Comet in September 2015

Originally posted by twhitehead
Err, no, we have not done a full survey yet. Not even close.

I admit this is from 2012:
http://www.nasa.gov/mission_pages/WISE/news/wise20120516.html
" So far, an estimated 20 to 30 percent of these objects have been found."

I also recommend you watch this:
https://www.youtube.com/watch?v=efz8c3ijD_A

Yes. however BIG asteroids, 1km plus, that cross the Earth's orbit have almost all be found. [95+%]

Its the smaller hard to see stuff, that could still cause a massive tsunami, or flatten a city,
that we haven't pinned down.

I did post a link to that effect, last time this conversation came up.


We still need to do better, and spend more time/money on this... but if we are talking about BIG
killer asteroids... Those we've pretty much got pinned down.

Comets on the other hand...

Originally posted by googlefudge
Yes. however BIG asteroids, 1km plus, that cross the Earth's orbit have almost all be found. [95+%]

Its the smaller hard to see stuff, that could still cause a massive tsunami, or flatten a city,
that we haven't pinned down.

I did post a link to that effect, last time this conversation came up.


We still need to do better, and spend more time ...[text shortened]... IG
killer asteroids... Those we've pretty much got pinned down.

Comets on the other hand...

Why are comets harder? Hyperbolic orbits, in fast and out?

Originally posted by sonhouse
Why are comets harder? Hyperbolic orbits, in fast and out?

Comets come from the Oort cloud/Kuiper belt. [OCKB]

We have to date [to my knowledge] spotted precisely zero objects in the OCKB smaller
that minor planets. We know there are millions of comets out there, and we can see
none of them. [if we have spotted any such objects, the percentage of those discovered
out of those believed to exist is still effectively 0%]

Those that we see regularly we can predict. [and if close enough, track]

New ones, on orbits so infrequent that we haven't seen them in recorded history, or on their first
time into the solar system.... We find them when they start dropping into the solar system proper
maybe 8~12 months before they cross Earth's orbit [if they do].

Of course as you noted the probability of such an object hitting us in any given millennia is microscopic.

But it's the most likely scenario for a massive object we spot on a collision course without enough
warning to do anything about it.

Which means it's not something to worry hugely about.

Smaller objects that can still cause massive damage and casualties, but can sneak up on us...

Those are a much bigger concern.

By the time people realized what was happening they would all be in their bunkers and disappear.

As for doing something about it, could they land rockets on the comet and then strap them on and then ignite the rockets to change their tragectory?

NASA has already proven then can land on them.

Originally posted by whodey
By the time people realized what was happening they would all be in their bunkers and disappear.

As for doing something about it, could they land rockets on the comet and then strap them on and then ignite the rockets to change their tragectory?

NASA has already proven then can land on them.

That would probably be a really bad way of trying to deflect a comet.***

However it's far from the only options.

Which option will depend on how big it is, and how much warning we have.

If you want to do something drastic, the Orion project has a lot going for it.


*** It depends what it's made of. [among other things]

Originally posted by googlefudge
Yes. however BIG asteroids, 1km plus, that cross the Earth's orbit have almost all be found. [95+%]

http://en.wikipedia.org/wiki/Near-Earth_object

Still, that leaves maybe 50 or so we haven't found. That's a lot. Although I agree that the risk of them hitting earth is tiny.

Nevertheless, if one of them was on a collision course with earth, there is a pretty good chance we would not see it coming. Certainly we wouldn't automatically have the weeks or months you suggested earlier in the thread.

Maybe an astronomer here can tell us, if a 2km diameter NEO were headed our way, how long before impact it is visible to the naked eye? My guess: hours or minutes and that is assuming it is night time and you are told exactly where to look.

Originally posted by twhitehead
Maybe an astronomer here can tell us, if a 2km diameter NEO were headed our way, how long before impact it is visible to the naked eye? My guess: hours or minutes and that is assuming it is night time and you are told exactly where to look.

It depends from which direction it comes.

If the object is inbound towards its perihelium and nears the Earth, then we see it much easier against the night sky. When the object is above the horizon then the sun below the horizon.

If the object is outbound from its perihelium and nears the Earth, it's much harder to see it visually, because when it is above the horizon, so is the sun, and we cannot see it usually through the blue sky. If this is the case it is only detectable with the aid of a radar.

The question is - when are we able to do anything about the situation if we know an 2km NEO object will collide with the Earth? A week before? A month? A year ahead?

