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astromark
2010-May-27, 04:33 AM
Almost reluctant enough not to ask. But, could a dark object of some size. Say 30 or 40 km in diameter approach earth from a angle where we might not 'see' it. Like from a opposite side of the solar system and than from behind the sun...
Being of a non reflective dark rock... or would other methods of detection declare it to us. No, not a real concern... just a question of interest ?

CaptainToonces
2010-May-27, 04:39 AM
I would say unlikely.
Our blindsides lay mainly in the skies of the Southern hemisphere because we have fewer telescopes there. The Sun obscures only a small part of the sky because we are quite far away from it, and given a year's time we make a full course around the sun giving us a complete view of all directions around us. Even in just a day's time, the Sun has moved 1 degree off its previous position in our sky, and the amount of sky it obscures has a radius of either less than or not much more than 1 degree of arclength.

astromark
2010-May-27, 10:10 AM
Thats cleared that up nicely, its what I thought and am now pleased that I bothered.
So to all those 2012 doomsday proponents... Who have wanted to argue this with me... " Naa na na naa na na !"

WayneFrancis
2010-May-28, 04:16 AM
Send any of the doomsday proponents to me. I'll buy their houses off them in advance for 5% of the market value. So if they have a half million dollar house I'll pay them $25k to sign a contract saying that I've bought it but they can live there free of rent until Dec 13, 2012. I'm also willing to buy gold, luxury cars and any blue chip stock they may have at the same 5% of market values all to be handed over to me on Dec 13th. This will give them extra cash to live up the last year of their life.

Spoons
2010-May-28, 04:50 AM
Don't go to Wayne, people, I'll give you 6%!

astromark
2010-May-28, 08:10 AM
Actually I wanted to send them some place...
I had fifteen people in the Observatory and just three of them insisted that we are facing the end of humanity and the whole 2012 thing spewed forth... No, I do not have the speed of mind to offer to purchase their estates. Good on you Wayne...Lol.
I did have a victory as such because I led with the no object has yet been observed and it would need to be inside the solar system by now if its going to get here by December 2012. Which is why I asked this question.... just backing up my own thoughts.
Then I dribbled on about the Central Americas indigenous race that had a want and need to display a calendar...we only print ours a year or two in advance. Does that mean.... Naaa. That would be silly.

Nereid
2010-May-28, 08:37 AM
Almost reluctant enough not to ask. But, could a dark object of some size. Say 30 or 40 km in diameter approach earth from a angle where we might not 'see' it. Like from a opposite side of the solar system and than from behind the sun...
Being of a non reflective dark rock... or would other methods of detection declare it to us. No, not a real concern... just a question of interest ?
If it's truly dark, it will emit blackbody radiation; if it's at least a few tens of K, it could be detected by something like WISE.

There is indeed a blindside, but it's mostly within ~20o of the Sun ... and if this object's trajectory is dominated by gravity, and on a collision course with us, it's highly unlikely it would stay within that cone of blindness.

If it's not totally dark, it will reflect the Sun's light; even if only 1%, it would still likely be picked up by one of the various sky patrols.

So, is it possible to dream up a trajectory, for either a totally dark 40 km diameter object or one with an albedo of only 1% (say), on a collision course with Earth, that the existing facilities we have would miss?

I think the answer is yes, such trajectories do exist (think of an Oort cloud black comet, or a stray black asteroid from the Milky Way halo).

astromark
2010-May-28, 08:59 AM
~20deg., To be on such a close path past the Sun... would that be possible, and still get near Earth ? I would think the Solar mass would turn it.
Yes, I can see it as possible. and still I will not sell to Wayne...

Nereid
2010-May-28, 02:26 PM
I think it's worth looking at this (general) question in the light of what we already know about potential 'dino-killer' impactors.

First, dino-killer asteroids.

All such have already been identified, as in those large enough to cause global devastation within the next century or so (with, perhaps, one caveat), and we have a very good handle on the distribution of sizes, compositions (well, surface compositions anyway), albedos, orbits, etc. The only unknown (AFAIK) is the likelihood of such an asteroid being created by perturbation of its orbit (several potential causes) or by a collision involving a bigger asteroid.

Next, dino-killer comets.

These could come from perturbation of the orbit of a Centaur, a Kuiper Belt object (defined broadly), or on Oort cloud one (the first two would become comets once they got close enough to the Sun). The good news here is that comets tend to be anything but dark! So they will surely be discovered while they are quite some distance from us (though really unfortunate coincidences might let one get close); my WAG is there'd be at least a year's warning.

