This mosaic is made up from Magellan orbits 146 and 147, obtained on August 16, 1990 in the Helen region of the southern hemisphere of Venus and centered at 36.5 degrees south latitude, 293.3 degrees longitude. Resolution of the Magellan data is about 120 meter (400 feet). The mosaic is about 40 kilometers (24 miles) wide and about 80 kilometers (50 miles) long, and shows a portion of a corona in a highland region called Themis Regio. Coronae are large [>250 kilometers (150 miles) across] circular structures surrounded by a ring of ridges. Coronae were first identified in Soviet radar images of Venus. Coronae usually average about 1 kilometer (0.6 mile) high, and are thought to form due to the rise of hot material from the interior of the planet, similar to Hawaii on the Earth. The mosaicked Magellan images show the interior of the corona and a portion of its rim. Ridges appear to radiate out from the center of the corona, perhaps produced due to extensional stresses caused by uplift of the surface. Geologists and geophysicists will be analyzing the morphology, spacing, and topography of this complex tectonic feature to understand more about the origin of coronae and how they relate to similar features on Earth.
