Pluto and the Dwarf Planets
Since its discovery in 1906, Pluto held the title of the 9th planet from the Sun. In 2006, Pluto was demoted after the discovery of 2 large planetoids orbiting nearby. The decision came down to adding 2 new planets or removing Pluto. In the end, it was decided that Pluto and the new planetoids should form a new group called the dwarf planets.
Planet vs. Dwarf Planet
WHAT IS A DWARF PLANET ANYWAYS?
|Orbits the Sun and isn’t a moon||✓||✓|
|Enough mass to hold a spherical shape||✓||✓|
|Orbital path is cleared of other objects||✓||✗|
IN OTHER WORDS…
The main difference between a planet and a dwarf planet is that dwarf planets orbit within debris fields. Pluto lies within the Kuiper belt, similar to the asteroid belt in that there are a large number of objects orbiting within the same space.
The Dwarf Planets
DON’T THINK OF IT AS LOSING A PLANET, BUT AS GAINING A DWARF PLANET (OR FIVE)
Ceres – 963 km across
The largest asteroid and smallest known dwarf planet
Pluto – 2,370 km across
The largest dwarf planet, has 5 moons
Makemake – 1,434 km across
Appears to be red in color
Eris – 2,326 km across
Almost as large as Pluto, has one known moon
Haumea – 1,920 km x 990 km across
Rotates once every 4 hours, so fast its shape is stretched into an oblong sphere. Two known moons.
Asteroid & Kuiper Belts
HOME OF THE DWARF PLANETS
Home to the dwarf planet Ceres which contains about a quarter of the entire mass of the asteroid belt. The asteroids are thought to be leftover material from a planet that failed to form due to gravitational disturbances from Jupiter.
The Kuiper belt lies beyond Neptune and appears to be doughnut-shaped. The rest of the dwarf planets reside here.