Asteroid lost 1M kilograms after collision with DART spacecraft
nature.com
nature.com
drives me nuts. How long did the orbit originally take? Without this information it very much obscures the point.
Edit: I looked it up
"Before the impact, the orbital period was 11 hours, 55 minutes. It now is 11 hours, 22 minutes. NASA's previous estimate, announced in October, was an orbital change of 32 minutes. The benchmark for success had been set as a change of at least 1 minute, 13 seconds."
So it reduced it by about 1%. Pretty cool.
Edit2: as pointed out correctly by @statusgraph it's actually close to 5%. I fumbled the math on that.
https://www.voanews.com/a/asteroid-bashing-spacecraft-phenom....
$ units '1-(11hr+22min)/(11hr+55min)'
Definition: 0.046153846However I just discovered that if you hit command spacebar and paste that into the spotlight search it gives the right answer! Spotlight has always done simple unit conversions but it didn't used to be able to do calculations with units in them. I wonder when that was introduced...
GNU Units is far more featureful (and useful IMO).
You can install that, as "gunits", using Homebrew.
The command to use it is `gunits` though.
It's trivial to find the actual package name using 'brew list | grep units'.
See note 2: <https://news.ycombinator.com/item?id=31449413>
So if Dimorphos would be an object orbiting the sun by itself, then its location in its orbit would be shifted by about an Earth radius over 10 years.
(In reality, Dimorphosis is paired with the 100x heavier Didimos, so their orbit around the sun was affected much less.)
However, I think that for such a small velocity change, it is a reasonable approximation to assume that the ellipsis around the sun stays pretty much the same, and only the phase of the object (i.e. where it is on the ellipsis at which time) is affected.
https://www.google.com/search?q=Double+Asteroid+Redirection+...
We once had an awesome IE bug where a style applied to a spinner made the whole page rotate. QA thought it was a prank.
First off, I thought that it would be cool if they rotated a proportion of 360 degrees equal to the proportion of the change in orbital time period to the previous orbital time period of the asteroid. Then I realized that it changed by around 5%, so that would be 360 * 0.05 = 18 degrees. Not really readable.
That's 2 minutes that I'll never get back, but it's left me amused for some reason. Heh.
top of the page
The Expanse, a board game based on the Syfy television series of the same name, focuses on politics, conquest and intrigue similar to the board game Twilight Struggle, although with a shorter playing time. The card-driven game uses key images from the show, along with action points and events that allow players to move and place "Fleets" and "Influence".
In more detail, players represent Earth's UN forces, the military of Mars, the rebels of the O.P.A., and the mysterious corporation Protogen Inc. Each player has special abilities that must be maneuvered to gain advantage. Players increase their control over the solar system using characters and events from the universe of The Expanse.
(There's also expansion, The Expanse: Doors and Corners, that adds new tech, leaders, the protomolecule, etc.)
The only problem would be finding a reasonably-priced copy as it appears to be out-of-print, which can lead to the price of second-hand copies going way up.
[0] https://boardgamegeek.com/boardgame/220792/expanse-board-gam...
- With goose down having a density of 0.00286 g/cm^3.[1]
- The area of a football pitch being roughly 0.714 hectares.[2]
You could cover one football pitch to a depth of nearly 50 meters:
You have: (1000 tonnes / (0.00286 g/cm^3)) / 0.714 hectare
You want: m
* 48.970637
/ 0.0204204
If you spread the feathers to a depth of 1 cm, you'd get roughly 5,000x more coverage, or 5,000 football pitches. Give or take.
________________________________
Notes:
1. Jing Gao, Weidong Yu, & Ning Pan. (2007). Structures and Properties of the Goose Down as a Material for Thermal Insulation. Textile Research Journal, 77(8), 617–626. doi:10.1177/0040517507079408 <https://sci-hub.ru/10.1177/0040517507079408> p. 624.
2. Football Pitch, Wikipedia, <https://en.wikipedia.org/wiki/Football_pitch>
I feel like there's a physics joke in here, assuming weightless feathers piled on a football stadium in outer space ;)
Then there's the prospect of a goose-down singularity. The ultimate soft-landing black hole.
How many football fields is it?