Finally, extra-solar system dino-killer objects.

The best news here is that, to date, no such objects have been observed (the biggest extra-solar system objects observed to date are some interstellar dust grains, though perhaps some interstellar meteors may have been a bit bigger); the worst news is that past performance is not a perfectly reliable indicator of future performance.

Based only on what's well established, today, from astronomical observations (and astrophysical models), what doomsday scenarios can you come up with?

Ken G
2010-May-28, 06:17 PM
One point to add-- I believe it is very possible that we could get whacked by a dark, small (30 - 40 km) asteroid (indeed, any normal asteroid is perfectly dark enough) that we never saw coming. It is also extremely unlikely, based on Nereid's point about the rate that these things appear (which do you trust more, our current inventory of what's out there, or the very clear historical data about how rarely such impacts occur?). The reason we could get whacked without warning is that we are constantly discovering new small Earth-crossing asteroids, and we tend to see them in the antisolar direction. That means about half of them are on their way in toward us, but the other half are on their way out-- after already missing us! Had any of that latter half not missed us, we'd never have seen them coming.

I've been told the reason they tend to either approach us from the antisolar direction, or pass by us in that direction, is that Earth-crossing asteroids tend to be on circular orbits that are very similar to the orbit of the Earth. If they have less circular orbits than the Earth does, their orbits are like an Earth orbit that has received a "kick", and is oscillating radially in and out relative to the Earth. If they have more circular orbits, then it is like the Earth is radially oscillating, relative to them. Either way, half the time they appear to be "coming out of the Sun" when they are inbound-- like the Red Baron. I'm not really sure why this is the case, or even if it is the case, but I was told it by an astronomer.

As for 2012, it is very unlikely that the Mayan calendar actually ends on that date, there is no evidence that the ending of their calendar was intended to signify anything but the end of a calendar, and the Mayans did not even know asteroids existed, let alone have any special knowledge about their orbits.

Nereid
2010-May-28, 10:24 PM
One point to add-- I believe it is very possible that we could get whacked by a dark, small (30 - 40 km) asteroid (indeed, any normal asteroid is perfectly dark enough) that we never saw coming. It is also extremely unlikely, based on Nereid's point about the rate that these things appear (which do you trust more, our current inventory of what's out there, or the very clear historical data about how rarely such impacts occur?). The reason we could get whacked without warning is that we are constantly discovering new small Earth-crossing asteroids, and we tend to see them in the antisolar direction. That means about half of them are on their way in toward us, but the other half are on their way out-- after already missing us! Had any of that latter half not missed us, we'd never have seen them coming.

I've been told the reason they tend to either approach us from the antisolar direction, or pass by us in that direction, is that Earth-crossing asteroids tend to be on circular orbits that are very similar to the orbit of the Earth. If they have less circular orbits than the Earth does, their orbits are like an Earth orbit that has received a "kick", and is oscillating radially in and out relative to the Earth. If they have more circular orbits, then it is like the Earth is radially oscillating, relative to them. Either way, half the time they appear to be "coming out of the Sun" when they are inbound-- like the Red Baron. I'm not really sure why this is the case, or even if it is the case, but I was told it by an astronomer.
I'm not so sure about this, Ken G.

Small asteroids - even up to ~1 km diameter? - may indeed still lurk in near-Earth orbits.

However, bigger ones have all already been found - they are pretty easy to spot at all points on their orbits except when within some modest angle from the Sun (~20o?), they show up in the various space-based IR all-sky surveys (e.g. WISE), etc.

The small ones escape notice because they are below the detection threshold (brightness) except when very close to Earth, and, as you say, they are then picked up when coming 'out of the Sun' just as much as otherwise.

I suppose an extremely low albedo, largish, asteroid (aka very dark) might slip by, but then why would there be such an object? After all, no such incredibly low albedo asteroid, of any size, has been found anywhere else (and the space-based IR surveys would certainly have found any big ones; being extremely dark means they'd radiate as an almost perfect blackbody whose temperature is in equilibrium with the solar radiation incident on it).

Ken G
2010-May-29, 06:52 AM
I'm not so sure about this, Ken G.

Small asteroids - even up to ~1 km diameter? - may indeed still lurk in near-Earth orbits.

