NASA's Crash Into an Asteroid May Have Altered Its Shape (nytimes.com) 34
Robin George Andrews writes via The New York Times: In 2022, when NASA's $325 million spacecraft crashed into an asteroid named Dimorphos at 14,000 miles per hour, cheers and applause erupted back on Earth. NASA's Double Asteroid Redirection Test (DART) mission deliberately targeted Dimorphos to change its orbit around the larger asteroid Didymos as a dress rehearsal of sorts for thwarting a deadly space rock that might someday head toward Earth. The world's first-ever planetary defense experiment was deemed a triumph: The asteroid's orbit shrank by 33 minutes, far above the minimum threshold of 73 seconds. But what the DART team didn't realize then was just how bizarrely Dimorphos responded to that punch. A new study, published on Monday in Nature Astronomy, has concluded that DART hit Dimorphos so hard that the asteroid changed shape.
Simulations of the impact suggest that the spacecraft's death did not excavate a normal, bowl-shaped crater. Instead, it left behind something that resembles a dent. And although the artificial impact blasted millions of tons of rock into space, plenty splashed back onto its sides like tremendous tidal waves. It widened Dimorphos, transforming it from a squat orb into a flat-topped oval -- like an M&M candy. That the asteroid acted like a fluid comes down to its peculiar composition. It's not a solid contiguous rock, but more like "a pile of sand," said Sabina Raducan, a planetary scientist at the University of Bern in Switzerland and the study's lead author. And a low-density asteroid barely held together by its own gravity was never going to respond in a straightforward manner when a van-size spacecraft flew into its face.
Dimorphos's response is "completely outside of the realm of physics as we understand it" in our day-to-day lives, said Cristina Thomas, the lead of the mission's observations working group at Northern Arizona University who was not involved with the study. And "this has overarching implications for planetary defense." DART showed that a tiny spacecraft can deflect an asteroid. But the study indicates that crashing a similarly disjointed space rock too forcefully risks fragmenting it, which, in a real asteroid emergency, could create multiple Earthbound asteroids. Planetary defense, as a concept, clearly works. "We know we can do it," said Federica Spoto, an asteroid dynamics researcher at the Center for Astrophysics, Harvard and Smithsonian, who was not involved with the new study. "But we have to do it right."
Simulations of the impact suggest that the spacecraft's death did not excavate a normal, bowl-shaped crater. Instead, it left behind something that resembles a dent. And although the artificial impact blasted millions of tons of rock into space, plenty splashed back onto its sides like tremendous tidal waves. It widened Dimorphos, transforming it from a squat orb into a flat-topped oval -- like an M&M candy. That the asteroid acted like a fluid comes down to its peculiar composition. It's not a solid contiguous rock, but more like "a pile of sand," said Sabina Raducan, a planetary scientist at the University of Bern in Switzerland and the study's lead author. And a low-density asteroid barely held together by its own gravity was never going to respond in a straightforward manner when a van-size spacecraft flew into its face.
Dimorphos's response is "completely outside of the realm of physics as we understand it" in our day-to-day lives, said Cristina Thomas, the lead of the mission's observations working group at Northern Arizona University who was not involved with the study. And "this has overarching implications for planetary defense." DART showed that a tiny spacecraft can deflect an asteroid. But the study indicates that crashing a similarly disjointed space rock too forcefully risks fragmenting it, which, in a real asteroid emergency, could create multiple Earthbound asteroids. Planetary defense, as a concept, clearly works. "We know we can do it," said Federica Spoto, an asteroid dynamics researcher at the Center for Astrophysics, Harvard and Smithsonian, who was not involved with the new study. "But we have to do it right."
Exactly like the DC-3 (Score:2)
The DC 3 is “a collection of parts flying in loose formation.”
An Asteroid is very similar : “a collection of rocks orbiting in loose formation.”
Re: (Score:2)
For people who are wondering [lonestarflight.org].
Although we can probably update that joke now, replacing "DC-3" with "737 Max".
Self fulfilling prophecy denied? (Score:2)
How can they say 'Dimorphos's response is "completely outside of the realm of physics as we understand it" in our day-to-day lives', given they've only simulated the response, presumably based on physics as we understand it.
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From the "Press Release Hyperbole Playbook", translation of "It's not quite what we expected."
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Thinking about it, he was trying to say that the conditions in such an event is so different from what we're used to, that it takes careful work to figure out what is really happening. The "in our day-to-day lives" bit is critical. The quotes are honestly around a bad part of the talk, disassociating "in our day to day lives" from it.
We're used to 1G - the asteroid would fall to bits in that. We're used to an atmosphere - it'd corrode and shift around. We're used to situations where seconds often matter
Re: (Score:2)
They lack the mass to actually fuse together, not enough heat or pressure.
you clearly understand the physics involved in that. the question is why a nasa mission lead would say she doesn't when asked in public.
we have plenty and spectacular evidence of how aggregates of rock and sand behave like fluid here on earth, even at 1g. we have known for ages that asteroids can have very low density. they might have misjudged the composition of this particular target, or the effect of the impact (in the end simulations are made on assumptions, and those may be wrong) but still there is no
Re: (Score:2)
I'd be exceptionally hesitant to say that though. I'd have a LOT of questions. For example, while the forces acting things should be very close to zero, could thermal cycling from an elliptical orbit bringing the asteroid closer and further from the sun at intervals, solar winds, and radiation eventually cause things to fuse? Over the course of millions of years?
