IAU Draft Definition Of Planets And Plutons
This will be in the next issue of News but since that wont be out for a couple of days I figured I post it here first. Patrick http://www.spacedaily.com/reports/The_IAU_Draft_Definition_Of_Planets_And_Pl...
There seems to be some indecision as to whether a planet can be defined solely by size, or distance from the sun & orbital inclination with respect to the ecliptic. The cosmos- and the solar system- is a big place- what would a hypothetical body be called with an orbit longer than 200 years, yet earth-sized or larger? And if it's orbital plane coincided with the ecliptic? Also, none of this seems to address classifying extra-solar planets. As more planetary systems are discovered among other stars, the solar system apparently becomes more and more unique. Will every system have it's own classification system? While not currently practical, it would be nice to see at least medium-resolution images of some of these bodies before pigeonholing them, especially Ceres. Humans have this need to make lists. I suppose it's out of the question to teach our youth that the solar system is composed of the sun, and many other smaller, non-fusing bodies of various sizes orbiting at various distances- a list that will change as discoveries are made. --- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
This will be in the next issue of News but since that wont be out for a couple of days I figured I post it here first.
Patrick
http://www.spacedaily.com/reports/The_IAU_Draft_Definition_Of_Planets_And_Pl... __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
--- Patrick Wiggins <paw@wirelessbeehive.com> wrote: <snip>
http://www.spacedaily.com/reports/The_IAU_Draft_Definition_Of_Planets_And_Pl... The draft definition makes no sense: "Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. The shape of objects with mass above 5 x 1020 kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation." Io: It has a diameter of 3643 km. It has a mass of 8.93 x 10^22 kg. Ganymede: It has a diameter of 5262 km. It has a 1.48 x 10^23 kg mass. Callisto: It has a diameter of 4821km. It has a mass of 1.08 x 10^23 kg. Europa: It has a diameter of 3122 km. It has a mass of 4.8 x 10^22 kg. But the Jovian Moons (and the Earth's Moon) are excluded by the qualifier: "First, the object must be in orbit around a star, while not being itself a star." "If the proposed Resolution is passed, the 12 planets in our Solar System will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313." So the Earth's Moon, which is gravitationally spheriod (3,476km) and three times the size of Ceres (975Ã909 km), isn't a planet, but Ceres, essentially the biggest big rock in an orbit filled with rubble, is? Not that I'm against calling Ceres a planet. Maybe that will assure funding for the fly-by mission that almost got cancelled this year. - Kurt __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
participants (3)
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Canopus56 -
Chuck Hards -
Patrick Wiggins