Cool Science thread

[jono]

The logic is this: when you bump two things together in a frictionless environment they change course. They didn't really need to do this to show that the asteroid would move. Maybe to find out how much it moved, but whether or not was never in doubt. But the unaimed arrow never misses, so it's easier to declare success by claiming they're gonna check and see if it moved when they moved it.

I'm not objecting to the test. There are things they proved: namely the ability to do it. Cool. But the major achievement here is providing proof for people who thought this was hard to do. Deniers and such.

To address your earlier question: a planet killer that's pointed at us just needs enough time because any impact will change its course, it's just a question of how much. The earlier the impact the less is needed.

[J. Barron DeJong]

The logic is this: when you bump two things together in a frictionless environment they change course. They didn't really need to do this to show that the asteroid would move. Maybe to find out how much it moved, but whether or not was never in doubt. But the unaimed arrow never misses, so it's easier to declare success by claiming they're gonna check and see if it moved when they moved it.

I'm not objecting to the test. There are things they proved: namely the ability to do it. Cool. But the major achievement here is providing proof for people who thought this was hard to do. Deniers and such.

To address your earlier question: a planet killer that's pointed at us just needs enough time because any impact will change its course, it's just a question of how much. The earlier the impact the less is needed.

Wouldn’t proving out the targeting capability be the primary reason to do this test?

It’s easy enough to just hit the asteroid, but to actually change it’s trajectory you need to hit it at high speed to impart enough energy, and you can’t line up straight-on at it or it’s not changing it’s path, just it’s speed (I know, path is dependent on speed when gravitational pull is involved, not sure if it’s a factor here or not).

Seems non-trivial.

(I haven’t looked into this any further than reading a headline and watching the impact video, so potentially off base here.)

[neufox47]

^^I heard NASA has some decent engineers and physicists.


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[Supermoon]

Wouldn’t proving out the targeting capability be the primary reason to do this test?

It’s easy enough to just hit the asteroid, but to actually change it’s trajectory you need to hit it at high speed to impart enough energy, and you can’t line up straight-on at it or it’s not changing it’s path, just it’s speed (I know, path is dependent on speed when gravitational pull is involved, not sure if it’s a factor here or not).

Seems non-trivial.

(I haven’t looked into this any further than reading a headline and watching the impact video, so potentially off base here.)

They used an automated targeting system that locked onto the asteroid and did the guidance on its own. Pretty cool stuff and takes away the latency of long distance communications

[jono]

Wouldn’t proving out the targeting capability be the primary reason to do this test?

It’s easy enough to just hit the asteroid, but to actually change it’s trajectory you need to hit it at high speed to impart enough energy, and you can’t line up straight-on at it or it’s not changing it’s path, just it’s speed (I know, path is dependent on speed when gravitational pull is involved, not sure if it’s a factor here or not).

Seems non-trivial.

(I haven’t looked into this any further than reading a headline and watching the impact video, so potentially off base here.)

If we're talking about risks to prove out, I'm pretty sure you're right that the targeting was the top of that list. Which isn't completely trivial, but I'd guess it's more reliable than launch itself, so pretty high probability once it's on the way.

My point wasn't that this whole thing was meaningless, but that the repeated headline of "we hope it moved!" is nonsensical. They hit it, so its trajectory changed.

You can't actually change the speed of an orbital object without changing its trajectory, even if you impact it tangential to its orbit (straight on, as it were) because just slowing it down or speeding it up changes its orbit. But in the case of a real threat, just slowing it down (by itself, if that were possible) might be as effective as anything, since it would alter the timing of its approach to the Earth's orbit.

Or, in the case of a real threat, we might (but probably wouldn't) just tip it out of plane by 0.01 degrees so it goes over our heads by a few million miles a couple years later. There are just a ton of ways to do it, the important thing is spotting it in time and not wringing our hands over it. Which seems easy enough if you read science threads, but pretty significant if you read the political ones.

[J. Barron DeJong]

If we're talking about risks to prove out, I'm pretty sure you're right that the targeting was the top of that list. Which isn't completely trivial, but I'd guess it's more reliable than launch itself, so pretty high probability once it's on the way.

My point wasn't that this whole thing was meaningless, but that the repeated headline of "we hope it moved!" is nonsensical. They hit it, so its trajectory changed.

You can't actually change the speed of an orbital object without changing its trajectory, even if you impact it tangential to its orbit (straight on, as it were) because just slowing it down or speeding it up changes its orbit. But in the case of a real threat, just slowing it down (by itself, if that were possible) might be as effective as anything, since it would alter the timing of its approach to the Earth's orbit.

Or, in the case of a real threat, we might (but probably wouldn't) just tip it out of plane by 0.01 degrees so it goes over our heads by a few million miles a couple years later. There are just a ton of ways to do it, the important thing is spotting it in time and not wringing our hands over it. Which seems easy enough if you read science threads, but pretty significant if you read the political ones.

