Question How much more likely it would be that a meteorite or an asteroide would hit us if we didn't have a moon

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Catastrophe

"There never was a good war, or a bad peace."
And the certainty is that Earth will be impacted again - it just depends on the sizes of the impactors. Fortunately, the Late Heavy Bombardment is long over, but who knows what 'rogues' are out there? Apart from comets, it is now recognised that there may be more rogue (separate) planets out there than had been thought, and that's not to mention rogue stars.

Cat :)
 
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And the certainty is that Earth will be impacted again - it just depends on the sizes of the impactors. Fortunately, the Late Heavy Bombardment is long over, but who knows what 'rogues' are out there? Apart from comets, it is now recognised that there may be more rogue (separate) planets out there than had been thought, and that's not to mention rogue stars.

Cat :)
'Till the mountains crumble into the plain ... we'll keep on trying.'

'- it just depends on the sizes of the impactors', also I would add 'it depends on location', meaning habitats.

In sake of common sense, the effort put to observation refinement and facilities improvement should be worth it.
Confusions always make a lot of ripple in a community/society.
Distinguishing 'Rocket science' into two branches of science itself and engineering not often spotlighted.
Though, from astronauts' and engineers' interviews I concluded that they do.
Optimistic, of course.
 

Catastrophe

"There never was a good war, or a bad peace."
Yes, we should distinguish between the more common smaller impacts affecting only the smaller community level, and larger Earth threatening impacts which might affect the integrity of the planet, or 'only' life on this planet (the latter types being hopefully very rare).

It is worth mentioning that the Tunguska Event could have wreaked considerable havoc had it exploded over a large conurbation.

Cat :)
 
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Yes, we should distinguish between the more common smaller impacts affecting only the smaller community level, and larger Earth threatening impacts which might affect the integrity of the planet, or 'only' life on this planet (the latter types being hopefully very rare).

It is worth mentioning that the Tunguska Event could have wreaked considerable havoc had it exploded over a large conurbation.

Cat :)
One of an articles, which I have encountered, saying: '... of course it will not help dinosaurs, though...'
 
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Catastrophe

"There never was a good war, or a bad peace."
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Oh, yes. This facts came to my child egg-shelled mind (I didn't witness:)). Despite all the facts, still feels like mystery around it.
 
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Catastrophe

"There never was a good war, or a bad peace."
No mystery. Just exploded in the air, as some do. Cat :)

The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). ... Due to its high velocity and shallow angle of atmospheric entry, the object exploded in an air burst over Chelyabinsk Oblast, at a height of around 29.7 km (18.5 mi; 97,000 ft).

Chelyabinsk meteor - Wikipedia
 
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No mystery. Just exploded in the air, as some do. Cat :)

The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). ... Due to its high velocity and shallow angle of atmospheric entry, the object exploded in an air burst over Chelyabinsk Oblast, at a height of around 29.7 km (18.5 mi; 97,000 ft).
Chelyabinsk meteor - Wikipedia
Chelyabinsk the case when unexpected, and almost catastrophe. Shock. So close. People should still feel that emotion and even pain.
News came instantly from the web videos.
Telecom and internet are always put to test as a part of globalization (pro's and con's).
This is an example of spotlight for every one to keep in mind. Which is 'talk and talk', and which is 'walk'. Thinking of several hundred meters in the universe scale is nothing.
I am going to an essay:)
But to think, even Chernobyl and Fukuhsima are not well known and remembered.
Good that it is possible to ask, search and get educated.
When one wishes :)
 
As I'm used to be in certain cases, I want to begin saying that I'm not an expert. :)
I'm not an expert, but if I understand correctly from the OP, he tells us that the moon is the one-hundredth of our planet...
The moon is about 100 times lighter at a distance of about 400,000 km, so the center of gravity of the system is somewhere 4000 km from the center of the earth towards the moon. I guess the number is between 10 and 100 times more impacts but i would prefer an expert opinion.

barycenter earth moon
Is this possible???
I remember that our Moon is one-sixth of Earth...

However, letting this possible misunderstanding down, I think that the post #13 is something good to take into account since I think that the gravity of the two isn't so important in comparison to the scale of te distance...
 
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Catastrophe

"There never was a good war, or a bad peace."
Sorry, I thought I had posted Tunguska.
Strange, because I had Googled Tunguska explosion.

