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Scientists against the demotion of objects like Pluto, Eris, Sedna, etc. to "dwarf planet" status have crafted a new definition:
It's no secret that Alan Stern and other scientists who led the New Horizons mission were extremely displeased by Pluto's demotion from planet status in 2006 during a general assembly of the International Astronomical Union. They felt the IAU decision undermined the scientific and public value of their dramatic flyby mission to the former ninth planet of the Solar System.
But now the positively peeved Pluto people have a plan. Stern and several colleagues have proposed a new definition for planethood. In technical terms, the proposal redefines planethood by saying, "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters." More simply, the definition can be stated as, "round objects in space that are smaller than stars."
From the proposal:
The eight planets recognized by the IAU are often modified by the adjectives "terrestrial," "giant," and "ice giant," yet no one would state that a giant planet is not a planet. Yet, the IAU does not consider dwarf planets to be planets. We eschew this inconsistency. Thus, dwarf planets and moon planets such as Ceres, Pluto, Charon, and Earth's Moon are "fullfledged" planets. This seems especially true in light of these planets' complex geology and geophysics. While the degree of internal differentiation of a given world is geologically interesting, we do not use it as a criterion for planethood in the spirit of having an expansive rather than a narrow definition.
Here's another article about the significance of the New Horizons mission. New Horizons will fly by 2014 MU69 on January 1, 2019.
(Score: 2) by melikamp on Wednesday February 22 2017, @05:56PM
(Score: 1) by khallow on Wednesday February 22 2017, @07:05PM
and their orbital neighborhoods meet
Neptune never gets closer to Pluto than the Sun. Also, "orbital neighborhood" remains solidly undefined.
(Score: 2) by melikamp on Wednesday February 22 2017, @09:10PM
Orbital neighborhood is a neighborhood of an elliptical orbit, an elongated donut, at least that's one obvious way to define it. Just because you do not have a definition, doesn't mean it's undefined. Also, no one says there has to be one true definition. Neptune would have "cleared" its orbit, with Pluto accounted for, by many similar definitions. Likewise, Pluto would have failed to do the same using the same definitions. I am sure if you go through the relevant discussions by astronomical union members, you will see the definition examined, picked apart, and fleshed out in detail.
Once again, this classification in no way extends our knowledge of the natural world, so going along with the traditional use is the non-controversial solution. Pluto used to be a planet until astronomers decided to define the word planet for the first time, and then they realized Pluto shares so many parameters with KBOs, that any objective, not-entirely-ad-hoc definition including Pluto would sweep them in as well. The new definition from TFA is exactly what they already rejected: extending the notion of a planet to dozens, and most likely hundreds of icy snowballs in the KB, for no reason other than keeping Pluto a planet. To see how invasive and arbitrary Stern's definition is, consider this: the official definition reduced the number of planets by 11%; Stern's definition increases the number of planets by hundreds, and likely thousands of percent. It makes a mockery of the traditions which go back thousands of years (e.g. how we call a certain black rock the Moon, and not a planet) in order to rescue one recent tradition because the latter has some reputations riding on it.
(Score: 1) by khallow on Wednesday February 22 2017, @09:49PM
Orbital neighborhood is a neighborhood of an elliptical orbit, an elongated donut, at least that's one obvious way to define it. Just because you do not have a definition, doesn't mean it's undefined.
I did have an implied definition, you just missed it. A natural neighborhood of an orbit or other trajectory is a locus of points near the object at a given time. Neptune never gets close to Pluto (I was incorrect earlier, it does get closer to Pluto than the Sun at some points of the pair's orbits (around 17 AU). Uranus at times is closer than Neptune can be. That's pretty distant for a body that supposedly is in the neighborhood of Pluto.
And if you look at the official IAU definition, they don't actually define an orbital neighborhood.
The new definition from TFA is exactly what they already rejected: extending the notion of a planet to dozens, and most likely hundreds of icy snowballs in the KB, for no reason other than keeping Pluto a planet.
Which let us note would be just fine. There's no actual problem here.
To see how invasive and arbitrary Stern's definition is, consider this: the official definition reduced the number of planets by 11%; Stern's definition increases the number of planets by hundreds, and likely thousands of percent.
So what?
It makes a mockery of the traditions which go back thousands of years (e.g. how we call a certain black rock the Moon, and not a planet) in order to rescue one recent tradition because the latter has some reputations riding on it.
It doesn't. This is absurd claim to make particularly since we know more than those people thousands of years ago, and we'd have to exclude Neptune and Uranus as well because they weren't known for thousands of years.
(Score: 2) by melikamp on Thursday February 23 2017, @12:51AM
I don't think it's absurd. None of the science matter is affected by classifying Pluto one way or the other, so the state of knowledge is irrelevant for the purposes of evaluating how traditional something is. Seniority, on the other hand, as well as the actual scope of the definition do seem to be relevant. Pluto has the lowest seniority among the planets, with Neptune having 84 years on it. The decision to dump it was not taken lightly, either, but was a result of a prolonged discussion. And increasing the number of planets 10- or 100-fold by admitting a bunch of snowballs with absolutely no seniority seems much less of a break with tradition than dumping 11% of least senior planets.
(Score: 2) by melikamp on Thursday February 23 2017, @01:20AM
s/less/more
(Score: 2) by melikamp on Thursday February 23 2017, @01:24AM
(Score: 1) by khallow on Thursday February 23 2017, @04:21AM
None of the science matter is affected by classifying Pluto one way or the other, so the state of knowledge is irrelevant for the purposes of evaluating how traditional something is.
And as I noted, planets which can't be seen with the naked eye aren't traditional in the very sense you invoked at the time.
The decision to dump it was not taken lightly, either, but was a result of a prolonged discussion. And increasing the number of planets 10- or 100-fold by admitting a bunch of snowballs with absolutely no seniority seems much less of a break with tradition than dumping 11% of least senior planets.
Sure it was a prolonged discussion. Sounded more like an afternoon vote packed by the side that wanted to throw out Pluto. Second, how traditional again is it to call something a "dwarf planet" and then say it's not a real "planet"? Potentially hundreds of objects just fell into that silly semantics game.