Writing New Worlds: Asteroids

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Ceres, image courtesy of Wikimedia Commons

The anti-hero has grabbed a vessel, whether his personal property or not, and is fleeing the forces of the evil empire. Their ships are huge; his is small. And lo! an asteroid belt appears. Problem solved, plus or minus a few parts on the hull.

Yes, the character is a he, and we need more anti-heroic women in fiction, but whenever the story needs a boost, a charming rogue who dances a foot over the edge of disaster is an easy module to insert, and audiences surely will be familiar with a bunch of rocks of varying sizes bouncing off each other and across the escape route of the plot.

If what you are going for is pure entertainment — a beach read, a popcorn film, a tale to fill a few hours after a long day in the salt mines — a cloud of rubble athwart the path is good stuff. But if you are concerned with realism in your fiction, physics is against the common presentation of an asteroid belt.

Consider the spread of such bodies in our own solar system. Ceres, round enough to be counted as a dwarf planet, holds one third of the total mass of all asteroids that orbit between Mars and Jupiter, and the four largest, adding in Vesta, Pallas, and Hygiea — account for half the mass.

The reality of space is hard for planet-bound people to feel. As Douglas Adams told us a while ago, space is big. The asteroid belt is a doughnut that is an astronomical unit wide and an astronomical unit deep. An AU is roughly the distance of the Earth to the Sun, 150,000,000 kilometers or 93,000,000 miles. I write out the digits there to point out how large the quantity is. Into that volume fits objects that total some 0.00045 Earth masses.

In other words, navigating through might occasionally require a slight adjustment. The dodging and weaving and barely scraping by as rocks crash into each other is not any kind of realistic.

This is not unique to our solar system. The distribution of asteroids or of any objects with mass cannot exist for any length of time as they are often presented, thanks to gravity. Mass attracts mass, all things being equal.

There are some ways around this. If two large bodies collide, blowing each other into debris, this junkyard condition can last for some time — hundreds of thousands of years, even. But that state of affairs becomes increasingly rare as a system ages. The available material gets swept up into planets, and those planets settle down into stable orbits. (A nebula, one of the favorites of Star Trek writers, has the same truth. It will be expanding or contracting, and the density of the gas will be very low.) Saturn provides an out, but its rings are made of small particles whose collective structure is maintained by shepherd moons, but passing through the rings would be more like a sandstorm — damaging at high speeds without a deflector, but not the sort of thing in which tricky piloting skills would offer any advantage.

There is another kind of system that does allow for fancy flying: the accretion disk of a black hole. The matter spinning around on its way into the gravity well provides a rapidly shifting field of junk to dance about. Star Trek: Enterprise had a rare moment of accuracy in this regard in the episode, “Singularity.” But as always, things are a bit more complicated. No, a black hole cannot reach out to grab a passing ship from far off, and if the ship is close enough to be put into trouble by the gravitational field, time dilation, the slowing down of time relative to the rest of the universe, will be a factor. If the ship manages to avoid chunks of rock and break free, the clocks on board will have fallen behind Federation or Imperial or Hegemonic Standard Time.

If the story you are writing is meant only to be quick entertainment, the cliché version of an asteroid field might work, though cheap thrills get old after a while. But realism presents its own possibilities for storytelling. If asteroids are mined, the distances that separate them — and the distances from larger bodies in the system — create a challenge to overcome if the extracted minerals are desperately needed somewhere else or the miners are unable to work until supplies or equipment come in. If the residents of asteroids — hollowed out, say, and set to rotating to generate artificial gravity — decide to tell the system’s government where to shove some directive, the story now has a good revolution going. And with a bank of ion drives, an asteroid has a lot of potential as a ship itself.

Playing with rocks is fun for children. With attention to physics and engineering, playing with rocks can have monumental and sky scraping results. And in fiction, solid realism produces a more interesting narrative than a cloud of fluff.

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