Astronomers have spotted thousands of comets in the solar system, but how did they form?
Comets are small, icy objects that circle the sun. They can be thought of as floating time capsules, preserving a chemical record of the early solar system. Astronomers believe comets materialized more than 4.5 billion years ago from the dust and gas of the protoplanetary disk, a donut-shaped cloud of debris surrounding our newborn star. On the fringes of the disk, far from the sun’s heat, fine grains of dust coated with frozen gases and water ice began clumping together. Over time, clumps of dust assembled into ice-rich rocks, which later evolved into the mile-sized bodies that we observe today traveling among and far beyond the planets. Watch the video to see an artist’s interpretation of the birth of a comet.