September 16, 2010 | David F. Coppedge

Many Stars Are Planet Destroyers

A NASA study is being called “Bad news for planet hunters.”  A survey of stars in globular clusters has not turned up the number of planets expected.  Astronomers conclude that stars in these presumably ancient clusters have long since devoured their planets or sent them careening out into oblivion.
    The leading popular science outlets, including Science Daily, PhysOrg and Live Science covered the story that was published in Astrophysical Journal.  Since at this time it is simpler to look for “hot Jupiters” (large planets close to the star), and none were found in the large globular cluster 47 Tucanae, the research team concluded that they have been destroyed.  They believe that violent tidal forces caused early planets to spiral into the stars or be flung out of orbit.  It also seems apparent that planet-building material has been depleted around these stars.  “Globular clusters turn out to be rough neighborhoods for planets,” said Brian Jackson [NASA-Goddard], “because there are lots of stars around to beat up on them and not much for them to eat.”
    Speaking of eating, Space.com added the thought that when alien worlds collide, the chances for finding life in extrasolar systems dwindle.  Based on Spitzer Space Telescope data, researchers at the Harvard-Smithsonian Center for Astrophysics publishing in Astrophysical Journal Letters believe that the large amounts of dust around tight double-star systems they observed are also evidence for destroyed planets – planets that collided with each other.  Dust should be long gone in these stars’ life cycles, they surmised.  That dust is still present implies that planetary collisions “must be kicking up fresh dust.”  The four dusty binaries Spitzer has found so far implies also that “the observations are not a fluke: something chaotic is very likely going on.”  Consequently, double stars “may not be the best places to look for extraterrestrial life,” the article said. The study leader called their results “real-life science fiction” if there is such an oxymoronic category.

Results like these are statistical and preliminary, so no firm conclusions should be drawn.  SETI hopefuls can argue that there are quintillions of other stars out there.  Still, both types of systems (globular cluster members and tight binaries) are assumed to be ancient.  There’s no reason that these stars should lack planets, if planets are a natural consequence of stellar evolution.  If so, the lack of planets around them suggests that planets have limited lifetimes.  It could be argued that binaries and globulars have more destructive tidal forces than single stars like our sun, meaning that the multitude of single stars may still have long-lived habitable zones.  Perhaps.  The most interesting aspect of the reports may be that survey results were not what the scientists predicted.

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Categories: Physics, SETI, Solar System

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