Pluto is no longer a planet, but not without a struggle. After tumultuous discussions at the general assembly of the International Astronomical Union in Prague, Czech Republic, several hundred astronomers have agreed for the first time on a definition of a planet.
Three attempts at a definition were needed, and the discussion was sometimes heated, but there was widespread support among astronomers for the final result.
According to the new definition, a planet is a celestial body that (a) is in orbit around the sun, (b) has enough mass to be nearly round and (c) dominates its orbit. The astronomers were trying to define only what "planet" means in our own solar system, without considering planets around other stars.
The new resolution also defines a class of "dwarf planets" that meet the first two criteria above, but not the last. This class includes Pluto as well as a slightly larger object known as 2003 UB313 that was discovered in 2005, and probably several other icy bodies in the Kuiper Belt beyond Neptune. It also includes Ceres, the biggest of the rocky asteroids circling the sun between the orbits of Mars and Jupiter.
And will the New Horizon's mission(here) be demoted to a dwarf planet?
Poor New Horizons. When it launched in January 2006 it was with all the prestige of the first spacecraft to study Pluto, the last unvisited planet in the solar system.
That changed seven months later, when astronomers decided that Pluto was not a planet. For the time being, New Horizons is at least the first mission to a dwarf planet -- the new class of objects into which scientists dumped Pluto.
But that doesn't mean it will be the first spacecraft to visit a dwarf planet. Under the new definition (it's still unclear), Ceres may be upgraded from asteroid to dwarf planet, and if NASA's Dawn mission launches as planned next summer, it will arrive at Ceres in February 2015, five months before New Horizons gets to Pluto.
In the meantime, New Horizons' mission remains the same: to unlock one of the solar system's last, great secrets. The spacecraft will cross the orbits of all the planets from Earth to Neptune and fly by Pluto and Charon in July 2015.
Update: A Simi Valley Assemblyman has proposed legislation here:
Frustrated over the Legislature's inability to pass legislation to create an independent redistricting commission or make other political reforms, Richman on Thursday penned a resolution asking the Assembly to condemn the International Astronomical Union for its decision to strip Pluto of its planetary status.
"The downgrading of Pluto reduces the number of planets available for legislative leaders to hide redistricting legislation and other inconvenient political reform measures," the resolution says in part. "The California Legislature, in the closing days of the 2005-06 session, has been considering few matters important to the future of California, and the status of Pluto takes precedence."
In a few short hours, Richman was able to round up 53 co-authors — 26 Republicans and 27 Democrats.
The resolution notes the matter is of particular concern to California, since the slighted former planet shares the name "of California's most famous animated dog."
It also notes that the action constitutes "an unfunded mandate" on public schools since it "renders millions of textbooks ¿ obsolete."
In an e-mail to associates, Richman notes, "Sadly, there is probably a much better chance that the Assembly will vote on HR36 than independent redistricting."
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