# An asteroid will hit Earth at some point. What can we do about it?

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#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
Think carefully about solar sails. They need to be large to be effective, but strength and resistance to puncture/tear require rapid increase in weight to match increasing size. Durability requires greater mass.

Cat

#### Atlan0001

The questions about feasibility depend on how big it is, how far we have to move it and how long we have. Just to pick some reasonable numbers:
- 100 meter diameter, density of rock, 4.5
- Ten years to move it
- Must move one Earth radius to get it out of the way

Volume = 523,000 m^3
Mass = 2,360,000 tons
Distance = 5,500,000 m
Time = 3e8 s

Distance = 1/2 a t^2
5,500,000 = 1/2 a (9e16)
a = 1.2e-10 m s^-2
F = ma
F= (2.36e9 kg ) (1.2e^-10)
F = 0.28 Newtons or about 28 grams, or one ounce, delivered for ten years.

If done in one, ten minute burst, a 600 pound force would suffice.
Bill, you are thinking in absolutes again ("a 600 pound rock").

I have one absolute for you to consider: "The total mass matter and energy of the universe equals zero."

Yet another that I consider opposing the local relative "600 pound rock", self-similar fractal zooms universe structure.

Yet another is that is that infinity is (infinities are) the constant, finite is not a constant!

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#### billslugg

"The total mass matter and energy of the universe equals zero."
Yes, this is true, however neither is evenly distributed. My plan is to redistribute some of that energy into a rock so it does not distribute itself upon the Earth. I JUST had my lawn mowed and if it gets mussed I'm going to get peeved and annoyed.

Atlan0001

#### Atlan0001

Yes, this is true, however neither is evenly distributed. My plan is to redistribute some of that energy into a rock so it does not distribute itself upon the Earth. I JUST had my lawn mowed and if it gets mussed I'm going to get peeved and annoyed.
Bill, I do enjoy our back and forth very much. No one causes me to have to think harder than you do. Nor is anybody else more understandable to me than you are from the consistency of your posts and responses.

Plus, often, your maintenance of humor.

#### billslugg

Thank you for your kind words! I struggle to understand the cosmos as we all do. When we get something figured out we need to share it.

Atlan0001

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
Zero-energy universe - Wikipedia

Some interesting background here.

QUOTE
Experimental constraints
Experimental proof for the observable universe being a "zero-energy universe" is currently inconclusive. Gravitational energy from visible matter accounts for 26–37% of the observed total mass–energy density.[15] Therefore, to fit the concept of a "zero-energy universe" to the observed universe, other negative energy reservoirs besides gravity from baryonic matter are necessary. These reservoirs are frequently assumed to be dark matter.[16]
QUOTE

Cat

Atlan0001

#### Atlan0001

Zero-energy universe - Wikipedia

Some interesting background here.

QUOTE
Experimental constraints
Experimental proof for the observable universe being a "zero-energy universe" is currently inconclusive. Gravitational energy from visible matter accounts for 26–37% of the observed total mass–energy density.[15] Therefore, to fit the concept of a "zero-energy universe" to the observed universe, other negative energy reservoirs besides gravity from baryonic matter are necessary. These reservoirs are frequently assumed to be dark matter.[16]
QUOTE

Cat
My loose quote comes from one of my absolute favorites, Stephen Hawking's book, 'A Brief History of Time'. I assume the intent of his response to those who calculated the total always and forever being "zero," then sort of went into a panic over it, was to realize on the spot it ties to a constant of creativity of the universe, which from that and other things presented in cosmology and physics, I altogether see as and term as "spontaneous concurrent REALTIME (t=0)."

My idea of cosmic "creativity" and others' ideas of it, obviously, do not necessarily meet in the same definition, the same realization, of it.

As with Bill, I'm glad you qualified with "currently." When we do get out to the ground, I'm certain we will learn something new, or simply different (still new), about cosmology and the physics.