Chelyabinsk was only a 20m asteroid, yet thousands were injured and a lot of damage was done. It's not inconceivable that in the next couple decades, we could predict that sort of event years out, and send a (likely much smaller) redirector mission to give it a tiny push, preventing the asteroid from entering Earth's atmosphere.
What scares and fascinates me though is what happens when we start asking 'okay, but where is it going to hit, and how many of my voters live there?'
On the other hand, getting a near-miss asteroid to orbit Earth instead means taking it from above escape velocity (11.2 km/s) to an orbital velocity, which means at least a thousand times more delta-V (more like 4 km/s). And that's the easy case -- getting an asteroid from the belt to fall toward Earth is another several km/s on top of that. Besides, ejecting 1M kilograms into a busy Earth orbit in order to slow the asteroid down sounds like a pretty scary idea. Especially since we'd have to do it hundreds of times for one asteroid.
So no, it wouldn't be the same technology at all.
And if it's the former, giving it a small bump is just as likely to put it on an actually-collision course as not doing anything at all.
There’s at least a plausible need there, what with the whole “don’t want to slam an asteroid into the planet” problem.
Mining is still an utter fantasy. It’s completely economically unviable to mine anything from an asteroid and bring it down the gravity well, and we have close to zero ability to actually mine and manufacture anything in space. We are a long long long time away from that.
That said; what the bigger issue - for in situ operations, the distance to get the raw materials or just doing anything with the raw materials at all? Is it going to be - we could do anything at all but going all the way past the orbit of Mars is too much trouble - or - Getting to a rock past Mars is easy but it's hard to do anything practical with it (compared to just getting it off Earth presumably)
I got no clue as to which way it could go but it doesn't seem a question that answers itself to me.
It's either the guests at the restaurant at the end of the universe.
Or just a universal peanut gallery that we all can imagine we belong to.
Edit: I mean gigagram
Did you mean gigagram?
Human brains sure do funny things sometimes.
"one million kilograms" = one gigagram
"4.3-billion-kilogram" = 4.3 teragram
"tens of thousands of kilometres" = tens of megametres.
I don't understand the media's reluctance to use large SI prefixes for mass and distance, when they'll happily use them for electrical units.
Thus it's normal to use e.g. 1e6 kg rather than 1e9 g.
OTOH, 1KHz has no basis in physical reality for normal people but they know 1KHz is 1000x faster than 1MHz so it works nicely for things like "is my new computer faster than my old computer" (at least a decade ago, I don't see clocks advertised much at all anymore).
It stops on the ton, though - “40 thousand tons of grain” - gigagram isn’t used.
Re kHz, I think most people understand frequencies we can hear. (1 kHz is close to a high C note). MHz and GHz are radio frequencies.
Only place where I've witnessed it's use is during my own personal musings while sitting on the loo. Same goes for money. "Gigadollars" has a nice ring to it but it's not used :(
There are other units of measurement when the numbers get really big, like AU, lightsecond/minute/year, Solar Mass, etc. I'm no scientist, but I also think when you get to the astonomical scale, order-of-magnitude relative measurements is more useful knowing a galaxy's mass to the nearest gram.
Case in point, people might think you are conflating nuclear bombs and mass if you say "this ship weighs 5 megatons".
Also depending on who you ask, gigagram either sounds like way more, or way less, than 1000 tons.
And for scientific writing, 1e9g is about as clear and explicit as it gets.
Ah, the wonders of the imperial system ;-)
Also, ChatGPT trivializes sarcastic responses that involve a bit of math.
[1]: https://www.esa.int/Space_Safety/Planetary_Defence/NEOMIR_fi...
I expect that a 90 degree angle would maximize the effect but would also make it hardest to hit the target.
They hit it "head on" ... or you mean the actual angle?
> Other work Ernst and her colleagues are doing recreates the impact itself. They calculated that the spacecraft flew in on a trajectory about 73 degrees above the local surface. "So not quite vertical, but pretty close," she said.
https://www.space.com/dart-asteroid-smash-mission-impact-det...
speak for yourself.
The best way to deal with the inevitable Martian uprising is to eliminate Mars before it is ever colonized.
