Dwarf Planets According to IAU (International Astronomical Union), a "dwarf planet" is a celestial body that 1) is in orbit around the Sun, 2) has sufficient mass for its self-gravity to assume a nearly round shape, 3) has not cleared the neighborhood around its orbit, and 4)is not a satellite.

A dwarf planet has been referred to by some astronomers as “something that looks like a planet, but is not a planet.” There are five known dwarf planets – Ceres, Pluto, Makemake, Eris and Haumea. Dwarf planets may also be called minor planets, subplanets or planetoids.

Ceres Discovered on January 1, 1801 Considered as a planet for half a century before it was reclassified as an asteroid Classified as a dwarf planet on September 13, 2006

Pluto Discovered on February 18, 1930 Classified as a planet for 76 years Classified as a dwarf planet on August 24, 2006

Makemake Discovered on March 31, 2005 Classified as a dwarf planet on July 11, 2008

Eris Discovered on January 5, 2005 The media once referred to it as the “tenth planet” Accepted as a dwarf planet on September 13, 2006

Haumea Discovered on December 28, 2004 Accepted as a dwarf planet on September 17, 2008

Orbital Attributes of Dwarf Planets Dwarf Planets Region of Solar System Orbital Radius (AU) Orbital Period (Earth years) Mean Orbital Speed (km/s) Ceres Asteroid belt Pluto Kuiper belt Makemake Kuiper belt Eris Scattered disc Haumea Kuiper belt

Physical Properties of Dwarf Planets Dwarf PlanetEquatori al Diamete r Relative Mass (w/ respect to Earth) Density (g/cm 3 ) Surface Gravity (m/s 2 ) Rotation Period (days) Moons Ceres947.6 ± Pluto2306± Makemake − ~2?~0.5-0 Eris2400± ~0.8~0.31 Haumea − ~0.44-2

Pluto Second largest known dwarf planet in the solar system Tenth largest body observed directly orbiting the sun Largest member of a distinct region called Kuiper Belt Composed of rock and ice Relatively small, approximately one-fifth the mass of the Earth and one-third its volume Highly eccentric and highly inclined orbit Charon is classified as its moon Has two known smaller moons, Nix and Hydra

Asteroids Pieces of irregularly shaped, solid bodies or rocks orbiting around the sun All are moving counterclockwise around the sun, just as planets do Vesta is the brightest asteroid but it cannot be seen by the naked eye In the asteroid belt, they range in size from tiny particles to about 1000 km in diameter

Asteroids Ceres, the largest asteroid and first one to be discovered has a diameter of about 940 km Some asteroids have orbits that cross the orbit of Mars Trojan asteroids follow the same orbit as Jupiter One group of Trojan asteroids travels ahead of Jupiter, while the other group trails behind

Asteroids Other asteroids are outside the orbit of Jupiter Over 2000 asteroids measuring 1 km in diameter cross Earth’s orbit at times Asteroid belt is an area between the orbits of Mars and Jupiter where most asteroids exist Asteroid belt may have been formed when a planet was pulled apart into fragments by gravitational force of Jupiter

Asteroids Some larger asteroids may have been ejected from the asteroid belt and are currently scattered in the solar system Several asteroids have been named after Filipino scientists and educators, Kintanar, Edwelda, Badillo, Biyo and students who won in the Science and Engineering Fair, Estrella, Rara, and Macalintal