Astronomy Notes – Unit 2d – Dwarf Planets
q (1) Ceres - the Roman goddess of agriculture (Greek – Demeter)
o Discovered in 1801 by Giuseppe Piazzi
o Distance from the Sun is 257 million miles (414 million kilometers, 2.7 AU)
§ It takes sunlight 23 minutes to reach Ceres
o Size in diameter is 585 miles (942 kilometers)
o Period of revolution of 4.6 years
o Period of rotation of 9 hours, 4 minutes
o Gravity - 100 lb. on Earth would weigh 3 lb.
o Classified
as a planet for about 50 years, then an asteroid
(along with 2 Pallas, 3 Juno and 4 Vesta)
o Contains
about 1/3 of the estimated total mass of the asteroid belt
q (2) Pluto - the Roman god of the underworld (Greek – Hades)
o Discovered
in 1930 by Clyde Tombaugh, but predicted for years
because of “wobbles” in
o Distance from Sun averages 3,674 million miles (5,913 million kilometers)
§ more elliptical orbit, from 2,750 to 4,853 million miles
§
actually closer to the Sun than
§ plane of orbit is tilted 27°
§ It takes sunlight 5.5 hours to reach Pluto
o Size in diameter is 1,413 miles (2,274 kilometers)
§ smaller than the Earth’s moon
o Period of revolution of 248 years
o Period of rotation of 6 days, 20 hours
o Gravity - 100 lb. on Earth would weigh 7 lb.
o Moons: 3 known natural satellites
§ Charon - ferryman for the dead
· discovered 1978
· half the size of Pluto (dual dwarf planet?)
§
Nix – Greek goddess of darkness and night,
mother of Pluto
Hydra –Seven-headed beast defeated by Hercules
· Both discovered in 2005 using the Hubble Space Telescope
o The New Horizons mission launched in 2006, and is due to arrive in 2015.
q (3) Eris
– the Greek goddess of strife, discord
o Discovered
in 2003 by a team of astronomers from Mount Palomar Observatory (
o Announcement in 2006 led to the IAU classification of “dwarf planet”
o Distance
(average) from the Sun is 6,288 million miles
(10,120 million kilometers, 67.7 AU)
§ It takes sunlight 9.4 hours to reach Eris
o Size in diameter is 1,491 miles (2400 kilometers)
o Period of revolution of 557 years
o Plane of orbit is tilted 44°
o Period of rotation is estimated to be 8 hours
o Gravity – unknown at this time
o Moons: 1 known natural satellites – Dysnomia (demon of lawlessness, child of Eris)