Hopefully this is better:

BBC - Earth - In Siberia in 1908, a huge explosion came out of nowhere

Fortunately, the area in which this massive explosion occurred was sparsely inhabited. There were no official reports of human casualties, though one local deer herder reportedly died after he was thrust into a tree from the blast. Hundreds of reindeer were also reduced to charred carcasses.

Cat :)
 
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Sorry, I thought I had posted Tunguska.
Strange, because I had Googled Tunguska explosion.

Hopefully this is better:

BBC - Earth - In Siberia in 1908, a huge explosion came out of nowhere

Fortunately, the area in which this massive explosion occurred was sparsely inhabited. There were no official reports of human casualties, though one local deer herder reportedly died after he was thrust into a tree from the blast. Hundreds of reindeer were also reduced to charred carcasses.

Cat :)
This is a good story from BBC, thank you,.
Balanced between "People who like secrets and 'theories" and facts.

Interesting thing, that one of global problem is over crowded cities (big known ones,
Paris, London, New York, Melbourne, Beijing Cairo and less have projects to overcome it. The list is larger.
1. Common solution (looks very temporary) to reconstruct parts of the city with new buildings, use reclaimed industrial territories.
2. Build a new city nearby.

In the same time this 'overcroudness' is about 5% of territory where people can live.
Most of the places are deserted (not wild, this is another issue).
So, chances are little, that 'it' will hit a lot of people. But the Chance never asks our opinion or statistics :)
Actually, here it also comes to a logarithmic straight line, like coin tossing up.

Some sources say, there are recorded human deaths thousands years ago in China.
When I encounter a liable ones, I will share.

All the collected facts, calculations, insights would be under 'inhabitant [me] and comets' headline.)
 
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Catastrophe

"There never was a good war, or a bad peace."
As you rightly point out, just because impacting a large city would be disastrous, it does not mean that it it probable. Impactors are more likely to land in oceans (which does not necessarily mean harmless). The point is, that the lottery ticket has to turn up somewhere. That does not mean that it cannot hit just you.

Cat :)
 
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Here some update (double checked with other sources).

Is it there are only about 15% of asteroids have known orbits, which are still changing?

What we have as savior action:
1. Nuclear destruction. It still come back in pieces or gravitate back again to the same size. Also possible the pieces come as a dust to the atmosphere and cover the Sun.
How many ready to go facilities there should be?
Nuclear explosions were conventionally prohibited in the Earth proximate. Almost 100 years race to maintain nuclear power seems vague to be started easy and even possible (statistically war vs threat from cosmos).
2. Attach a rocket to change the trajectory. We don’t know how to do, the fact of an asteroid is rotating makes it more unpredictable.
3. Boil with a laser. Possible.
4. Wrap into a ‘cooking foil’. Still we don't know how to do that.
5. City evacuation. Every time should be (in my opinion), but from the experience, evacuating even not a large city is hard or not possible in time.

Asteroid ablation using highly concentrated heat is the only method that meets all of the following criteria: scalability up to global-threat sizes and any type of hazardous bodies as well as low cost and environmental friendliness.

And, of course, DART
References:

P.S. Comet part not more to add yet. Though it has another question: what are the capabilities to detect 'new comers'. Can we compare history activities and today searches beyond?
On - going.
 

Catastrophe

"There never was a good war, or a bad peace."
What exactly are you getting at?

" According to the European Space Agency, roughly 10,000 of the known asteroids are NEAs."

If they are NEAs their orbits must be known, at least partially, to categorize them as NEAs. Maybe eccentricity is not closely defined. I don't know.

"With regard to Trojans, more than 6035 (2014) are known, 2/3 at Lagrange 4 and most (all?) of the rest at L5. Since these orbits are quite stable (which L1, L2, and L3 are not) these orbits must be known. Capital T Trojans means with Jupiter/ Small t (comparably not very many) trojans means around other planets, e.g., 2014 figures give Neptune 9, Earth and Uranus 1 each, Mars 2.

WISE reported 76 families (May 2013) after studying 120,000 Main Belt objects, and there were 38,000 within these families. Due to their origin, the orbits of families must be known, at least approximately.

Approximate numbers reported for the following categories must also have orbits known, at least approximately, to come within the stated categories:
Amor asteroids > 4119 asteroids, Apollo > 4892, Aten > 19, Atira >19, Hilda >3774, Centaurs > 245, and Main Belt > 576,902. Technically you should take > to mean greater than or equal to, especially for the smaller numbers.

