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The article presents an account of a scientific expedition to Lake Cheko, near the Tunguska river in Russia, to investigate the site of the Tunguska Event, an catastrophic explosion which took place in the Siberian wilderness on June 30, 1908, and is thought to have been caused by a large asteroid or comet entering the earth's atmosphere. INSETS: Was Lake Cheko Created by the Tunguska Event?;TRACKING A DEATH STAR.

Discusses the possibility that an asteroid or comet struck the Earth and wiped out 95 percent of life in the oceans. How this collision allegedly occurred before the extinction of the dinosaurs; Use of iridium and other elements to determine where and when the object struck the Earth.

Reports on the May 28, 1997 announcement made by Louis A. Frank of the University of Iowa, that miniature comets are slamming into the earth's atmosphere at a rate of some 40,000 a day. Statements from Heinrich Holland of the Harvard University; Similar announcement made by Frank in 1986; Improved data used by Frank to represent his findings.

The article discusses the development of astronomical telescopes with the capability of detecting asteroids, comets, and other near-Earth objects (NEOs). Topics include efforts to prevent meteor impacts like the one in Chelyabinsk, Russia in 2013, asteroid detection research and defense strategies, and the Catalina Sky Survey project for the detection of NEOs at telescope sites in Arizona and Australia.

The article examines the possibility that an asteroid, or a near-Earth object, could hit the Earth. The article is part of a special section of the magazine in which factors of change concerning life on Earth are examined. The article notes that an event that could result in extinction of man is unlikely. A number of issues are discussed including the threat posed to the Earth by comets, U.S. government funding for near-Earth object research, and the measures that could be taken should an object be headed toward Earth.

The article discusses a model for comet production that revises the theory of their origins. Chunks of ice and dust that reside in the Oort cloud, beyond the orbit of the dwarf planet Pluto, become dislodged and enter the solar system as streaking comets. Topics include an overview of how the planets Jupiter and Saturn influence comet dynamics, a computer simulation by researchers Nathan Kaib and Thomas Quinn hypothesizing comet production, and the role of comets in major extinctions on Earth.

The article discusses a theory that a comet collision caused a global-cooling anomaly that contributed to the extinction of dozens of mammal species nearly 13,000 years ago. The theory has received support from the discovery of nanodiamonds in North America. Nanodiamonds only occur in sediment that is exposed to high temperatures and pressures.