Expert: Courtney Seligman - 4/4/2011

Question
I have a question regarding magnetic keyholes. This will sound crazy at first but please read all of it please.In 2012 during the winter equinox there will be a galactic alignment along with a solar one and  I know that won't do anything directly to us but what about magnetic keyholes? In 2036 there is to be a asteroid in the neighborhood called 99942 or Apophis and would miss the Earth if it doesn't hit the keyhole. So if the galactic alignment does have a reaction with keyholes could it effect the asteroid?
Thank you for your response in advance.

Answer
I believe you mean gravitational keyholes, not magnetic; but either way, the only thing that affects them is the position of objects in our Solar System. All the stars, and the galaxy itself, are too far away to have any effect on the motion of things well inside our Solar System. For objects near the outside of the Solar System, such as in the Oort Cloud, passing stars could affect the motion of a given object by perhaps a percent of so; but tens of thousands of times closer to the Sun, where we are, the effects of other stars can be completely ignored.

In other words, whether Apophis can pass through a particular gravitational keyhole has nothing to do with the rest of the Universe, but only with objects inside our own Solar System. The rest of the Universe could cease to exist, and it would make no difference in the path of the asteroid.

However, considering the question of keyholes, and what do they do, I have seen the term used in two ways which seem of some relevance. The first, which is not related to your question, has to do with something called Lagrange Points (see http://cseligman.com/text/sky/lagrange.htm), in particular L1, L2 and L3. At these points, the combined gravity of the Sun and a planet (or in rarer situations, a planet and one of its larger moons) can cause small "hills" and "valleys" of gravitational potential, which are points or relative stability (or instability). For instance, L4 and L5, the places where the Trojan Asteroids are found in front of and behind Jupiter (a
page covering that is linked from the one already noted above), are gravitational "valleys", in which objects tend to roll back and forth, like marbles in a bowl, relative to a point of relative stability. The exact motion of the objects in the bowl is a bit chaotic, but they tend to stay "in the bowl", so their overall motion is stable.

However, L1, L2 and L3 are gravitational "hills", and this is one sense of the word "keyhole". There are a number of places in space and time (time is involved because
the gravitational effects of the planets add to or subtract from that of the Sun and the other planets in different ways at different times) where an object could find itself near a gravitational "hill". At such a place, just a very small push in one direction or another could send it in a completely different direction in space, completely changing its future orbit around the Sun. Such places are surprisingly common, but move around in very complex ways (save for L1, L2 and L3, which are fixed in place), and NASA is very interested in exploring the possibility of using such gravitational hills to move spacecraft from one place in the solar system to a very different place (over long periods of time, but with very little expenditure of fuel) by taking advantage of the chaotic motion of objects near the hill. (In this case, "chaotic" means that if an object starts to roll down one side of the hill, it will keep going in that direction, while if it starts to roll down the opposite side, it will keep going in that direction; but before it starts rolling one way or the other, which way it will roll is impossible to predict. If it could be predicted, the motion would not be considered chaotic.)

Now, such gravitational hills are very interesting, and could prove very useful (in fact, as noted on the page about Lagrange Points, the SOHO spacecraft orbits L1, and the WMAP spacecraft orbits L2). However, they are not the sort of "keyhole" being discussed for Apophis.

What is meant there is that in 2029, Apophis will pass very close to the Earth. Exactly how close isn't known, but no closer than 10 to 12 thousand miles from the center of the Earth (that is, no closer than 6 to 8 thousand miles from the surface of the Earth on that side of the Earth), and no further than 24 to 26 thousand miles from the center of the Earth (that is, no further than 20 to 22 thousand miles from the surface of the Earth on that side of the Earth, which happens to be the side away from the Sun, as Apophis
will be closest to that part of the Earth where it is local midnight.)

So in 2029, the asteroid will have a very near miss, but absolutely a miss. There is, based on current observations and calculations, absolutely no way that it can come any closer than 6 to 8 thousand miles to the night side of the Earth on that passage. HOWEVER, during that passage, our gravity will change its orbit, and the amount of the change will depend upon how close it comes to us, which we won't know until 2029 (sort of; but
see the note about 2013 below). If the asteroid passes closer to the Earth, its future path will be altered more. If it passes further from the Earth, its future path will be altered less. Now, as it happens, somewhere within the approximately 12 to 14 thousand mile wide region of uncertainty as to exactly where it will pass us, there is a region about a dozen miles wide (that is, less than a thousandth as wide as the overall range of possibilities) which, IF the asteroid passes through it, will cause it to hit the Earth in 2036, THAT is the "keyhole" that is being discussed in this particular situation. It isn't a true gravitational keyhole, just a statistical keyhole -- out of all the range of possibilities, a very tiny region of space and time where if things went just the wrong way, the asteroid could end up hitting us.

Now, as it happens, in 2013 Apophis will pass by our orbit (it has a small orbit, and passes ours frequently; we just don't usually pay much attention unless it happens to pass very close to us) at a distance which is fairly large, but not large enough to be out of reach of radar ranging. At that passage, it should be possible to measure the position and motion (and size and shape) of the asteroid many times more accurately than now. The odds are about a thousand to one that following the analysis of the data from that passage, we will know exactly where Apophis will pass the Earth in 2029, and (with 1000 to 1 odds) be able to absolutely rule out any chance of a collision in 2036.

Of course, if the 2013 data say that in 2029
the asteroid will pass very close to the region which might cause it to
run into us in 2036, then people will need to start thinking about what to do, to prevent that from happening (the Russians are already thinking about it, but it's really a bit early to do so, as any change made in the orbit of the asteroid before we know the results of the 2013 passage may increase the chance of a collision, instead of decreasing it).

I hope that clears up what the situation is, in terms of so-called keyholes, real (like gravitational hills and valleys), and statistical (like the chances of our being hit by Apophis). The only thing left is to remind you that absolutely none of the discussion above is in any way affected by anything outside the Solar System; so although we may need to keep a watch on Apophis for a while, we needn't worry about how the rest of the galaxy might affect it, because it just can't.