As you say, the quote is likely missing something. I think, given the "day to day lives" after the quote, that she was indeed not saying that i
Re: (Score:2)
How can they say 'Dimorphos's response is "completely outside of the realm of physics as we understand it" in our day-to-day lives', given they've only simulated the response, presumably based on physics as we understand it.
It's the "Scientists are baffled and stunned" effect.
Scientists get excited and are happy to have something to science about. And in the end, a bit of info is added to our knowledge. What also never happens is an end to our understanding of physics.
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This was my take, too. This is why we run experiments rather than just draw it on paper and say "Yeah, that'll do it. Ship it!"
Anyone working in any realm of physics knows that our knowledge of physics is still incomplete, thus we still need to experiment to confirm / disprove theories.
"outside of the realm of physics" - really? (Score:5, Insightful)
If you disturb something consisting of jagged rocks of different sizes and shapes and a lot of dust that possibly acts as a kind of lubricant then there's no way in hell you could predict how it would behave beyond basic momentum calculations even IF you knew every position and shape of every rock inside it.
As it is it would be like taking a box of breakfast cereal, shaking it vigorously and then trying to predict where all the flakes would end up without even looking inside first.
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Quite possibly worse, in that you're not sure how much of your momentum is going to actually transfer to the target object either - how much will end up as a vector change, how much in the ejecta, how much just turns into heat, etc...
Even basic momentum calculations are going to have huge error bars.
That said, if they're true scientists, "results not as expected" can be a positive thing, because that means that at least one of their assumptions was bad, and now they get to track that down, and that means ne
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What the quote actually was was "outside of the realm of physics as we understand it."
I think they're saying they don't have models for this, not that the impact produced results outside the physical laws of the universe.
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What the quote actually was was "outside of the realm of physics as we understand it."
And I cringed when I read that. Every time.
I think they're saying they don't have models for this, not that the impact produced results outside the physical laws of the universe.
You are absolutely correct, it isn't modeled - yet.
"outside the realm of physics" sounds more like people promoting the EM drive, or cold fusion. Why anyone would use it as a term about a pile of rocks changing shape more than expected (or at all) is hyperbole.
I have a strong suspicion that Ms Thomas wishes she had that moment back to say something different.
Re: (Score:2)
It is a bit hyperbolic for my tastes, too.
did it look like this? (Score:2)
Yosemite Sam [youtube.com]
What shape is NASA now? (Score:3)
Wasted science money (Score:1)
If anything big ever headed our way Bruce Willis will save us.
Now its name fits (Score:1)
I simply don't understand... (Score:3)
...the hyperbole about breaking apart impactors.
Dimorphos is 160m across, 4,8b kg, implying a density of 2238kg. Let's calculate an impact [ic.ac.uk] of it striking 20km into sedimentary rock at a typical asteroid velocity of 17km/s and a typical angle of 45 degrees.
Mean Fragment Diameter: 1.01 meters ( = 3.33 feet )
Peak Overpressure: 34800 Pa = 0.348 bars = 4.95 psi
Max wind velocity: 72.1 m/s = 161 mph
Sound Intensity: 91 dB (May cause ear pain)
Wood frame buildings will almost completely collapse.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
Yeah, that's pretty bad.
Now, looking at Dimorphos, what do you think is the largest [nytimes.com] fragment there? I think 5m diameter would be highly optimistic. Say 5m and 3500kg/m3. Impacting that at the same velocity/trajectory, the same 20km away:
Ejecta: None
Peak Overpressure: 162 - 323 Pa = 0.00162 - 0.00323 bars = 0.0229 - 0.0459 psi
Max wind velocity: 0.38 m/s = 0.851 mph
Sound Intensity: 44 dB (Easily Heard)
Basically, nothing whatsoever. Okay, let's cut the distance from 20km to 5km.
Ejecta: None
Peak Overpressure: 187 - 374 Pa = 0.00187 - 0.00374 bars = 0.0266 - 0.0532 psi
Max wind velocity: 0.441 m/s = 0.986 mph
Sound Intensity: 45 dB (Easily Heard)
Nothing. Okay, *one* kilometer.
Ejecta: None
Peak Overpressure: 189 - 379 Pa = 0.00189 - 0.00379 bars = 0.0269 - 0.0538 psi
Max wind velocity: 0.446 m/s = 0.997 mph
Sound Intensity: 46 dB (Easily Heard)
100 meters?
