Planetary rings count comets
Subtle ripples recently discovered in planetary rings, akin to the corrugations of a tin roof, provide a record of collisions with comets or their debris, two new studies suggest. The ripples, identified in the rings of both Jupiter and Saturn, persist even decades after a collision and can reveal how often debris clouds from comets and other small objects smack into planets and how many of these objects exist in the outer solar system. Teams led by Matt Hedman of Cornell University and Mark Showalter of the SETI Institute in Mountain View, Calif., report their findings March 31 online in
Telling one oldster from another
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An international team of astronomers has succeeded in telling apart two groups of elderly stars by the stars’ vibrations, a feat that could shed light on the fate of the sun. The stars, known as red giants, fall into two classes — one that still burns hydrogen in a shell around its core and another, slightly older, that has begun to burn helium at its core. Using NASA’s Kepler spacecraft, the researchers discerned differences in the oscillations of the two types of red giants. The team reports the findings in the March 31
. The sun will become a red giant in about in about 5 billion years. —
Solar twin peaks
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A new study provides an explanation for why solar activity cycles, defined by the waxing and waning of sunspots, have two peaks rather than just one. The twin peaks are due to two surges in magnetic activity, Katya Georgieva of the Space and Solar-Terrestrial Research Institute in Sofia, Bulgaria, suggests in an upcoming
ISRN Astronomy and Astrophysics
. One surge is generated by the flow of ionized gas that travels like a conveyer belt near the sun’s surface from the equator to each pole and back again far beneath the surface. The other surge is due to a flow that short-circuits that path, diffusing directly into the solar interior. —