Planetary Defense Test Deflected An Asteroid But Unleashed a Boulder Swarm (ucla.edu) 63
A UCLA-led study of NASA's DART mission found that the collision launched a cloud of boulders from its surface. "The boulder swarm is like a cloud of shrapnel expanding from a hand grenade," said Jewitt, lead author of the study and a UCLA professor of earth and planetary sciences. "Because those big boulders basically share the speed of the targeted asteroid, they're capable of doing their own damage." From a news release: In September 2022, NASA deliberately slammed a spacecraft into the asteroid Dimorphos to knock it slightly off course. NASA's objective was to evaluate whether the strategy could be used to protect Earth in the event that an asteroid was headed toward our planet. Jewitt said that given the high speed of a typical impact, a 15-foot boulder hitting Earth would deliver as much energy as the atomic bomb that was dropped on Hiroshima. Fortunately, neither Dimorphos nor the boulder swarm have ever posed any danger to Earth. NASA chose Dimorphos because it was about 6 million miles from Earth and measured just 581 feet across -- close enough to be of interest and small enough, engineers reasoned, that the half-ton Double Asteroid Redirection Test, or DART, planetary defense spacecraft would be able to change the asteroid's trajectory.
When it hurtled into Dimorphos at 13,000 miles per hour, DART slowed Dimorphos' orbit around its twin asteroid, Didymos, by a few millimeters per second. But, according to images taken by NASA's Hubble Space Telescope, the collision also shook off 37 boulders, each measuring from 3 to 22 feet across. None of the boulders is on a course to hit Earth, but if rubble from a future asteroid deflection were to reach our planet, Jewitt said, they'd hit at the same speed the asteroid was traveling -- fast enough to cause tremendous damage. The research, published in the Astrophysical Journal Letters, found that the rocks were likely knocked off the surface by the shock of the impact. A close-up photograph taken by DART just two seconds before the collision shows a similar number of boulders sitting on the asteroid's surface -- and of similar sizes and shapes -- to the ones that were imaged by the Hubble telescope. The boulders that the scientists studied, among the faintest objects ever seen within the solar system, are observable in detail thanks to the powerful Hubble telescope.
When it hurtled into Dimorphos at 13,000 miles per hour, DART slowed Dimorphos' orbit around its twin asteroid, Didymos, by a few millimeters per second. But, according to images taken by NASA's Hubble Space Telescope, the collision also shook off 37 boulders, each measuring from 3 to 22 feet across. None of the boulders is on a course to hit Earth, but if rubble from a future asteroid deflection were to reach our planet, Jewitt said, they'd hit at the same speed the asteroid was traveling -- fast enough to cause tremendous damage. The research, published in the Astrophysical Journal Letters, found that the rocks were likely knocked off the surface by the shock of the impact. A close-up photograph taken by DART just two seconds before the collision shows a similar number of boulders sitting on the asteroid's surface -- and of similar sizes and shapes -- to the ones that were imaged by the Hubble telescope. The boulders that the scientists studied, among the faintest objects ever seen within the solar system, are observable in detail thanks to the powerful Hubble telescope.
Soft landing and a big push afterwards (Score:1)
That might be a better option, just need to generate that big push.
Re:Soft landing and a big push afterwards (Score:5, Insightful)
Re:Soft landing and a big push afterwards (Score:5, Informative)
It depends on the asteroid. When the sampling craft Osiris-Rex briefly touched asteroid Bennu, its sampling probe sunk so deep into the asteroid (20 inches) that it clogged the sampling tube. Many asteroids are just list collections of rocks, sand, and dust that cannot be pushed by a single large thruster.