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#### Cisventure Astronot

The DART experiment knocked a lot of debris off of the asteroid. If used near the Earth, it could deflect the asteroid, but not the debris of boulders. Also consider what happens if the first shot misses, or doesn't deflect the asteroid enough ‒ will we need launch several impactors for a single asteroid?

A powerful laser might be more effective at deflecting the entire mass, especially if the laser can be pulsed in time with the asteroid's rotation. Possibly pulsing a giant laser will be cheaper and easier than launching a series of masses. And it certainly could be used to propel solar sails.

Hmm... Maybe SETI should be looking for laser light.
If such a laser can be reasonably built, then I think it'd be the better solution. But I don't know whether that's the case. I think DART and Starlink prove that the impactor method is practical, though. Assuming Wikipedia is right, and all Starlink satellites are V1, then SpaceX has deployed a metric kiloton into orbit via >5000 satellites. We don't need that many nor that much mass, so the most difficult part would be the complexity in the satellite.

I don't think the ejecta would be a problem. I just feel like they would accelerate more than the main body, but even if they didn't, then they might just burn up in the atmosphere.

Fire-Starter James

#### Atlan0001

Too many are missing the point! Any object coming from interstellar space toward us will more than likely be coming at speeds near the speed of light, observed! As such they will be too near, too soon, to be dealt with and stopped. With the opening of space, the expansion to space, there will be more and ever more searching eyes, human and instrumental, farther and ever farther out in the search. And it is the ever growing numbers and that reach and grab ever farther and farther out that will be necessary!

#### Unclear Engineer

Something coming at us from interstellar space is not likely to be traveling at anything like the speed of light.

But, it could be coming too fast for us to react to deflect it in the time available after we discover it.

So, far, the probability for that to happen seems to be less than the probability that an asteroid we find will eventually hit us during a future orbital conjunction. So, we at least need a defense system to address that scenario.

Other scenarios would be more difficult. An extremely powerful laser seems like a good idea, and some are already being built for various reasons (fusion, weapons, etc.). A laser would be much faster than anything that must travel to the object via orbital mechanics. And aiming errors could be corrected much sooner. Plus, the push on the object could be more evenly distributed.

One nice thing about comets is that the are easy to evaporate with a laser, so they could be pushed more effectively than less volatile asteroids. Which would help to compensate for their greater probability of not being detected before their trajectory would make them hit Earth on the current orbit.

Fire-Starter James

#### Cisventure Astronot

Too many are missing the point! Any object coming from interstellar space toward us will more than likely be coming at speeds near the speed of light, observed! As such they will be too near, too soon, to be dealt with and stopped. With the opening of space, the expansion to space, there will be more and ever more searching eyes, human and instrumental, farther and ever farther out in the search. And it is the ever growing numbers and that reach and grab ever farther and farther out that will be necessary!
I don't think we're missing the point. Half of the problem is detecting the meteoroid early enough, and the other half is dealing with it. I think it's easier, and more fun, to talk about dealing with it. You're right about the detection being very important, though. By the time we detected ʻOumuamua it was already on its way out! But I don't know the first thing about meteoroid detection.

#### Classical Motion

We need enough time for 3 tries. Plan A, B, and C.

#### Fire-Starter James

If such a laser can be reasonably built, then I think it'd be the better solution. But I don't know whether that's the case. I think DART and Starlink prove that the impactor method is practical, though. Assuming Wikipedia is right, and all Starlink satellites are V1, then SpaceX has deployed a metric kiloton into orbit via >5000 satellites. We don't need that many nor that much mass, so the most difficult part would be the complexity in the satellite.

I don't think the ejecta would be a problem. I just feel like they would accelerate more than the main body, but even if they didn't, then they might just burn up in the atmosphere.
I think you're right about the ejecta. Maybe the best choice for now is to not restrict ourselves to a single method.

