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What are the real chances of an asteroid hitting Earth?

Catastrophe

There never was a good war, or a bad peace
Feb 18, 2020
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There are all sorts of calculations saying nothing (asteroid, bolide, comet, what you will) is going to hit us in the next 20 minutes (Ooops sorry, I meant years) but how reliable are they?
How are we to see objects with an albedo less than soot coming 'out of the Sun'?
NEAs, especially those sharing our plane, and especially coming around in short order are affected on each return by our gravity. Large error margins start creeping into those calculations.
Are we doing enough to protect our planet? Is the Late Heavy Bombardment repeatable?
What are your views?



 
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The worst case scenario cannot be modeled or predicted. That would be a long-period comet (LPC) that is first seen a few months before impact, and the knowledge of our trouble would become apparent only after significant data had been obtained on its path and interception confirmed.

It is estimated that an impactor of ca. 2 km in diameter is big enough to take out humanity. Hale-Bopp was about 40-80 km in diameter, with a period of about 2,500 years. So let's hope we don't have any problems with LPCs. There is likely nothing we can do about one of those.
 
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Catastrophe

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"In 2006 Toutatis came closer than 2 AU to Jupiter; its orbit lies inside of Jupiter's.[12] In the 2100s, it will approach Jupiter many times at a similar distance.[12]" Wiki

And they still say Toutatis' orbit can be calculated hundreds of years into the future? And with the Earth Jupiter resonance as well?

Remember Shoemaker–Levy 9?
 
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Catastrophe

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Ah! This is where I saw it! "Asteroids, Meteorites and Comets" by Elkin-Tanton.

Quote
The largest asteroid that is a potential Earth hazard is 4179 Toutatis. This asteroid is nearly one mile long . Its orbit makes it particularly dangerous, since it lies almost perfectly in the same plane as the Earth's, inclined from it by less than half a degree . . . . . . The more coplanar the orbits, the more likely a collision.
Quote
 
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Calculations would require good data. I know of at least one buried impact crater (3500ft down 18km diameter) that does not show up in any database. It is known by a few oil companies but is publicly denied by the United States Geological Survey.

My guess is because of economic secrecy that the existence of (buried) standard impact craters are probably under reported by 80-90%. For every impact crater that the public knows about there are probably ten others.

For interstellar asteroids which create volcanoes and large igneous provinces the data situation is much worse.

One there is a total categorical denial for the existence of interstellar asteroid impacts.

Two there are some 40,000 seamounts the majority of which are not connected to any tectonic features like plate boundaries. The majority of these seamounts are volcanic and I argue that they are the direct result of interstellar asteroid impacts.

The most disturbing interstellar impact marker is the Eastern Mediterranean Sapropels. They are indistinguishable from black shale impact markers. The published dates for these sapropels are likely fictional with exaggerated ages.

These sapropels appear to occur within the beginning of human civilization in the Fertile Crescent.

The real chance of an asteroid hitting Earth is… one.

If you want to stop the next one, I strongly suggest pre-positioning nuclear weapons across the Solar System. The sooner you hit an asteroid the more you can deflect it.
 
Mar 19, 2020
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Ah! This is where I saw it! "Asteroids, Meteorites and Comets" by Elkin-Tanton.

Quote
The largest asteroid that is a potential Earth hazard is 4179 Toutatis. This asteroid is nearly one mile long . Its orbit makes it particularly dangerous, since it lies almost perfectly in the same plane as the Earth's, inclined from it by less than half a degree . . . . . . The more coplanar the orbits, the more likely a collision.
Quote

This was quoted from wiki* :

"Given that Toutatis makes many close approaches to Earth, such as in 1992, 1996, 2000, 2004, 2008, 2012, and 2016, it is listed as a potentially hazardous object.[12] With an uncertainty parameter of 0,[3] the orbit of Toutatis is very well determined for the next few hundred years.[12] The probability of the orbit intersecting Earth is essentially zero for at least the next six centuries.[23] The likelihood of collision in the distant future is considered to be very small.[24]"

* https://en.wikipedia.org/wiki/4179_Toutatis

You might have to look for a more likely killer, Cat. For a great overview of all the risk currently known ( a lot of NEOs have not be i.d.ed as you know), see:



The risk estimates are typically based on two scales :


Torino scale : https://en.wikipedia.org/wiki/Torino_scale


and the more complex : https://en.wikipedia.org/wiki/Palermo_Technical_Impact_Hazard_Scale


Sorry to provide a bunch of "answers" that cause you to go look somewhere else! But the data is scattered as badly as the objects!!
 
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Catastrophe

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dfj

Just for the record, my quote above was not from Wiki but from a very interesting book entitled "Asteroids, Meteorites and Comets" by Elkin-Tanton.

