Is {pluto|sedna} A Planet?

Dr. Zowie writes "NASA's announcement last week of Sedna's discovery reignited the debate over whether Pluto is a planet. Dr. Alan Stern a noted planetary scientist and leader of the New Horizons mission to Pluto, pours on some gasoline with this article in which he skewers the various arguments against Pluto-as-planet. Choice quotes include 'You wouldn't deny a chihauhau a place among dogs because it is too small,' and 'if your brain was so completely full of names of people that it just couldn't take any more, would anyone new who you met after that, therefore not be a person?'"

Comments

Re:I love this stuff

[Anonymous Coward]

Well Pluto's moon is called Charon. The ferryman of the dead. Is that good enough for you.

Re:I say it isn't a planet, Harvard

[saskboy]

Harvard has a nice page with lots of links an references for people looking to dig deeper into the Minor Planet definition under which asteroids like Ceres and Sedna fall under.

Re:I love this stuff

[Unknown Kadath]

I cite Cecil Adams of The Straight Dope, font of all knowledge, to say with authority:

The tomato is botanically a fruit.

Brontosaurus never existed.

And you can blame the Greeks for the continent thing.

That Cecil! Is there anything he doesn't know?

-Carolyn

Re:Well..

[PatientZero]

It's a body of matter vastly more massive than other matter in the vicinity.

From the article:

Location Rules. "Let's use an object's location as the criterion to establish or reject it from planethood."

The most common form of this idea is to classify an object as a planet if it is the largest thing in its region. By this criterion, objects like Ceres and Sedna are planets, for they are the largest known things in their regions of the solar system.

The main problem is that as we discover new objects, some planets may cease to become planets. And what happens if a planet shifts its orbit closer to a bigger planet? Does it stop being a planet until it moves far enough away?

Having read the article, I like his criterion: massive anough for gravity to form it into a spherical object. This doesn't change over time; it's based on physics; and it's very similar to the criterion for whether or not an object is a star (massive enough for fusion to provide the majority of its energy).