More than 400 years after its discovery by astronomer Galileo Galilei, Jupiter’s moon Ganymede – the largest moon in the solar system – has finally claimed a spot on the map.
A group of scientists led by Geoffrey Collins of Wheaton College has produced the first global geologic map of Ganymede, Jupiter’s icy, seventh moon. The map combines the best images obtained during flybys conducted by NASA’s Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) and is now published by the U. S. Geological Survey as a global map.
Animation of a rotating globe of Jupiter’s moon Ganymede, with a geologic map superimposed over a global color mosaic. The 37-second animation begins as a global color mosaic image of the moon then quickly fades in the geologic map.
“The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from,” Collins said. “Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity.”
“This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface,” said Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “This map is helping planetary scientists to decipher the evolution of this icy world and will aid in upcoming spacecraft observations.”
According to the scientists who have constructed this map, three major geologic periods have been identified for Ganymede that involve the dominance of impact cratering, then tectonic upheaval, followed by a decline in geologic activity. The map, which illustrates surface features, such as furrows, grooves and impact craters, allows scientists to decipher distinct geologic time periods for an object in the outer solar system for the first time.
“The highly detailed, colorful map confirmed a number of outstanding scientific hypotheses regarding Ganymede’s geologic history, and also disproved others,” said Baerbel Lucchitta, scientist emeritus at the U.S. Geological Survey in Flagstaff, Ariz., who has been involved with geologic mapping of Ganymede since 1980. “For example, the more detailed Galileo images showed that cryovolcanism, or the creation of volcanoes that erupt water and ice, is very rare on Ganymede.”
The Ganymede global geologic map will enable researchers to compare the geologic characters of other icy satellite moons, because almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede.
Amateur astronomers can observe Ganymede (with binoculars) in the evening sky this month, as Jupiter is in opposition and easily visible.