Astronomers Spot Most Distant Object In the Solar System (sciencemag.org)

sciencehabit writes: Astronomers have found the most distant known object in our solar system, three times farther away than Pluto. The dwarf planet, which has been designated v774104, is between 500 and 1000 kilometers across. It will take another year before scientists pin down its orbit, but it could end up joining an emerging class of extreme solar system objects whose strange orbits point to the hypothetical influence of rogue planets or nearby stars. In other planetary science news, UCLA professor Jean-Luc Margot has proposed a new definition of the term "planet" which would allow for the inclusion of exoplanets. His metric is laid out in an academic paper available at the arXiv.

Comments

i identify as a planet

[turkeydance]

and i demand to be treated as one.

Re: i identify as a planet

[Anonymous Coward]

You were born a moon and, by God, you'll act like it! And enough of this filthy talk of astroid drilling, it's unnatural!

Re:i identify as a planet

[Maritz]

Clear out your orbit and we'll talk.

It's so ridiculously easy

[Rei]

.. to make up a formula to say what you want it to say for data like this.

Here, want an alternative formula to declare the 8 IAU "planets" as planets as well as exoplanets but exclude the IAU "dwarf planets", without using any of the terms he uses, and to be able to classify 100% (rather than the 99%) of exoplanets?

MeanDistanceFromTheSun / DiscoveryYear ^5 > 0.21mm/y^5

It's a functional formula. Does this mean that it's a reasonable formula? Of course not; it has no connection with the reality of what they actually are. But you know what? Neither does his or the IAU's "cleared the neighborhood" concept. There are no credible planetary models that show for example that Mars cleared its own neighborhood. While they differ on the details, they all agree that Jupiter cleared it (and cleared most of the debris from the inner solar system in general, with some help from Saturn). Neptune has (despite its distance from the sun) orders of magnitude more orbit-clearing power than Mars yet nonetheless contains multiple objects a couple percent the size of Mars in its "neighborhood". Is Mars not a "planet"?

I have a giant list of reasons why the IAU decision is poor and unscientific, but no need to post it again.

Re:It's so ridiculously easy

[Anonymous Coward]

You seem obsessed over something most people don't care about and are able to back it up.

I like you.

Re: It's so ridiculously easy

[Rei]

but simulations show Mars is more than capable of doing so on its own

Mars has a tiny fraction the Stern-Levison parameter of Neptune, and Neptune hasn't gotten rid of large bodies from its "neighborhood" (they're small compared to Neptune, but not compared to Mars).

What matters is it is much more difficult to develop any formula that has some relevance to planetary dynamics which doesn't make Pluto look like an outcast, and that is the problem.

It's not a "problem" at all. The definition that most planetary scientists wanted the IAU to choose (if they felt the need to pick one at all) was hydrostatic equilibrium, meaning there would be dozens of planets. Achieving a rough hydrostatic equilibrium is a very meaningful dividing line - it means differentiation, mineralization processes, alteration of primordial materials, and so forth. It's also often associated with internal heat and, increasingly as we're realizing, a common association with subsurface fluids. In short, a body in a category of "not having achieved hydrostatic equilibrium" describes a body which one would study to learn about the origins of our solar system, while a body in a category of "having achieved hydrostatic equilibrium" describes a body one would study, for example, to learn more about tectonics, geochemistry, (potentially) biology, etc. By contrast, a dividing line of "clearing its neighborhood" - which isn't actually what half of the planets in our solar system have done - says little about the body itself.

And yes, there are many reasons why the whole process was grossly unscientific. I've first already covered the voting process above, which is absurd, especially in a day where they could have handled such a thing online. There's the obvious criticism of it being sun-centered, having no clear definition on what defines a "neighborhood" or "cleared", the pseudoscience of the planets all having cleared their own neighborhoods, the lie about how they planned to review further "dwarf planets" for inclusion (they haven't), the comparative inconsistency (really, Earth is more like Jupiter than it is like Pluto?), the atrocious name where a "dwarf X" isn't an "X", and on and on. But these are just minor points.

First off, the primary reason cited by virtually every scientist I've seen interviewed about their vote in favor of an exclusive standard over an inclusive standard is along the lines of, "It would be too hard for schoolchildren to memorize the names of all of them". This is such a blatantly unscientific standard that it doesn't even bear going into, and leads to absurd consequences when applied to other fields, such as the AMA declaring that there's only 8 bones in the human body and all others are "dwarf bones" that aren't real bones, or the USGS declaring that there's only 8 rivers in the world and all others are "dwarf rivers" that aren't real rivers, all for the purpose of making things easier for students to memorize. They decided that they wanted schoolchildren to be able to memorize the names of all the planets around the sun, and then contrived a definition of "planet" to try to make that happen. This is not science, it's idiocy.