As far as destroying or diverting asteroids on potential impact courses is concerned, you must also remember that some may already be loose aggregations, which means that some suggested courses of action may be counter-productive.

Cat :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Trouble with comets is that they can come at any angle to ecliptic, including coming over poles. Makes detection more difficult. And, of course they are dark lumps of dirt/ice etc until they get close to Sun when tail develops.

Cat :)
 
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What exactly are you getting at?

" According to the European Space Agency, roughly 10,000 of the known asteroids are NEAs."

If they are NEAs their orbits must be known, at least partially, to categorize them as NEAs. Maybe eccentricity is not closely defined. I don't know.

"With regard to Trojans, more than 6035 (2014) are known, 2/3 at Lagrange 4 and most (all?) of the rest at L5. Since these orbits are quite stable (which L1, L2, and L3 are not) these orbits must be known. Capital T Trojans means with Jupiter/ Small t (comparably not very many) trojans means around other planets, e.g., 2014 figures give Neptune 9, Earth and Uranus 1 each, Mars 2.

WISE reported 76 families (May 2013) after studying 120,000 Main Belt objects, and there were 38,000 within these families. Due to their origin, the orbits of families must be known, at least approximately.

Approximate numbers reported for the following categories must also have orbits known, at least approximately, to come within the stated categories:
Amor asteroids > 4119 asteroids, Apollo > 4892, Aten > 19, Atira >19, Hilda >3774, Centaurs > 245, and Main Belt > 576,902. Technically you should take > to mean greater than or equal to, especially for the smaller numbers.

As far as destroying or diverting asteroids on potential impact courses is concerned, you must also remember that some may already be loose aggregations, which means that some suggested courses of action may be counter-productive.

Cat :)
Thank you for reminding the key concern.
I forgot to mention, that yes, any kind of playing snooker with asteroids is especially unpredictable and dangerous.
My point is that, any 'surprise' asteroid may come just within hours noticed, because exact trajectory of all of NEO is approximately known. What is deviation 'equals or closer than..', I don't know (yet?) :)
Eccentricity plus their own interaction. I would say: 'approximately known' is one of the points of my previous post.

P.S. 'As of 2020, of the more than 7,000 Jupiter Trojan asteroids discovered, about two-thirds are located near L4, and the remainder are near L5'. Matches from here.
 
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Trouble with comets is that they can come at any angle to ecliptic, including coming over poles. Makes detection more difficult. And, of course they are dark lumps of dirt/ice etc until they get close to Sun when tail develops.

Cat :)
For me, detection really comes to the spot as a the main drawback.
 
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I was inclined to the opinion that the following was pretty convincing:

"To protect the tennis ball from snowflakes, have someone hold a marble a meter and a half (5 feet) away, and move it around your tennis ball. The snow flakes that hit the marble will not hit your tennis ball, so it is protecting it a bit."

I am getting a little lost with "moonlight, tides, eclipses, contributing to + ".

Does that mean that the Sun similarly protects the Earth from impacts?
Vide sunlight, tides, eclipses contributing.

Cat :) :) :)
Your tennis ball is static, in the system earth-moon also the earth spins around the baricenter.
 

Catastrophe

"There never was a good war, or a bad peace."
So . . . . . . . . . . . . . . .

I don't see that that makes any difference. The same cross-section-area is exposed, although the actual geographical area on the Earth is attenuated. Just impacts spread out instead of all being on the same geographical area - like the Americas for example. Only so many snowflakes per square mile, wherever that square mile happens to be.

Cat :)
 
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Genuinely.
Sorry for any inconsistency or bald approximation in advance.

Input:
NEO Asteroids number:
Apollos: 10,000
Amors: 8,000
Atens: 1,400
Atiras/Apohele: 31

Potentially hazardous asteroids (PHA): 157

Earth disc, sqm: 124,000,000
Moon disc, sqm: 9,000,000

Earth to Moon distance, km: 384,000

Assumption:
  • All NEO asteroids presence in the same time;
  • According to simulations from asteroid presence from internet, the Moon is roughly covering the Earth from directed asteroids in half day time;
  • Calculate 1 year protection impact;
  • The asteroid’s position uncertainty region at the time of the potential impact is much larger in both length and breadth than the size of the Earth. Impact could occur anywhere on the forward hemisphere during the hour or so when the Earth crosses the asteroid orbit and sweeps through the uncertainty region (NASA exercise);
  • Taking into account inverse square law and Kepler’s 2nd law.

