Subscribe free to our newsletters via your
. 24/7 Space News .




OUTER PLANETS
The Great Planet Debate: Dwarf Planets Are Planets Too
by Alan Stern
Boulder CO (SPX) Jun 23, 2008


There are currently three known types of planetary scale objects within our solar system. Firstly, the inner rocky planets with high concentrations of metals. Secondly, the middle gas giants and thirdly the outerplanets that are largely water ice and frozen gases found within the Kuiper Belt - of which there could be hundreds of Pluto sized worlds. Beyond the Kuipers there may be a fourth class of planetary sized objects within the Oort Cloud. And finally in lands beyond beyond there is clearly even more classes of super size planets found both close and far from their primary star - as evidenced by the hundreds of extra solar planets so far discovered.

Classification is an important and productive scientific tool which is employed in many branches of science, from biology to geology to chemistry and astronomy. Planetary science today faces a significant classification challenge: defining what objects are and are not "planets."

This challenge has come to the fore owing to the discovery of numerous dwarf planets in the outer solar system, the recognition that Ceres is a dwarf planet (a fundamentally different body than the smaller asteroids), the discovery of planets around a pulsar, and the numerous discoveries of hot Jupiters orbiting other stars.

Geophysicists have come up with a planetary definition that makes a lot of sense. They define a "planet" as a natural object in space that is massive enough for gravity to make it approximately spherical, but not so massive that it has generated energy by internal nuclear fusion.

This definition nicely separates planets (i.e., objects larger than a few hundred kilometers across) from both smaller bodies that are too small to be fundamentally shaped by gravity, and larger bodies (very many times the mass of Jupiter) that manifest themselves as brown dwarfs and stars.

Scientists and the public would be much better off if we adopted a comprehensive planetary definition that is a self-consistent and that allows astronomers to reliably and consistently sort objects into "planetary" and other categories. The geophysical definition does just that because it allows scientists to reliably categorize bodies based on a single, simple, robust observable property-their known or estimated mass.

The geophysical planetary definition avoids the severe difficulties associated with other concepts. Some definitions depend on how objects affect their orbital zones. But these definitions result in identical objects being classified differently depending on their circumstance.

Earth, for example, would not be considered a planet if it orbited the Sun beyond Neptune, because its gravitational influence would be insufficient to clear out the Kuiper Belt. Definitions based on origin are problematic because we can rarely determine how an object formed, especially if it's outside the solar system.

Definitions based on the presence of an atmosphere or satellites are also problematic, since they can be exceedingly difficult to determine observationally, and each of these factors would rule out various objects commonly regarded as textbook examples of planets in our solar system.

The geophysical planetary definition does not tilt the population of planets in a system based on scientific biases such as preference for a limited number of planets in our solar system. Instead, it embraces the diversity of planetary types being discovered in our solar system and around other stars.

Unfortunately, the International Astronomical Union (IAU), populated primarily by astronomers who do not even study planets, has resisted the geophysical planetary definition that is popular among planetary scientists. The IAU's president has recently said that few scientists or laypeople are unhappy with the IAU's planetary definition, which excludes dwarf planets.

But this statement is false. Public polls like this one produced many tens of thousands of votes, slanted heavily in favor of dwarf planets being full fledged planets. Further, more planetary scientists pledged not to use the IAU's definition than were even in the IAU meeting room in Prague when the IAU voted on this matter.

Of course, the IAU has no police force and no army, and many scientists, educators, and lay people have correctly said that they need not follow the IAU's flawed nomenclature for planet definition - see a Goofball Called Pluto by Bruce Moomaw.

Editorials in Nature, Sky abd Telescope, and other scientifically literate publications have also opposed the IAU on this matter, and this years, the American Association for the Advancement of Science (AAAS) and the European Geophysical Union (EGU), organizations far larger than the IAU, have each recently sponsored debates to address the need for a comprehensive definition of planetary types.

Consider attending the Great Planet Debate this August in Maryland. You can make your own opinion known to the IAU at these two addresses: catherine.cesarsky @ cea.fr and iau @ iap.fr.

Planetary scientist Alan Stern is a planetary scientist and writer. He is the former Associate Administrator of Space Science for NASA.

.


Related Links
Great Planet Debate
The million outer planets of a star called Sol






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





OUTER PLANETS
Stripped of planet status, Pluto saves face
Paris (AFP) June 12, 2008
Two years after Pluto was struck from the planetary A-list and downgraded to "dwarf-planet" status, the ninth rock from the Sun regained some dignity Thursday by lending its name to a new category of celestial bodies. In a revised taxonomy of the mainly lifeless objects circling the Sun, those fulfilling all the criteria of planets except one - the ability to "clear the neighborhood" around ... read more


OUTER PLANETS
Looking For Early Earth...On The Moon

Moon-Bound NASA Spacecraft Passes Major Preflight Tests

Northrop Grumman Completes LCROSS Thermal Vacuum Testing

NASA Study Provides Next Step To Establishing Lunar Outpost

OUTER PLANETS
NASA's Phoenix Mars Lander Puts Soil In Chemistry Lab

Phoenix Returns Treasure Trove For Science

Martian Soil Good Enough For Asparagus

Game of two halves: Scientists solve Martian riddle

OUTER PLANETS
Fly Your Thesis - An Astronaut Experience

New Developments On The Road To Cosmos 2

Options For Space Tourists

Russian businessmen book spaceship rides: report

OUTER PLANETS
A Better Focus On Shenzhou

Gallup Poll Shows Americans Unconcerned About China Space Program

Chinese company develops 'UFO': report

China manned space flight set for October: state media

OUTER PLANETS
Discovery undocks from ISS

Shuttle astronauts bid farewell to space station crew

Shuttle Astronauts Bid Farewell To Space Station Crew

Astronauts test Japanese robotic arm

OUTER PLANETS
Successful Ariane 5 Solid Rocket Booster Test Firing

CU-Boulder Students Set To Launch Student Rocket Payloads June 27

ProtoStar I And BADR-6 Are Ready For Next Ariane 5 Launch

Kourou Spaceport Receives Fifth Ariane 5 For 2008

OUTER PLANETS
Chemical Clues Point To Dusty Origin For Earth-Like Planets

Astronomers discover clutch of 'super-Earths'

Vanderbilt Astronomers Getting Into Planet-Finding Game

NASA Selects MIT-Led Team To Develop Planet-Searching Satellite

OUTER PLANETS
BAE Computers To Manage Data Processing For Satellite Missions

Space Radar To Improve Mining Safety

'Spore' computer game aliens coming to virtual life

Integral Systems Integrated Solution To Support JCSAT-12




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement