What are the real chances of an asteroid hitting Earth?

[Helio]

Helio, am I not correct in saying that the tractor system requires a large mass (and hence great fuel consumption) ...

[I missed this one. ]

Yes, that has to be the big question that must be addressed. I don't know the answer, though the math wouldn't be all that hard to add to the analysis. It must not be too bad because I think it is still considered a valid possibility. Perhaps fuel supply ships would be needed for the extended tractoring efforts. These resupply vessels would be helpful since we would already know a lot more about the object from the first arriving vessel (tractor).

Another advantage with this method is that the tractor would allow for even greater trajectory projections, critical to any game plan.

 

[Catastrophe]

[I missed this one. ]

Yes, that has to be the big question that must be addressed. I don't know the answer, though the math wouldn't be all that hard to add to the analysis. It must not be too bad because I think it is still considered a valid possibility. Perhaps fuel supply ships would be needed for the extended tractoring efforts. These resupply vessels would be helpful since we would already know a lot more about the object from the first arriving vessel (tractor).

Another advantage with this method is that the tractor would allow for even greater trajectory projections, critical to any game plan.

The supply ships could latch on to the main tractor to add to its mass.

 

[Catastrophe]

This is the first book I picked up; edited by an Astronomer Royal - Martin Rees, but I have seen exactly the same diagrams and explanations in many books.

Quote
The effect of a collision between asteroids depends on the sizes of the bodies involved. If a very small body hits a larger one it will produce a crater on the surface. The crater will be about ten times the size of the incoming body. As asteroids are much smaller than planets, the material blasted out of the crater will escape and move off into an independent orbit around the Sun. This orbit will. however, be very similar to that of the impacted asteroid, and there is a good chance that the ejected material will hit the cratered asteroid again.
A bigger impactor can break up the asteroid that it hits. But so much energy is used to do this that the resulting fragments cannot escape from the gravitational field, and they will all fall back to form an irregular ball of rubble. Subsequent minor impacts will break up the surface, covering the asteroid in a dusty, rocky layer. A casual observer will not realize that the underlying asteroid is actually in pieces.
A large impactor will not only shatter the asteroid, but the fragments will also escape. These will form a family of asteroids that eventually spreads out around the orbit of the original body.
Quote

Source: Universe: The Definitive Visual Guide, Gen. Editor Martin Rees.DK 2012.

Of course, this is in the context of your last resort nuke.

Cat

P.S. I still doubt the feasibility of getting a large enough mass tractor to the target in time to have any effect against any asteroid large enough to do serious damage.

 

[Catastrophe]

Given an asteroid that was not too big (definitely not safe, but not so large that we could not divert it) I would 100% support diverting by change of momentum. Tractor efforts - I would resign myself to certain death.

Cat

P.S. And an addition to the asteroid collision (with another asteroid) story. I wish I had found this first, as it encapsulates the situation very succinctly:

Fig. 10. Stages in the fragmentation history of a moderately large asteroid. Originally composed of strong rock (1), the asteroid is cratered (1,2), and then, catastrophically fragmented by a more energetic impact (3). Most of the ejects fail to reach escape velocity, and the body is reassembled (4) Later impacts (4,5) further fragment the body, converting it into a gravitationally bound pile of boulders. Finally, (5,6), a sufficiently gigantic collision occurs to completely disrupt and destroy the asteroid. My emphasis.

The New Solar System ed. Beatty et ali., Book Club Associates.

Last one. There are many more:
Asteroids by Michael J Shepard, Cambridge University Press, 2015.
Discussion of both these and other methods.
"The technology to ram an asteroid has been demonstrated, with the Deep Impact mission, which slammed a 370 kg missile into Comet Temple I in July 2005.
The difficulty is (I am being very fair ) is that if the asteroid is a pile of rubble, it does not work. Nature of the asteroid, critically, must be known.

Of the tractor method he writes: "The main technological hurdle with this method is launching something as heavy as possible with enough fuel (or the ability to be refuelled) to maintain the gravitational pull for decades."

 

[Helio]

Given an asteroid that was not too big (definitely not safe, but not so large that we could not divert it) I would 100% support diverting by change of momentum. Tractor efforts - I would resign myself to certain death.

If tractoring takes place, can I have your K&E slide rule in advance of this "certainty", or do you have another brand?

Fig. 10. Stages in the fragmentation history of a moderately large asteroid. Originally composed of strong rock (1), the asteroid is cratered (1,2), and then, catastrophically fragmented by a more energetic impact (3). Most of the ejects fail to reach escape velocity, and the body is reassembled (4) Later impacts (4,5) further fragment the body, converting it into a gravitationally bound pile of boulders. Finally, (5,6), a sufficiently gigantic collision occurs to completely disrupt and destroy the asteroid. My emphasis.

The escape velocity is determined by the mass of the asteroid, so for small asteroids, escape velocity is likely reached, IMO.

The other element not mentioned is the time frame for reassembly, which can be quicker than one might think but for deflection we are talking months not years. Recall that at least the mass of Moon did not reassemble onto Earth but formed the Moon. Hopefully it doesn't reassemble.

Of the tractor method he writes: "The main technological hurdle with this method is launching something as heavy as possible with enough fuel (or the ability to be refuelled) to maintain the gravitational pull for decades."

Yes, but my math (subject to change w/o notice ) demonstrates that diversion is possible given enough time (implying distance as well).

But, yes, the heavier the tractor the better the deflection. I found a paper that uses the clever idea of using the tractor to grab a sizeable mass from the asteroid to augment its mass. This is called EJT (Enhanced Gravity Tractor) technique. See this paper.

The tractor becomes a type of wheel or crawler space loader, I suppose. [A wheel loader is actually a tractor with a bucket digging/lifting/dumping system.]

But I would expect any such trips to include all the tools to affect orbital change. Lasers, for instance, hold promise since they can trigger out-gassing to cause the asteroid itself to provide thrust. An array (ie drones) dispersed by the tractor should be easy to properly control the lasers given that the control is there and not remote from Earth.

 

[Misha Marchuk]

I think that in order for a meteorite to fly into the earth capable of causing significant harm to it, it must be very large initially, and an asterite, meteorite, etc. and such a meteorite will already be very difficult not to notice and not to carry out calculations. Yes, these calculations may be with errors and perhaps we will all die, and the earth will reboot.

 

[Catastrophe]

"I think that in order for a meteorite to fly into the earth capable of causing significant harm to it, it must be very large initially"

You might be surprised. It is not just the point of impact that is important. It is all the dust and other materials blown into the atmosphere, which diminish the Sun's light, reduce photosynthesis, interrupt the food chain, kill vegetarians, kill the carnivores that feed on vegetarians . . . . . . . . . . . . . . .

Cat

 

[Misha Marchuk]

"I think that in order for a meteorite to fly into the earth capable of causing significant harm to it, it must be very large initially"

You might be surprised. It is not just the point of impact that is important. It is all the dust and other materials blown into the atmosphere, which diminish the Sun's light, reduce photosynthesis, interrupt the food chain, kill vegetarians, kill the carnivores that feed on vegetarians . . . . . . . . . . . . . . .

Cat

The consequences of the blow are yes, all this dust is also harmful. But I meant precisely the harm from the collision of a cosmic body with the earth itself, and not harm from the consequences of this collision.

 

[Catastrophe]

MM, these go together. Also, some asteroids are too big to move. If you look at the possibilities:
1) Gravity. Put another body near it to change its direction. You would need another Mars-size body to move something very large. Also some large bodies are fragmented and not susceptible to this method.
2) Explosion. Same problem. You would need more energy than could be made available. You could make it worse by multiple fragments hitting Earth.
3) A year's notice will not help with an asteroid above a certain size. Maybe the Earth will not reboot.

Cat

 

[Misha Marchuk]

MM, these go together. Also, some asteroids are too big to move. If you look at the possibilities:
1) Gravity. Put another body near it to change its direction. You would need another Mars-size body to move something very large. Also some large bodies are fragmented and not susceptible to this method.
2) Explosion. Same problem. You would need more energy than could be made available. You could make it worse by multiple fragments hitting Earth.
3) A year's notice will not help with an asteroid above a certain size. Maybe the Earth will not reboot.

Cat

I agree, if the asteroid is too large, then there will be nothing to reboot)

 

[Helio]

I think that in order for a meteorite to fly into the earth capable of causing significant harm to it, it must be very large initially, and an asterite, meteorite, etc. and such a meteorite will already be very difficult not to notice and not to carry out calculations. Yes, these calculations may be with errors and perhaps we will all die, and the earth will reboot.

Fortunately, we can calculate accurately the orbital trajectory of a small asteroid or meteoroid (meteorite is the term for a meteor having already hit the Earth).

