1. PLUTO

2. Motion and discovery of Pluto
As faint as stars, Pluto is seen to change its position significantly in
one day

3. Pluto by HST

4. Pluto
Not like a Jovian planet; more like an asteroid, minor planet, or planetesimal  Kuiper Belt Object
Mass ~ x Earth’s; 6 times lighter than the Moon,
but similar size
Though small, Pluto has a moon – Charon; largest satellite/planet ratio (8%, vs. 1% for Earth)
Pluto-Charon as a double planetesimal
Pluto-Charon are tidally locked to each other; both with rotation/revolution period of 6.4 d; face each other all the time
Atmosphere: Gaseous methane, N, CO !! pressure ~ 10-6 bars, T ~ 40 K
Very eccentric orbit; at perihelion Pluto can be closer than Neptune