PLUTO

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

Pluto by HST

Pluto Not like a Jovian planet; more like an asteroid, minor planet, or planetesimal  Kuiper Belt Object Mass ~ 0.0022 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