Cat :)
 
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Catastrophe

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Just to complete what I posted, which was:

"Asteroids, Meteorites and Comets" by Elkin-Tanton.


The full name of the author is Linda T. Elkins-Tanton
Series: The Solar System Chelsea House (InfoBase Publishing)
ISBN 0-8160-5195-X.

Copyright (C) 2006 by Linda T. Elkins-Tanton

This referenced the close orbital inclination of Toutatis and possible danger coming therefrom.
 
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Catastrophe

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Wiki on Toutatis (my emphasis)
Quote
"The gravitational perturbations caused by frequent close approaches to the terrestrial planets lead to chaotic behavior in the orbit of Toutatis,[17] making precise long-term predictions of its location progressively inaccurate over time.[17] Estimates in 1993 put the Lyapunov time horizon for predictability at around 50 years,[17] after which the uncertainty region becomes larger with each close approach to a planet. Without the perturbations from the terrestrial planets the Lyapunov time would be close to 10,000 years.[17] The initial observations that showed its chaotic behavior were made by Wiśniewski.[18]"
Quote

This is in response to your:
"You are likely going to have to look for a more likely killer, Cat."

I am very aware that there are (actually) millions of potential candidates "further out" (my new shorthand for 'that lot in Kuiper, Oort and places west') but I am still concerned about Toutatis (not personally): 10,000 to 50 years and counting in my (as ever) humble opinion.

Cat :)
 
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Catastrophe

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BTW the reference (24) goes back to 1993!

"Close call for earth ahead? – possible collision with asteroid Toutatis". USA Today (Society for the Advancement of Education). 1993. Archived from the original on 28 June 2012.

And (23) is from 1998.

The probability of the orbit intersecting Earth is essentially zero for at least the next six centuries.[23]

Ostro, S. J.; Hudson, R. S.; Rosema, K. D.; Giorgini, J. D.; et al. (1998). "Asteroid 4179 Toutatis: 1996 Radar Observations" (PDF). Icarus. 137 (1): 122–139. Bibcode:1999Icar..137..122O. doi:10.1006/icar.1998.6031. hdl:2014/19433.

HeHe! Any 21st Century predictions yet?

Cat :)
 
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There is a probability chart from the Planetary Society that's easy to read, though a surprise comet, though unlikely, must be taken seriously.

Impact Hazard chart

There is a mission that will alter an asteroid (an asteroid moon) by impacting it in 2022.

I feel pretty safe as long as Bruce Willis is still around. ;)
 
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Catastrophe

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OK, well comets were further down my list but, since you mention them, here are some more numbers: Source as #8.

"Short period comets are thought to originate in the Kuiper Belt . . . . . . . . . Judging from luminosity, the total mass of these objects may be about 20% of Earth's mass. While this is a small mass by solar system standards it is still about 100 times the mass of the main Asteroid Belt." [My emphasis]

Just one may be enough . . . . . . . . .
 
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Catastrophe

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Well, might as well throw in another. I think, by now, you will realize how high a regard I have for the book:
"Asteroids Meteorites and Comets" by Linda T. Elkins-Tanton. the following may be assumed to be quotes from that excellent source:

Asteroids in the Outer Solar System
"There are also as many as 13,000 unstable Jupiter-crossing asteroids. These bodies can have inclinations up to 90 degrees and very eccentric orbits. They are good candidates for disruption into the inner solar system."

Well, there are plenty more possible sources of "THE ONE" still to come. Whether they come from the inner or outer solar system or even beyond does not matter - well the practice matters, but not the theory - the fact of the matter is that it only takes one "baddie" to do "the job".

Have I made my point yet? Or are there some "statisticians" who are going to tell me that there is a 0.00000% chance of even a minor incident before 2066?

Let's hear from you!!

Cat :)
 
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OK, well comets were further down my list but, since you mention them, here are some more numbers: Source as #8.

"Short period comets are thought to originate in the Kuiper Belt . . . . . . . . . Judging from luminosity, the total mass of these objects may be about 20% of Earth's mass. While this is a small mass by solar system standards it is still about 100 times the mass of the main Asteroid Belt." [My emphasis]

Just one may be enough . . . . . . . . .
It was actually mentioned by dfj. But he also gave, importantly, a long period example. A big problem with those is that they can come in from any direction so we are more likely to catch them later than sooner. However, a lot of those will not have a perhelion <= 1 AU, IIRC.

Then there is that odd ball, the new Planet IX, that may be 6x that of Earth. It's not a threat, but the problem is that it is a strong indication that our formation theories still are out of whack. Even if it's not out there, and the competitive model is more likely -- it predicts a number of objects serve to offer the c.g. as that of a single body, indicating that too will be a bit problematic with our formation theories, but less so than an massive object.

There is extremely little reason to be worried at the moment, for those concerned about impacts from large objects.
 
