Ultimate Cycle Catcher

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The Asteroid Belt: Ceres, Vesta and Pallas

Between Mars and Jupiter lies the main asteroid belt. In Ultimate Cycle Catcher it is the setting of The Belt route and a waypoint on the way to Jupiter, with stops at the three largest bodies there.

What the belt really looks like

Films often show asteroid fields as crowded rock storms, but the real belt is overwhelmingly empty space. Most of its objects orbit between about 2.1 and 3.3 times Earth's distance from the Sun. Millions of asteroids larger than a few hundred metres are spread across that enormous volume, so the average distance between sizeable ones is hundreds of thousands of kilometres or more. Spacecraft have crossed the belt many times without needing to dodge anything.

All of the belt's material put together would make a body with only a few percent of the Moon's mass, and a large share of that is in just four objects: Ceres, Vesta, Pallas and Hygiea. The game shows this sparseness by zooming the camera out to a wide Sun-centered view in which the asteroids are tiny.

Ceres, the dwarf planet

Ceres is the largest object in the belt, about 940 kilometres across, and it is classified as a dwarf planet: massive enough to have pulled itself into a nearly round shape, but not massive enough to have cleared its orbit of other bodies. It orbits the Sun in about 4.6 years. Ceres appears to contain a great deal of water ice mixed with rock, and bright deposits of salts on its surface hint at briny liquid beneath. That combination of water and low gravity is why Ceres often appears in ideas about future refuelling depots, which is the role it plays in the game.

Vesta

Vesta is the second most massive asteroid, a little over 500 kilometres across, and the brightest one seen from Earth. Unlike Ceres it is dry and rocky, with a layered interior and a metal core, more like a small planet that never finished forming. An enormous impact crater covers much of its southern hemisphere, and fragments blasted off by such impacts have reached Earth as a recognisable family of meteorites. Vesta orbits in about 3.6 years.

Pallas and its lopsided orbit

Pallas is similar in size to Vesta but follows a much more unusual path. Its orbit is tilted by about 35 degrees to the plane in which most planets travel, and it is markedly stretched, with an eccentricity of about 0.23. That eccentricity means Pallas speeds up when it is closer to the Sun and slows down when it is farther away, exactly as described by the rule that orbiting bodies sweep out equal areas in equal times.

The game draws everything in a flat plane, so the tilt is not shown, but the changing speed is. That is why the Pallas leg of The Belt is labelled ECCENTRIC, and why you should trust the ring rather than the rock's apparent motion.

Gaps carved by Jupiter

The belt is not evenly filled. At certain distances, where an asteroid would complete exactly three orbits for every one of Jupiter's, or five for every two, there are noticeable gaps. Repeated tugs from Jupiter at the same points in the orbit gradually push asteroids out of these resonant zones. It is the same principle of resonance that shapes the orbits of Jupiter's large moons later in the tour.

Useful numbers

Continue to Jupiter's moons, or go back to Mars.

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