The Osiris-Rex samples return next month, softly parachuting down to earth somewhere in the Utah desert. From there they will be taken to Houston, TX for detailed analysis. https://www.nasa.gov/feature/n... [nasa.gov]
The Osiris-Rex craft has been repurposed to make another sample return. Dani DellaGiustina, deputy principal investigator for OSIRIS-REx, will become principal investigator of the extended mission, called OSIRIS-APEX for "Apophis Explorer," after the Bennu samples are returned to Earth. "We were stoked to find out the mission was extended." https://spacenews.com/nasa-to-... [spacenews.com]
OSIRIS-REx [Re:Soft landing and a big push...] (Score:3)
...The Osiris-Rex craft has been repurposed to make another sample return. ...
Minor correction, the OSIRIS-REx spacecraft has been repurposed to visit and orbit another asteroid (Apophis). It won't make a sample return from Apophis, because it no longer has a sample return capsule (that's on its way back to Earth with pieces of Bennu).
https://news.arizona.edu/story... [arizona.edu]
Re: (Score:3)
That's a lot of fuel we're talking here. First, to slow the probe down to land softly and then to speed up again to move the boulder.
Re: (Score:2)
Re: (Score:2)
Absent the influence of gravity from anything in your flight path, the only way to adjust your velocity is to use fuel to push yourself in a different dir
Re: (Score:2)
Any change of speed in space requires fuel. On the highway, you can just decelerate by taking your foot off the throttle and the friction between asphalt and tires and the wind drag will slow you down. Neither applies to space. The only way to change your speed (barring slingshot maneuvers where you essentially use the gravity of a planet to change your speed, while, and we should probably note that, also changing the speed of the planet... albeit in so tiny amounts that it doesn't matter) is by expending f
Re: (Score:3)
That's a lot of fuel we're talking here. First, to slow the probe down to land softly and then to speed up again to move the boulder.
And even if that happens, the device will need something solid to push against. Many of these objects are just loose agglomerations of rocks
What I found interesting is the last quote:
“If we follow the boulders in future Hubble observations, we may have enough data to pin down the boulders’ precise trajectories,” Jewitt said. “And then we’ll see in which directions they were launched from the surface and figure out exactly how they were ejected.”
That's the crux. The
Re:Soft landing and a big push afterwards (Score:4, Interesting)
The thing is, boulders of this size don't matter.
Even if we were talking about bigger boulders, it seems highly implausible that having such boulders hit Earth would be worse than decreasing the mass of the main body by not just the mass of the boulders, but the (exponentially greater) mass of all the smaller debris ejected. Let alone the benefits of deflecting the main body entirely. Just to get something Meteor Crater-sized requires a ~50m (160ft) body. That's beyond some random boulder sitting on the surface.
Also with smaller bodies: most of what crashes on Earth lands in the oceans, and smaller impactors don't kick up devastating ocean-traversing tsunamis:
Basically, boulders are pretty meaningless in terms of tsunamis.
And then there's the issue that most debris emitted from an impact is greater than escape velocity. So the orbits drift apart over time. So instead of all the mass hitting at once (and all the energy injected into the global system at once), the impact is spread out over years, decades, centuries, millenia or more. Which simultaneously gives more opportunities for interdiction.
The short of it is, small asteroids really don't matter that much. It's the really big ones that can devastate our planet. Stopping them is what matters, even if it kicks off boulders. You really want 10000 boulders on potentially Earth-crossing trajectories, each a few to a dozen or so meters in diameter, rather than one kilometer-wide asteroid on an impact trajectory.
Re: (Score:2)
The thing is, boulders of this size don't matter.
I'm not certain who you are replying to,
But your sig is pretty awesome!
Re: (Score:2)
Which one? My sig autorotates :)
Re: (Score:2)
A wave of smaller boulders and rocks, even if not penetrate the atmosphere, will probably shower alot of satellites with hard hitting "stuff". Especially with Starlink and other already having 1000s of sats out there or planning to.
Kessler syndrome anyone?
