Is Earth A Dwarf Planet?

   The title is sort of misleading but after reading a press release from the NASA WISE (Wide-field Infrared Survey Explorer) mission I started thinking about the IAU official definitions for a planet that distinguishes a planet from a dwarf planet. In particular definition # 3. (see below) This thinking resulted from reading the press release which described success in determining the colors of the Trojan Asteroids that orbit at two specific points along Jupiter’s orbital path. I thought, “wait a minute”, if a planet had to have cleared its orbital path (# 3) then Jupiter with these Trojan Asteroids, and in fact Earth, Mars, and Neptune with their own Trojan Asteroids, may need to be considered as dwarf planets — by the definition.
   However the authors of the definitions took these Trojan asteroids into consideration and as the full definition explains there may be objects like the Trojan Asteroids that while orbiting the Sun along a planet’s orbital path, these objects are where they are as a result of gravitational interactions or orbital resonances with that planet, Jupiter for example. The bottom line is that there are no other objects along Jupiter’s orbital path other than those placed and held there by Jupiter’s gravitational field. And the same applies to Mars, Earth, and Neptune. Interestingly there are even moons having Trojan Satellites.
   Is Earth a Dwarf Planet? No, it is one of the 8 planets in our solar system.

   The Trojan Asteroids near Jupiter are interesting in many ways including that they are different from the asteroids we find in the main asteroid belt for example. The colors of these Jupiter Trojan asteroids are also different. Did you know that asteroids had color? Jupiter has two pair of Trojan asteroids – both at the same angle from Jupiter with one leading and the other trailing Jupiter.

  1. Orbits the Sun
  2. Has enough mass to have a spherical or round shape (at or near what is called hydrostatic equilibrium)
  3. Has cleared its neighborhood – objects along its orbital path.

Click here to go to the Qué tal in the Current Skies web site for more observing information.

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