But if it is coming from a direction near the Sun, we are blinded and we will be caught off-guard. We have been surprised more than once by objects zipping by us almost undetected.

 

[Helio]

It may help to know that the larger, and thus more dangerous, an object is, the easier it is to detect.

Assuming all other conditions the same (e.g. albedo), an object that is, say, 2x the diameter of another will be equally detectable when it is about 50% farther away. But those greater distances buys us more than 50% more time since the more distant orbital speeds are much slower, plus the extra distance it must travel as well gives us more time.

 

[Catastrophe]

Fortunately, we can calculate accurately the orbital trajectory of a small asteroid or meteoroid (meteorite is the term for a meteor having already hit the Earth).

But if it is coming from a direction near the Sun, we are blinded and we will be caught off-guard. We have been surprised more than once by objects zipping by us almost undetected.

Helio, "But if it is coming from a direction near the Sun, we are blinded and we will be caught off-guard. We have been surprised more than once by objects zipping by us almost undetected."

Fortunately, this is now being taken care of by satellites outside Earth orbit. But, in the complete context, it is still too little too late.

I seem to remember reading recently about sensors being placed on a NEO.

 

[Helio]

Fortunately, this is now being taken care of by satellites outside Earth orbit.

I suspect those satellites aren't configured to take in the whole sky, or even the plane of the ecliptic region. But I could be wrong, and I hope I am. STEREO and Parker are the only two probes that I can recall that are in a position around the Sun to help image objects, but they were designed for solar studies, which means they will likely be useless in seeing dim objects since the Sun ain't.

But, in the complete context, it is still too little too late.

Well, not too, too late since we're still here.

I seem to remember reading recently about sensors being placed on a NEO.

It may be that they are using advanced masking techniques on the solar disk in order to see dim objects making their perihelion passage and directed toward us, but their light will be only from a sliver in the crescent phase so they will be extra dim. Perhaps there is a detailed article on current observing status.

 

[Misha Marchuk]

Fortunately, we can calculate accurately the orbital trajectory of a small asteroid or meteoroid (meteorite is the term for a meteor having already hit the Earth).

But if it is coming from a direction near the Sun, we are blinded and we will be caught off-guard. We have been surprised more than once by objects zipping by us almost undetected.

Interesting information, I didn't even know about this thing with the sun, thanks for telling me, now I will know more about it.

 

[Catastrophe]

I suspect those satellites aren't configured to take in the whole sky, or even the plane of the ecliptic region. But I could be wrong, and I hope I am. STEREO and Parker are the only two probes that I can recall that are in a position around the Sun to help image objects, but they were designed for solar studies, which means they will likely be useless in seeing dim objects since the Sun ain't.

Well, not too, too late since we're still here.

It may be that they are using advanced masking techniques on the solar disk in order to see dim objects making their perihelion passage and directed toward us, but their light will be only from a sliver in the crescent phase so they will be extra dim. Perhaps there is a detailed article on current observing status.

Helio, I think the point is that, if they (satellites) are taken out of the Sun-Earth alignment, they are no longer seen as near the Sun (in alignment of course). I will try to find the reference

 

[Catastrophe]

NASA Approves Asteroid Hunting Space Telescope to ...
https://www.jpl.nasa.gov › news › nasa-approves-astero...
11 Jun 2021 — The infrared space telescope is designed to help advance NASA's planetary defense efforts by expediting our ability to discover and ...

* “By searching for NEOs closer to the direction of the Sun, NEO Surveyor would help astronomers discover impact hazards that could approach Earth from the daytime sky,” said Amy Mainzer, survey director for NEO Surveyor at the University of Arizona. “NEO Surveyor would also significantly enhance NASA’s ability to determine the specific sizes and characteristics of newly discovered NEOs by using infrared light, complementing ongoing observations being conducted by ground-based observatories and radar.” *

Cat

 

[Patrick fenex]

If you're referring to an extinction level event, then not very likely in the near term. When I say near term I'm referring to between now and a million years from now. However, an extinction-level event impact is inevitable in the long term. It takes approximately 250 million years to make one orbit around the Galaxy. Between now and 250 million years ago approximately 4 extinction level events occurred that were extraterrestrial in origin. This is why we need to become a galactic species. Otherwise we most assuredly will become extinct like the dinosaurs. If that happens then all the great works of the past, present, and future will mean nothing. All of our great works of art, throughout the ages, all of our great poetry, architecture, all of the great music, everything would be utterly meaningless. Lost forever