Ejecta: None
Peak Overpressure: 189 - 379 Pa = 0.00189 - 0.00379 bars = 0.0269 - 0.0538 psi
Max wind velocity: 0.446 m/s = 0.998 mph
Sound Intensity: 46 dB (Easily Heard)
Why isn't distance mattering? Because:
The projectile begins to breakup at an altitude of 49000 meters = 161000 ft
The projectile bursts into a cloud of fragments at an altitude of 35200 meters = 115000 ft
The residual velocity of the projectile fragments after the burst is 13.9 km/s = 8.64 miles/s
The energy of the airburst is 1.09 x 1013 Joules = 0.26 x 10-2 MegaTons.
No crater is formed, although large fragments may strike the surface.
Basically, it explodes 35km up people hear a "pop", and if you're lucky you might find a meteorite (or really, really unlucky you might have one strike your windshield). Remember: the Chelyabinsk meteor was 18m in diameter - 47 times the volume.
Remember that we're talking about the largest fragments of Dimorphos. The vast majority would just be shooting stars, if that. And this is all assuming that it all still hits Earth. Which there's no reason to believe would happen in most scenarios unless the intercept is very late - the Earth is a pretty tiny target when viewed on the scales of orbital mechanics, and things don't have to drift far off their trajectory for errors to amplify and the result to be "near miss, with an ejection into a radically different orbit"
Impact effects are highly nonlinear. Many small fragments is generally vastly superior to one large body.
Let's do a Chixulub-scale impactor.
Distance from Impact: 1000.00 km ( = 621.00 miles )
Projectile diameter: 14.00 km ( = 8.69 miles )
Projectile Density: 1740 kg/m3
Impact Velocity: 27.00 km per second ( = 16.80 miles per second )
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Results, from 1000km away:
The fireball appears 26.2 times larger than the sun
Radiant flux (relative to the sun): 86.2
Clothing ignites
Much of the body suffers third degree burns
Newspaper ignites
Plywood flames
Deciduous trees ignite
Grass ignites
Richter Scale Magnitude: 10.2 (This is greater than any earthquake
Re: (Score:3)
It's also worth noting that this assumes some sort of peaceful disassembly of the target, but that's not what happens. I've seen simulations of the destruction of asteroids with nuclear weapons before. First off, there's a massive shockwave that runs through it, which pulverizes the rock. Everything on the near side - or in some cases, through the whole body - gets heated as well. This causes it to outgas and radiate, acting like little thrusters, helping disperse the fragments into different orbits.
I mea
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You wouldn't even need the biggest nukes we've ever made, and those also have a ridiculous amount of mass requiring far more expensive and bespoke launch systems to get it where you need it.
A good ol' W88 from a Trident II would throw 450kt at it which would be more than enough to bust up and / or deflect a great many threats. And there's no reason we would need to use just one, when a Trident II carries more than one for it's intended purpose of vaporizing cities.
Sounds like we need to create some hardwar
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I've seen simulations of the destruction of asteroids with nuclear weapons before. First off, there's a massive shockwave that runs through it, which pulverizes the rock.
And those are hysterically optimistic scenarios. Explosives don't go "bang" in space, there's no atmosphere to create pressure so there's no shockwave. Unless you pack the bomb inside the object... which ends up just being a crappy thruster if you don't seal it shut.
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Nuclear bombs behave very different in space than on Earth. There's neither a huge shockwave nor fireball from the bomb itself. Instead, there is an *insane* X-ray flux, which can travel *extremely* far from the bomb (highly damaging even hundreds of kilometers away) if nothing is nearby. Whatever it hits, it heats up. The explosion, basically, comes from whatever is in the way of the radiation flux of the bomb - *it* blows up.
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Also don't forget that if you bust one rock into many smaller rocks, you have greatly increased the surface area by which velocity will be reduced by atmospheric drag, and also greatly increased the dynamic pressure applied to each and every fragment as the atmosphere thickens, causing fragments to heat and break up even smaller, increasing surface area more, etc.
And that's just from a kinetic impactor. Now put a chemical or nuclear explosive on there and we're talking about a big heap of gravel moving in
science reporting 2024: +/- 3 orders of magnitude (Score:2)
https://www.nasa.gov/solar-sys... [nasa.gov] ...as much as "1 million kg displaced..."
Says
To the NYT "...millions of tons" which, if you think even briefly, is pretty unlikely from a van sized object hitting anything at 22000 kph.
Sigh...this is supposedly the acme of American print journalism.
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I came looking for a comment like this... was going to post similar... "millions of tons"... really?
implications for planeterary defense? (Score:2)
So would you say... (Score:1)
Money quote from the paper abstract (Score:2)
"These findings suggest that Dimorphos is a rubble pile that might have formed through rotational mass shedding and reaccumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater."
So, yeah - slamming a probe at high speed into a loose pile of rocks could have a significantly different (and more significant) effect than slamming the probe into a
Disjointed space rock: Wost Band Ever (Score:2)
Okay I'll bite, if these are "disjointed" rocks and dust that are not a single big solid scary planet killer then why worry about us breaking it up?
From the description the thing is a bunch of broken parts.
Wouldn't these parts separate on their own once they get too close to an Earth size object and also suffer from more fragmentation from any interaction with an atmosphere?
I'm just asking cause I have no idea at all, maybe the XKCD could explain it which reminds me that I haven't checked XKCD for a long ti