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Old 11-13-2017, 08:51 AM   #241
johndallman
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

The people who run the current asteroid-finding projects are serious astronomers who are actually interested in the stuff they find. They wouldn't miss that. Now, if you want to make it a Hollywood-style project, feel free, but it will have been a lot more expensive that way.
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Old 11-13-2017, 09:27 AM   #242
robkelk
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

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Originally Posted by malloyd View Post
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.
Citation, please.

I think you're confusing linear distance with angular difference from the ecliptic. I see no reason why an orbit's aphelion or perihelion has to be on the ecliptic (in fact, I can think of reasons why they wouldn't be, unless they're both on the ecliptic), or that the points of an orbit's intersection with the ecliptic cannot be at 1 AU.
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Old 11-13-2017, 01:38 PM   #243
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

The impact only has to intersect Earth's orbit once. If some unknown Kuiper belt object perturbed it just enough to change its path, that's good enough for a Lucifer world to suffer.
Maybe that reality really does have a giant planet X like ours may or may not have.
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Old 11-13-2017, 02:07 PM   #244
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

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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...
In order to predict if an asteroid is going to hit earth five or ten or a hundred years out, the moon's gravitational influence must be taken into account... which implies some level of awareness as to if the asteroid's going to actually hit the moon or not.
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Old 11-13-2017, 02:42 PM   #245
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

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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.
What if it's new to our solar system? An exo-planet/moon that arrived and is now in an orbit that brings it closer & closer to the Earth. That could explain its shifting orbit.

If a near-moon size body passed earth by close enough to be within the moon's orbit, would that effect tides significantly? And would its velocity matter - if it was faster, would that have more or less of an effect?



This is getting more & more outlandish/unlikely.

An arriving body of that size that near-misses Earth, with collision later, sounds a lot like it was designed that way (and it is, in world-building terms) - which would raise the idea of it either being from aliens, or even being an alien planet/moon/starship.
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Old 11-13-2017, 04:00 PM   #246
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

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In order to predict if an asteroid is going to hit earth five or ten or a hundred years out, the moon's gravitational influence must be taken into account... which implies some level of awareness as to if the asteroid's going to actually hit the moon or not.
The moon is around 30 Earth diameters away. Thinking it's going to hit one "BB", but it actually hits the other one "close" by seems like a very unlikely mistake to make.
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Old 11-13-2017, 06:51 PM   #247
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

I think you might want to re-roll that reading comprehension check.
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Old 11-13-2017, 07:09 PM   #248
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

I was agreeing, not arguing with the person I quoted.
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Old 11-14-2017, 08:35 AM   #249
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Default Re: Lucy's Choice: Let's make Lucifer Parallels!

Calculating the effects of a near Lunar miss on a passing space rock years out still strikes me as tricky. That there would or would not be an effect, yes, but not being able to plot the exact effect until it gets closer sounds more realistic.

Having a near Lunar miss happen and then realizing the new course of the object impacts Earth some years in the future is quite doable.

I still wonder about that dinosaur killer rock hitting the moon. What are the best/ worst cases? I doubt Luna's orbit would shift enough to be worrisome, but how bad would the shrapnel be to Earth?
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Old 11-14-2017, 08:40 AM   #250
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...

I still wonder about that dinosaur killer rock hitting the moon. What are the best/ worst cases? I doubt Luna's orbit would shift enough to be worrisome, but how bad would the shrapnel be to Earth?
Anything large enough to not be burned up in Earth's atmosphere would probably - but not be guaranteed to be - captured by Luna's gravity. And if the rock hit Lunar farside (except relatively near the terminator), Luna would serve as a shield.

So probably just a meteor shower.
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