Sports on Phobos

Because of their small sizes, Phobos and Deimos have very low gravitational accelerations. Their gravities do not pull very hard. The pull on Phobos is only about one one-thousandth of that on Earth. If you can perform a standing high jump of two or three feet on Earth, you could perform a standing high jump of half a mile on Phobos. It would not take many such jumps to circumnavigate Phobos. They would be graceful, slow, arcing leaps, taking many minutes to reach the high point of the self-propelled trajectory and then to return gently to the ground.

Even more interesting would be a game like baseball on Phobos. The velocity necessary to launch an object into orbit about Phobos is only about twenty miles per hour. An amateur baseball pitcher could easily launch a baseball into orbit around Phobos. The escape velocity from Phobos is only about thirty miles per hour, a speed easily reached by professional baseball pitchers. A baseball that had escaped from Phobos would still be in orbit about Mars – a man-launched moonlet. If Phobos were perfectly spherical, a lonely astronaut with an interest in baseball could invent a curious but somewhat sluggish version of this already rather sluggish game. First, as pitcher, he could throw the ball sidearm – at the horizon at between twenty and thirty miles per hour. He could then go home for lunch, because it will take about two hours for the baseball to circumnavigate Phobos. After lunch, he can pick up a bat, face the other direction and await his pitch of two hours earlier. Apart from the fact that good pitchers are seldom good hitters, hitting this pitch would be pretty easy: About fifteen seconds elapse from the appearance of the baseball at the horizon to its arrival in the vicinity of our astronaut. If he swings and misses – or, more likely, if the ball is wide of the plate – he can then go home for a two-hour nap, returning with his catcher's mitt to catch the ball. Alternatively, if he succeeds in hitting a fly ball at a velocity somewhere between twenty and thirty miles per hour, he can go home and take his nap, returning this time with a fielder's mitt, awaiting the return of the ball from the opposite horizon two hours later. Because Phobos is gravitationally lumpy, the game would be more difficult than I have indicated. Since daylight on Phobos lasts only about four hours, lights would have to be erected, or the game modified so that all pitching, hitting, and catching events happen on the day side.

These sports possibilities may, one day a century or two hence, provide a tourist industry for Phobos and Deimos. But baseball on Phobos is no more an argument for going there than, to take a random example, golf is for going to the Moon. The scientific interest in the moons of Mars – whether captured asteroids or debris from the formation of the planet – is, however, immense. Sooner or later, certainly on a time scale of centuries, there will be instruments – and then men – on the surface of Phobos looking up with awe at an immense red planet that fills the sky from zenith to horizon.

How the low gravity and tiny size of Mars' moon would affect the game.