Billion-ton clouds of charged gas hurled from the sun can overtake and eat their slower-moving gaseous brethren, complicating predictions of when and if one of these clouds might strike Earth. (p. 267)

A gamma-ray burst recorded Feb. 22, one of the brightest ever detected, is proving to be the strongest evidence so far that these cosmic flashbulbs originate in star-forming regions of distant galaxies and are generated by the explosive death of massive stars. (p. 267)

A recent Department of Defense analysis of images of the Red Planet may have located a lost spacecraft on Mars, but NASA says the images could just be electronic noise. (p. 232)

Far beyond the solar system's nine known planets, a body as massive as Mars may once have been part of our planetary system, and it might still be there. (p. 213)

Scientists have found another indicator that the sun has reached the maximum of its current activity cycle: The polarity of its magnetic field has reversed. (p. 139)