Mass of Dwarf Planet Eris 27% Greater than Pluto

jcgam69 writes "When it was discovered in 2005, some thought Eris should be considered the 10th planet of our solar system. Everyone still considered Pluto a planet then. At first, Eris was thought to be slightly larger. Now — with the help of Eris' moon — Eris is known to be 27% more massive than Pluto. If Pluto had remained a planet to the entire community of astronomers, surely Eris would be considered the 10th planet."

Re:So let 'em both in

[ushering05401]

The funniest thing to me is that we are so fixated on the planet/not-a-planet debate. Let em both in, don't let either in...

Both bodies will continue to be studied, and when the time comes, they will be exploited for their natural resources.

This debate will only matter fifty years from now when we actually begin mining other planets and mining related laws discriminate between bodies with different scientific designations.

Regards.

Re:Haiku on a Distant Rock

[Ucklak]

Poor Pluto [mathiaspedersen.com]

Re:What can I say...

[stefanlasiewski]

I thought Pluto got Erised from history.

Re:If it's round

[Pfhorrest]

it's a planet. If it's orbiting a larger planet, then it's a moon.

What, no distinction between round moons and non-round moons?

I think we need to have our system of classifications able to accurately distinguish between:

- Bodies of sufficient mass that they would undergo fusion if of fusionable composition (stars).
- Amongst those, ones which are of fusionable composition (active stars) versus those which no longer are (inactive stars).
- Amongst non-stars, bodies which are of sufficient mass to be approximately round (major planets) versus those which are not (minor planets or asteroids)
- Amongst planets, those which have an orbit centered on a star (regular planets) versus those which do not (irregular planets).
- Amongst irregular planets, those which have an orbit centered on another planet (moons) versus those which do not (asteroids).

Thus, Phobos and Deimos are minor irregular planets, and also moons (call them just "minor moons" since all moons are irregular planets); while similar bodies in the asteroid belt are also minor irregular planets, but are not moons but rather asteroids. Europa and Ganymede are a major irregular planets and also moons ("major moons"). Luna is a major moon. Eris and Pluto (if I understand the irregularity of their orbits correctly) are major irregular planets and also asteroids (or just "major asteroids", for all asteroids are irregular planets). Earth, Mars, etc are major regular planets, and schoolkids can memorize those and ignore the rest; for simplicity of terminology we can always assume "major" and "regular" unless specified otherwise, so "planet" alone refers just to bodies like those.

There now, everybody happy? Pluto is a planet; it's even a major planet; however, it's an irregular major planet and thus not a "planet" simpliciter.

Mistaken assumption

[aafiske]

I think the mistake in the logic here is assuming that Pluto was kept a planet because it had a certain mass, or orbit, or whatever. Pluto was kept a planet because of tradition, in essence. If it were found today, I don't think it would be considered one. So no opening of the floodgates for every hunk of rock that has some number that measures larger than Pluto.

Re:Gah, cut it out

[Pfhorrest]

You are of course completely right that naming conventions per se tell us nothing about the physical universe. However, good taxonomies and naming conventions will allow someone to tell a lot about the physical attributes of something which has previously been examined and classified by someone else just be hearing it's name. For example, "lion" and "tiger" are two names which refer to very similar objects, but you wouldn't know that just by their names. Panthea leo and Panthera tigris, on the other hand, let you know that these are both subtypes of some object class Panthera, and if you know what that entails, then you'll know a lot about both of those objects. If I overheard that there's a wild Fubar on the loose, I'd have no idea what that was until it was explained to me (though by context I could guess that it's some sort of animal); however, if I overheard that a Panthera fubaris had escaped, while still not knowing what exactly that was, I'd know it was some sort of large carnivorous feline, and thus just by convenient naming, I'd be able to learn (and communicate) new information much more quickly.

Re:uhhhhhhh

[dltaylor]

Ceres was a "planet", or, at least, called one (1802), long before Tombaugh found Pluto (1930). So were some of the other asteroids. When they figured out it was just one instance of a large class of similar objects (asteroids), they changed its designation. Pluto/Charon (with the twins) has now been demonstrated as an instance of another large class of similar objects (Kuiper Belt Objects - KBO) that just happens to orbit noticeably closer than its siblings.

To the ancient Greeks a "planet" was any apparent celestial object, other than Earth's moon, that moved noticeably against the background stars. Working with just the unaided eye, Pluto doesn't count, because it cannot be seen. Working with telescopes, we've got effectively uncountable numbers of asteroids, KBOs, and galaxies that move against a galactic star field that is itself composed of relatively moving objects.

Between the time of Neptune's discovery and the asteroids' reclassification there were more than 10 planets, then back to 8. Pluto was prematurely added so we called it 9, then reclassified it, so now we're back to 8. Many objects have been mistakenly and/or prematurely classified (humans as an intelligent species, as opposed to the small number of intelligent individual humans, for example), then the classifications adjusted upon reexamination of the evidence or discovery of new evidence.

We throw labels at things. Sometimes they stick, sometimes they don't. Get over it.