However, bigger ones have all already been found - they are pretty easy to spot at all points on their orbits except when within some modest angle from the Sun (~20o?), they show up in the various space-based IR all-sky surveys (e.g. WISE), etc.You could be right-- 30 km didn't sound all that big, but I guess it's a doomsday asteroid-- I'm probably thinking more in terms of the 1 km versions, that would be unpleasant if you were under them.


The small ones escape notice because they are below the detection threshold (brightness) except when very close to Earth, and, as you say, they are then picked up when coming 'out of the Sun' just as much as otherwise.It appears my comments are only applicable to this type-- I can believe that.

astromark
2010-May-30, 10:44 AM
Thanks ... So, 'My lets not be concerned' might be a little bit premature.
As has been said a few recent fly by's have been not seen until they were past us...
and at least one was inside lunar distance and over 50 meters wide.
Is this just emotive hype or is there a real risk. ?
Should we demand greater expenditure on this field of research for the sake of humanity...
From the last couple of posts. You are not telling me what I wanted to hear..
I want to know that there is a very slim chance of a devastating or life ending impactor risk.
You are telling me that we should not be too complacent.

Nereid
2010-May-30, 11:56 AM
Thanks ... So, 'My lets not be concerned' might be a little bit premature.
As has been said a few recent fly by's have been not seen until they were past us...
and at least one was inside lunar distance and over 50 meters wide.
Is this just emotive hype or is there a real risk. ?
Should we demand greater expenditure on this field of research for the sake of humanity...
From the last couple of posts. You are not telling me what I wanted to hear..
I want to know that there is a very slim chance of a devastating or life ending impactor risk.
You are telling me that we should not be too complacent.
There's a real risk, but not of the dino-killer kind (unless you consider a completely unknown kind of object 'real').

All PHAs (potentially hazardous asteroids) ~1 km and bigger have been found (or is it only ~90%?); such an asteroid could do serious damage, including wiping out a city if it hit directly (but the total area of all cities is trivially small compared to the total surface of the Earth).

Asteroids down to ~100 m have the potential to be quite damaging too, so the current aim is to find all those too. IIRC, when the LSST and Pan-STARRS have been going for a decade, all such PHAs should have been found (that'll be ~2025 though).

The risk from long-period comets is, perhaps, the greatest ... but comets big enough to wipe out a city are likely to be found ~a year before collision.

astromark
2010-May-30, 07:48 PM
This is the very reason I asked this OP.. Could a dangerous impacting object sneak up on us ?
and it would seem that you's suggest that a object. Not of large all life ending.., but of some real risk.
That we still face the reality that a Ort Cloud object could be on its way in and it could be large enough and fast enough to be a risk..
I have every confidence that the plethora of equipment is looking and advancements being made are working to protect us.
I still have a concern that is the next step. Are there plans ? Is there a method ? Can we send out a rendezvous craft to nudge, bend, or otherwise deflect this in bound object. and then,. Do we spend what could be millions on a risk that we may never need to use.
Having the thought that what is the point of this ability if we need it but can not use it because we were saving money... sitting on our hands.
I have never been a great history student. Being far to busy for the what if game... History should be a great teaching tool.
If humanity wants to prevail we must budget to protect our interests... 'We' being the persons with astronomical leanings need to lobby this argument better. Where do I start ? and will 'they' listen ?

DrRocket
2010-May-30, 08:27 PM
This is the very reason I asked this OP.. Could a dangerous impacting object sneak up on us ?
and it would seem that you's suggest that a object. Not of large all life ending.., but of some real risk.
That we still face the reality that a Ort Cloud object could be on its way in and it could be large enough and fast enough to be a risk..
I have every confidence that the plethora of equipment is looking and advancements being made are working to protect us.
I still have a concern that is the next step. Are there plans ? Is there a method ? Can we send out a rendezvous craft to nudge, bend, or otherwise deflect this in bound object. and then,. Do we spend what could be millions on a risk that we may never need to use.
Having the thought that what is the point of this ability if we need it but can not use it because we were saving money... sitting on our hands.
I have never been a great history student. Being far to busy for the what if game... History should be a great teaching tool.
If humanity wants to prevail we must budget to protect our interests... 'We' being the persons with astronomical leanings need to lobby this argument better. Where do I start ? and will 'they' listen ?

Large objects have hit the Earth in the past, and caused catastrophes of varying magnitude (from really bad to boing!!).

