Creating the scenario

A lot of people have told me I should start blogging about this little project, and they're probably right, so here goes...

Around mid-2005 I started thinking seriously about writing a story where the Earth gets ejected into interstellar space. Why I was thinking of that will be the topic of another post, but suffice it to say that before I got too far, I knew I would need to come up with a concrete scenario.

Some of the constraints I needed for the plot to work out were things like

• The object should not pass too close to the Earth, because I didn't want it to destroy it outright through tidal disruption. And to pass very close would compound improbability on improbability.
• The object could not be too large, because it needed to be plausible that it had not been previously detected.
• The Earth had to be actually ejected permanently from the sun, not just thrown into a weird orbit.

I had written my own numerical simulator and loaded it with data from the JPL Horizons database, and I started firing black holes through the solar system. I soon realized that it would be extremely helpful to have a graphical display of the results, and after some searching I found the Gravity Simulator program, which turned out to be good for this purpose.

I initially experimented with some intermediate-mass black holes, which have the advantage of doing the job without having to pass particularly close to the Sun, but IMBHs have some serious drawbacks, such as 1) it's not certain that they even exist, and 2) they would be much easier to detect, even very far away. I finally settled on 14.3 solar masses, since that was on the upper end of what has actually been observed.

Another thing I realized right away was that the black hole was much more likely to eject the Earth if it was traveling close to the ecliptic. I tried firing black holes through the solar system at various random angles, and in most  cases, I just ended up with solar system objects being thrown into more or less eccentric orbits; unless an object came very close to the black hole, it would not be ejected. Of course, there are certain plot elements which I won't spoil here that help explain why the black hole just happens to be roughly in the plane of the solar system. One big reason is the fact that the black hole is heading toward the center of the galaxy, and by chance, the spot where the galactic central plane crosses the solar system central plane is near the direction to the center of the galaxy. If you think about this (and maybe draw a diagram) you can convince yourself that it would indeed be likely that something heading to the center of the galaxy would travel through the solar system near the plane of the planets.

Once these issues were settled, it was a matter of finding the right position and velocity to get the scenario I wanted. It was disturbingly easy to do so. I think I spent a total of four or five hours one afternoon, playing with the parameters until I had something that worked well for my purposes. Given the mass, position, and velocity, the rest is up to the laws of physics.