Then there's the basic issue of scientific categorizations altogether. In every scientific field, the universe continually presents those making discoveries with a wide range of diversity. This is almost universally accepted in an inclusive manner, subdividing groups into subgroups, and subdividing those further. We will continue to find new types of planetary bodies in a wide range of diversity - large terrestrial planets, dwarf-scale planets, gas giants, ice giants, hot jupiters, super-earths, water worlds, supercomets, extremely large bodies orbiting as moons, planets without parent stars, and so forth. Rather than trying to hide diversity, science is supposed to embrace it.

Then there's the issue of the timing. For most of the history of humankind's knowledge of Ceres and Pluto, we have

Re: It's so ridiculously easy

[Rei]

Mars does not gravitationally dominate its neighborhood and force things into resonance with it. The vast majority of asteroids are locked into resonances with Jupiter, not Mars. There's only about 1500 known asteroids, the Polana group, which are locked into a 2:1 resonance with Mars (Mars also has 4 trojans which do not appear related to each other).

The Stern-Levison parameter is based around the principle of scattering small bodies, bodies far smaller than the parent, which can be scattered on a single pass at distance b to an angle greater than or equal to a given value. Pluto is a "small body" compared to Neptune, but not so compared to Mars. And Mars's Stern-Levison parameter is, again, far less than Neptune's.

The claim that "a value of over 900 for Mars is more than enough to clear out other bodies" is false even if we ignore this troublesome "small body" aspect. Again, read the Stern-Levison paper. The value of 900 for Mars comes from assuming a scattering angle of one radian from its approach angle, which hardly means ejection or single-pass domination. It assumes 12 billion years for the age, several times older than the solar system. It relies on the "small bodies" having high eccentricities, which would probably not be the case in a gas-giant-less solar system - the lower the eccentricity, the far weaker the scattering potential. And of course, they assume actual small bodies - typical asteroid sizes.

Interestingly enough, I would have been happy with the classification actually laid forth in Stern-Levison (2002). They proposed a size/composition matrix similar to that of stars, with all objects large enough to be in hydrostatic equilibrium included. The mass would be grouped into "subdwarf" (Ceres, Pluto, Charon, etc), "dwarf" (Mercury, Venus, Earth, Mars), "subgiant" (Uranus, Neptune, Saturn), "giant" (Jupiter), and "supergiant" categories, while the composition grouped into "rock" (terrestrial planets, asteroids), "ice" (KBOs, uranus, neptune), and "hydrogen" (saturn, jupiter). So for example Jupiter would be a "hydrogen giant planet". Pluto would be a "rocky subdwarf planet". Titan would be a "icy subdwarf satellite". Etc.

Re: It's so ridiculously easy

[Rei]

Oh, and while we're at it, according to the IAU's definition, Jupiter shouldn't be a planet. They define planets as bodies that orbit the sun that have cleared their neighborhoods. Jupiter does not orbit the sun. It orbits the Sol-Jupiter barycentre, which is outside of the sun - the sun and Jupiter roughly co-orbit this point.

Re:Does this mean??!

[Rei]

Nope. A tiny fraction of a group who is overwhelmingly not planetary scientists has spoken and made their internally-inconsistent definition. It stands until they revoke or alter it.

Re: Does this mean??!

[Rei]

Except a tiny fraction of planetary scientists actually disagree with the classification of Pluto.

In the words of Wikipedia, "Citation needed". The planetary scientists at the IAU meeting had been by and large pursuing a definition involving a body reaching gravitational equilibrium. They've also been leading the charge to get it overturned. There are numerous published papers by planetary scientists who continue to refer to large KBOs and the like as planets. The New Horizons team is particularly notable in continued references to them as planets.

The vote passed via a non-randomly-selected 4% of the IAU's membership who were - as previously mentioned - overwhelmingly not planetary scientists. Letting people who study stars (by the way, a "dwarf star" is still a "star") decide what a planet is is just plain stupid - it's not their field of expertise. The first draft proposal indeed went with the planetary scientists' version - hydrostatic equilibrium being the criteria, and was confirmed on the 18th, with intent to vote on the 24th. Many people left the IAU meeting thinking that this was the version that was going to be voted on, and since they supported either having it or no definition at all, they didn't need to be there. The proposal was changed however on the 22nd. Due to dischord among the IAU members there were "secret" negotiations held on the proposal on the evening of the 23rd, and it looked increasingly unlikely that anything was going to be agreed upon. But then they came out with the current version on the 24th - after most of the membership had left - and had it voted on during the same day, when most of the people remaining were the ones who had been fighting against the planetary scientists' equilibrium definition. They furthermore reverted the standard rules which only allow people in a specific field to vote on matters related to their field, declaring the definition of planet a matter applicable to the whole union, so that everyone, not just planetary scientists, could vote.

There are not little complaints about "the exact wording" - do I really need to go into a breakdown of all of the arguments against it?

Re: Does this mean??!

[Rei]

I described the process that led up to the vote, which you can easily read anywhere on the net. You can also readily find no shortage of planetary scientists complaining about it on the net. If there's any specific fact you disagree with, state it and I will reference it for you.