#### Ken Fabian

Just what many Europeans called the Americas circa 1490s-1510s, the "Louisiana Purchase," "Seward's Alaska Folly," and so on throughout history both before and ever since, "a money sucking fantasy"! Throughout history, people haven't changed, not one bit! You have the imperative [the future is now] frontier expansionist-energy minded and then you have . . . the other kind (oh, it's important but Earth first, last, in between and always, never ending (and always failing))!

They can't even see life's real relationship -- particularly mankind's real relationship -- to the Earth, much less to the world, the universe, outside the womb-world in a "due time of birth"!

Whatever their goals, including Earth defenses against extraterrestrial dangers, they won't attain them in a coming decline and decay of a world closed systematically isolated from frontier; Isolated from the expanding energies of an opening system which would as always be bound to frontier colonization (permanent occupancy). They won't have their world if they win their way! They will have what they made, if even that, and they won't like it one little bit! With their kind of minds they would deny even to themselves that they made it . . . as they are denying it today!

So, as always with frontiers in history, to borrow from Winston Churchill: Never in the field of human endeavor will so much be owed by so many to so few, the openers who find a way no matter the seeming invincible barriers (of not now!) always in place and always being raised. Given enough time, soon enough, they will one day see and capture the asteroid no one else saw in the first place to stop . . . or could stop.
In this case it really is a money sucking fantasy - and so fundamentally different to any prior colonizations that there are no valid comparisons. The Americas presented readily exploitable economic opportunities using already existing technologies based on true abundance of familiar resources, earning real returns - extraordinary returns - for the homeland.

Colonising space is not viable and the principle reason is extreme costs. When asteroid resources worth \$10,000 per ton raw and unprocessed exist in great abundance, that contain materials worth millions per ton with refining cost so much to exploit that they are not worth the effort the barrier to doing it isn't shortsighted parochialism by people like me. The same level of costs that makes asteroid PGM's not worth the effort makes colonies non-viable, only much more so.

I think your "expand or perish" view of human progress is naive and simplistic and false; there are multiple motivations for advancing technology, including space capabilities without depending on those unrealistic ambitions and exaggerated expectations.

#### Atlan0001

In this case it really is a money sucking fantasy - and so fundamentally different to any prior colonizations that there are no valid comparisons. The Americas presented readily exploitable economic opportunities using already existing technologies based on true abundance of familiar resources, earning real returns - extraordinary returns - for the homeland.

Colonising space is not viable and the principle reason is extreme costs. When asteroid resources worth \$10,000 per ton raw and unprocessed exist in great abundance, that contain materials worth millions per ton with refining cost so much to exploit that they are not worth the effort the barrier to doing it isn't shortsighted parochialism by people like me. The same level of costs that makes asteroid PGM's not worth the effort makes colonies non-viable, only much more so.

I think your "expand or perish" view of human progress is naive and simplistic and false; there are multiple motivations for advancing technology, including space capabilities without depending on those unrealistic ambitions and exaggerated expectations.
You seem not to have not the slightest clue of either history or physics, that you keep on proving! Learn, please!

The "extreme" costs, or as Stephen Hawking among others have put it, the "extinction" costs, are the costs of not doing it! Money is a token of energy! What is the world's deficit(!), the world's sink(!) . . . the world's ever increasing debit and debt?! Your technological understanding, and understanding of history and shrinking distances via increasing energy, structure and infrastructure complexity, is that mankind never advanced beyond the Stone Age and dugout canoes! Really it is not due for birth and breakout to Space, it is overdue, the same as the Earth is becoming overdue for the next 'Ice Age' of Earth!

The chips in our computer systems, among other technologies, are 'Space Age' technologies! Our shrinking the distances of the planet are advancements to 'Space Age' expansion! Our ever increasing conflicts, and rising virulence of those conflicts, those strange attractors of chaos, vast movements across the landscape of the planet, both local and remote, bespeak no civilization . . . bespeak a due time of birth to new frontiers outside Earth, else a new Dark Age of Un-Civilization! And Ken Fabian, among many others, I will continue to take the part of a composite Old Testament Biblical 'Moses' calling for Genesis, Space (island) 'Arks', and Exodus! You (you people in a generality of the blind) are deliberately blindly facing and bringing on everything Hawking and all the other futurist prophets have been prophesizing for a century and more!

