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Nerd Word of the Day: Planemo

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Astronomers are in quite a pickle when it comes to what a planet is and what it is not. It used to be, if you could see them moving around in the night sky, they were planets (or "wanderers") Now, however, bigger and better telescopes are finding stuff all over the place. Hundreds of planets have been found in orbit around other stars, and Pluto is going to have a fight on its hands if it wants to stay a planet -- many more objects in our solar system are bigger than Pluto and are NOT planets.

Adding to the fun, scientists are just now beginning to study free-floating planets, that is, planets that were ejected from their system and now roam the universe all alone. Are these planets too? Do planets have to have a sun associated with them?

From an article in PhysOrg today:


The cast of exoplanets has an extraordinary new member. Using ESO's telescopes, astronomers have discovered an approximately seven-Jupiter-mass companion to an object that is itself only twice as hefty. Both objects have masses similar to those of extra-solar giant planets, but they are not in orbit around a star - instead they appear to circle each other. The existence of such a double system puts strong constraints on formation theories of free-floating planetary mass objects.

The new buzz word is "Planemo" Wiki describes it like this:


Planemo is a term proposed to the IAU by Gibor Basri, Professor of Astronomy at the University of California, Berkeley, to help clarify the nomenclature of celestial bodies. Under his definition a planemo would be "an object [rounded by self-gravity] that does not achieve core fusion during its lifetime", regardless of its orbit.

It is deliberately contrasted with Basri's suggested definition of planet ("a planemo that orbits a fusor") and was designed as a potential solution to the debate over what constitutes a planet. It can be considered helpful as it creates a designation for so-called "interstellar planets" that are otherwise not covered by suggested definitions for 'planet', and it also creates a category to group large, compositionally-similar moons with their planetary counterparts.

The term is a contraction of planetary mass object.

I dunno. I kind of liked "planet". Planemo sounds like somebody Batman would fight. "Look out Batman! It's Planemo! And he's got a huge asteroid!"


UPDATE: Some comments about Planemos from the web:


I like Planemo and Planelarry, implying, of course, the future discovery of Planecurly and a receding Planeshemp.

"The pair belongs to what some astronomers believe is a new class of planet-like objects floating through space; so-called planetary mass objects, or "planemos", which are not bound to stars.'" -- Once again proving that astronomers should not be naming things while drunk. Here's a handy reminder: "Remember the Planemos!"

So. Which one is the evil twin?

Snakes, on a PLANEMO????

PlanemO's are actually God's cereal.

"Finding Planemo" -- Smell that ? It's the smell of rendering farms heating up at Pixar.

They'll love teaching this in Texas. "Remember the Planemo!"

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This page contains a single entry by Daniel published on August 4, 2006 6:28 PM.

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Daniel Markham