asteroid that picks up pieces and accelerates them in a direction that can alter the orbit.
The worst case scenario would be a fast-moving solid rock that's big enough to end civilization but moving too fast to detect in time. Then nuking it might be the only option.
(Score: 2) by hendrikboom on Monday January 30, @03:43PM
Why destroy it? Because you may not detect it in time to deflect it.
(Score: 2) by Freeman on Monday January 30, @06:15PM
Thus, the premise of "Armageddon" being to split the rock in two and make both pieces miss the planet. Not sure how good the "science" was on that film, but certainly better than a "destroyed/vaporized" kind of premise.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by mcgrew on Monday January 30, @06:42PM (1 child)
Why destroy something when the most minor deflection is enough to make it miss?
A minor deflection early enough works for a solid asteroid, they proved that. but a pile of rocks, each with the weight of a piece of paper despite their mass, would be impossible to nudge, you would just change the shape of the pile.
One of these is what you would want to nuke, nudging most rocks away and leaving a few to burn up in the atmosphere.
Carbon, The only element in the known universe to ever gain sentience
(Score: 2) by Immerman on Monday January 30, @07:15PM
Not so - momentum will ALWAYS be conserved, regardless of any deformation.
One of the first rules you learn in the physics of collisions is that while conservation of energy is generally useless since energy can be unpredictably dumped into deformation, heat, etc., conservation of momentum will never let you down. Throw a firecracker through the air (well, though a vacuum anyway, air resistance complicates thing), and the combined center of mass of the exploded scraps and combustion gasses will continue on *exactly* the same trajectory as the intact firework without even a jiggle.
So long as the average center of mass of a asteroid and impactor will miss Earth before impact, it will miss after impact. The only potential problem is if the impact just blows a chunk off instead of deflecting the main body, in which case the chunk may take all the deflection while the main body continues largely unaffected.
As a bonus though, any the material ejected from an impact crater essentially acts as rocket propellant, amplifying the push of the impactor - the average center of mass will still follow the exact same trajectory, but since a bunch of mass was ejected at high speed in direction X, the main body must travel a little faster in the -X direction to keep the center of mass on the same trajectory. Which is why the DART mission was able to deflect the asteroid by more than expected.
(Score: 2) by Nuke on Monday January 30, @08:10PM (1 child)
Depends on what you mean by "destroy". Agreed there is no need to vapourise the whole thing. However "destroying" a rubble pile can simply mean breaking it up into bits which individually would not harm Earth much. But most or even all of those bits would miss Earth anyway because you can't break up a rubble pile without deflecting its bits.
In fact, the self-gravity of the asteroid is so weak that your "minor deflection" would break it up anyway - just about any disturbance would. You would need to put a net around it for it not to break up. A nuke next to it, enough to cause some local vapourisation, would do the job.
(Score: 3, Touché) by Immerman on Monday January 30, @08:27PM
You are literally replying to an article referencing the DART mission, which successfully imparted a minor deflection to a rubble-pile asteroid without significantly breaking it up.
(Score: 2) by Barenflimski on Monday January 30, @03:53AM (1 child)
These stories are great. It's one of them, "It's coming right for ya, and there isn't nothing yas can dos abouts it!" stories. Youtube is going to make millions off of this. Million or so on the advertising for the people espousing that nasa can't save earth, no matter what they say. And then multi-millions on the debunkers.
I can't wait to see Ms. Gina Maria Colvin get ahold of this one -> https://www.youtube.com/watch?v=laVv0kHN2NQ [youtube.com]
Let the games begin! She's coming right for ya!
In all seriousness, a large space net made out of carbon nanotubes to harness the comet for towing by a light sail, is our best bet.
(Score: 0) by Anonymous Coward on Monday January 30, @04:58AM
It's full of tin. And aluminium, iron, nickel, gold, etc. These aren't rubble piles, they're money piles!
(Score: 4, Interesting) by Tork on Monday January 30, @07:51AM (5 children)
Slashdolt Logic: "25 year old jokes about sharks and lasers are +5, Funny." 💩
(Score: 2, Informative) by khallow on Monday January 30, @02:18PM (4 children)
(Score: 4, Interesting) by Immerman on Monday January 30, @07:48PM (3 children)
Depends - as loose, widely scattered gravel even an originally 1km wide asteroid would mostly burn up in the atmosphere - each piece of gravel individually does not care how many pieces came before it as it burns up - in fact having the atmosphere pre-heated will likely accelerate the process.
Of course rapidly dumping all that energy into the atmosphere could be a lot worse for us than dumping it into the ground. Temperatures are going to be insane, and the high-temperature shockwave could be devastating.
I think you're underestimating the energy though - a 1km sphere of rock is likely to mass around 2 gigatonnes. Minimum collision speed (assuming it started at rest before falling to Earth) is going to be 11km/s, so the energy will be around 120x10^18J, or about 30 gigatons TNT. And you could easily get 2-3x that number once you include its starting velocity.
But to put that in perspective, a quick google suggests that's still considerably less energy than in a typical hurricane, while the "dinosaur killer" is estimated to be around 1000 to 100,000x more massive depending on just how fast it was traveling.
(Score: 2, Interesting) by khallow on Tuesday January 31, @03:03AM (2 children)
I strongly disagree. At hypersonic speeds, atmosphere is just something that gets pushed out of the way. The Tunguska object was thought to be of similar composition and it turned into a ~12 megaton blast that clobbered a bunch of trees. This object if of the same composition would be about 20 times larger - that means it's pushing 400 times as much atmosphere out of the way, but weighs 8000 times as much. The atmosphere isn't going to stay put with that much mass pushing through. Most of the asteroid, whether solid or gravel isn't going to see stationary atmosphere.
My take is that Tunguska was right at the upper limit of how big an asteroid could be and not hit the Earth's surface.
(Score: 2) by Immerman on Tuesday January 31, @02:56PM (1 child)
>This object if of the same composition would be about 20 times larger - that means it's pushing 400 times as much atmosphere out of the way
It isn't though. If it's scattered if becomes billions of individual pebbles rather than one object. And each individual pebble will burn up - it doesn't care about what came before or what will come after.
(Score: 1) by khallow on Tuesday January 31, @05:58PM
That's why atmosphere could stop Tunguska, but won't stop this. You need a lot more mass to stop this - water or dirt. It doesn't matter if the asteroid is solid or plasma by the time it hits the surface, the momentum won't be sufficiently dissipated.
(Score: 4, Informative) by Immerman on Monday January 30, @07:59PM
Please people - gravity is an acceleration, not a force. The apparent force scales perfectly with the mass of the object so that all objects accelerate at the same speed, and any discussion of force meaningless without knowing the object's mass.
The forces on what? An average-mass person? A million ton bolder? A couple sheets of paper? Slight difference there - the paper is already getting that force right here on Earth.