Re: (Score:2)
A giant fishing net with three to five weighted crafts along the edge of it. Transfer the impact energy over a larger area. A pentagon or 120 degree triangle arrangement would wrap around the spheroid and contain larger debris. Accurately applying a force vector would be more difficult, as the shape of the object would alter how the net wraps around, but perhaps the range of acceptable trajectories are wide enough to cover the error tolerance of such a project.
Impact ejection is the whole purpose (Score:5, Informative)
Except the purpose of deflection is to hit hard.
Blowing off pieces of the asteroid was the whole purpose of the impactor, because all of the asteroid material you blow off the surface adds to the momentum transfered.
If you impact but only capture the spacecraft's momentum you don't get nearly as much delta-V as you get if you capture the spacecraft's momentum plus the momentum of amount of dirt and debris that's twenty times the mass of the spacecraft.
(that's why they did the test. Any high school student can tell you the delta-V achieved if all you transfer is the spacecraft's momentum. The question was, how much is the multiplier when you blow off asteroidal material?)
Re: (Score:2)
acceleration of a portion of the asteroid will not necessarily transfer as much energy to the total mass. chipping away at something only flicks high velocity objects off it while possibly transferring some rotational energy.
what you do want is to take a high velocity mass so that its vector summed with the asteroid's vector becomes the new vector. anything you fling off it is wasted energy in transferring energy to two masses in two different vectors. because unfortunately an asteroid will never have enoug
Re: (Score:2)
Conservation of momentum says tells you that for a given amount of energy in the impact, the more mass is in the ejected material, the more momentum you transfer to the asteroid.
Re: (Score:2)
Not relevant to this particular scenario. You are not trying to move a portion of the asteroid. You want all of it to miss the Earth. You can do that by breaking it into smaller piece and reliably sending them off course (hard), or you can do that by moving the entire mass. But either way you need the same amount of energy because you are moving that same total mass.
Re: (Score:2)
I regret that I don't have time to do a tutorial on the physics. About all I can say is do the numbers and focus on conservation of momentum.
Re: Impact ejection is the whole purpose (Score:2)
Re: (Score:2)
No.
Conservation of momentum is absolute. If the impact imparts momentum to the fragments, that momentum must be transferred to the main rock.
Re: (Score:2)
Re: (Score:2)
Right, you got it.
The ejected fragments go one way, the reaction force on the asteroid must be the opposite direction to conserve momentum, and thus all the momentum of the fragments is transmitted to the asteroid. This turns out to be larger than the incident momentum of the incident projectile.
Small rocks break up (Score:4, Insightful)
The article makes it sound like "boulders" 3 to 22 feet across are a problem.
They really aren't. These are tiny as asteroid go. Rocks that size break up in the atmosphere and ablate. They really aren't the problem.
It's the big ones we worry about, not the small ones.
Re: (Score:1)
Small boulders is preferable (Score:5, Insightful)
Re:Small boulders is preferable (Score:5, Informative)
Indeed. With Chicxulub, 99.9% of the dust came from the impact, not the asteroid. So if it was just a bunch of boulders of the same mass, the effect would have been a thousandfold smaller.
That is assuming all the boulders would hit the atmosphere, which is unlikely. A breakup occurring a few weeks before impact would scatter rocks more than the diameter of the earth. Many, perhaps most, would miss the earth.
All Burn Up (Score:5, Informative)
Re: (Score:2)
Re: (Score:2)
Re: (Score:3)
Re: (Score:1)
If the 'boulders' are too close together the problem shifts from being shot by a small caliber bullet to a shotgun containing pellets the size of that small caliber bullet.
Even if the first boulders are completely vaporized at say... 100km, the following ones will go deeper before vaporization happens because the ones in front create an shock layer that effectively push the atmosphere out of the way.
If the
Space is Big (Score:2)
If the 'boulders' are too close together
If you want to deflect the asteroid then you need to hit it millions of kilometres from Earth because you can only effect a tiny delta-v to the main object. To have two boulders produced by the impact then arrive at Earth within less than 10 metres of each other would require them to have identical velocities to an unbelievable degree of precision.
