On the Cover: Vredefort is the oldest and largest visible meteor impact crater on Earth. With a diameter of roughly 300 kilometers (about 190 miles), it is twice the size of the Chicxulub crater associated with the extinction of the dinosaurs. Named after the town of Vredefort, which is situated near its center, this crater is located in the Free State Province of South Africa. Vredefort is one of Earth's few multi-ringed impact craters; they are more common elsewhere in the solar system. This image was taken on August 29, 1985 by an astronaut on board the space shuttle. NASA
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10 The Quest to Find the Next Killer Asteroid—Before it Finds Us! Steve Chesleydiscusses how the Pan-STARRS telescope is helping to protect Earth.
16 Annual Report to Our Members
19 World Watch Europa of Titan: Which will we visit next?
20 Q&AExoplanet orbits and extraterrestrial coordinate systems.
21 Factinos More moons for Saturn; Pluto's atmosphere
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22 Members' Dialogue Save money and the environment
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