Fun Facts

Cool facts about Pluto, the Kuiper Belt and the first mission to explore this mysterious region


  • Pluto orbits the Sun once every 248 years.
  • A person on Pluto would weigh 1/15 what they weigh on Earth - for comparison, the astronauts on the Moon had 1/6 of their Earth weight.
  • Pluto is named after the Greek god of the underworld.
  • The symbol for Pluto ("PL") is tribute to Percival Lowell, who started the search for the ninth planet in the early 1900s.
  • Pluto was discovered in 1930 by American astronomer Clyde Tombaugh.
  • Atmospheric surface pressure on Pluto is about 100,000 times less than on Earth.
  • At 1,470 miles (about 2,370 kilometers) across, Pluto could fit between Washington, D.C. and Denver, Colorado.
  • Pluto's surface is among the most contrasty in the solar system.
  • Pluto has weather, winds, hazes, chemistry and an ionosphere.
  • Pluto's estimated surface temperature falls between -378 to -396 degrees F (-228 to -238 C).
  • Pluto is one of only two planets that rotates on its side - Uranus is the other.
  • Pluto's surface has nitrogen, methane and carbon monoxide ices on it.
  • A radio signal moving at the speed of light takes about 4 hours to reach Pluto from Earth.
  • Pluto's brightness changes as it rotates, revealing large light and dark regions.
  • Student Venetia Burney suggested the name 'Pluto' in 1930; our student-built interplanetary dust counter is named in her honor.
  • Pluto atmospheric models reveal that both ethane and acetylene should be produced by chemical reactions and found on the surface.
  • Pluto's last time at aphelion - the farthest point in its orbit - was 1865.
  • Pluto next reaches aphelion - the farthest point in its orbit - in 2112.
  • Scientists once thought Pluto was a moon of Neptune or an escaped giant asteroid.

Charon and Pluto's Small Moons

  • Pluto-Charon is the solar system's only known b378 inary planet.
  • Charon is half of Pluto's diameter - making it the largest satellite relative to the planet it orbits.
  • Charon is 20 times closer to Pluto than our moon is to Earth.
  • American astronomers James Christy and Robert Harrington discovered Charon in 1978.
  • Charon is named after the mythological boatman who ferried souls across the river Styx to Pluto for judgment.
  • Pluto's moons are named Charon, Nix, Hydra, Kerberos and Styx.
  • An American team led by Alan Stern and Hal Weaver discovered Nix and Hydra in 2005.
  • The first letters of Nix and Hydra are a nod to the New Horizons mission.
  • Mark Showalter led the teams that discovered Styx and Kerberos.
  • Moons Nix and Hydra are roughly 5,000 times fainter than Pluto itself.
  • Nix and Hydra are two to three times as far from Pluto as Pluto's largest moon, Charon.
  • Nix is named after the goddess of darkness and night.
  • Hydra is named after the terrifying monster with nine heads and a serpent's body.
  • Kerberos is named after the three-headed dog that guards the underworld.
  • Styx is named after the goddess of the river with the same name in Pluto's underworld.
  • The discovery of Styx was announced in July 2012.

Kuiper Belt

  • The Kuiper Belt is a collection of icy, rocky objects residing beyond Neptune's orbit.
  • The first Kuiper Belt Object (after Pluto) was discovered in 1992.
  • Some Kuiper Belt Objects (like Pluto) have an average reddish color, while others are gray.
  • The Kuiper Belt is often called the -Third Zone- of our planetary system, swirling beyond both the inner zone of rocky planets and middle zone of gas giants.
  • The Kuiper Belt is the largest structure in our planetary system.
  • The Kuiper Belt holds an estimated 100,000-plus miniature worlds with diameters larger than 100 kilometers.

New Horizons

  • New Horizons' science instruments were built in Texas (SWAP, Alice), Colorado (Ralph, SDC) and Maryland (LORRI, PEPSSI, REX).
  • The New Horizons dust counter is the first student-built instrument on a NASA planetary mission.
  • The RTG that powers New Horizons is a spare from Galileo-Cassini, rebuilt for this mission.
  • New Horizons arrived at Pluto exactly 50 years after the first successful Mars mission, Mariner 4.
  • New Horizons is the first mission since Voyager to launch to an unexplored planet.
  • New Horizons' high-gain dish antenna is 2.1 meters (83 inches) in diameter.
  • New Horizons' Atlas V551 launch vehicle was nearly 200 feet tall.
  • The 2007 Jupiter gravity assist added about 9,000 mph to New Horizons' speed.
  • New Horizons carries the most capable science payload ever launched on a first reconnaissance mission to an unexplored planet.
  • New Horizons carries a CD containing some 435,000 names of people who signed up online to send their names to Pluto.