Or perhaps we cannot do anything anyway? Perhaps we will take the hit and deal with the consequences later? Every country for themselves? Those who have survived...

Who is able to do anything? And will it be necessary to involve politicians? Perhaps it is better to let NASA, or whomever, deal with it first and then send the bill to the rescue mission to the government?

Originally posted by FabianFnas
It depends from which direction it comes.

If the object is inbound towards its perihelium and nears the Earth, then we see it much easier against the night sky. When the object is above the horizon then the sun below the horizon.

If the object is outbound from its perihelium and nears the Earth, it's much harder to see it visually, because when it i ...[text shortened]... or whomever, deal with it first and then send the bill to the rescue mission to the government?

Well one thing that would happen, a lot of religious conversions, 'The end days are here brothers and sisters, let us pray' kind of stuff WOULD go on repeated a billion times over. Right, like we can pray away an incoming asteroid.

The truth is if we only had one year to deal with it we are history. 10 years maybe we can do something, launch a few dozen, hell, a few hundred missiles to try to steer it off course or blow the dam thing up if nothing else. A couple of 10 megaton bombs going of after penetrating few hundred feet deep would pretty much reduce it to a cloud of dust size particles which would still hit the Earth but do a lot less total damage, if that was the last resort. I would also think such an explosion would propel a good portion of the asteroid off course so a lot of it would slide by the Earth and just go on down the road.

The thing is, we are building defense systems right now, telescopes that don't have to be Hubble sized but just a bunch of them in orbit and on the ground patrolling the skies looking for outliers that suddenly appear, hopefully a couple billion kilometers out.

Originally posted by sonhouse
Well one thing that would happen, a lot of religious conversions, 'The end days are here brothers and sisters, let us pray' kind of stuff WOULD go on repeated a billion times over. Right, like we can pray away an incoming asteroid.

The truth is if we only had one year to deal with it we are history. 10 years maybe we can do something, launch a few dozen ...[text shortened]... the skies looking for outliers that suddenly appear, hopefully a couple billion kilometers out.

Nukes almost universally suck for anything over a ~100 meters across.

With 10 years notice we can shift it with a gravity tractor, or asymmetrically painting it... etc.

1 year out... turning it into a pile of rubble makes the effects worse.

Originally posted by whodey

NASA has already proven then can land on them.

Not NASA mate!

Originally posted by googlefudge
1 year out... turning it into a pile of rubble makes the effects worse.

I don't think so. A pile of rubble would burn up in the atmosphere. Also a well placed nuke could alter the course of the asteroid - but it would probably have to eject a significant amount of mass to achieve it, so you would want to get the nuke inside the asteroid somehow.

Originally posted by twhitehead
I don't think so. A pile of rubble would burn up in the atmosphere. Also a well placed nuke could alter the course of the asteroid - but it would probably have to eject a significant amount of mass to achieve it, so you would want to get the nuke inside the asteroid somehow.

Googlefudge is right.

An asteroid might miss the Earth, a shower of hundreds of smaller peaces will hit Earth. Only really small bits will be burned up in atmosphere.

The only way is to deflect the asteroid, and today we don't have the technology to do that.

Originally posted by FabianFnas
Googlefudge is right.

An asteroid might miss the Earth, a shower of hundreds of smaller peaces will hit Earth. Only really small bits will be burned up in atmosphere.

The only way is to deflect the asteroid, and today we don't have the technology to do that.

I suspect if an asteroid was discovered it would be hit with a dozen nukes, hydrogen bombs of 10 megatons, all set to go off at the same time but scattered over the surface with some of them being bunker busters that can penetrate a few thousand feet before detonation. The sum total of 120 megatons going off I would think alter the orbital course enough so 99% of the stuff would go by Earth scattered to the winds of the Solar system. The one percent left would still do significant damage but it would not be a civilization buster.

Originally posted by FabianFnas
Only really small bits will be burned up in atmosphere.

Rubble, is really small bits.

What size pieces do you estimate would cause a problem ie not burn up before exploding catastrophically or hitting the ground?

Originally posted by twhitehead
Rubble, is really small bits.

What size pieces do you estimate would cause a problem ie not burn up before exploding catastrophically or hitting the ground?

I'm not talking about rubbles, I'm talking about a crater producing meteors.
If you split an asteroid in a thousand peaces, then you will have a thousand hits instead of one big one.
Do you really believe a rock asteroid can be vaporized with a nuclear blast?