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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."
Poor lonely Pluto;
No one loves you now but me.
And Clyde Tombaugh's urn.
My Very Excellent Mother Just Serverd Us Nine Pizzas- Excelsior!
All Hail Discordia!
Hail yes!
fnord.
...our beloved ninth planet just got plutowned!
This message printed on 100% post-consumer recycled electrons.
Some of us still consider that the world is flat.
Change can be hard.
The Kruger Dunning explains most post on
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.
Xena was never more than an unofficial nickname. No one, including the person who discovered it, ever intended for Xena and Gabrielle to be the official names for this pair of heavenly bodies.
Remember: just now they figured out which of Eris and Pluto is more massive...
but they also know the internal density distributions of extrasolar planets that barely take up a pixel on the most powerful telescopes.
Apology to Ubuntu forum.
Gravity provides the centripetal force needed to keep satellites in orbit. If you focus on the simple case of circular orbits, you can use the centripetal force formula with the law of gravity to determine the mass of a planet. Simply set the force of gravity equal to the centripetal force and solve for the mass of the planet M.
M = r * v^2 / G
The period of Eris' moon provides another way to calculate its mass.
Period T = 2pi * sqrt(r^3 / G*M)
Thus I imagine the various images of the moon provided a way to calculate its period and indirectly determine the mass of the central body.
However the article doesn't give any specifics. It would be interesting to know what methods they used and the degree of accuracy of their measurements.
JJ +
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.
-Forrest Cameranesi, Geek of all Trades
"I am Sam. Sam I am. I do not like trolls, flames, or spam."
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.
Pluto and Eris prefer the term "Gravitationally Challenged".
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
OK, look up. A little more to your left. A bit more. OK, just a little bit more. Nope, that's too far. Just a hair back to your right. There! See it?
At the least, Ceres, Vesta, Pallas and Hygiea ( http://space.newscientist.com/article.ns?id=dn9761 &feedId=online-news_rss20F53 ). Admittedly not as many as I'd first thought there might be.
Pluto won't clear its orbital path in the lifetime of the sun for a few reasons. The Kuiper Belt (where Pluto resides) is a very excited region of the solar system in terms of orbital eccentricities and inclications, which results in a very high mean impact velocity between objects out there. This means impacts tend to be destructive rather than letting anything grow larger. Additionally the number of particles in the Kuiper belt is sufficiently small impacts are fairly rare. Basically, the Kuiper Belt never became a planet for much the same reason the asteroid belt hasn't.
Regarding the two planets bit, that's a highly unstable orbital configuration. If they orbited a common center of mass (like the Earth and moon) it would be feasible, but then we'd just call them a twin planetary system, or the smaller of the two would be considered a moon.
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.
-Forrest Cameranesi, Geek of all Trades
"I am Sam. Sam I am. I do not like trolls, flames, or spam."
"I've got moons that are bigger than you."