User:Homo Cosmosicus

Homo Cosmosicus


Dwarf planets

Main article: Dwarf planet

In recent years there has been much debate over the definition of planet and thus many objects were proposed by astronomers, including at one stage by the IAU, as planets. However, this debate was officially resolved in 2006 when several of these objects were reclassified as dwarf planets. They share many of the characteristics of planets. However, astronomers like Alan Stern, Steven Soter and others, point that our Solar system clearly has only 8 planets and far larger number of (what is now known as) dwarf planets. Main difference is that 8 planets have been able to clear the neighborhood around their orbits while dwarf planets have not been able to do so. That difference between 8 planets and dwarf planets is more then 5 orders of magnitude (more then 100,000 times) as shown below in a table by Steven Soter in his work "What is a planet?":

Planetary discriminants
Body Mass (ME*) Λ/ΛE** µ***
Mercury 0.055 0.0126 9.1 x 104
Venus 0.815 1.08 1.35 x 106
Earth 1.00 1.00 1.7 x 106
Mars 0.107 0.0061 1.8 x 105
Ceres 1.5 x 10-4 8.7x10-9 0.33
Jupiter 317.7 8510 6.25 x 105
Saturn 95.2 308 1.9 x 105
Uranus 14.5 2.51 2.9 x 104
Neptune 17.1 1.79 2.4 x 104
Pluto 0.0022 1.95x10-8 0.077
Eris 0.005 3.5x10-8 0.10

*ME* is Earth masses.
**Λ/ΛE = M2/P, where M is in Earth masses and P is in years.
***µ = M/m, where M is mass of body, and m is the aggregate mass of all the other bodies that share its orbital zone.

Currently three dwarf planets in the Solar System are recognized by IAU, those are Ceres, Pluto and Eris. The last two dwarf planets are also members of Trans-Neptunian objects, and Ceres is by far the largest and most massive body in the asteroid belt: it contains approximately a third of the belt's total mass. According to Mike Brown very soon there might be over 40 dwarf planets since most of the known objects in Solar system who are not planets, not satellite of planets, are in orbit around Sun and have over 400 km in diameter will pass the test of IAU to get dwarf planet status.

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