I don't think a lot of official thought has gone into countermeasures, but there has been some thought -- mostly in Hollywood.

I don't doubt that with sufficient forwarning and a lot of effort quite a bit might be done. We might even figure out how to stop a rogue oil well.

But without both adequate warning and some preparation, success on the first try is probably not likely -- and with an incoming asteroid a second chance is asking too much.

The U.S. abandonment of the manned space program is not a step in the direction of preparedness. Preparedness would require greater, not lesser, allocation of resources. So the first step would be to make your concerns known and advocate use of resources to prepare for the threat that you recognize --- maybe an enhanced New Zealand space program.

The other alternative is to do nothing and merely contemplate and study black bodies without ability to take effective action -- but there are sometimes interesting aspects to just such contemplation.

http://maaadddog.files.wordpress.com/2010/01/big_hot-women-halle-berry01.jpg

astromark
2010-May-31, 08:15 AM
Confusion rains supreme... your link is 'Forbidden' and I seem to detect a note of sarcasm unwarranted... I do not understand you.
Particularly as let alone a space program we hardly have an air force... in New Zealand.
But as an aside a New Zealand Space program does exist. They, a Mr Rocket ( He actually changed his name.) have had a successful launch. Its for real. But No, realistically I would agree with you. We need to wise up the politicians... is that being realistic. ?
NASA has the infrastructure to do the difficult. It lacs the funding.
Yes I see a need as do you. All jocking aside we need to work this out better. Extinction is a option I find unacceptable.

astromark
2010-May-31, 08:48 AM
Some things we know. While some things we think we know.
The risk to humanity is real and perhaps the most likely scenario for the downfall of the human being as a dominant species...
OK it might not be from a space rock or comet. Our own greed and stupidity might actually feature as greater risks... I except that as true.
If we assume that as a greater number of people gain a better education the odds of us killing each other should drop.
Oh, I so wish that was true... I fear a good argument can be presented its not.
I do not think it is within my abilaty to change the maner of peoples globaly.
I will however argue that as a astronomer I have a better than basic understanding of the universe.
How do we up skill the mindset of the masses, ( and politicians ). Do you agree that is a worthy coarse of action ?

Ken G
2010-Jun-01, 05:05 AM
I think it's pretty clear from the historical record that asteroids and comets are never going to compete with hurricanes, floods, and tidal waves for human destruction. And upping the ante and lowering the likelihood, megavolcanoes. If we did have warning that a very big comet might hit the Earth in 1 year, what would we do about it anyway? Comet orbits are too hard to predict in terms of where they'd hit, though I suppose if it was large enough we wouldn't care where it would hit. I don't know if we could be certain enough of a hit at all to mobilize the kind of response it would take to safeguard our civilization, we might have to settle for basic disaster preparedness and hope that humanity itself could survive. But it's just so incredibly unlikely to happen in a timeframe where we don't have vastly more pressing concerns. What preparedness does California have for a mega-earthquake? Heck, what preparedness did Haiti have? It's pretty cheap to at least monitor the asteroids and comets, but anything more substantial (or expensive) should come well after a long list of more urgent concerns-- and it seems to me that disease and war have always been the two leading causes of human suffering and premature death.

DrRocket
2010-Jun-01, 05:14 AM
Confusion rains supreme... your link is 'Forbidden' .

Link replaced. I don't know what that was all about.

DrRocket
2010-Jun-01, 05:18 AM
... It's pretty cheap to at least monitor the asteroids and comets, but anything more substantial (or expensive) should come well after a long list of more urgent concerns-- and it seems to me that disease and war have always been the two leading causes of human suffering and premature death.

And Bruce Willis has been a movie about nearly all such possibilities. But Armageddon is one of the better ones.

DrRocket
2010-Jun-01, 05:45 AM
Do you agree that is a worthy coarse of action ?

I agree that some black bodies are worthy of study. See replacement link above.

I think that any sort of major effort to develop countermeasures will have to take its place in line with other concerns. It is a long line and other concerns are more immediate.

Spoons
2010-Jun-01, 05:47 AM
Link replaced. I don't know what that was all about.

Well, that's one way to arouse interest in the topic.

