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Q: How small would a planet have to be before you could throw a baseball into orbit?

A: A satellite in a low-Earth orbit travels about 7.9 kilometers (5 miles) per second. Professional pitchers can throw a ball about 100 miles per hour or 44 meters per second, a mere 0.56% of orbital speed on Earth. According to physicist Robert Ehrlich in “The Cosmological Milkshake,” that speed would be sufficient to reach orbit on a planet whose radius is 0.56% that of Earth’s, or 36 kilometers (22.3 miles). If the planet were spinning, however, the feat could be achieved on a slightly bigger planet by throwing the ball in the direction of the spin.