Is this really the end for Pluto?
The former ninth planet was demoted again Thursday when scientists determined it no longer even reigns as king of the dwarf planets, a subclass to which astronomers relegated Pluto last summer after deeming it unworthy of standing alongside the solar system's larger bodies.
The bigger dwarf planet, Eris, is 27 percent more massive than Pluto, California Institute of Technology scientists reported in the journal Science. One of them, Michael Brown, led the discovery of Eris in 2003 that precipitated a reconsideration of the solar system's familiar nine planets.
"I think this result definitely cements Pluto's demotion into the dwarf-planet category," said Patricia Reiff, a Rice University astronomer and director of the Rice Space Institute. "There was an outcry in the beginning, but I think it's died down."
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The angry din following last summer's decision in Prague, Czech Republic, by the International Astronomical Union came primarily from American astronomers and stargazers, on whom it was not lost that Pluto discoverer Clyde Tombaugh was the only American to find a planet in our solar system.
Pluto's proponents noted that only about 4 percent of the astronomy organization's 9,000 astronomers were present at the meeting to vote on Pluto's status.
But campaigns for Pluto's restoration appear to have lost stream since then. One Web site, PlutoPetition.com, vowed to present the international astronomers with its results when "1 million votes (or some similarly impressive number) have been collected." Ten months later the Web site remains far from that goal.
At the time of Pluto's demotion there weren't enough observations of Eris to determine whether it was as large as or larger than Pluto. Since then, the Hubble Space Telescope found that Eris' diameter exceeds Pluto's, if only by a few dozen miles.
And the new measurements by Brown and his colleagues, made while observing the interaction between Eris and its tiny moon, Dysnomia, definitively show Pluto to have significantly less bulk.
"I worry about ever saying that anything is a final nail in Pluto's coffin," Brown said. "I suspect Pluto has zombie and/or vampire tendencies, and that we have not yet had the final stake through the heart."