Ken G
2010-Jun-01, 05:58 AM
And Bruce Willis has been a movie about nearly all such possibilities. But Armageddon is one of the better ones.
Yes, he really has become a kind of personal expert on extinction scenarios, hasn't he? Maybe we should make him the keeper of the doomsday clock.

astromark
2010-Jun-01, 07:23 AM
It must be a Americanism.... "put the wagons in a circle." John Wayne. Bruce Willis saving all of humanity... Wow..... Now I did enjoy that
link Dr Rocket... Not the Body I was thinking of when I started this thread, but you have modified my thought process considerably, Thankyou.
For me it was Captain Picard and Data. Yes, they set my interest candle alight. Seven of Nine from the spin off, was particularly interesting....
So returning to this nagging uncertainty of a asteroid or comet impacting and creating a doomsday event with all the bells and whistles.
No Bruce Willis. I am pleased to be reminded of the small fraction of likelihood. I agree that humanity faces bigger and more urgent dangers and that we are our worst allies and enemies. Spotting the difference is not so easy.
Back to my point. How do we educate the masses. ?
I can see my paranoia is becoming obsessive... this only happens when the sky is cloudy.... :o

Nereid
2010-Jun-01, 07:29 AM
This is the very reason I asked this OP.. Could a dangerous impacting object sneak up on us ?
Yes, indeed it could.



and it would seem that you's suggest that a object. Not of large all life ending.., but of some real risk.
"such an object"? Indeed, and not just one, but at least hundreds.



That we still face the reality that a Ort Cloud object could be on its way in and it could be large enough and fast enough to be a risk..
Yes, that is indeed the reality.

But the thing missing from the above is exactly what we, here, should be asking - how likely is "could"?
how do measure "risk"?
how do you even define "risk"?!?

One can dream up all kinds of doomsday scenarios; the Earth's climate is right at the knife edge of a runaway greenhouse, and our planet will turn into a Venus within a century; a megavolcano will erupt somewhere in the western US within a decade; the common cold will hook up with AIDS and Nipah and Ebola and 99% of humans will die within five years; ...

The point is that while the risk of something nasty in the way of a PHA collision is real, it can be quantified, and likewise our confidence in estimates of such risks.

The risk from a large, long period or brand new comet is less well quantified ... but it's also very likely much lower than the risk from a PHA collision.

The risk from a totally unknown space object is, by definition, impossible to estimate reliably.



I have every confidence that the plethora of equipment is looking
On the whole, the 'scanning of the skies', and analysis of the results, has improved a lot over the last century, or even generation.

It's also true that quite modest incremental investments would improve our understanding, and so help increase our confidence in the estimates of the various risks - see the Planetary Society (http://www.planetary.org/explore/topics/asteroids_and_comets/) and NASA's NEO program (http://neo.jpl.nasa.gov/news/news126.html), for example.


and advancements being made are working to protect us.
I still have a concern that is the next step. Are there plans ? Is there a method ? Can we send out a rendezvous craft to nudge, bend, or otherwise deflect this in bound object.
There have been a number of studies on how to mitigate various potential collision hazards (there was a write up of one in Scientific American, I think, some time in the last few years, to take just one example).

They have tended to focus on PHA-type risks, as these are both more likely and have, potentially, the shortest lead-times (as I said, 'new' comets tend to be discovered a long way out).


and then,. Do we spend what could be millions on a risk that we may never need to use.
Here history strongly suggests that, collectively, we humans are rather bad at taking sensible precautions against known, but relatively unlikely, risks - for example, the likely effects of a category 5 hurricane on New Orleans were well documented and well-understood, and the estimates of the risk of such a 'hit' happening well-constrained. Despite that, were the necessary preparations and precautions taken?


Having the thought that what is the point of this ability if we need it but can not use it because we were saving money... sitting on our hands.
I have never been a great history student. Being far to busy for the what if game... History should be a great teaching tool.
If humanity wants to prevail we must budget to protect our interests... 'We' being the persons with astronomical leanings need to lobby this argument better. Where do I start ? and will 'they' listen ?
Read the material on NEOs, and on the studies on various hazard mitigation options.

That'd be a good start.

