Taking a yardstick to a killer crater.
Hidden beneath the surface of Mexico's Yucatan Peninsula lies the giant Chicxulub crater, carved by a comet or meteorite that smacked Earth silly 65 million years ago. Geologists originally estimated the diameter of the crater as 180 kilometers, but a 1993 study indicated that the structure stretched 300 km across, making it one of the largest craters in the solar system (SN: 4/3/93, p. 212). Not so, report Alan R. Hildebrand of the Geological Survey of Canada and his colleagues in the Aug. 3 Nature. The group asserts that new gravity measurements made over the crater fix its size at 180 km, still one of the largest on Earth. The pattern of sinkhole lakes at the surface, which follows the crater's outer rim, also supports this smaller diameter.