Scientific American October 2000 29www.sciam.com

D AT A P O I N T S

The Sky’s the LimitEstimated minimum diameter of asteroid that would have global consequences if it hit the earth: 1 kilometer

Explosive yield: 100,000 megatons

Estimated number of such asteroids near the earth: 900

Percent so far detected: 40

Approximate size of object that leveled Tunguska forest in Siberia in 1908: 100 meters

That killed the dinosaurs: 10–15 kilometers

Largest identified terrestrial impact craters:Crater Name Location Crater Diameter Impact (millions

(kilometers) of years ago)

Vredefort South Africa 300 2,023

Sudbury Canada 250 1,850

Chicxulub Mexico 170 65

Manicougan Canada 100 214

Popigai Russia 100 35

SOURCES: NASA Ames; Science, June 23, 2000; National Weather Service; National Space Science Data Center

AT M O S P H E R I C S C I E N C E

Dingy SkiesThe northern Pacific Ocean, once the only atmosphericarea in the Northern Hemisphere untarnished by pollutants,now reportedly contains toxic aerosols originating fromAsia. These results, announced at a July meeting, come fromthe University of California Pacific Rim Aerosol Network. Thegroup sampled the air to detect aerosols containing pollu-tants, including minerals and radioactive lead isotopes,which can point to the country of origin. Asian countries areheavily dependent on coal-burning industries, and theyemit more aerosols than any other region in the world. Theminerals in the aerosols could interfere with the PacificOcean’s heating and cooling cycles, severely perturbingweather patterns. —Rebecca Lipsitz

A S T R O N O M Y

Mr. Spock,Phone HomeResearchers announced at the Au-gust gathering of the International As-tronomical Union the discovery of ninenew planets outside our solar systemand several candidate planets, bring-ing the total to at least 50 since the firstwas discovered five years ago. Onenew find orbits Epsilon Eridani, only10.5 light-years away—and one of thepossible stars around which the homeplanet of Star Trek’s Mr. Spock circles,according to Treksperts. Some of theother new bodies belong to a family ofplanets—there’s one new extrasolarsystem, with two low-mass planets,and five others are suspected. Extraso-lar systems may therefore be common;previously, astronomers knew of onlyone, around Upsilon Andromedae. Seehttp://obswww.unige.ch/~udry/planet/planet.html for more informa-tion. No word yet on the whereaboutsof the Klingon sun. —P.Y.

B I O L O G Y

Stressed for LifeIt’s not news that early childhood traumacan exert lifelong emotional influences. Butresearchers from Emory University may nowhave found a physiological basis. In the Au-gust 2 Journal of the American Medical Associ-ation, they report that early-life abuse makesthe brain hyperreactive to stress in later life.They studied four groups of women—de-pressed and nondepressed women with and

P S Y C H O L O G Y

Down with E-reading?

Prefer reading Scientific American in print rather thanat our Web site? Perhaps you find print versions moreinteresting and comprehensible. Those were the feel-ings of test subjects—even computer-savvy undergrad-uates—who read essays from another magazine, Time.On-line readers also found authors less credible and ar-guments less persuasive. The reason may be that stu-dents need to learn different processing abilities when

they are attempting toread text on computerscreens, speculatesOhio State University’sP. Karen Murphy, co-au-thor of the study. Thefindings were presentedat a recent AmericanPsychological Associa-tion meeting. —S.M.

Paper isbetter

without a history of childhood abuse—andthen stressed them by having them speakand solve a mental math exercise in front ofan audience. Levels of ACTH, a stress hor-mone, were higher in the abused women,most strikingly in those who were also de-pressed. Stress hypersensitivity due tochildhood abuse may increase the risk formood and anxiety disorders, and drugs in-terfering with the hormonal stress responsemight help prevent them. —Julia Karow

DOUG MARTIN Photo Researchers, Inc.

getting the dirt:Thomas Cahill of the Universi-ty of California at Davis holdstwo filters: one clean and oneexposed to air in Kyoto, Japan.

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