How Comets Are Born

  • Released Tuesday, December 16th, 2014
  • Updated Wednesday, May 3rd, 2023 at 1:50PM
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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.

Particles of dust coated with water ice and other molecules serve as a comet's building blocks.

Particles of dust coated with water ice and other molecules serve as a comet's building blocks.

Dust particles combine to form icy rocks that join together under the force of gravity.

Dust particles combine to form icy rocks that join together under the force of gravity.

High-speed collisions result in a loosely bound collection of fused rock and ice.

High-speed collisions result in a loosely bound collection of fused rock and ice.

When a comet passes through the inner solar system, its ice warms, releasing a trail of gas and dust.

When a comet passes through the inner solar system, its ice warms, releasing a trail of gas and dust.


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Credits

Please give credit for this item to:
NASA's Goddard Space Flight Center
Cover image courtesy of NSF
Video courtesy of NASA/JPL-Caltech