If you place a laser pointer on its side on a table and point it at the wall across the room, there will be a straight beam of light, of course. Then, if you twist the laser pointer on the table only 2-5 millimeters, the location where the laser was hitting the wall will move much greater than 2-5 millimeters; it will move maybe an inch or more. So, a very small movement of only a few millimeters on the table produces a much larger effect/offset on the wall across the room-maybe an inch or more.

If you increased the distance from instead of across the room to a mile, then twisting the laser pointer the same 2-5 millimeters on the table would offset the laser at the other end many many feet. So you've increased the offset from a inch to many many feet by increasing the length of the laser beam to a mile.

So, as you increase the length of the laser beam, the offset at the other end becomes larger and larger by only twisting the laser pointer 2-5 millimeters.

This concept means that an asteroid/comet that is on a collision course with Earth would have to be moved less and less the farther you went out to meet it. At 500,000 miles out from Earth, you'd have to move the asteroid/comet maybe miles. At 4 million miles out from Earth, you'd only have to move the asteroid/comet a few millimeters. This is better because it is possible; to move the asteroid a few millimeters can be accomplished with 1-4 nuclear weapons, depending on the asteroid's/comet's size.

Moving the asteroid/comet a mile cannot be accomplished. It is too big to be moved that far.

The farther out you go from Earth, the less the asteroid/comet has to be moved, so the easier it becomes to move. Once the asteroid/comet is on top of you (close to Earth) it's too late.

So, the solution is that you have to "chase it down". When you see an incoming asteroid/comet you have to intercept it as far out into space away from Earth as possible, whereby you have a good chance of moving it.

The only downside to this plan is that your computer trajectory calculations would have to be unimaginably precise. You could accidentally cause an asteroid/comet (that was originally supposed to miss us) to slam into us by changing its trajectory.

The lengths that I used in this post are just examples. You'd have to take actual readings to get correct numbers.

Edited July 24Jul 24 by Nvredward
Clarity.

Yes, this is based on first-semester physics and high-school geometry. As far as trajectories go, we’ve landed a probe on an asteroid. The skills exist.

This is a discussion board — was there something you wanted to discuss?

18 hours ago, swansont said:

Yes, this is based on first-semester physics and high-school geometry. As far as trajectories go, we’ve landed a probe on an asteroid. The skills exist.

This is a discussion board — was there something you wanted to discuss?

Reading through the opening post, I thought it was going to be about the notion that the laser point, if far enough away, would be travelling faster than the speed of light.

In the movie Armageddon they drill into the asteroid/comet and in the movie Deep Impact they fly into a fissure. Doing those things could create multiple smaller pieces, which could be dangerous within themselves. Something to be cautious about.

@Nvredward

1 m^3 of water/ice has ~900- 1000 kg. e.g. comet.

1 m^3 of iron has ~ 7900 kg. e.g. iron asteroid.

(so on average it will be a value between these two values)

The deadly asteroid ranges in size from several hundred meters to several kilometers and more.

Calculate its hypothetical volume.

Knowing its average density and volume you can estimate its mass.

The velocity can range from 30 km/s to 60 km/s or more in the case of interstellar objects.

Based on mass and velocity, you can calculate the kinetic energy of an object and the amount of energy needed to change its trajectory.

15 minutes ago, Sensei said:

The deadly asteroid ranges in size from several hundred meters to several kilometers and more.

The "and more" seems quite certain. 😀

On 7/24/2025 at 11:10 PM, KJW said:

Reading through the opening post, I thought it was going to be about the notion that the laser point, if far enough away, would be travelling faster than the speed of light.

That's the one where the "motion" of the laser point is only apparent? A fun conundrum.

2 minutes ago, TheVat said:

The "and more" seems quite certain. 😀

“The sky is the limit”... you can always come across a black hole that has been gravitationally ejected from a binary system and is now wandering through the vastness of space...

On 7/24/2025 at 10:02 AM, Nvredward said:

If you place a laser pointer on its side on a table and point it at the wall across the room, there will be a straight beam of light, of course. Then, if you twist the laser pointer on the table only 2-5 millimeters, the location where the laser was hitting the wall will move much greater than 2-5 millimeters; it will move maybe an inch or more. So, a very small movement of only a few millimeters on the table produces a much larger effect/offset on the wall across the room-maybe an inch or more.

This sounds wrong. Changing the angle a laser pointer is aimed changes where it hits - it isn't moving the position of the laser pointer that is important. If you move it across and keep the orientation angle exactly the same - parallel - where it hits will move the same amount. But change the angle a laser pointer is aimed and that changes where it hits even without moving it. However the idea that changing the direction (not position) of an asteroid is moving a small amount when it is far away will change where it hits by a lot is correct.

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Ongoing efforts for identifying and tracking asteroids/comets with potential to hit Earth continue - at least so far, don't know what Trump's interventions will do to that. NASA has been aiming to find every object of sufficient size and orbit to do serious damage. Nothing dinosaur killer sized within the solar system represents a threat - those objects are big enough to find relatively easily and have already been identified and their orbits determined. It is the ones not that big but big enough to do serious damage, that exist in large numbers. that have not all been found. Identify them, track their orbits and we can have a lot of advance warning.

Something coming from outside the solar system would be much more difficult; they seem likely to have higher velocities than any solar system objects, making the damage they can do greater. Those would be the most difficult to do anything about because of very little warning time between seeing it and hitting, whereas those within the solar system have orbits around the sun that can be determined a long way in advance. That gives a lot of time to prepare and act. Early warning is essential and something interstellar probably won't give it. Fortunately those appear to be very rare.

Dealing with asteroid/comets seems to require either deflection - changing the trajectory - or explosively dispersing them. You can't do the latter too close or the cloud of debris will still hit and it won't require the pieces to be large to be dangerous and damaging; a whole lot of small pieces hitting the atmosphere will heat it up. But a few weeks away is a long way. Done far enough out very little will hit. (It is thought the Chicxulub impact threw huge amounts of debris into space and it rained back down and that caused so much atmospheric heating that it set forests on fire even around the other side of the world, just from radiant heat.)

Deflection of an object can be done by throwing mass at it (like the Dart experiment). This can work by adding momentum in the direction of the impact, but also, with high enough velocity impact, explosively throwing material outwards from the impact site, ie sideways to the direction of the hit. (If I understand correctly a lot of the energy converts to extreme heat and the effects of that are independent of the direction of the impact.)

Deflection can be done by rockets - either pushing directly or 'gravity tractor' style, which keeps the thrust at what is needed to balance with the gravity. The gravity of the rocket itself pulls on the object but needs to have a lot of mass to do much. If has a lot of mass it needs more power. Given that moving anything around in space typically uses a lot more fuel than payload fueling rockets to push or pull something very massive is logistically problematic. Proposals for 'mining' the object and shifting mass to the rocket have been suggested but I am doubtful. But I am doubtful of the effectiveness of using rockets to change any dangerously large object's trajectory, whether pushing or pulling.

A mass launcher and robots loading rocks into it, throwing them out to space would be another hypothetical option. But without a very long time to work that too seems unlikely to be effective to me.

There is pushing with explosive detonations that throw material outwards without blowing the object to piece and the use of explosives to shatter and disperse. Radiant heat and light from a nuclear detonation above the surface can be expected to cause 'outgassing' that will impart a push as well. One thing human ingenuity has been good at is explosive detonations and delivery systems. I'm inclined to think this will deliver the best results; nuclear explosives can deliver more energy for the payload than any other option.

A solid mass of nickel-iron will probably resist explosive dispersal whereas it may work with 'rubble pile' type objects.