"Maybe the big take-home point on this one is it's a pretty big object and it was only found 10 or 12 days before closest approach,"
I've said this before. The way they find these things is looking for movement against the distant background / starfield. That works pretty well for finding things, but there is one problem. Any object on a collision course with earth will NOT be moving across the background in the days leading up to the collision. It will appear stationary against the stars, so will not be detected by these systems. To some extent it also doesn't matter that we are orbiting the sun because while near, earth and asteroid will be in the same accelerating reference frame.
Another way to model it is to think of firing a projectile from earth into deep space and see how that tracks against the background. That'd be the reverse scenario and there will be no relative motion until it's far enough to not get the same influence from the sun.
What you're describing is known as Constant Bearing, Decreasing Range (CBDR), https://en.wikipedia.org/wiki/Constant_bearing,_decreasing_r... and generally doesn't apply to to the case of a nearby asteroid on a collision course with Earth. For the parallax created by our orbit to be negligible, the object would have to be very distant.
Sounds related to motion camouflage, which dragonflies use to hunt. Allows them to appear stationary, with the only sign they are on an intercept course is looming as their image slowly grows larger.
CBDR only requires constant velocity. Similar triangles are all you need. On short time scales even orbits are approximately straight. It still applies and may well be the reason this one was missed until so close.
This is an incredibly naive approach. All asteroids emit light in the infrared, to detect and track asteroids just takes an infrared telescope making apparent motion against any background completely irrelevant. NASA is working on this: https://en.m.wikipedia.org/wiki/NEO_Surveyor
I work on NEO Surveyor, I replied to the parent comment largely agreeing with you, however I wanted to mention that we do rely on apparent motion for determining if a source is moving (asteroid/comet). However IR is ideal for spotting asteroids for a few different reasons, a big one is that asteroids have a wide range of surface brightness. Think bright concrete to black coal, so in the visible spectrum a 100m light stony asteroid can be just as bright as a 500m coal colored one. It is very difficult to determine size from the brightness alone. However in IR everything is approximately the same temperature (largely proportional to the distance from the sun), so these things all glow in the IR directly proportional to their diameter.
>It will appear stationary against the stars, so will not be detected by these systems. To some extent it also doesn't matter that we are orbiting the sun because while near, earth and asteroid will be in the same accelerating reference frame.
I dont think that is true aside from the case where the asteroid vector is the exact opposite of the earth.
Even if the earth and the asteroid are in the same accelerating reference plane, the background is not.
If you have two race cars going in around a track and at one from the other, it still appears to be moving relative to the stands.
> If you have two race cars going in around a track and at one from the other, it still appears to be moving relative to the stands.
Right. Now put the stands on another planet and you start to understand the problem.
We need to be able to see an asteroid at a minimum of of 3-4x the distance between the earth and the sun to have enough time to do anything about it based on the average speed of 40k mph.
Now keep in mind that at that distance you are looking for something as "tiny" as 60 miles across, the accepted size that would unquestionably end life on earth. Something ~1km across would cause mass famine. In 1908 an asteroid less than 200 feet across flattened 80 million trees over an 830 square mile area.
Even if the stands are far away, even light years away, you pan through 360° every year. The fact that the background is far away means that it moves even quicker relative to a nearby object in a rotational frame.
If you spin around in a circle, hold your hand out and look at it, it will be moving very quickly against a distant background, like the horizon.
My point is that the distance to the background helps detection, not hurts it. If the background was nearby and co-rotating around the Sun, detection would be a near impossible.
Firstly, the several different unit systems in this comment give me a headache.
Next,
> We need to be able to see an asteroid at a minimum of of 3-4x the distance between the earth and the sun to have enough time to do anything about it based on the average speed of 40k mph.
Not really. The important variable is not distance, but rather the mass and velocity vector.
There could exist an asteroid that is currently barely 1 moon orbit away (~400 000 km), but has a velocity vector almost equal to that of Earth's. This asteroid could then be predicted to impact upon the next close encounter with Earth.
