Given the considerable debate as to whether such outer solar system objects as Pluto and Eris should be counted as planets, and the not-entirely satisfactory resolution on the matter recently passed by the International Astronomical Union, we offer the best possible definition of a planet--the TEXAN definition:
Regarding the confusion over a definition separating planets from other Sun-orbiting bodies:Since any object too small to be considered a planet is a "minor planet", a "small solar system body", or a "dwarf planet", and
Since anything bigger than TEXAS is certainly not minor, not small, and not a dwarf,
Therefore, a planet must be any star-orbiting, non-fusing celestial body larger than the smallest sphere containing TEXAS.
| Using the present boundaries of Texas, this works out to a definition of a planet as an object with a diameter of at least 1,298.5 km (806.9 miles). (Strictly, "object" here includes celestial objects--other than stars and brown dwarfs--orbiting the Sun or another star.) This is the distance (through the Earth) between the northwestmost point in the Texas Panhandle and the southern tip of Texas near Brownsville. With this definition, our solar system has at least 12 and perhaps 15 known planets, so far (given that sizes are not firmly known for some objects): |
|
| Planet | mean diameter* (km) | status | mean distance from Sun (AU) | number of moons | year discovered |
|---|---|---|---|---|---|
| Mercury | 4879 | planet | 0.39 | 0 | pre-Texas |
| Venus | 12102 | planet | 0.72 | 0 | pre-Texas |
| Earth | 12742 | planet | 1.00 | 1 | pre-Texas |
| Mars | 6779 | planet | 1.52 | 2 | pre-Texas |
| Jupiter | 139640 | planet | 5.20 | 67 | pre-Texas |
| Saturn | 116160 | planet | 9.54 | 62 | pre-Texas |
| Uranus | 50730 | planet | 19.19 | 27 | 1781 |
| Neptune | 49240 | planet | 30.07 | 14 | 1846 |
| Pluto | 2380 | planet | 39.59 | 5 | 1930 |
| Haumea | 1300±100 | probable planet | 43.33 | 2 | 2003 |
| Makemake | 1430 | planet | 45.76 | 1 | 2005 |
| 2013 FY27 | 1100±500 | possible planet | 58.94 | 0 | 2013 |
| (225088) 2007 OR10 | 1535±150 | planet | 66.99 | 1 | 2007 |
| Eris | 2330 | planet | 67.66 | 1 | 2003 |
| Sedna | 1000±80 | possible planet | 499.43 | 0 | 2003 |
* mean diameter is diameter of sphere of equal volume
Here they are compared:
Of course, the original Republic of Texas extended to 42° north latitude, and using the full extent of the Republic of Texas, the definition of a planet is an object with a diameter of at least 2,012.6 km (1,250.6 miles). By this threshold, the solar system has ten planets: the traditional nine including Pluto plus the newly discovered planet Eris. Surely it is not coincidental that one definition for a planet previously considered by the International Astronomical Union used a minimum diameter of 2,000 km. The final International Astronomical Union decision, to classify Pluto and other objects as "dwarf planets", however, cannot be accepted as appropriately TEXAN.
© 2006-2015, 2016 by Wm. Robert Johnston.
Last modified 22 October 2016.
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