Nereid
2010-Jun-01, 07:35 AM
I think it's pretty clear from the historical record that asteroids and comets are never going to compete with hurricanes, floods, and tidal waves for human destruction. And upping the ante and lowering the likelihood, megavolcanoes. If we did have warning that a very big comet might hit the Earth in 1 year, what would we do about it anyway? Comet orbits are too hard to predict in terms of where they'd hit, though I suppose if it was large enough we wouldn't care where it would hit. I don't know if we could be certain enough of a hit at all to mobilize the kind of response it would take to safeguard our civilization, we might have to settle for basic disaster preparedness and hope that humanity itself could survive. But it's just so incredibly unlikely to happen in a timeframe where we don't have vastly more pressing concerns. What preparedness does California have for a mega-earthquake? Heck, what preparedness did Haiti have? It's pretty cheap to at least monitor the asteroids and comets, but anything more substantial (or expensive) should come well after a long list of more urgent concerns-- and it seems to me that disease and war have always been the two leading causes of human suffering and premature death.
It would be an interesting exercise to put the many Shoemaker-Levy 9 (http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9) impacts into an "Earth" perspective.

At what level of (well-constrained) risk of a dino-killer impact - or even a civilization-ending one - do we, collectively, think it's worth putting serious effort into at least studying potential mitigation strategies?

astromark
2010-Jun-01, 08:24 AM
I am simply attempting to quantify the risk. Risks. So yes, war and intolerance are the demons we create.
I am also aware that there's little chance I can disarm the stupid... So lets just educate them.
I would like to put aside the fear of a unseen object coming at us undetected.
In reality the possible may never happen.
From the tone of this thread we have greater dangers to worry about.
I can move away from the Dark Body Blasting a hole in humanities future...
But still a budget of very little will find very little.
For the sake of the next generation we should expand this science.

Looking at countless images. Looking for the next earth crosser...." Whats that little fuzzy thing, It was not there last week." Oh.... call Bruce.

Hungry4info
2010-Jun-01, 12:00 PM
I didn't see this brought up yet, but another thing to consider is that these dark asteroids would be IR-bright, and be picked up by WISE.

Ken G
2010-Jun-02, 02:37 AM
At what level of (well-constrained) risk of a dino-killer impact - or even a civilization-ending one - do we, collectively, think it's worth putting serious effort into at least studying potential mitigation strategies?
We would probably want to begin by sorting the probabilities-- what are the chances, right now, in each year, of civilization being ended by:
1) a comet
2) a global nuclear war
3) a killer virus, accidental or contrived
4) megavulcanism
Then we'd want to devote resources proportionally. To me, the one that stands out as probably the most likely is also the one that receives not only no resources, but the resources that are devoted are not even on the side of reducing its likelihood. Strictly scientifically, and looking at nothing but the historical record, I'd offer these chances per year:
1) one in 107
2) one in 102
3) one in 103
4) one in 108
These are all quite rough estimates, of course, but if they are anywhere close to true, it suggests that if comet-strike mitigation deserves a million dollar budget, then mitigating disease outbreaks deserves a ten billion dollar budget, and mitigation of world war deserves a 100 billion dollar budget.

astromark
2010-Jun-02, 03:31 AM
We and I are not, and not even expecting to change the mindset of humanity. To not blow the environment to hell in a hand cart...
\I simply ask could a non reflective body of mass approach Earth undetected. The fact that other natural events could bring us to our knees is a given...
The chances of such an event happening might be very small. It has happened before. We watched as the Shoemaker Levey comet brock up and slammed into Jupiter. Had that been Earth, I would not be asking, would I. ?
Its a bit like saying that drilling for oil on the continental shelves is safe... maybe its not.
As long as we recognise a risk. No matter how small that eventuality is. Its still a risk that can be managed.
I still see a need to increase the awareness of this sort of probability and move forward to prepare to lessen it.

Ken G
2010-Jun-02, 03:39 AM
The chances of such an event happening might be very small. It has happened before. We watched as the Shoemaker Levey comet brock up and slammed into Jupiter. Had that been Earth, I would not be asking, would I. ?There's no fault in asking the question, to be sure. But bear in mind that the Jupiter analogy is limited, because it was Jupiter's huge gravity that brought the comet to it, it did not happen there on its own (i.e., Jupiter is a way larger target because of the gravitational net it casts, it is the "vacuum cleaner" of the solar system and is one of the reasons we so rarely get hit by comets like Shoemaker-Levy).

