Word: cometted
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...light-years from the sun, halfway to Alpha Centauri, the next nearest star. Occasionally one of the icy lumps in these outer regions is nudged toward the sun by a passing star or gas cloud. As it falls toward our world, it flares into view as a streaking comet...
Ever since these vast comet nurseries were first proposed four decades ago, the only evidence for them has been indirect and theoretical. At last there is something concrete. A tiny reddish spot of light recorded on a sensitive electronic detector in Hawaii last month appears to be the first component of the Kuiper belt ever observed. The body, known for now as 1992 QB1, is about 200 km (120 miles) across, and a preliminary calculation puts it at more than 5.1 billion km (3.2 billion miles) away. That doesn't necessarily make it the most remote object in the solar...
...called gas giants: Jupiter, Saturn, Uranus and Neptune. The rest was blown by solar heat and wind to the outskirts, where it presumably congealed into chunks of ice and dust. (Rocky Pluto is an anomaly, and many astronomers believe it isn't a planet at all but a giant comet or asteroid flung into its present position when it had a close gravitational encounter with one of the outer planets...
...comet or an asteroid strike about 65 million years ago is the favored explanation for why dinosaurs vanished from the earth so abruptly after having dominated the planet for the preceding 70 million years. The tremendous plume of smoke and dust thrown into the atmosphere by the space intruder's impact, equivalent to perhaps a million hydrogen bombs, would have blocked out sunlight for months. The globe would have gone into a dark, deep freeze, killing first the plants and then the giant lizards that fed on them, directly or indirectly -- paving the way for mammals, and eventually humans...
...report in Science suggests that 370 million years ago, during the Late Devonian period, a comet or asteroid caused an even greater catastrophe, one that wiped out fully 70% of all marine species on earth. American and Belgian scientists have found tiny glass beads just .3 mm (.004 in.) across, embedded in underground sediments in Belgium. The beads, called microtektites, are thought to be caused when silicon and other minerals melt and then cool following either a volcanic eruption or a high-speed impact. The chemical composition of these beads seems to point much more convincingly to an impact...