National Aeronautics and Space Administration Logo
Follow this link to skip to the main content NASA Banner
Small Worlds, Big Discoveries Banner
Color image of comet against a background of stars.
This image of Comet C/2001 Q4 (NEAT) was taken at Kitt Peak National Observatory near Tucson, Ariz. in 2004.

BREAKING NEWS: On 19 October 19, Comet Siding Spring (C/2013 A1) will pass by Mars only about 82,000 miles (132,000 km) away--which would be like a comet passing about 1/3 of the distance between Earth and the Moon. The nucleus of the comet won't hit Mars, but there could be a different kind of collision -- a the first observed collision of two atmospheres.

For more details on this exciting near-miss, visit:

Comet Watch: Siding Spring (C/2013 A1)

10 Need-to-Know Things About Comets:

  1. If the sun were as tall as a typical front door, Earth would be the size of a nickel, dwarf planet Pluto would be the size of a head of a pin and the largest Kuiper Belt comet (about 100 km across, which is about one twentieth the size of Pluto) would only be about the size of a grain of dust.
    Link to Rosetta mission to a comet
    Rosetta: Comet Chaser
  2. Short-period comets (comets that orbit the sun in less than 200 years) reside in the icy region known as the Kuiper Belt beyond the orbit of Neptune from about 30 to 55 AU. Long-period comets (comets with long, unpredictable orbits) originate in the far-off reaches of the Oort Cloud, which is five thousand to 100 thousand AUs from the sun.
  3. Days on comets vary. One day on comet Halley varies between 2.2 to 7.4 Earth days (the time it takes for comet Halley to rotate or spin once). Comet Halley makes a complete orbit around the sun (a year in this comet's time) in 76 Earth years.
  4. Comets are cosmic snowballs of frozen gases, rock and dust.
  5. A comet warms up as it nears the sun and develops an atmosphere, or coma. The coma may be hundreds of thousands of kilometers in diameter.
  6. Comets do not have moons.
  7. Comets do not have rings.
  8. More than 20 missions have explored comets from a variety of viewpoints.
  9. Comets may not be able to support life themselves, but they may have brought water and organic compounds -- the building blocks of life -- through collisions with Earth and other bodies in our solar system.
  10. Comet Halley makes an appearance in the Bayeux Tapestry from the year 1066, which chronicles the overthrow of King Harold by William the Conqueror at the Battle of Hastings.
More on Comets

Awards and Recognition   Solar System Exploration Roadmap   Contact Us   Site Map   Print This Page
NASA Official: Kristen Erickson
Advisory: Dr. James Green, Director of Planetary Science
Outreach Manager: Alice Wessen
Curator/Editor: Phil Davis
Science Writer: Autumn Burdick
Webmaster: David Martin
> NASA Science Mission Directorate
> Budgets, Strategic Plans and Accountability Reports
> Equal Employment Opportunity Data
   Posted Pursuant to the No Fear Act
> Information-Dissemination Policies and Inventories
> Freedom of Information Act
> Privacy Policy & Important Notices
> Inspector General Hotline
> Office of the Inspector General
> NASA Communications Policy
> NASA Advisory Council
> Open Government at NASA