What is a planet?
This week the International Astronomical Union will hold its XXVIth General Assembly in Prague, Czech Republic. & even though most people have no idea who they are 1 of their discussions will have an effect on all of us. OK, it won't be Earth shaking, but it may change the way we define what a planet is. So, I guess maybe in a way it will be, at least for text book publishers & science teachers.
Isn't it a fact that we have 9 planets in the Solar System? That is what most of us have been taught since the discovery of Pluto in 1930. But what most of us haven't been aware of is the debate about whether Pluto reall ys a planet or not.
When Pluto was 1st discovered most people were expecting another gas giant like Uranus & Neptune. But it was quickly realized that Pluto was anything but a gas giant. As time went on & measuerments got more accurate Pluto kept on shrinking in size & the debate kept growing. Recent discoveries added to the debate. When the 1st moon orbiting Pluto, Charon, was found, some people used that as an arguement in favor of Pluto being a planet. Charon added to the problem because it was another tool to more accurately determine the size of Pluto, shrinking it even more. Since then 2 more smaller moons, Hydra & Nyx, have been discovered.
In 2002 Quaoar was discovered at 1/2 the size of Pluto. Then in 2003 another trans-Neptune object was found in the Kuiper Belt. Designated "2003 UB313", it also has moon. It is larger in size than Pluto. More fuel for the fire was added. If Pluto is a planet than it should also be considered as 1. Not officially named the object has been unofficially nicknamed Xena & its moon Gabrielle. Meanwhile, another object, "2003 VB_12" with the proposed name of Sedna was also discoverd. It is smaller than Pluto.
This debate actually began with the discovery of Ceres in the 1800s. Ceres is the largest object in the asteroid belt. But at the time of its discovery, it was the only known object in the area between Mars & Jupiter. Again, it is smaller than Pluto.
Whiles Ceres is currently defined as an asteroid, the debate is going on for what to call the rest of these objects. Are they planetoids? Should they be called ice dwarf planets. & at what size does an asteroid become a dwarf planet?
& to top things off what size defines a moon orbiting a planet vs considering it a double planet. Mercury is smaller than Jupiter's moon Ganymede. & Titan, orbiting Saturn runs a close 2nd in size to Ganymede in size. In comparison to the planets they orbit they are clearly much smaller. When you compare the size of Charon to Pluto or Earth to our moon you find them much closer in relative size. The arguement could be made for calling them double planet sytems.
Clearly some arbitrary definitions are going to have to be made. & no matter what, not everyone will be happy. These decisions have to be made. That is part of the reason the International Astonomical Union was created about 80 yrs ago. They are the body recognized by the scientific community, as well as the rest of us, to do this. Their job is to help clarify astronomical terms. & that includes what a planet is. Another major responsiblity they have is that of settling on a name for a planet, moon, star or other astronomical object. More info about what they do can be found at their website: http://www.iau.org/
Meanwhile, for what it is worth, my suggestion is to set a 3rd set of planets in addition to the terran & gas giant types. The ice dwarf name would be fine with me. The reality is, no matter what they decide, someday some new object will come along that will create a new dilema for what makes a planet. God still has quite a few surprizes waiting for us out there that will raise more questions than they answer. As for the text book publishers, they will have to live with the changes. The reality is that discoveries are being made so regularly thanks to things like the Hubble Telescope, the Galileo, Cassini-Huygens, New Horizons missions, etc, that these ongoing discoveries make a textbook outdated almost as soon as they are published. & no matter what is decided, life goes on. Things went on before Uranus was found, it will be the same whether we have 9 or 23 planets of some sort or another. The info adds to our storehouse of knowledge. It adds to our understanding of how God set up our Solar System. But it doesn't determine where we will spend eternity. Our faith in Jesus & living out that faith is what determines that.
To follow what is going on at the general assembly from 14 -25 Aug 2006:
IAU XXVIth General Assembly
IAU General Assembly News
posted by Al @ 11:44 PM
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