Although Pluto was kicked out of the planetary club by the International Astronomical Union (IAU) four years ago, the passionate "Pluto debate" rumbles on.
But the fact remains that even before discovery of Eris in 2005 by a Palomar Observatory team headed by Caltech's Mike Brown, Pluto's ranking as a planet in the solar system was tenuous at best. Eris was measured to be nearly 30 percent larger than Pluto; did that make Eris a planet too? No, but its discovery began a series of events that changed our understanding of the solar system forever.
According to a paper presented at the Proceedings of the 9th Australian Space Science Conference, the "dwarf planet club" should start accepting applications from smaller members and according to Brown -- discoverer of over 100 Kuiper Belt objects (or KBOs) -- this is no bad thing for the beleaguered Pluto.
The solar system currently has six bona fide dwarf planets: Eris, Makemake, Haumea, Quaoar and Pluto in the Kuiper Belt and Ceres in the asteroid belt (between the orbits of Mars and Jupiter).
However, in this proposal, smaller wannabe dwarf planets could be considered for promotion.
For 50 or so small rocky and icy bodies in the Kuiper Belt, Pluto's loss could be their gain; where Pluto was demoted, they could be promoted. Who said there were no winners to come out of Pluto's re-classification?
"Small Solar System objects are irregularly shaped, like potatoes," said Charley Lineweaver of the Australian National University in Canberra, who headed the research. "If an object is large enough that its self-gravity has made it round, then it should be classified as a dwarf planet."
Indeed, one of the criteria for a celestial body to be considered a planet is that it must be round (i.e. it must be massive enough to achieve "hydrostatic equilibrium" -- in other words it must have enough gravity for its surface to be rounded, rather than chunky or potato shaped). But this criterion also extends to dwarf planets, and there are plenty of rounded large asteroids that would make happy dwarf planets.
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Saturday, April 10, 2010
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Adding more dwarf planets is in no way another demotion for Pluto. The reason is that in spite of the controversial IAU decision, dwarf planets are planets too. Dr. Alan Stern, who coined the term, intended it to refer to a subclass of planets large enough to be in hydrostatic equilibrium (pulled into a round shape by their own gravity) but not large enough to gravitationally dominate their orbits. He never intended dwarf planets to be designated as not planets at all. And he said he anticipates there being hundreds of these small planets in our solar system.
ReplyDeleteOnly four percent of the IAU voted on this, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. Under this definition, our solar system has 13 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.