These days if you look toward the west after sunset you'll see a bright star that's the first to appear in the sky – except it's not a star at all, but our neighboring planet Venus. Covered in a dense layer of thick clouds, Venus not only reflects a lot of sunlight but also keeps its surface well concealed from visible-light observations.
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But Venus' clouds can be easily penetrated by radar, which was used by NASA's Magellan spacecraft to map nearly all of its surface from orbit in the early 1990s as well as by the previous Pioneer and Soviet Venera spacecraft in the early 80s. While these missions provided incredibly detailed maps of Venus' rugged terrain, they lack the ability to monitor for surface changes that may occur either suddenly or over short time frames - changes that could indicate ongoing geologic or weather-related processes unique to the planet.
Fortunately with the capabilities of powerful ground-based radar observatories, scientists have been able to create global maps of Venus from right here on Earth... no rockets necessary.
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The image above was created by bouncing radar waves transmitted from the Arecibo Observatory in Puerto Rico off Venus and receiving their echoes at the 100-meter Green Bank Telescope in West Virginia. Such observations had been performed in 1988, 1999, 2001, and most recently in 2012, and the comparison allows researchers to hunt for clues to any surface activity.
"It is painstaking to compare radar images to search for evidence of change, but the work is ongoing," said Bruce Campbell, Senior Scientist with the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum in Washington, D.C. "In the meantime, combining images from this and an earlier observing period is yielding a wealth of insight about other processes that alter the surface of Venus."