How many planets? #PlutoIsAPlanet? #TheMoonIsAPlanet?

Is it time to restore Pluto back to the planet club?

A new effort to restore Pluto to the so-called Planet club is underway.

As reported at

Rather than focusing on “external” factors such as whether a body has cleared its orbit (the portion of the IAU criteria that Pluto failed in 2006), the new geophysical definition instead brings to the forefront the intrinsic properties of the body itself. It takes into account the fact that many of the solar system’s worlds are physically complex and geologically active, from Ceres’ ice volcano to Pluto’s slushy heart.

In essence, rather than focusing on the orbit, this proposed new definition suggests we focus on the object itself. Questions like. Is it round? Is is complex on the surface? Is it active? Unfortunately this approach may suffer the same fate as many others, in that this new definition is too open. It would result in over 100 new ‘planets’ in our solar system alone. Even our Moon would now be a planet. As such, maybe this new definition is doomed to failure.

So, adopt this new approach of Pluto-as-a-planet, at the cost of labeling 100 other objects as planets? Or leave things as they are?


Name that moon


Want to name Pluto’s two tiniest moons? Then you’ll need to dig deep into mythology. Astronomers announced a contest last week to name the two itty-bitty moons of Pluto discovered during the past two years.

Pluto is the Roman equivalent of the Greek Hades, lord of the underworld, and its three bigger moons have related mythological names: Charon, the ferryman of Hades; Nix for the night goddess; and the multiheaded monster Hydra. The two unnamed moons need similarly shady references. Right now, they go by the bland titles of P4 and P5.

Online voting will end Feb. 25. Twelve choices are available at the Web site Among the choices: Hercules, the hero who slew Hydra; Obol, the coin put in the mouths of the dead as payment to Charon; Cerebrus, the three-headed dog guarding the gates of the underworld; Orpheus, the musician and poet who used his talents to get his wife, Eurydice, out of the underworld only to lose her by looking back; and Styx, the river to the underworld. The vote tally is updated hourly.

Select your favorite name, or even better, come up with your own!.

Pluto full house


Pluto appears to have its own mini solar system. There are now five confirmed moons for this rocky outcrop. Once the last known planet, it is now deleted from the planet club. Unfortunately for Pluto, the ability to host moons does not help its case for re-entry into this the current gang of eight. In fact it does the opposite in some ways. Pluto was always a bit of a strange one. It was too small, too far away and its main moon was too big. New it seems to have a surplus of smaller moons. This may shake up our current theories of how these outer solar system objects are formed, but it’ll not get Pluto back into the planet club.

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My students hate it when I tell them Pluto is not a planet. After all, many are from las cruces and even went to the Tombaugh school. But the one thing they hate even more than being told it, is when they work through the logic themselves and then decide it is not a planet. It raise tow interesting debates though.

The first stage of all science seems to be noticing and grouping. Then, after years of making new discoveries we always go back to the the grouping. Somehow we feel the need to reclassify

Second, who should make these decisions on reclassifying. The scientists or the public?