Dwarf Planets Pluto Neptunes orbit also didnt quite

Dwarf Planets

Pluto • Neptune’s orbit also didn’t quite match Kepler’s laws. • In the late 1800’s Lowell predicted a ninth planet. • It was discovered in 1929 as a faint star that moved slightly each day. • Pluto’s orbit is sometimes inside Neptune’s. Neptune Sun Pluto

New Horizons • In 2015 the New Horizons spacecraft became the first to fly by Pluto and photograph its surface. • Pluto is small. – Seven moons are larger – Earth’s Moon is 6 times more massive

Ice Ball • Pluto has low density. • 60% stony core. • 40% frozen gas: nitrogen, carbon monoxide, methane, and water. • Pluto has a thin atmosphere. – 1/100, 000 or Earth’s pressure – Active volcanos ejecting water and ammonia.

Charon • Pluto’s moon Charon is almost as big as Pluto. • The pair can be viewed as a double planet and they are locked to each other by tidal forces. • Charon has more water ice on the surface than Pluto. Wikipedia animation of Charon and Pluto

Classifying Pluto • The inner planets (Mercury, Venus, Earth, Mars) are rocky. • The outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants. • Pluto doesn’t fit in; it’s icy mixed with rock and carbon.

Kuiper Belt • Gerard Kuiper suggested in the 1940’s that there was a ring of icy objects from the early solar system beyond the orbit of Pluto. – Confirmed in 1992 – Many times the mass of the asteroid belt Pluto Neptune’s orbit Kuiper Belt

Kuiper Belt Objects • Hundreds of Kuiper Belt Objects (KBOs) have been found. – Sizes from 50 to 2400 km across. – Eris is the largest KBO • Astronomers estimate 100, 000 KBOs larger than 100 km.

Planets Redefined • The discovery of Eris forced astronomers to create a better definition of a planet (2006). – In orbit around the Sun – Sufficient mass to assume a nearly round shape – Cleared the neighborhood around its orbit • A dwarf planet was defined as a new category. – Not cleared the neighborhood around its orbit – Not a satellite of a planet

History of Planets Scientific American