Pick one and don't pick the wrong one (Score:5, Insightful)
Whether it's Imperial or Metric, pick one and stick to it.
Re:Pick one and don't pick the wrong one (Score:5, Funny)
When it hurtled into Dimorphos at 1.04x10^5 furlongs per hour, DART slowed Dimorphos' orbit around its twin asteroid, Didymos, by 5.3 million pica per Mercury-year. But, according to images taken by NASA's Hubble Space Telescope, the collision also shook off 0x24 boulders, each measuring from 2 to 15 cubits across.
Re:Pick one and don't pick the wrong one (Score:5, Insightful)
Come on, this was the perfect time to use stones as a unit.
Re: (Score:2)
Please use the Imperial standard barley-corn [youtube.com] for all such measurements in future.
Re: (Score:2)
Whether it's Imperial or Metric, pick one and stick to it.
When it hurtled into Dimorphos at 80640012 furlongs per fortnight, DART slowed Dimorphos' orbit around its twin asteroid, Didymos, by a around .01 Cubits per second. But, according to images taken by NASA's Hubble Space Telescope, the collision also shook off 37 boulders, each measuring from 108 to 792 barleycorns across.
FTFY! 8^)
How was this a surprise? (Score:3)
Did none of these people ever play Asteroids?
Re: (Score:2)
Shhh! Are you trying to summon an alien saucer??
Haven't we learned from Asteroids? (Score:3)
When you shoot at a big asteroid, it splits into two smaller ones. When you shoot those, they split yet again. You need to shoot everything three or four times, then the asteroid and all its remnants are magically gone.
Re: (Score:2)
How about splitting the projectile, instead?
Shortly before impact, have impactor fall apart into a number of smaller ones. Like a cluster bomb or multi-warhead missile. Drifting apart just enough to hit asteroid with many small impacts across a large area. Overall pushing effect on the object would be about the same.
In case that mechanism failed, you'd still have the object-pushing single impact like the one observed here.
Re: (Score:2)
A shotgun like blast might result in several glancing blows that could kick material off at an incredible velocity. Even if the impactor were made from a frangible material I think it could still have this problem if a piece were to hit a relatively low mass object. Low being categorized as loose objects that are similar to the mass of the projectile element.
Re: (Score:2)
Wee-wee wee-wee wee-...Panic! Mash. Die in a slow motion shatter. Weird lesson. Still haven't found a good use for that.
ignoramuses (Score:5, Insightful)
What kind of unqualified fool writes an article like this? And what moron editor duplicates it?
No one in their right mind would think that an inconsequential change in kinetic energy of an asteroid would otherwise save a planet doomed to destruction. That is not the point of the experiment at all and, yes, it is the sum of the kinetic energies of the subsequent field that matters. Duh.
AND...an asteroid that blows apart when struck is likely to blow apart when hitting the atmosphere as well, BUT the smaller pieces burn up more quickly. By breaking the larger object up earlier, fewer pieces may enter the atmosphere and will be distributed over a larger area, burning them up even faster.
BUT that's not even the point, the point is to change the trajectory of the object enough that it misses the planet entirely. However, the goal is to prevent a cataclysmic impact with the planet regardless of how it's a accomplished, a cloud of smaller object is NOT the same a single larger one in this respect AND literally everyone that thinks for a moment about this realizes that a debris cloud might form. I don't think the article could have been more worthless if it tried. Let's hope our survival doesn't depend on these stooges.
Re: (Score:1)
Re:ignoramuses (Score:5, Informative)
It's change in course they are seeking, not velocity
Those two are entirely equivalent. Even discounting that velocity is vector valued and has direction, even changing the speed without changing the direction alters the course because the asteroid is following an orbit.
Re: (Score:2)
Re: (Score:2)
He kind of said that - "the point is to change the trajectory"
Diameter of the earth - 13k km. Let's keep things round and say that 10k km of change is enough.
