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Honey, I shrunk the solar system NASA/JPL RELEASE Posted: August 24, 2006
The International Astronomical Union, wrapping up its meeting in Prague, Czech Republic, has resolved one of the most hotly-debated topics in the cosmos by approving a specific definition that gives our solar system eight planets, instead of the nine most of us grew up memorizing. NASA has already visited all eight planets that retain their official title: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. In addition, the agency has its New Horizons spacecraft en route to Pluto, which the astronomical union has designated as the prototype for a new class of celestial objects, to be called "dwarf planets." "NASA will, of course, use the new guidelines established by the International Astronomical Union," said Dr. Paul Hertz, Chief Scientist for the Science Mission Directorate at NASA Headquarters. "We will continue pursuing exploration of the most scientifically interesting objects in the solar system, regardless of how they are categorized." Ceres, which orbits in a belt between Mars and Jupiter and is the largest known asteroid, is one of those interesting objects. In 2007, NASA will launch the Dawn spacecraft on a mission to study Ceres, which the astronomers have placed in the dwarf planet category, alongside Pluto. The dwarf planet family also includes 2003 UB313, nicknamed "Xena." When Dr. Mike Brown of Caltech and his colleagues announced last summer that they'd discovered the object, which is bigger and farther away than Pluto, many astronomers decided it was time to figure out once and for all, "What exactly is a planet, anyway?" Here's how it all shakes out. The International Astronomical Union has decided that, to be called a planet, an object must have three traits. It must orbit the sun, be massive enough that its own gravity pulls it into a nearly round shape, and be dominant enough to clear away objects in its neighborhood. To be admitted to the dwarf planet category, an object must have only two of those traits -- it must orbit the sun and have a nearly round shape. And no, moons don't count as dwarf planets. In addition to Pluto, Ceres and 2003 UB313, the astronomical union has a dozen potential "dwarf planets" on its watchlist. What's to become of the other objects in our solar system neighborhood, the ones that are not planets, not dwarf planets and not moons? The organization has decided that most asteroids, comets and other small objects will be called "small solar-system bodies." Despite the establishment of these three distinct categories, there are bound to be gray areas. As technologies improve and more objects are found, the International Astronomical Union will set up a process to decide which of the three categories are most appropriate for specific objects. Even before the discovery of Xena, not all was calm in the planetary world. There was debate after Clyde Tombaugh discovered Pluto in 1930. With its small size, distant location and odd orbit, some questioned whether Pluto was really a planet or just an icy remnant of the planet-forming process. That issue has been resolved by the International Astronomical Union. Among those most keenly following the debate -- Mike Brown, who has been awaiting word on Pluto and the object he found, Xena. "I'm of course disappointed that Xena will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision," said Brown. "It is scientifically the right thing to do, and is a great step forward in astronomy." Although the revamping of our solar system might seem unsettling, it's really nothing new. In fact, when Ceres was first discovered in 1801, it was called a planet, as were several similar objects found later. But when the count kept on growing, astronomers decided "enough is enough," and they demoted Ceres and its siblings, placing them in a new category, called asteroids. |
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The Hubble Space Telescope has become astronomy's crown jewel for knowledge and discovery. The great observatory was placed high above Earth following its launch aboard space shuttle Discovery on April 24, 1990. The astronauts of STS-31 recount their mission in this post-flight film presentation.
Space shuttle Atlantis is delivered to Kennedy Space Center's launch pad 39B on August 2 to begin final preparations for blastoff on the STS-115 mission to resume construction of the International Space Station.
Just after 1 a.m. local time August 2, the crawler-transporter began the slow move out of the Vehicle Assembly Building carrying space shuttle Atlantis toward the launch pad.
Astronauts Jeff Williams and Thomas Reiter will conduct a U.S.-based spacewalk outside the International Space Station on August 3. To preview the EVA and the tasks to be accomplished during the excursion, station managers held this press conference from Johnson Space Center in Houston.
The long voyage of exploration to Jupiter and its many moons by the Galileo spacecraft began on October 18, 1989 with launch from Kennedy Space Center aboard the space shuttle Atlantis. The crew of mission STS-34 tell the story of their flight to dispatch the probe -- fitted with an Inertial Upper Stage rocket motor -- during this post-flight presentation film.
Space shuttle Atlantis is transported to the cavernous Vehicle Assembly Building where the ship will be mated to the external fuel tank and twin solid rocket boosters for a late-August liftoff.