If anything, these few days have shown to me that many on HN don't seem to get the metric system at all. Broken math and silly conversions everywhere, baby
Just this week we had the highest rated comment present completely incorrect kg to ton conversion: https://news.ycombinator.com/item?id=34955578
Who cares, though, right? What's important is sounding right
It's a gigagram, not a milion kilos
The other is lalaland non-sense.
I'd have even preferred "Billion grams" over gigagram. Although a gram is really hard to intuit about, since it's basically just too small. I can probably reliably tell you if an object I pick up weighs 1kg or 2kg, I probably can't reliably tell you if it weighs 1g or 2g.
A triangular spaceship is not necessary.
Also, this mission was to demonstrate could move asteroid without large explosion. There is fear that most asteroid are loose rubble and would be blown apart by blast.
They seem to want just three unit scales, "smaller than me", "the same size as me", and "larger than me." They will fit the entirety of their experience and frame of reference into these three scales, even when they know there are other options.
It's probably the reason they punted and let a _kilo_gram be a base unit in the first place, and why everyone represents the distance to the sun in kilometers instead of gigameters; even though they round the kilometer figure down to a point where gigameters would clearly be the most warranted.
All of them??
Not quite - it's so that the system is coherent.
https://en.wikipedia.org/wiki/Coherence_(units_of_measuremen...
which makes a whole bunch of other things simpler. The other option to meter-kilogram-second would have been the centimetre-gram-second, but then you're not using the metre as your base unit for length. Scale is probably the reason for picking MKS over CGS, but it's only moving the weird-base-unit problem around.
ISTR reading once that MKS has coherence advantages over CGS with regards to electromagnetism (probably current), but I can't find the reference now.
The point is, it's obvious that they didn't define the system on first principles, but allowed "creature comforts" to creep into the scope of the system.
For example the needless definition of Hz which conflicts with radians, and the needless definition of the unitless mol. These are obvious conveniences. They're not first-class members of the system.
Anyone within one or two hundred miles of the impact site would have an incredibly bad day, but it's not civilization-ending.
The Chelyabinsk meteor, FYI, weighed ~12M KG.
If the impact speed were ~30 km/s [1], breaking it up in the atmosphere through friction would create about...
E = MV^2/2 = 3.87 10^18 joules.
For contrast, the energy released by the Tsar bomba was 2.45 * 10^17 joules. The Tunguska meteor impact was something on the order of ~1 * 10^17 joules.
Even if much of the energy dissipates in the upper atmosphere, and does so over multiple seconds, I'd say that anyone within ~150 miles of the point of 'impact' will likely have a very, very, very bad day.
[1] Which is a pretty bad case. The Chelyabinsk meteor was traveling at ~18 km/s - a 30 km/s impact would be close to a 'head-on' collision.
That would be a fun sci-fi story.
I presume that if it wasn't such a loose collection the result would be quite different.
Given that it is a loose collection it wouldn't be a real threat to earth anyway (if for instance it was heading towards us) because that would cause it breakup in the atmosphere easier.
they seem to be surprised by these equations.. I thought this was all fairly established science.
> The impact ejected at least one million kilograms of rock from Dimorphos’s 4.3-billion-kilogram mass.
It does make sense to develop spacecraft so it can be launched quickly without going through years of development. Maybe build two and test one out. Then we would be ready to build more if needed.
Launching Project Orion from the ground would dump a ton of radioactive fallout. Unfortunately, it is expensive to launch with rockets because of the heavy plate and having to assemble it.
Launching it from orbit will knock out most of the satellite and could cause EMP over wide area. It doesn't do any good if you deflect asteroid, and one this size would only cause regional damage, if destroy civilization.
The Starship is big enough that can launch spacecraft with a few nukes and rocket to reach asteroid. Assuming that Starship is being launched regularly, then launching or building the spacecraft would be sufficient.
This whole mission of colliding with asteroid was done because it is uncertain if nukes could be used to deflect asteroid. There is a danger that nuke would blow the asteroid apart instead of deflecting it. For one this size, that probably wouldn't be a problem but turning larger one into few smaller ones would be bad.
1) it was predesigned/ready
2) the asteroid was too close and you needed it there as fast as possible
because as the original article points out, the closer it is / more deflection you need, the more firepower/energy you need. Heck as a last resort you can use the ship to simply push the asteroid.
