Many maps of the solar system make it look as though everything in space moves in perfect, concentric circles. Planets orbit the sun, and moons orbit the planets. So that must be the case for everything in space, right?
Not quite. Orbits form all sorts of shapes. “Planets and other bodies rarely go around in perfect circles,” Paul Wiegert, an astronomer at the University of Western Ontario, told Live Science. Comets have so-called hyperbolic orbits, meaning they slingshot from one point and back again. Asteroids can travel in complicated loops around planets. Even the moon’s orbit is wobbling, slowly expanding year after year as it twirls around the Earth.
So how do these diverse paths form?
First, it’s important to understand the physics behind motion in space. When it comes to orbits, there are two main forces at work. The first is momentum: When an object is in motion, it has momentum that propels it in a specific direction. The second is gravity, an attractive force, said Renu Malhotra, a professor at the University of Arizona who studies orbital dynamics. Objects, especially large ones like planets, have strong forces of gravity and so can pull moving objects toward them. Together, the push of momentum and the pull of gravity form orbits.
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