Its a bit like saying that drilling for oil on the continental shelves is safe... maybe its not.
As long as we recognise a risk. No matter how small that eventuality is. Its still a risk that can be managed.
I still see a need to increase the awareness of this sort of probability and move forward to prepare to lessen it.
It's never a bad idea to recognize a risk, and it's certainly a lot cheaper to assess risk than to mitigate it. The price tag of failing to mitigate is the source of the old saw "a stitch in time saves nine". But you still don't stitch the sock in places it is unlikely to tear, you stitch it where you find signs of tearing.

astromark
2010-Jun-02, 04:41 AM
Yes Ken., I have understood the gravity of Jupiter pulled that comet apart and into Jupiter.
I have also seen it argued that as many can miss and carry on to become an issue for Earth. Jupiter might not be the mine sweeper at all.
Some historic chap has said that " For evil to prevail. A few good men need do nothing."... :eh:
All I really want is a commitment to protect at whatever the cost. As long as cost is a factor... We are in trouble.

DrRocket
2010-Jun-02, 06:13 AM
Yes Ken., I have understood the gravity of Jupiter pulled that comet apart and into Jupiter.
I have also seen it argued that as many can miss and carry on to become an issue for Earth. Jupiter might not be the mine sweeper at all.
Some historic chap has said that " For evil to prevail. A few good men need do nothing."... :eh:
All I really want is a commitment to protect at whatever the cost. As long as cost is a factor... We are in trouble.

Cost is always a factor.

It is only not a factor for people who expect someone else to pay the cost.

Spoons
2010-Jun-02, 08:08 AM
If humanity wants to prevail we must budget to protect our interests... 'We' being the persons with astronomical leanings need to lobby this argument better. Where do I start ? and will 'they' listen ?
Where do we start? The ground up - start by inspiring and educating the kids, get them interested in this sort of stuff and then you've got more voters supporting the cause. Most people are generally just out for their own interests, so make this area their interest.

Ken G
2010-Jun-02, 01:24 PM
I agree that potential asteroid and comet hits can be used as a point of contact with people's general astronomical curiosity. I just don't like the idea of forcing that interest by fomenting doomsday fears, it reminds me of what some religions do. It's a fine line between creating a responsible concern and generating 2012 hysteria.

Nereid
2010-Jun-02, 02:19 PM
We and I are not, and not even expecting to change the mindset of humanity. To not blow the environment to hell in a hand cart...
\I simply ask could a non reflective body of mass approach Earth undetected. The fact that other natural events could bring us to our knees is a given...
The chances of such an event happening might be very small. It has happened before. We watched as the Shoemaker Levey comet brock up and slammed into Jupiter. Had that been Earth, I would not be asking, would I. ?
Its a bit like saying that drilling for oil on the continental shelves is safe... maybe its not.
As long as we recognise a risk. No matter how small that eventuality is. Its still a risk that can be managed.
I still see a need to increase the awareness of this sort of probability and move forward to prepare to lessen it.
These happen every day, astromark, in their hundreds. When they hit the Earth, at night, we call them 'shooting stars'.

The record of sizable impact craters on Earth is far from complete, but there seem to have been a few (~<10) in the last million years, and from that and the observed size distribution of asteroids, you can work out an estimate of the likelihood of the Earth being hit again by one of these. YMMV, but one sometime in the next 20,000 years isn't going to get many people terribly excited, especially if there's a pretty darn good chance (>95%?) that one such would be detected early enough to take at least some mitigation measures - evacuate the 'ground zero' city/coastal flood plain/etc.

Now if one of these landed in a particularly, um, worrisome location - a weak point in a large Antarctic glacier/ice sheet say, or near the Dutch dyke system - feasible, short-term mitigation might turn out to be rather ineffective.

How large does an impact have to be to wreck havoc with the world's economy? civilized society? trigger a mass extinction? Build yer models and turn the handle! The Earth's record of impact craters that large suggests asteroids big enough to do the deed are likely to hit us much less than once every 10 million years or so. Have we discovered all such PHAs, out to, say, a century away? Almost certainly (and there are none) ... but there are caveats!!

With comets the calculations become more difficult (though comets over ~10 km, say, are no different from asteroids, in terms of the damage they'd cause). Was the Tunguska event caused by a comet? if so, how big? How does the damage caused by airbursts due to a comet of size X compare with the crater impact (etc) damage due to an asteroid of the same size? And so on.

A Tunguska comet with 'ground zero = New York City' written on it would be hard to mitigate, on the ground, even given a year's warning; but if it said 'Tanami desert, Australia', a very great deal easier!

The trouble with new/long period comets is that we have much less of a handle on them than asteroids, so the range of likelihoods, estimated from the very best data and models, is quite large.

