Magellan radar image of part of the Phoebe region of Venus. Mosaic of part of revs 146 and 147 acquired in the first radar test on August 16, 1990. The image is located at 292 degrees E. longitude, 24 degrees south latitude. This image is 30 km (19.6 miles) wide and 70 km (43.5 miles) high. This Magellan radar image of Venus shows an area to the southeast of Phoebe Regio, an upland region characterized by major rift zones. The irregular-shaped depressions near the middle of the image are interpreted as volcanic calderas, the larger of which is 8 x 3.6 km (5 x 2.2 miles) across. Unlike impact craters, volcanic calderas are not usually circular in map view. Irregular calderas such as these occur on basaltic shield volcanoes on Earth, such as those in Hawaii. The radar illumination comes from the left causing the caldera walls that face the spacecraft to be brightly illuminated. Another factor that makes the walls bright is that the walls may be rough and blocky.
