In less that 24 hours late last month, the ball of ice, rock, and dust, named Comet17P/Holmes suddenly grew 400,000 times brighter than normal. Three weeks after the flare up, people could still see the object without telescopes. Scientists were puzzled over the event. As the comets get closer to the sun, the star's heat vaporizes ice on their surfaces. The process releases fine dust, which reflects light. As a result, the heated comets look extrabright. To explain the rapid brightening, scientists speculate that a layer of material lifted off the comet and disintegrated. The resulting halo of dust around the objest would have reflected lots of light. It's possible that the entire comet may be made up of similarly fragile layers stacked one atop of another and glued together by ice. Some scientists think that earlier event and the modern one are related. It's possible that dust from the first event fell back onto Holmes. That could have dimmed the comet for more than a century. Last month, internal pressure may have finally become strong enough to enject the debris.
by Sierra and Sierra
http://www.sciencenewsforkids.com/articles/20071128/Note3.asp
