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Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

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Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#51

Post by Modified3019 »

EA-3167 wrote: post #16
phkahler wrote: post #4

"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…

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.

https://en.m.wikipedia.org/wiki/Motion_camouflage

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#52

Post by alkyon »

dylan604 wrote: post #41
alkyon wrote: post #30

Earlier quoted context omitted.

I haven't done any calculations but wouldn't they use nuclear warheads to deflect it?

Maybe if this was a Michael Bay movie, but real scientists know that an Earth ending level event would just laugh at your nukes as it just flew on by. In the grand scheme of the cosmos, man made nukes are but a mere gnat at the picnic nuisance.

If it isn't the Moon but an asteroid of 100m radius then deflecting or breaking it apart is feasible.

https://www.llnl.gov/article/50716/new-nuclear-deflection-si...

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#53

Post by throwthrowuknow »

tedunangst wrote: post #40
throwthrowuknow wrote: post #25

Earlier quoted context omitted.

Cool but what’s its orbital period and how does this close pass effect future crossings?

Presumably irrelevant since we didn't care about the previous crossing.

We just discovered it, how could we know about the previous ones?

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#55

Post by funcDropShadow »

delta_p_delta_x wrote: post #45
mike_d wrote: post #21

Earlier quoted context omitted.

> 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 mi…

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 bar…

> About 5-10 years' warning would be enough time for a large nuclear device to deflect such an asteroid

The asteroid in this article was detected 2 weeks ago.

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#56

Post by delta_p_delta_x »

funcDropShadow wrote: post #55
delta_p_delta_x wrote: post #45

Earlier quoted context omitted.

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 bar…

> About 5-10 years' warning would be enough time for a large nuclear device to deflect such an asteroid The asteroid in this article was detected 2 weeks ago.

Precisely why we ought to step up our detection.

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#58

Post by kurthr »

dylan604 wrote: post #41
alkyon wrote: post #30

Earlier quoted context omitted.

I haven't done any calculations but wouldn't they use nuclear warheads to deflect it?

Maybe if this was a Michael Bay movie, but real scientists know that an Earth ending level event would just laugh at your nukes as it just flew on by. In the grand scheme of the cosmos, man made nukes are but a mere gnat at the picnic nuisance.

To estimate this order of magnitude. A typical (non MERV) 1.2Mt B83 in the active US nuclear arsenal would likely vaporize ~100m diameter hemisphere to deflect a relatively large 3km asteroid. Assuming an asteroid at 1-10 km/sec relative velocity 12 days out is 1-10M km away and earth is ~10k km across. So a deflection angle of ~1-10mrad is needed for a 3km (~10km3) spherical asteroid mass of ~10^13kg.

A 5E15 J/Mt 1000kg bomb with a half momentum of about 10^9 kgkm/sec could deflect an angle of 0.1mrad 12 days out. Half energy conservation would gives you a similar ~0.01km/sec dV, so you'd need >10x more time or >10x more 1Mt nukes for a 3km asteroid. It gets much worse for larger asteroids, but interestingly dV doesn't change quickly with relative velocity since the required angle falls as the velocity rises.

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#59

Post by dard »

phkahler wrote: post #4

"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…

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.

Re: Discovered June 16th, large asteroid to pass between Earth and moon on Saturday

#60

Post by dard »

pocketstar wrote: post #31
phkahler wrote: post #4

"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…

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.
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