Equatorial radius (km): 1150
Mass (relative to Earth): 0.0022
Density (g/cm3): 2.0
Surface gravity: 0.059
(relative to Earth)
Rotation period: 6.39 days
Axial inclination: 119.6°
Distance from Sun (AU): 39.5
Orbital period: 248 years
Orbital eccentricity: 0.249
Composition of surface: icy (nitrogen, methane, carbon monoxide, ethane)
Mean surface temperature: -230°C
Composition of atmosphere: mostly nitrogen, possibly also mehtnae, carbon monoxide and ethane
Number of satellites: 1
Discovered in 1930, Pluto has always appeared as nothing more than a dot of light in even the largest earth-based telescopes because Pluto's disk is much smaller than can be resolved from beneath the Earth's turbulent atmosphere. Pluto is 2/3 the size of Earth's Moon but 12,000 times farther away. Viewing surface detail is as difficult as trying to read the printing on a golf ball located thirty- three miles away!
Hubble imaged nearly the entire surface of Pluto, as it rotated through its 6.4-day period, in late June and early July 1994. These images, which were made in blue light, show that Pluto is an unusually complex object, with more large-scale contrast than any planet, except Earth.
Pluto itself probably shows even more contrast and perhaps sharper boundaries between light and dark areas than is shown here, but Hubble's resolution (just like early telescopic views of Mars) tends to blur edges and blend together small features sitting inside larger ones.
The two smaller inset pictures at the top are actual images from Hubble. North is up. Each square pixel (picture element) is more than 100 miles across. At this resolution, Hubble discerns roughly 12 major 'regions' where the surface is either bright or dark. The larger images (bottom) are from a global map constructed through computer image processing performed on the Hubble data. The tile pattern is an artifact of the image enhancement technique.
Opposite hemispheres of Pluto are seen in these two views. Some of the variations across Pluto's surface may be caused by topographic features such as basins, or fresh impact craters. However, most of the surface features unveiled by Hubble, including the prominent northern polar cap, are likely produced by the complex distribution of frosts that migrate across Pluto's surface with its orbital and seasonal cycles and chemical byproducts deposited out of Pluto's nitrogen-methane atmosphere.