You're going to take a bit of fallout (and there was lots of work in orion in making the "cleanest" explosions) vs an asteroid strike... you'll take a bit of fallout.
Orion is the only ship design with current tech (heck 1960s tech) that can get there fast enough with enough payload. You know, if one was ready, etc etc etc.
I'm not saying it would be feasible, just that within the "oh my god asteroid" scenario it might be the only design that could work.
It's obviously debatable, but Orion might be able to be chucked together in a short time. You don't need to optimize weight, you just need a big shield and the nukes, and a nuke firing system. (you know, just that).
The test one is small enough that it wouldn’t do that much damage. Worth the expense to send spacecraft to divert something that could destroy a city. Not worth wrecking civilization to protect a city. Most of asteroids we haven’t detected are the smaller size.
Finally, Orion isn’t necessary. Nukes are small, you could send up a bunch in Starship. We could also come up with better propulsion, like nuclear rocket, that would be useful. Orion would be stupid expensive for very unlikely contingency.
The only real thing that Orion has going for it is that it is brutally effective. If we need something to launch fast, it might not be that much on civilization level effort to get a big honker going.
Again, big IFs.
That’s not even an asteroid speedbump.
the original A bomb was 17 kilotonnes. explosive equivalent. I have no idea what a kilotonne of friable matter entering the atmosphere represents, in explosive equivalent.
> The impact ejected at least one million kilograms of rock from Dimorphos’s 4.3-billion-kilogram mass.
Just say "lost one gigagram"!
"[Dimorphos] ... seems to be a loose pile of rubble barely held together by gravity — whose surface would probably shatter spectacularly when DART hit it.
DART [impacted] Dimorphos at more than 6 kilometres per second. The impact caused the asteroid’s orbit around another [larger] space rock [Didymos] to shrink — Dimorphos now completes an orbit 33 minutes faster than before the impact.
The impact ejected at least one million kilograms of rock from Dimorphos’s 4.3-billion-kilogram mass. The debris formed a tail that stretched for tens of thousands of kilometres behind the asteroid. Various telescopes watched over weeks as the tail shifted and evolved under the pressure of the Sun’s rays; the Hubble Space Telescope even detected a second tail, which had disappeared by 18 days after the impact.
One factor [in successfully changing Dimorphos's orbit] is that the spacecraft hit a spot around 25 metres from the asteroid’s centre, maximizing the force of its impact. Another is that large amounts of the asteroid’s rubble flew outwards from the impact. The recoil from this force pushed the asteroid further off its previous trajectory. Researchers estimate that this spray of rubble meant Dimorphos’ added momentum was almost four times that imparted by DART4."
It's good that this technique worked on a "loose pile of rubble", but I'm not sure we can assume all asteroids are composed in the same way. A denser rock of iron or similar might be more difficult to divert.
What we do need is time. If the asteroid is weeks away, we've got a great chance of deflecting it. If it's hours, we'll certainly be struck.
Alternatively, if we knew a particular asteroid would threaten us in one decade, that one decade might be enough to do something about it. Many asteroids won't give us that sort of notice, since orbits can have century-long periods.
I'm still intrigued at a possibility of detonating a megaton-classl nuclear device at a very close proximity to a tough metal / rock asteroid. Consider the blast happening close to the surface but on the "side", as much off-center as possible. Won't it evaporate enough material for a jet of it to significantly push the orbit sideways, thus shifting it enough away from a collision course?
(Much if the energy will anyway be wasted on beams / jets that are symmetrical and thus compensating each other.)
May be, or may be not. But I think it doesn't make it impossible to divert them, even if it is more difficult. The idea is to struck it in a carefully chosen moment, when small differences in delta-v can translate into huge differences in a probability of the impact with Earth.
A pile-of-rubble kind of asteroids seemed the most troublesome, because when you shoot it bullets can just pass through. Or asteroid can break into a lot of pieces amplifying a probability of the impact with Earth: one of pieces can strike Earth and it is can be enough for a catastrophic consequences. But the outcome of an experiment assures us that it is not a case. A lot of small boulders fly on a lot of different trajectories, but they are small, they will burn in atmosphere if they get here.
ps. I feel it is important to state that I'm not an astrophysicist or someone like this, so all written above is my own opinion that can be completely wrong.