* Space rock risk underreported, researchers say:
Growing numbers of astronomers are questioning traditional estimates of how often comets or asteroids hit Earth.
* In new state of matter, echoes of an old symbol:
A medieval emblem of three interlocking circles is finding new life as a description of some special atomic interactions.
* Was 'extinct' woodpecker sighting real?:
Scientists debate whether a long-lost bird was really caught on videotape.
* Astronomers peer into the 'first trillionth of a second':
New data help confirm that the newborn cosmos underwent a stupendous growth spurt, scientists say.