If you seek a war, a total war, a world war, the take out of civilization in barbarism and savagery, Ken Fabian, you've got one on your hands you've made, right now, not tomorrow! Look around you at home and the world over! There is no peace, no world's rise out of a sinkhole of deficit of positive energies and wealth, no gravitation to unity in 'One World' of Earth, and none coming on the horizon until there is breakout, a beginning of birth and expansion to Space and a New Frontier, a 'New World' out there and a rebirth in the other 'New World' in here (two worlds . . . and the other not Mars)!

You want to try to slap down what is become so obvious not in some distant world but in personal experience to so many in the world...?! You're not going to lose . . . you've already lost!!!

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George²

#### Atlan0001

The Roman and Chinese, and other great empires and nations (peoples) of history, shone hottest burning meteoric brightest not in their breakout frontier beginnings and rises but in their in-turning Utopian (again meteoric hottest burning!) "Decline and Fall" into Utopian (Dystopian) 'Dark Ages'!

In in-turning, they "deficit spent" themselves into darkness, into oblivion!

The world isolated from breaking out and opening the frontier universe is into "deficit spending" of wealth, of energy, on a "money (energy ("money is a token of energy")) sucking fantasy" of impossible Utopia Earth, BIG TIME! It's an Orwellian psycho-drug addiction, a mass addiction that debilitates and kills "en masse"!

Life, especially higher far more complex and therefore more chaotic, human life, is a combustion engine that is always in need of exhausting to outer spatial frontiers.

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#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
Has anyone considered the following?

Now consider how far an asteroid may travel after it has been seen, recognised as a potential threat, and preparations completed to launch, and despatch?

How fast will our countermeasure travel? How long will it take to slow it down, if, as in some scenarios, its speed must to reduced to match that of the asteroid? Vide gravitational effects?

How far away (or how close) will any potentially hazardous asteroid (or other body) be before it is discovered? Remember comets only develop visible tails on approaching the inner solar system.

Of course, impacts with very large bodies are unlikely. But . . . . . .

Cat

I am sure you will be interested in my confidence in reading the following in All About Space Issue 156, May 2024, page 37:

As of yet, there's no known weapon system capable of shooting down asteroids in the minutes or hours before impact, because of their sheer velocity.

For those interested, it is in an article entitled "72 hours until impact" by Libby Plumber

Cat

#### Unclear Engineer

Um, don't we want to "shoot it up", not "down"? No, wait, that's not it, either. We want to "deflect" it, so it never gets "down" to us.

(English idioms are such fun - who else gets to chop trees down then chop them up?)

Catastrophe

#### Atlan0001

This one we know is coming is said to be a thousand feet wide, not fifteen miles wide. Knowing it's coming by the Earth and when, If the distance from the Earth has been miscalculated, we've the means of blasting it to hell and gone. It's only a matter of prepping for it or sitting on our hands and allowing it to...!

#### billslugg

Suppose a potential impactor of 1000 foot (300 meters) diameter is detected with, say, 10 years to push it aside, how hard would we need to push on it? Assume a density of 4.5 which is typical silica based rock. Assume the impact point is dead center on the Earth, the worst possible point.
The volume in cubic meters is 4/3 * pi * (300/2)^3.
V = 1.4e7 m^3
At 4.5 specific gravity the mass is 6.4e7 tons, or 6.4e10 kg
It must be moved sideways a distance equal to Earth's radius, which is 6.4e6 m.
The kinematic equation is S1 = S0 + V0* t + 1/2* a* t^2
S1 = 6.4e6 m
S0 = 0
V0 =0
t= 10 years = 3.1e7 s
We get: 6.4e6 m = 0 + 0 +1/2 * a * (3.1e7 s)^2
Reducing and reorganizing we get: a = 1.3e-6 m/s^2
Now calculate the force. F = m * a
F = 6.4e10 kg * 1.3e-6 m/s^2
F = 8.3e4 newtons = 8,600 kg

There is not really any way with our current technology to make a 8,600 kg thrust on a far away asteroid for a ten year period.