 

[Patrick fenex]

Oumuamua, our first recognized visitor from Interstellar space. The mega comet, the first recognized Oort cloud visiter. Scientists have been looking for a Neptune sized 9th planet lurking well beyond Pluto's orbit. Two unprecedented objects that have never been seen before. If we continue to get more unprecedented objects coming from an elongated orbit from Deep inside the Oort cloud, then we must entertain the terrifying possibility that something massive must have Disturbed the Oort cloud in the past. And now we could be reaping The Unwanted benefits. The scars from the late heavy bombardment are still terrifying reminders of what another event like that could do, there would be no Escape. If anybody here likes a good spook story, this one will trump them all.

 

[p3orion]

What are the chances? One hundred percent. The real question is when.

 

[Catastrophe]

"One hundred percent. The real question is when."

I have to agree, but, of course, we are long past the Late Heavy Bombardment and there should not be another like it. Probably the main danger is from comets as, so far as we can guess, there are zillions out there in the Oort Cloud which, apparently, some doubt as still a model. Nevertheless, comets can come at much greater angles from the ecliptic, so we have to watch over a much a much larger area.
Anyway, there is still a lot of stuff out there, and we should be taking precautions. Possibly also to include rogue planets which, it seems, are now more plentiful than was thought hitherto.

Cat

 

[Catastrophe]

What I do have difficulty in understanding is how (or why) they calculate the orbits of NEOs (near Earth Objects) years ahead. Yet close passage by Earth can make a lot of difference to the orbit. (Inverse Square Law). Since the calculated orbit is approximate, surely how close they come to Earth affects future orbits?

Cat

 

[Lariliss]

1. Preparations.

• For the last 5 years of growing awareness the best collision evading is the planned launch of ‘Double Asteroid Redirection Test’ (DART) mission by 2021.
• ESA planned flight to Didymos by 2024.

2. Danger detection solutions are showing active development, but the precision looks far from enough.

As of June 2021, 26,115 NEAs and 2,185 potentially dangerous asteroids have been identified.
According to NASA analysis: ‘Apophis quickly gained notoriety as an asteroid that could pose a serious threat to Earth when astronomers predicted that it would come uncomfortably close in 2029. Thanks to additional observations of the near-Earth object (NEO), the risk of an impact in 2029 was later ruled out, as was the potential impact risk posed by another close approach in 2036. Until this month, however, a small chance of impact in 2068 still remained.’

• Sentry is a highly automated collision monitoring system that continually scans the most current asteroid catalog for possibilities of future impact with Earth over the next 100 years.
  
  
• Goldstone Deep Space Communications Complex.

The application for the 2021-2022 NASA Psyche Inspired internship program is open for new challenges of space exploration.

• Establishing an International Asteroid Warning Network (IAWN) is considered to be a critical step in collecting and sharing information about potentially hazardous NEOs.

3. Other evading asteroid collision technologies are in a development stage.

Statistically we win, waiting for the nearest collision will not happen.

Technically, numbers show there is not enough time. Not to mention projects’ budgeting and approval.

 

[Catastrophe]

That just says "detection, detection, detection," and then "other evading asteroid collision technologies are in a development stage".

Nothing whatsoever, as far as I can see, about preparing hardware.

Cat

 

[Lariliss]

That just says "detection, detection, detection," and then "other evading asteroid collision technologies are in a development stage".

Nothing whatsoever, as far as I can see, about preparing hardware.

Cat

The most information load is on detection, right. Thank you.

My apologies, for not going a bit deeper to the technical perspectives:

ESA Hera Mission
Hayabusa2 project
Making spaghetti from asteroids (quote)

Still, readability:
- probably x kiloton nuclear blast;
- approximately y time to travel;
- possibly z gravity pull to create.

Destroy - is the most probable.
Change trajectory - good concept.

And, yes, they didn't include Bruce Willis to the probabilities.

Also to add, I like activities on raising awareness and education on the subject.
Good example - Asteroid day.

 

[Catastrophe]

Asteroid Day was June 30th. Day of Tunguska.

"Asteroid Day is an annual global event which is held on the anniversary of the Tunguska event in 1908, when an asteroid leveled about 2,150 square kilometres forest in Siberia. The United Nations has proclaimed it be observed globally on June 30 every year in its resolution. Wikipedia"

Cat