Case 1 (‘snowflake’ approach):
PHA.
  1. The Moon takes about 8% of the asteroids: 12 instantaneously.
  2. Divide 2 (half of the day), multiply 365: 2190.
Case 2 (‘snowflake’ approach):
Only Apollos and Atens (leave Amors to Mars).
  1. The Moon takes about 8% of the asteroids: 912 instantaneously.
  2. Divide 2 (half of the day), multiply 365: 166,000.

According to Sentry table, not instantaneous coming of the asteroids, means not oftener that once in 30 years (worst).

In this case, PHA 5 asteroids could come in 1 year. The best help from the Moon would be 1.

Taking into account that PHA does not necessarily hit the Earth, the Moon’s help goes up to about 20%.

The already mentioned study shows 59 hazardous hit the Moon during the past several hundred million years. The investigated number for the Earth for the same period is about 170 asteroids, which is actually 34%.

So, we may conclude valuable impact of the Moon into asteroid hit protection for the Earth.
Thank you a lot for the research :).... I still think that there is even more Moon protection....and, planets with moons are beter for life in general.
 

Catastrophe

"There never was a good war, or a bad peace."
RogergR,

" I still think that there is even more Moon protection....and, planets with moons are beter for life in general."

You may well be correct, but I think the protection offered by the Moon is small, but, nevertheless, helpful.

Cat :)
 
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So . . . . . . . . . . . . . . .

I don't see that that makes any difference. The same cross-section-area is exposed, although the actual geographical area on the Earth is attenuated. Just impacts spread out instead of all being on the same geographical area - like the Americas for example. Only so many snowflakes per square mile, wherever that square mile happens to be.

Cat :)
Snowflakes in this case are not usefuly random. Falling objects in the direction earth-moon are atracted by gravity, and the baricenter of earthmoon is the center where they are "targeting", if we ignore the sun, the other planets and moons and the nonvacuum at all interspace.
 

Catastrophe

"There never was a good war, or a bad peace."
"If one of the two orbiting bodies is much more massive than the other and the bodies are relatively close to one another, the barycenter will typically be located within the more massive object. In this case, rather than the two bodies appearing to orbit a point between them, the less massive body will appear to orbit about the more massive body, while the more massive body might be observed to wobble slightly. This is the case for the Earth–Moon system, in which the barycenter is located on average 4,671 km (2,902 mi) from Earth's center,"

I think you are splitting hairs. The barycentre is just under 3000 miles from the Earth's centre, inside the Earth, and the Moon is 240,000 miles away. There is only a slight wobble involved. It comes back to swings and roundabouts. There is a see-saw action whereby each body slows down a little and then catches up. It does not affect the number of snowflakes hitting the fixed area - just which geographical area, e.g., Europe/Africa vs. Americas.

I am only using snowflakes to suggest coverage of an area, and thus the chance of any individual snowflake, bullet, meteorite, asteroid, whatever, hitting the Earth.

Cat :)
 
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"If one of the two orbiting bodies is much more massive than the other and the bodies are relatively close to one another, the barycenter will typically be located within the more massive object. In this case, rather than the two bodies appearing to orbit a point between them, the less massive body will appear to orbit about the more massive body, while the more massive body might be observed to wobble slightly. This is the case for the Earth–Moon system, in which the barycenter is located on average 4,671 km (2,902 mi) from Earth's center,"

I think you are splitting hairs. The barycentre is just under 3000 miles from the Earth's centre, inside the Earth, and the Moon is 240,000 miles away. There is only a slight wobble involved. It comes back to swings and roundabouts. There is a see-saw action whereby each body slows down a little and then catches up. It does not affect the number of snowflakes hitting the fixed area - just which geographical area, e.g., Europe/Africa vs. Americas.

I am only using snowflakes to suggest coverage of an area, and thus the chance of any individual snowflake, bullet, meteorite, asteroid, whatever, hitting the Earth.

Cat :)
But can you tell me how much is this "slight wobble" involved?

I can tell you how big is that "wobbleing", easy maths.
In terms of perpendicular to the system we get a circle area which is 3 times larger than 2D earths area, and in terms of horizontal (ecliptic) view of the system we get an ellipse that is 1,7 times larger that 2D earths area. Also the moon is 5 degreas inclinated to the ecliptic, so the true numbers are biger.

And pls dont troll in this thread anymore.
 
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