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#### Classical Motion

I'm thinking that with only a 10 year warning, our only solution is to hit the rock with a nuc right before dead center just as soon as possible. Hopefully no large fragments will be left on collision course. It's a dirty solution and can cause future close calls, but can be tracked. It would be interesting to see what degree of vaporization actually occurs.

We need to nuc one out there and verify the result. Watch the expression of the debris. This should have been done years ago, maybe it was.

#### billslugg

Let's look at the total energy needed to move a bunch of fragments out of the way. This equation does not include the energy needed to bust it up. Just assume the nuke was only needed to move the pieces out of the way.

The energy in joules = the amount of kilograms of push times the number of meters being pushed. Then assume a nuclear bomb with x megatons at 4.5e15 joules/megaton.

Total energy = 8,600 kg times 6.4e6 m = 5.5e10 joules. This is but a tenth of a percent of a one megation nuke. I will be going with the nuclear option.

#### Classical Motion

Yeah but what happens if a nuc in space just makes a space bubble, and all come back together when the bubble collapses?

We got to light one up and make sure it works.

#### billslugg

The nuke will be carefully selected such that the remnants of the asteroid are pushed away from each other at more than escape velocity. They won't come back together. Unfortunately public outrage would likely preclude any preemptive nuclear explosion in space since it would be a violation of the Space Treaty. Only when there is a public outcry to do something will we modify the treaty.

#### Unclear Engineer

Bill, I think you made a math error. I get the acceleration value needed for your calculation of "a" from
6.4e6 m = 0 + 0 +1/2 * a * (3.1e7 s)^2
to be 6.4e6m x2 / (3.1e7)^2 = 1.3e-8 m/sec^2.
So, F = 1.3e-8m/sec^2 x 6.4e10Kg = 8.5e2 newtons,
which is 8.5e2 newtons x 0.224809 pounds (force)/newton = 191 pounds of thrust for 10 years.

But, I don't think that is the way to do the calculation, anyway. For one thing, a dead center hit trajectory changed to just skimming the surface would be a disaster, anyway.

But, it really isn't a matter of moving the asteroid to the side, it is more a matter of changing its orbit enough to change the timing of when it crosses Earth's orbit.

We need to speed up the asteroid or slow it down, so that its timing for crossing Earth's orbit is changed enough to make it miss by a substantial distance. So, the actual calculation is going to depend a lot on the particular parameters of orbit of the asteroid around the Sun.

Think of it this way: a circular orbit around the Sun is roughly 93 million miles time 2 pi = 584 million miles around. And it takes 365.25 x 24 = 8766 hours, so the average orbital velocity is 584 million / 8766 = 67,000 miles per hour.

Let's say that a near Earth asteroid will have roughly similar average speed, on a more elliptical orbit that crosses Earth's orbit. So, it will go about 10 x 584 million miles in 10 years. If we slow it down by 1 miles per hour, in 10 years, that is a distance of 10 x 8766 hours x 1 mph = 87,660 miles away when the orbits cross.

That would be an acceptable distance, but it really is not that simple to calculate, because the point of crossing will also change, plus the Earth's gravity will be attracting the asteroid, rather than leaving it on its orbit unperturbed.

Still, it is a better way to think about what the delta V needs to be. So, maybe look at what it would take to slow the asteroid down by about 1 mph in a short period, or slowly for a total of about 2 mph over 10 years to get an estimate of how well our current technologies would be able to protect us.

It's bed time, so I will leave that calc to you.

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