In general, the more distant the predicted impact date, the less the delta-v required to push the asteroid off its current path and avoid an impact in future.
> Now keep in mind that at that distance you are looking for something as "tiny" as 60 miles across
NASA and ESA have databases of some 35000 near-Earth asteroids, and many of them are orders of magnitude smaller than 100 km[1]. Our detection capability has significantly improved since efforts first started in the 1980s.
Asteroid impact avoidance is amongst the few natural disasters humanity has the technological, financial, and engineering capability to completely avoid.
We have both the firepower and the lift capability (if not now, then in the near future, dictated by the urgency of the asteroid impact) to deflect even a 12 km, Chicxulub-size impactor if detected sufficiently early. About 5-10 years' warning would be enough time for a large nuclear device to deflect such an asteroid, which would be a major achievement for humanity.
Really, we should have a moon base, 6 years ago. This makes me very anxious. We have all our eggs are in one basket.
As for detection there's some of them are coming from the other side of the sun, the one that Jupiter throw at us, It would be good to have a few more detection at L4, L3, It would be good to know what part of the earth is going to get hit. And evacuate them. Having a moon base off planet would be able to make all this coordination possible, because the amount of chaos that it would cause.So it needs a large gain antenna like the one that's in Australia that the Intuitive Machines lander low gain antenna was able to make two way contact with. The same one that was used to televise the Apollo missions.
I just can't, I can't emphasize enough the advantages to working and living on the moon. Shift all energy production all these experiments terraforming and such eco engineering To there just terraform one crater and start growing some plants . It shouldn't have been done so many years ago. It could be done with one pre-supply mission with a Falcon 9 and an Oberth Pumping orbit and then followed by a manned mission. Where the falcon heavy and dragon? The mayby recovered the second stage on the moon.
It's just been over thought, overly planned. I mean, against nature, we're nothing. It's impractical to think that we can. can't stop a meteor. We're never going to see it coming. We don't have five years to plan that I mean. I'm even surprised that any of the simulations converge . You know, don't need to be adjusted. We don't even have gravity physics consensus.
I can't be done on a Earth because it becomes someone else's problem far away because it usually backfires diffuses through the air in the sea. It does not happen on the moon. So I mean, you can make this terrible meltdown reactor and then just leave. Leave it in a crater. Those gamma rays are not going anywhere except up. I just put a thing that says no fly zone over it.
Seems that we put a lot of effort and money into these overly ambitious projects like going to Mars, which has absolutely no practical advantage when leaving the moon up there, unused. I mean, this isn't about Space tourism t's about survival. making the moon an exporter. It has everything that we don't have, but that we're running out of, rare earth minerals. oxygen. The only thing that's missing is carbon dioxide. And we're going to be bringing that. And as soon as the plans we grow up there, using that 24/7 solar. solar power. and have a greenhouse. All we have to do is breathe the air they make. They can extract oxygen from the regular and we can do it too with heat. And we can sublimate iron and build stuff. We can, we can figure out how to sublimate titanium from titanium dioxide. I mean, the conditions are so ideal. We we would go there cause it because we think it's easy. When we go there because we thought it would be easy, right? But right now, I think we think is is going to be a lot harder than it really is. There's sweet spots on them. Lunar S pole that are just 20 degrees C. To send stuff back down to Earth, you just have to shoot it at 2400 kph The railgun. will fall back down to Earth will take long. Superconductor is in permanently shadowed craters are almost sort of Ambient temperature. if not already. Type B, type 2 or whatever.
I actually work on NEO Surveyor telescope (surveying for dangerous asteroids), writing the simulation code use to track expected performance. So simulating +20 million asteroids and what will be visible during the mission. Motion is how we determine if there is an asteroid or just some static sky source (IE: star).
However your comment is not correct, everything moves, even in the days leading up to a potential impact things are constantly in motion. The only asteroids which appear stationary actually tend to be quite far away and just happen to be moving at just the right speed.