Asteroid velocity change - 1mm/s
So we need around 10B seconds. (1k * 1k * 10k)
Seconds in a year: 3e7, 30M.
This would say that we need to shoot the asteroid over 300 years before impact to generate the necessary vector change, but this would assume a two body problem - just changing the orbit a bit, well, multiplies the change a lot more than the ini
Re: (Score:2)
Is it possible for a 25 meter or larger "boulder" to be dislodged by something like this? Yes. Is it possible for the asteroid's gravity to pull it back into a collision course? Also yes. But I'd argue that trading a dinosaur killer for a city killer asteroid is still a net positive. It'd just mean that we'd need to send another mission to deflect the big boulder sooner or later. With a fraction of the mass of the larger asteroid, the same size impactor could arrive much later and put a larger velocity change on it.
One of the trickiest parts of this whole thing is the sheer randomness of it all Different velocities and new orbits of the debris. It is definitely not the common idea of turning big boulders into tiny ones that all arrive at the same time. A successful modification of the asteroid will send stuff flying all over - anything that reaches escape velocity of the asteroid. We'll have to pay attention to the results.
So no it won't be precise, and yes, it will be a good thing even if the offending asteroid ca
Re: (Score:2)
Re: (Score:2)
velocity is speed in a direction. Changing the velocity IS changing the course.
Re: (Score:2)
velocity is speed in a direction. Changing the velocity IS changing the course
Wrong again. This is your homework assignment: to simplify it for you, take an object moving in a plane (2-dimensions) and demonstrate how to change the speed without changing the direction.
Re: (Score:2)
Re: (Score:2)
A 4.5% change in orbit time is not nothing, it's a significant result for an experiment. The larger amount we can change the an object's trajectory then the larger cone of possible trajectories we have. This can mean we can either act on the object later or move a small object further from Earth over a longer period of time. Ultimately we'll hit a wall where we can't change the trajectory no matter how powerful of an impact we use because the object will simply disperse instead. In many cases it's going to
Re: (Score:3)
a cloud of smaller object is NOT the same a single larger one
This.
The ratio of surface area to mass is important. Throw a few tons of sand into the atmosphere and most of it will likely vaporize on the way down. And over a wider area as well.
Interesting but not the important question (Score:2)
Of course this impact trick only works on small asteroids. Its worth investigating whether a nuke can deflect a kilometer scale asteroid.
Fate of the boulders? (Score:2)
So did they reach escape velocity from the asteroid, or are we witnessing a bunch of incredibly slow trajectories that will eventually bring them back together? With objects that small, I suspect gravity will be just one force at play. Solar wind may move them to independent orbits. Either we "momentarily" disturbed an asteroid system, or we created an asteroid field. This has interesting implications not only for planetary defense but future navigation. Creating Kessler Syndrome in the whole Solar Sys
Missing the Point (Score:2)
If there were a large rubble-pile asteroid targeted toward Earth, breaking it into a massive cloud of smaller rocks would be preferable to leaving it in one piece. If we break it up at a sufficient distance, then at least some of the boulders would miss completely, and each of the remaining smaller rocks would enter the atmosphere separately. Some of them would burn up in the atmosphere. and the ones that reached the ground would be reduced in mass.
And I think most of us would rather be hit with a handful
Not A Threat (Score:2)
Jewitt said that given the high speed of a typical impact, a 15-foot boulder hitting Earth would deliver as much energy as the atomic bomb that was dropped on Hiroshima.
Rocks of this size hit the Earth every few years [wikipedia.org] while (gasp the size of the Hiroshima bomb!) doing no damage whatsoever, and not at risk of doing any damage, because rocks of this size explode high in the atmosphere producing no dangerous effects on the ground.
Further, the reason why one whacks a rock to deflect it is that it is on a collision course and once deflected it is not on a collision course. All that debris blow off the rock? Absolutely not on a collision course because it is deflected orders of