A TEXAN definition of a planet

reported by Wm. Robert Johnston
last modified 19 July 2015

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 11 and perhaps 15 known planets, so far (given that sizes are not firmly known for some objects):

List of known and possible planets in the solar system:

Planetmean diameter* (km)statusmean distance
from Sun (AU)
Mercury 4879 planet 0.39pre-Texas
Venus 12102 planet 0.72pre-Texas
Earth 12742 planet 1.00pre-Texas
Mars 6779 planet 1.52pre-Texas
Jupiter 139640 planet 5.20pre-Texas
Saturn 116160 planet 9.54pre-Texas
Uranus 50730 planet 19.191781
Neptune 49240 planet 30.071846
Pluto 2370 planet 39.421930
Haumea 1300±150probable planet 43.222003
Makemake 1430±50 planet 45.712005
2013 FY27 1100±500possible planet 59.262013
(225088) 2007 OR10 1280±200possible planet 66.852007
Eris 2330 planet 67.782003
Sedna 1000±80 possible planet524.092003

* 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.

© 2006-2012, 2015 by Wm. Robert Johnston.
Last modified 19 July 2015.
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