For some reason, we humans, collectively, are very poor at judging certain kinds of probabilities, and even poorer at behaving rationally when given the hard facts - Hurricane Katrina is a perfect example of that, and the Challenger disaster shows that even the most hard-headed of engineers are all too easily over-ruled by considerably less numerate (shall we say) people in positions of power and authority^. And when you have a literally species-extinction event (which, rationally, should be priority #1) combined with very low probability (or, worse, great uncertainty over what the probability is), well ...

^ and even when highly numerate people are running the show (almost), the almost wilful blindness to risk and downsides is, depressing (there are many factors involved in the Global Financial Crisis, but the grotesque mis-use of mathematical models and quite blatant disregard of extremely well-quantified risks are among them).

utenzil
2010-Jun-02, 02:32 PM
As a related observation, the last two asteroid "impactor" events that made the news recently, the one that blew up over Indonesia and the one that lit up the midwestern US, seemed to have been totally unexpected and untracked.

Nereid
2010-Jun-02, 06:10 PM
As a related observation, the last two asteroid "impactor" events that made the news recently, the one that blew up over Indonesia and the one that lit up the midwestern US, seemed to have been totally unexpected and untracked.
Exactly.

I don't know if there have been reliable estimates of the sizes of these "impactors", but they were surely waaay smaller than ~100 m. 100 m is, IIRC, the current (lower) size limit that various searches and programs are aiming for, as in something like "identify 90+% of all 100+m sized PHAs, within a decade".

Spoons
2010-Jun-03, 02:09 AM
I agree that potential asteroid and comet hits can be used as a point of contact with people's general astronomical curiosity. I just don't like the idea of forcing that interest by fomenting doomsday fears, it reminds me of what some religions do. It's a fine line between creating a responsible concern and generating 2012 hysteria.
Oh, yes, I agree entirely. My "this sort of stuff" was intended as far more general than how it came off. What I was thinking of was something more along the lines of Carl Sagan's style - a schooling program where the kids watch one episode each week and then discuss all the questions and ideas it raises would generate a heck of a lot of interest, I would expect.

Even with many of the really simplistic things he touches on regarding the solar system, he manages to create a sense of, "Oh, yeah, of course - that makes sense" where you feel that you already knew what he tells you. It think it's a matter of the way he communicates things, and it's something that a number of people here have - it's something that a lot of teachers don't have, and children need in order to motivate them. One 30min or hour presentation to a class of children can generate a whole domino effect of learning, and something like that at an early age is what can help to create a knowledgable population who will see budget allocations to areas such as suggested in this thread as not just an acceptable or good idea, but as a necessary expenditure.

I think it's an uphill battle trying to steer enough adults into the interest, but as a long term plan it's relatively easy to get a fair percentage of the population interested in the field.

astromark
2010-Jun-03, 03:10 AM
@ Spoons; Great to see such a like minded response. From that a point of interest for me is this.
" I think it's an uphill battle trying to steer enough adults into the interest."... yes, and how do people reach maturity and not want to know the answers to the simple questions ? I could never except the simple but illogical and thus was ejected from a class because I asked too many questions. ( I do not need to tell you what that was about.) I hold that moment as pivotal in the formation of my inquiring mindset. As the observatory fills with children and caregivers its the children that ask the good questions. As its the parents and teachers whom get surprised by the hunger for knowledge. If I can help foster the quest I do. Science can not lose. So my motives are laid bare and, testing others views is a way of guiding my own enthusiasm. When I ask if a dark object could sneak up unseen. I am only testing the awareness and the responses suggested have helped. Thanks.

Spoons
2010-Jun-03, 03:50 AM
It's people like yourself who, in my opinion, fill some of the most important roles in our society, as a child fed knowledge in the right manner is like a shark that gets a whiff of blood.

I really would love to think that parents are creating the right environment for children to learn too. As a young child my father intilled in me and my brother that knowing what is great but more important is to know how and why, as that can often be applied elsewhere. There's knowing and there's understanding. Understanding leaves the door open to further knowledge, with a big welcoming neon light coaxing you in.

Unfortunately, there are a lot of parents who just want the easy way out via fast food type TV shows - in one end and out the other with nothing of value retained. I appreciate parenting must be a big effort, and from time to time that may be necessary, but I just think people shouldn't do something unless they are commited enough to doing it properly, and that should especially go for raising children.

I didn't see the series Cosmos for the first time until a few years back, but when I saw it I wondered how they could have not shown it to us in school. It seemed crazy to not include it.

Thank you, for your work with the young'uns.