Space missiles

Updated 3:16 PM ET, Wed January 23, 2013
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Herschel Space Observatory provided the first thermal infrared observations of Apophis at different wavelengths, which together with optical measurements helped refine estimates of the asteroid's size. Previous estimates put the asteroid's average diameter at about 885 feet, but Herschel's observations indicate the space rock is about 1,066 feet across. ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss (Konkoly Observatory
The giant asteroid Vesta is seen in an image taken from the NASA Dawn spacecraft. The Dawn spacecraft will next travel to the asteroid Ceres, arriving in 2015. Photo by NASA/JPL-Caltec via Getty Images
This shows the impact of a projectile, probably an asteroid, on Mars -- the 1,117- mile-diameter Hellas Basin, the largest basin on the planet. JPL/AFP/Getty Images
The Valles Marineris, shown in this composite image of Mars, is similar to Arizona's Grand Canyon, except it's as long as the U.S. is wide. Scientists theorize that water might have carved canyons like Valles Marineris after asteroids slammed into the Martian surface and melted underground ice. NASA/Getty Image
A Geminid meteor streaks diagonally across the sky -- against a field of star trails -- over a rock formation in Valley of Fire State Park in Nevada. The Geminid meteor shower happens every December, and is thought to be debris cast off from an asteroid called 3200 Phaethon. Ethan Miller/Getty Images
The concentric rings in this image, left of center, were made by an asteroid hitting the Sahara Desert in northern Chad several hundred million years ago. The image was taken on board the shuttle Endeavor. Space Frontiers/Hulton Archive/Getty Images
Astronomers say they have discovered an asteroid belt around the star Vega, seen in this illustration. NASA's Spitzer space telescope and the European Space Agency's Herschel Space Observatory were used to observe the star, which is the second brightest in the northern sky. NASA/ESA/Herschel Space Observatory
The March 1966 cover of Analog Science Fiction/Science Fact featured an illustration of a meteor hitting Earth. J.E. Enever published his ground-breaking article, "Giant Meteor Impact," in this issue, detailing what such strikes could do, and have done, to our planet. His vivid prose and terrifying physics woke scientists up to the potential of huge space boulders slamming into the Earth. Courtesy/Greg Bear