Is this really the end for Pluto?
The former ninth planet was demoted yet again Thursday when scientists determined it no longer even reigns as king of the dwarf planets, a sub-class astronomers relegated Pluto to last summer after deeming it unworthy of standing alongside Earth, Jupiter and other 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."
The angry din following last summer's decision in Prague 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 steam since then. One Web site, PlutoPetition.com, vowed to present the international astronomers with its results when "one 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 or larger than Pluto. Since then, the Hubble Space Telescope found that Eris' diameter exceeds that of Pluto, if only barely, 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."
There appears to be little organized support for Pluto now, even in America.
The council that establishes the formal positions of the American Astronomical Society has not raised the issue, said J. Craig Wheeler, a University of Texas astronomer who is the council's president.
"I know there are some astronomers who are unhappy with the designation of Pluto as a dwarf planet," he said. "I do not know how organized they are in terms of taking official action."
The International Astronomical Union will reconvene in two years, the earliest point at which Pluto's status could be revisited.
Harvard University professor emeritus of astronomy and history of science Owen Gingerich said he's still hopeful Pluto can get some recognition if it cannot be restored to its former status.
Gingerich, the chairman of the International Astronomical Union's Planet Definition Committee in 2006, was deeply disappointed by Pluto's demotion.
"I think these icy bodies beyond Neptune will eventually be known as Plutonians, thereby giving some nod to the historical status of Pluto," he said.
"And they may well be considered a type of planet and not simply dwarf planets, even though dwarves they will always be."