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Catastrophe

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Something else to ponder: [Ref: ibid p. 53]

"The solar system seems to contain about 2 million asteroids large enough to destroy civilisation on Earth through impact, and about 1,100 of these are already in Earth crossing orbits. The Earth’s orbit passes through the orbits of about 20 million asteroids of all sizes, and as a result, the odds that the Earth will suffer a catastrophe impact in the next 100 years is about 1 in 5000."

Cat :)
 

Catastrophe

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No one, to my knowledge, has tried to quantify hitherto unknown bodies (of any size) especially some with low albedos (some have albedos lower than soot) especially coming "out of the Sun" (meaning from the direction of the Sun and with no chance of being seen) - this has already happened within recent decades.

Why has this not been quantified? Because it cannot be.

Cat :)
 
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Are we doing enough to protect our planet? Is the Late Heavy Bombardment repeatable?
What are your views?
We are certainly not ready if there were an asteroid detected on collision course right now. Efforts are being made such as the AIDA mission in 2022, joint effort between NASA and ESA!

There are a few principles here:
- Big Sky principle such as often referred to by pilots. I've been there myself, and you're at a busy airport, but as soon as you take-off there is no plane to be seen. The chances of actually hitting another aircraft are minimal, hence labelled Big Sky principle. The same is true for space. Earth really is tiny compared to space, so thankfully the Big Space principle is valid
- Another principle taken from aviation is that objects on a collision course do not move in view. This is why other aircraft on collision course are very hard to detect, because they will be a stationary dot in the windscreen only getting bigger at the last moment. A lot of asteroid detections are done by relative movement against the background. Correct me if I'm wrong, but an asteroid on collision course would be virtually stationary against the background stars etc.

For example the recent 2020QG asteroid that was close pass, but only discovered six hours after passage.Asteroid 2020 QG at space.com
 

Catastrophe

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Thank you for your excellent perspective.
" Correct me if I'm wrong, but an asteroid on collision course would be virtually stationary against the background stars" You are correct.
Whilst we accept the Big Sky principle, one only has to look at the Moon, Mercury, Mars, or many solar system satellites, to see the density of cratering. Big space, yes, but also billions of pieces of junk flying around and probably as many still out there.
That is one reason I questioned the possibility of another Late Heavy Bombardment.
 
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I'm guessing that the combination of our circular orbit, the elliptical orbit of the asteroid, some parallax due to our rotation, and how fast it will brighten due to the inverse square law, will help give it some character. If it's coming out of the Sun's region, it could be a big problem.

An asteroid coming from outside our orbit actually should brighten more than the simple inverse square law since that law is based on sunlight that must travel to the asteroid and then that inverse square law must also be considered as the asteroid gets closer. For planets many AU away, if you cut their distance to us in half, then it could be as much as 16x brighter. For closer objects, even in opposition, it won't be close to that inverse fourth law.

The Late Heavy Bombardment is based on a major disturbance that triggered an avalanche of objects to come our way, and other ways, too. There doesn't seem to be any more recent activity that would suggest another round is likely.

But, I do recall discovery of a star (Scholz) that came near us about 75k years ago and is now about 20 lyrs. distant. Could it have disturbed many Oort Cloud objects? The free -fall time for the inner Oort Cloud I calculate to be about 175k years, and the outermost region will be about 2.6M years.
 
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Don't forget some albedos are less than soot.
Yes, though they vary. The more distant ones seem to be about the same albedo on average.

Asteroid albedos with inclination and distance

The Moon also has a low albedo of about 0.12. Worn asphalt (grayish) is about the same at 0.12, but fresh asphalt (black) is about 0.04.

Also, we don't know when some disturbance might have been triggered.
Yes, for the outer Oort Cloud with such a long time frame to come our way if disturbed, it's unlikely, I suppose, that we could rewind the clock enough to see if a star came close enough to be an issue.

Those giant telescopes coming may be worth every penny just on this issue, perhaps.

I think , but could be wrong, objects coming towards us from outside our orbit will be brighter than what the albedo tells us. A full moon is 12x as bright as a 1/2 moon (quarter phase) due to the way light reflects at ~ 180 deg., along with shadows, etc.
 
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Catastrophe

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You are quite correct about the Moon phase question, but it is easy to quantify. Just take the Sun-Moon-Earth angle.
180 deg is full mon, 0 deg is conjunction. Close to 0 deg is "coming out of the Sun" and most dangerous, graduating around to "full Moon" when there is maximum surface reflecting.
You have correctly pointed out that it is both albedo and surface area illuminated that are important. Of course there is a third factor which is the diameter of the object. The Moon is so bright because there is such a large area reflecting the available light.
Good news is - smaller the better? Less easy to see but less mass to cause damage.
The factor here is how large does it need to be to cause serious consequences.
 
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