Home | Site Map | What's New | Image Index | Copyright | Posters | ScienceViews | Science Fiction Timelines |

PHOTO INDEX OF
PRIMARY TARGETS
ASTEROIDS
COMETS
EARTH
JUPITER
KUIPER BELT
MARS
MERCURY
METEORITES
NEPTUNE
OORT CLOUD
PLUTO
SATURN
SOLAR SYSTEM
SPACE
SUN
URANUS
VENUS
ORDER PRINTS

OTHER PHOTO INDEXES
ALL TARGETS
PHOTO CATEGORIES

SCIENCEVIEWS
AMERICAN INDIAN
AMPHIBIANS
BIRDS
BUGS
FINE ART
FOSSILS
THE ISLANDS
HISTORICAL PHOTOS
MAMMALS
OTHER
PARKS
PLANTS
RELIGIOUS
REPTILES
SCIENCEVIEWS PRINTS

Iapetus

Target Name:  Iapetus
Spacecraft:  Voyager 2
Produced by:  Calvin J. Hamilton
Copyright: © 1999 Calvin J. Hamilton
(Publisher Permission Request)

Related Document
Download Options

NameTypeWidth x HeightSize
iapetus2.jpgJPEG500 x 51822K
iapetus2.jpgJPEG778 x 80640K
iapetus2.tifTIFF778 x 806327K

Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. Amazingly, the dark material covers precisely the side of Iapetus that leads in the direction of orbital motion around Saturn (except for the poles), whereas the bright material occurs on the trailing hemisphere and at the poles. The bright terrain is made of dirty ice, and the dark terrain is surfaced by carbonaceous molecules, according to measurements made with Earth-based telescopes. Iapetus' dark hemisphere has been likened to tar or asphalt and is so dark that no details within this terrain were visible to Voyager 2. The bright icy hemisphere, likened to dirty snow, shows many large impact craters. The closest approach by Voyager 2 to Iapetus was a relatively distant 600,000 miles, so that our best images, such as this, have a resolution of about 12 miles. The dark material is made of organic substances, probably including poisonous cyano compounds such as frozen hydrogen cyanide polymers. Though we know a ittle about the dark terrain's chemical nature, we do not understand its origin. Two theories have been developed, but neither is fully satisfactory--(1) the dark material may be organic dust knocked off the small neighboring satellite Phoebe and "painted" onto the leading side of Iapetus as the dust spirals toward Saturn and Iapetus hurtles through the tenuous dust cloud, or (2) the dark material may be made of icy-cold carbonaceous "cryovolcanic" lavas that were erupted from Iapetus' interior and then blackened by solar radiation, charged particles, and cosmic rays. A determination of the actual cause, as well as discovery of any other geologic features smaller than 12 miles across, awaits the Cassini Saturn orbiter to arrive in 2004. (Caption: Courtesy USGS)

This image is © Copyright 1999 by Calvin J. Hamilton. Any commercial/for-profit use of this image needs to be addressed to Calvin J. Hamilton.

Copyright © 1995-2016 by Calvin J. Hamilton. All rights reserved.