Asteroids have been of continued interest and research among scientists and the general public. This issue's Topic in Depth explores some of the Internet's offerings on the subject.

From Spaceflight Now, the first site (1) is an April 7, 2002 article that describes new research, showing that "there are between 1.1 million and 1.9 million 'space rocks' larger than 1 kilometre in diameter in the so-called main asteroid belt, about twice as many as previously believed." The next site, offered by Solarviews.com, is called Asteroid Introduction (2). Here, visitors can learn the basics about asteroids, including information on well known ones, pictures, animations, and more. NOVA maintains the next site, called Doomsday Asteroid (3). This site describes comets such as Hale-Bopp and others, while also providing teacher activities and great photographs. For a unique look at the effects that asteroids can have on the Earth, take a look at National Geographic's Web site Asteroids: Deadly Impact (4). Here, visitors get to play detective by looking at available evidence of impacts and then trying to figure out what sized meteor or comet caused it. From NASA, the next site is called Asteroid and Comet Impact Hazards (5), a comprehensive but approachable accumulation of information about the study and probability of asteroid-Earth impacts. Included are articles, photographs, animations, and more -- offering links such as the Torino Impact Scale page that describes how the scale assesses the probability of an asteroid impact. From the US Naval Observatory and called Asteroid Orbital Elements (6), the next site is a database that contains all known non-cometary and non-planetary bodies. Search results provide data such as the asteroid's name, number, diameter, orbital eccentricity, and more. The Smithsonian's National Museum of Natural History Web site, A Blast From the Past (7), is a short but interesting site that explores new evidence of an asteroid impact 65 million years ago when dinosaurs went extinct. The last site, from thursdaysclassroom.com, is a lesson plan for grade-schoolers called Crazy Craters (8). Students experiment to learn about what causes the various features of impact craters, including the rim of mountains around the edge and the streaks or rays that fan out from large craters.