The Asteroid That Thought It Was a Comet

The difference between an asteroid and a comet was always thought fixed—but now a new paper says the two celestial bodies may be more similar than we thought

Spotted: A Shooting Gallery for Comets

Astronomy is an imprecise business, and much of what skywatchers see depends on what tool they're using to look. In 1610, Galileo became the first person to spot...

New Proof That Comets Watered the Earth

By rights, the Earth should not be the cosmic garden it is. In a solar system of planets and moons that are solid rock or mostly gas, shrouded in clouds or...

Mystery Planet: Is a Rogue Giant Orbiting Our Sun?

The quest for Planet X always starts out with celestial objects behaving badly. Astronomers notice that a known planet, or a bunch of comets, begin moving in...

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