Patterns of cracks were found on Venus’ 500-degree
surface by NASA’s Magellan spacecraft in the early 1990s.
Using an analysis technique by Pierre Moreels, a French intern
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., the
patterns proved to be roughly hexagonal. This kind of cracking
pattern shows that the surface has heated and cooled by almost
200 degrees Celsius (392 degrees Fahrenheit) over long periods
of time.

Moreels adopted a modeling technique that was originally
developed for medical imaging to discern individual blood
cells, ensuring an accurate count. The technique is called the
watershed transformation and has also been used in Earth-
observing satellite images of fields.

“The program uses an analogy to the Earth’s watershed
process to filter out the noise from the radar imaging system
on Magellan,” Moreels said. “It finds the regions in the
surface covered with patterns of multi-sided shapes. The more
of these areas of multi-sided shapes we find, the better we
can understand the history of climactic change on Venus.”

Moreels and his mentor, Dr. Sue Smrekar, a research
scientist in JPL’s Geophysics and Planetary Geology section,
report their results today at the Lunar and Planetary Science
Conference in Houston, Texas.

The Magellan spacecraft took pictures of large areas of
fissures, analogous to cooling basalt fractures on Earth, but
on a much larger scale. The mathematical program filters out
recurring radar noise by mapping the cracks into a graph
simulating a field of mountains – the rougher the surface, the
higher the peak. The program fills in the valleys of the
simulated landscape, much as rain fills in a lake. This way,
small peaks of radar noise are covered over, and only the
dramatic changes in the surface’s roughness remain.

The program then evens out the edges and connects them.
The result is a map of the surface cracks that can easily sort
out the number and orientation of the cracks and the area
between them. The shapes generally have six sides of different
lengths and cover an area more than 100 square kilometers (39
square miles).

Slow heating and cooling globally could have formed large
areas of cracks on Venus’ surface. A major episode of
resurfacing occurred on Venus roughly 700 million years ago,
in which water and sulfur levels in the atmosphere rose.
Mapping the size and distribution of the cracks will help
determine whether they are the result of local or global
heating. Other models, in which volcanoes heat the surface or
flows erupt on the surface and cool, have difficulties in
explaining the size of these polygons.

More information on the Magellan mission is available at .

The California Institute of Technology in Pasadena
manages JPL for NASA.