A photo mosaic of Io. Image: NASA
than 400 years after its discovery by Galileo, the innermost large moon
of Jupiter—Io—can finally rest on its geologic laurels. A group of
scientists led by Dr. David A. Williams of Arizona State University has
produced the first global geologic map of the Jovian satellite. The map,
which was published by the U. S. Geological Survey, technically
illustrates the geologic character of some of the most unique and active
volcanoes ever documented in the solar system.
its discovery in January 1610, Io has been the focus of repeated
observation, first by Earth-based telescopes, and later by fly-by and
orbiting spacecraft. These studies depict an otherworldly celestial body
whose gravitational relationships with Jupiter and sister moons Europa
and Ganymede cause massive, rapid flexing of its surface and interior.
This flexing generates tremendous heat in Io’s interior, which is
relieved through surface volcanism, resulting in 25 times more volcanic
activity than occurs here on Earth.
than 130 years after the USGS first began producing quality geologic
maps here on Earth, it is exciting to have the reach of our science
extend across 400 million miles to this volcanically active moon of
Jupiter,” said USGS Director Marcia McNutt. “Somehow it makes the vast
expanse of space seem less forbidding to know that similar geologic
processes which have shaped our planet are active elsewhere.
Io geologic map is unique from other USGS-published planetary geologic
maps because surface features were characterized using four distinct
global image mosaics. Produced by the USGS, these image mosaics combine
the best images from NASA’s Voyager 1 and 2 missions (acquired in 1979)
as well as the Galileo orbiter (1995-2003).
uniqueness presented a particular cartographic challenge. “Io has
undergone major surface changes during the past few decades due to its
volcanic activity,” notes Dr. Ken Tanaka, a USGS research geologist who
coordinates the review and publication of planetary geologic maps.
“Conveying information from multiple image mosaics in a single map
necessitated the use of unique and complementary map symbols, colors,
and feature names.”
many cases, these maps show that, despite the many differences between
bodies in our Solar System, there are many notable similarities that
link the evolution and fate of our planetary system together.
highly detailed, colorful map reveals a number of volcanic features,
including: volcanic domes and depressions, lava flow fields, mountains,
plume deposits, and sulfur- and sulfur dioxide-rich plains. Despite this
geologic diversity, there is one particular feature that is common to
the Moon, Mars, and even Earth that is not depicted on the geologic map
of Io—impact craters.
has no impact craters. It is the only object in the Solar System where
we have not seen any impact craters, testifying to Io’s very active
volcanic resurfacing,” says project lead David Williams.
new geologic map of Io is just one of many cartographic products that
help drive scientific thought. The production of these products has been
a focal point of research at the USGS Astrogeology Science Center since
its inception in the early 1960s. “Remotely characterizing the surfaces
of planetary bodies [such as Io] forces scientists to carefully
consider and test hypotheses that address the evolution of an entire
planet,” says Dr. Ken Herkenhoff, Acting Director of the USGS
Astrogeology Science Center.
began producing planetary maps in support of the Apollo moon landings,
and continues to help establish a framework for integrating and
comparing past and future studies of extraterrestrial surfaces.
The project was funded by NASA through its Outer Planets Research and Planetary Geology and Geophysics Programs.
“Geologic Map of Io” (USGS Scientific Investigations Map 3168)
Animation called “Rotating Globe of Io Geology”
Source: U.S. Geological Survey