Lucy's Choice: Let's make Lucifer Parallels!

[johndallman]

The Gravity Tractor is a more complex and fiddly method, but doesn't depend on the composition of the asteroid.

[malloyd]

Originally Posted by fchase8

Oh, and there's the worry that any deflecting type mission could accidentally tighten the orbit, make it hit Earth sooner.

That's cinematic nonsense actually. Interceptions are very, very fiddly - any change whatsoever and it misses. Certainly any change big enough to alter the period of the orbit means it misses by a lot. The Earth is a moving target - about 8 minutes delay in crossing its orbit is enough to go from just grazing the leading edge to missing the trailing one.

[malloyd]

Originally Posted by Fred Brackin

This would be if the asteroid was a rubble pile or otherwise showed obvious structural faults. If it doesn't you really need to go and look closely for hidden ones. If the asteroid isn't very solid indeed you won't be landing a rocket engine (even an ion one) on it and changing its' course that way.

With this kind of lead time, you don't really need to. Crash your probe into it. Even that tiny momentum change is probably enough it misses. If it isn't structurally solid maybe even better - dumping a bunch of momentum into a pack of billiard balls disassembles them. Dispersing it into a huge cloud essentially turns it into a new periodic meteor shower.

[fchase8]

From what has been said, it actually seems too easy to deflect an orbiting asteroid like I had described. Any nudge will do, multiple attempts, lots of lead time, etc.

What if the asteroid is really big, like moon size or something? The bigger it is, the harder to nudge, correct? And even breaking it up, or if its some rubble pack, will be too big.


For added cinematic drama, could its pass-bys have effects on Earth, like mass tidal waves? Maybe the first time it just caused some increased waves, but the next time will cause mass tidal waves.

This could give added impetus to doing something, but also another problem to deal with. Each nation will want to prep for their own tidal effects, as opposed to the joint operation to save the world. Interestingly, the USSR would be relatively less effected, and thus more interested in saving the world, especially as compared to rich, seaside nations such as U.S., U.K., and Japan.

[sir_pudding]

Originally Posted by fchase8

From what has been said, it actually seems too easy to deflect an orbiting asteroid like I had described. Any nudge will do, multiple attempts, lots of lead time, etc.

Making it easy requires infrastructure: you only have long lead times if you are actively mapping, and you only can take advantage of it if you have vehicles and launch capability for an interception.

Realistically, under the present conditions in both of these requirements, scenarios where we detect something that we can't do anything about are still pretty likely.

[johndallman]

Originally Posted by fchase8

What if the asteroid is really big, like moon size or something?

There's no way anything as big as 100 miles diameter (the Moon is a bit over 2,000 miles diameter) orbiting in the inner solar system could be undiscovered as late as 1900. Something that small can't have significant effects on Earth's tides unless it gets ridiculously close, or the physics of tides are rewritten by Hollywood.

Originally Posted by fchase8

The bigger it is, the harder to nudge, correct? And even breaking it up, or if its some rubble pack, will be too big.

Yes, and yes. The really dangerous asteroids are the 1-10 mile diameter ones, big enough to cause an extinction event, too big to readily deflect, and small enough that they could go unnoticed (until we started looking for them seriously). We probably have all of those spotted by now.

There are probably still a fair few unspotted 100-yard to 1 mile asteroids, but we're getting better at spotting them. They could well be challenging to deflect, but their impacts on Earth are very rare. Ones smaller than that don't pose a risk to human civilisation as a whole, although they can make quite a mess of a large area.

[AlexanderHowl]

Another problem occurs if the object is coming at an extreme angle to the ecliptic plane. The majority of astronomers looking for asteroids look on the ecliptic plane.

[malloyd]

Originally Posted by AlexanderHowl

Another problem occurs if the object is coming at an extreme angle to the ecliptic plane. The majority of astronomers looking for asteroids look on the ecliptic plane.

If you aren't orbiting in the ecliptic plane, the odds you can hit Earth go down *drastically*. In the plane, any asteroid that has a perihelion less than 1 AU and an aphelion greater than 1 AU intersects the orbit of the Earth twice each orbit, the only moments it has a chance of hitting Earth. An asteroid out of the ecliptic doesn't do that. Unless its perihelion (or aphelion) is exactly 1 AU, it can never hit the Earth at all - when it is at the right distance at 1 AU it will be well above or below the Earth's orbit.

[Flyndaran]

Unlikely isn't impossible. And it's a great handwave for otherwise close parallels. Just enough for jumpers to get a hint nervous when visiting adjacent realities.

[Jasonft]

How much damage would one of these hypothetical rocks do if it hit the moon? I could easily see asteroid trackers dismissing it for a while as a near miss only to realize later it would impact Luna.

Luna being a much smaller target of course, but debris kicked up from the moon would stick close to Earth for a long time I would think. Close to Earth of course means risk of impact...