Things which are close to us, even impactors tend to have large angular velocities, very VERY few things come directly radially in. A part of this is that the Earth is rotating, if you are familiar with the parallax effect then the Earths rotation causes parallactic motion of the asteroids when close. IE, take a photo, wait 4 hours, and you, an observer on Earth, has now moved. The geometry has to be just right for close objects to be stationary, and a different observing position on Earth (or space) will see the object moving even if you see it stationary.
Earth is about 8000mi across. The moon is about 239000mi away. Looking at it from opposite sides would be about 0.016 degrees of angular displacement. And that's a couple days from impact.
>> So simulating +20 million asteroids and what will be visible during the mission.
How many impacts do you simulate? These are the ones we care most about, and I still think they will be the hardest to detect.
Here is a simulation I did in response to your comment, this is ~6 million impactors and their on sky velocity as they approach Earth. Dotted black line is our expected detectability limit, anything to the right of that is detectable.
On sky velocity is measured in degrees / day.
Thanks, that's really cool. And the detectability line is under 0.01 degrees per day, so the parallax from opposite sides of the earth is well within detectable at lunar distance. You also confirm that the detectability (due to motion) is dropping as the time to impact decreases, but this is apparently not a problem. Leave it to projects run by physicists to have exquisite measurement precision ;-)
thanks I think that that's really kind of scary, but motivational as to putting up a moon colony so that we just have a 2n base. H But I have. have a few questions. If you've got a minute, must be nerve wracking to work there.
looks like it would be coming from the sun's direction because it is kind of a. dominating force , but i wonder why a couple days after a flyby is when they are often detected. Is it just because the sun is able to light/heat it up more?
Also, I'm wondering what software you use to to do the modeling for one. And if it's open source. and if it's reversible , so you can back it up and fix positions when new datas comes in
https://en.wikipedia.org/wiki/Fermi%E2%80%93Pasta%E2%80%93Ul...
That was done at Los Alamos with a Maniac and the first version was fixed point, but as you can see it looks chaotic, but then there's a semi ring. There's a repetition. So I I'm guessing that's why that we care about are flybys. They go by once and at some point they'll come back.
This might help if you click the reversible to use fixed point. you can go back and and retrace.. the steps even with a rough integration.
as soon as you have a correction for any of them, you can place that correction. By reversing the entire model or the solver.
I'm guessing there's such a cloud of objects you use something like. Fluid solver, even if you had to do that to some other body, then may have had an influence on the body that's under investigation, and you have new data for that, it might help to make the prediction more accurate. And without introducing any discontinuities in the model, if the past positions help determine the future ones going back.
You can see here (Stam) that even though it's chaotic like an N body problem, there is a semi ring and it repeats. So what appears to be maybe chaotic over time would be periodicity of the lineup. Then it seems, though, when certain planets are lined up. It's more likely that it's gonna have this this. confluence of Of gravitational influence. that will bring it in our direction. I'm thinking thinking Jupiter, Mars, the moon and the sun and the earth in between. Jupiter all the way to the earth is basically one orbit. At that velocity S50 kilometers uh second.
Also, I wonder if. the if something hit the back of the moon, would we even notice that until we go to the back of the moon or with a lunar reconnaissance or over and we find some craters that have direct impacts so that it would have could have been our planet killer. I'm sure there's quite a few up there with some some markings that will indicate that it probably injected some heavy metal right at that very crater. A direct hit. The moon was in the way because the the lineup of the two bodies ,that caused the dynamic in the first place. I'm guessing here.
One more reason for deep space telescopes. A PHA about to impact will not have much movement in relation to the background stars when seen from Earth, but will be moving when seen from a different vantage point.
I've said this before. The way they find these things is looking for movement against the distant background / starfield. That works pretty well for finding things, but there is one problem. Any object on a collision course with earth will NOT be moving across the background in the days leading up to the collision. It will appear stationary against the stars, so will not be detected by these systems. To some extent it also doesn't matter that we are orbiting the sun because while near, earth and asteroid will be in the same accelerating reference frame.
Another way to model it is to think of firing a projectile from earth into deep space and see how that tracks against the background. That'd be the reverse scenario and there will be no relative motion until it's far enough to not get the same influence from the sun.