Agree that the ‘hope it moved’ part is weird.

Also, now that I’m not half asleep, seems like changing it’s path isn’t absolutely necessary, so a head on shot could be acceptable. If you slow it down enough, then Earth will have moved out of the way by the time the asteroid reaches it’s original ‘impact location’.

[subtle plague]

^^I heard NASA has some decent engineers and physicists.


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They're all hacks!

[jono]

Press statement video discussing the actual change in orbit (32 minutes versus a goal of 73 seconds minimum and hopefully over 10 minutes):

https://www.space.com/nasa-dart-aste...change-success

It'd be cool if they'd let the guy who commented that he saw a good impact coming as it came into view expand on that. I expect he also mentioned that the usefulness of the measurement is what it implies about the asteroid's density and impact characteristics (which could help improve guesses about future asteroids). He expected a collection of rocks and boulders to absorb more energy and it seems he was right.

The guy talking to the camera seems like he achieved the goals he stated at the start, too.

[MultiVerse]

‘pillars of creation’ nebula Hubble vs Webb

[PB]

Jeezo!! The universe has grown so much since Hubble!

[old goat]

That there are that many stars in whatever tiny section of the universe that picture includes is stunning and incomprehensible.

[JimmyCarter]

That there are that many stars in whatever tiny section of the universe that picture includes is stunning and incomprehensible.

And if you could zoom in on even the dark sections it would give you a similar view.

“You may think it’s a long way down the road to the chemist’s…”

[neufox47]

That there are that many stars in whatever tiny section of the universe that picture includes is stunning and incomprehensible.

I think a lot of those stars are galaxies.

[jono]

We're just going to ignore the 8 or 10 drives that obviously started a hard burn deceleration pointing right at us since the Hubble shot?

[PB]

We're just going to ignore the 8000 or 10000 drives that obviously started a hard burn deceleration pointing right at us since the Hubble shot?

FIFya

[MultiVerse]

And if you could zoom in on even the dark sections it would give you a similar view.

“You may think it’s a long way down the road to the chemist’s…”

"Space is big. You just won't believe how vastly hugely mind-bogglingly big it is."

Crazier still, there are probably galaxies in that shot moving away from us faster than the speed of light which means we'll never see them.

[ötzi]

Faster than the speed of light you say?

[MultiVerse]

Yep. Galaxies can move faster than the speed of light without violating special relativity. Special relativity is local. General relativity is motion in an expanding universe. So it's the speed of light plus the speed of light on a treadmill.

[Dantheman]

Faster than the speed of light you say?

From our perspective as a distant observer, yes. Beyond a certain distance from us space itself is expanding faster than the speed of light, so light from those objects will never reach us. Now, if you were a resident of one of those distant galaxies nothing in your local environment could exceed the speed of light same as here.

[Norseman]

The "expansion rate" is something that took a minute for my bottled mind to wrap... that it is an expansion per unit distance... about 70 (km/s)/Mpc. At small distances, we don't notice the stretching of spacetime... but for shit really far apart, even though matter only moves through local space at a few thousand km/s and light always moves locally at c, space itself is stretching apart fast af, faster than the speed of light beyond a certain separation, and we'll never see light from objects beyond a co-moving horizon of 19 billion parsecs, like Dan said.

[ötzi]

Well clearly if you were going the speed of light in one direction and I was going in the speed of light the other direction the distance between us would increase at twice the speed of light, but is anything itself moving faster than the speed of light? Ima say nope.

[Dantheman]

In it's own local environment, no. The point here is that since the tools we use to observe distant objects, EM radiation and gravitational waves, move at the speed of light the universe is fundamentally unobservable beyond a certain distance.

[MultiVerse]

Well clearly if you were going the speed of light in one direction and I was going in the speed of light the other direction the distance between us would increase at twice the speed of light, but is anything itself moving faster than the speed of light? Ima say nope.

What Norseman and DTM are talking about is space itself expanding. The distance itself is growing so special relativity no longer applies. It's called superluminal expansion. At the boundary of what is theoretically observable, the cosmic microwave background or outer edge of the Big Bang, things are moving away from us at 3X the speed of light.

[old goat]

I think a lot of those stars are galaxies.

Sure, but does it matter. I mean, what's a few hundred billion starts one way or the other.

Yep. Galaxies can move faster than the speed of light without violating special relativity. Special relativity is local. General relativity is motion in an expanding universe. So it's the speed of light plus the speed of light on a treadmill.

Treadmill? Now you've done it.

[jono]

Should it be the speed of light plus the speed of the truck carrying the treadmill? That feels like it makes more sense somehow. But I'm probably ignoring something about mirrors on the belt or SFT.