Philips Atlas of the Universe

THE SOLAR SYSTEM

PLANETARY DATA – PLUTO

nitrogen as well, while Charon shows signs of water ice;

it has no detectable atmosphere. The occultation results

even gave some clues as to surface markings. Pluto has a

darkish equatorial band and extensive polar caps, while

Charon may have a darkish patch in one hemisphere and

a brighter band in the other.

Pluto is too small to be ranked as a true planet, and is

now generally regarded as the largest known Kuiper Belt

object. Its magnitude is 14, so that a moderate-sized tele-

scope will show it as a starlike point; for all we know,

there may be other Kuiper Belt objects, further away,

equal in size to Pluto or even larger.

Sidereal period 90,465 days

Rotation period 6d 9h 17m

Mean orbital velocity 4.7 km/s (2.9 miles/s)

Orbital inclination 17.2°

Orbital eccentricity 0.248

Apparent diameter < 0.25”

Reciprocal mass, Sun = 1 < 4,000,000

Mass, Earth, = 1 0.0022

Escape velocity 1.18 km/s (0.7 miles/s)

Mean surface temperatureabout 
220°C

Albedo about 0.4

Maximum magnitude 14

Diameter 2324 km (1444 miles)

Sun

Uranus

Earth

Neptune

Pluto

Neptune

Pluto

1930

2113

1989

Orbit of Pluto.

Pluto’s eccentric path

brings it within the orbit

of Neptune, but its orbital

inclination of 17°means

that there is no fear of a

collision occurring.

Perihelion was passed in

1989, and aphelion will

occur in 2114.

Dome of the telescope

used to discover Pluto – then

at the Lowell Observatory,

now at the outstation

(Anderson Mesa).

Pluto and Charon:

Hubble Space Telescope,

21 February 1994.

The 9-inch refractor

used to discover Pluto.

Earth

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