Comments on: Eight Planets!

By: Leha

Leha — Thu, 03 May 2007 00:29:04 +0000

i think that Pluto exist!

By: Some Observations at Griffith Observatory - Asymptotia

Some Observations at Griffith Observatory - Asymptotia — Sat, 04 Nov 2006 20:45:36 +0000

[...] The lower portion of the underground space is really lovely. It is devoted mostly to the planets (ahem… including Pluto… although its display was incomplete… I hope that is not a bad sign… click on thumbs), with an interactive display booth for each. I was struck by the fact that there seemed to be no booth for Earth until I realized that it in fact had a whole room that opens up at the space where the booth would be. [...]

By: What’s in a Name? - Asymptotia

What’s in a Name? - Asymptotia — Sun, 17 Sep 2006 02:44:00 +0000

[...] Pluto, as part of its initiation into the family of rubble known as the Kuiper belt (a mass distribution so important to understanding our solar system…see here), has been given a number. It is minor planet number 134340. I hope you can remember that. Eris has the number 136199. [...]

By: Clues in the Blood Splatter Patterns - Asymptotia

Clues in the Blood Splatter Patterns - Asymptotia — Tue, 12 Sep 2006 17:56:11 +0000

[...] It is quite a fascinating subject, a detective story full of wonderful science, and illustrates -as I have said earlier in the post called “Spinach Blogging”- how the “demotion of Pluto” story opens the door to so much active planetary science. It also illustrates why it it is interesting to keep an eye on the debate about the “demotion”. which is still ongoing. The nature of the Kuiper belt is teaching us a huge amount about the other bodies in the solar system. For example: The distribution of Kuiper Belt objects has already provided decisive evidence that Neptune was once perhaps nearly a billion miles closer to the Sun and was then gravitationally nudged outward. Astronomers also hope that the Kuiper Belt preserves a frozen record of the earliest building materials of the solar system. [...]

By: From Dwarf Planets to Hobbit Galaxies - Asymptotia

From Dwarf Planets to Hobbit Galaxies - Asymptotia — Mon, 28 Aug 2006 15:16:37 +0000

[...] Sure this stuff is fun, but what’s the larger point, you might ask? Well, just as the discussion about Pluto’s status as a planet (see also here) touches on hugely important issues such as formation and evolutions of planetary systems, so the satellite galaxy issue touches on similar questions for galaxies (although it I were them I’d not take too seriously being called galaxies, in case the name is snatched away from them one day). [...]

By: Amara

Amara — Sun, 27 Aug 2006 09:28:59 +0000

Neptune today is not at the orbit where it was formed. It formed at about 18 AU and migrated outwards to 30 AU. Neptune actually might have moved further to 50 AU and then migrated inward to 30 AU (bouncing!). The other giant planets: Uranus and Saturn migrated outwards, and Jupiter migrated inwards.

Along the way, the giant planets scattered the planetesimals (asteroids, etc.) into the asteroid belt, the Oort cloud, and into the ’scattered disk’ part of the Kuiper Belt. Neptune had a large role in shaping the Kuiper Belt that we see today, according to Hal Levison, Alessandro Morbidelli, and their colleagues. For Papers, Morbidelli’s web site is a good start.

Go to Morby and his colleagues’ journal papers of which this 3 Nature papers combined with supplementary material might be most relevant. And here is his and his colleagues’ review papers. This “Planet migration in planetesimal disks” review paper by Levison H.F., Morbidelli A., Gomes R., Backman D. (2006) in the Protostars and Planets V conference proceedings could be best to cover the topic of the “why” and “how” of planetary migration.

You can see other (recent) papers by his colleagues on Google Scholar too: (not sure that this
link will turn out; so if not, then search on Levison, Morbidelli, Neptune)
http://scholar.google.com/scholar?q=Neptune+Levison+Morbidelli&ie=UTF-8&oe=UTF-8&hl=en&btnG=Search

By: ksh95

ksh95 — Sat, 26 Aug 2006 16:28:31 +0000

Keithe:

Well that sounds nice and rigorous, but the astronomers not adopt Steven Soter’s definition? They adopted some vague orbital-clearing definintion.

By: keithe

keithe — Sat, 26 Aug 2006 16:00:23 +0000

The IAU’s new definition of planet says a planet is a body that “has cleared the neighbourhood around its orbit”. Many people do not yet understand why this type of orbital-clearing criterion is so scientifically significant, nor do they understand how this criterion could be clearly quantified. I recommend the excellent and readable paper by Steven Soter named “What is a Planet” (http://arxiv.org/abs/astro-ph/0608359). Soter explains why mass dominance is significant. The IAU’s definition is not exactly the same as Soter’s, but it is the same idea, and they both conclude that there are eight planets. Soter defines a planet as “the end product of secondary accretion from a disk around a primary body”. He has a couple of parameters that can measure this. Lambda quantifies the extent to which a body scatters smaller masses out of its orbital zone. Lambda = kM^2/P, where k is a constant, M is the object’s mass, and P is the orbital period. Mass and orbital period are pretty easy to measure even for extra-solar planets. A second parameter is mu = M/m where M is the object’s mass and m is the mass of everything else in its orbital zone. In Soter’s paper, if mu is greater than 100, then the object is a planet. The remarkable thing is that both these measures (Lambda and mu) show an immense gap of five orders of magnitude (!) between the eight main planets in our solar system and all the other debris, like Pluto and Ceres. The log-log plots at the end of Soter’s paper show this gap very starkly. There is no gray area between planet and non-planet. Soter convinced me that nature has clearly sorted solar system bodies into two very distinct classes, the dominant (eight) objects and the non-dominant objects.

By: A Glimmer of Hope for Pluto? - Asymptotia

A Glimmer of Hope for Pluto? - Asymptotia — Fri, 25 Aug 2006 21:36:17 +0000

[...] So despite the announcement yesterday, sources tell me that some members of the astronomy community are hoping that there is still maybe a small window of opportunity for Pluto. [...]

By: astromcnaught

astromcnaught — Fri, 25 Aug 2006 20:07:40 +0000

Amara: That sounds very interesting. Could you direct us more precisely please?

By: Amara

Amara — Fri, 25 Aug 2006 18:47:41 +0000

k95: If you read recent papers by Morbidelli, Levison, et al, you will find that Neptune’s influence on the bodies in its vicinity are important indeed. The present orbital structure of the outer solar system could be due to Neptune.

By: Spinach Blogging - Asymptotia

Spinach Blogging - Asymptotia — Fri, 25 Aug 2006 02:25:24 +0000

[...] With that in mind, I’d like to offer some words about this week’s science coverage of the two big Astronomy/Astrophysics stories. I’ve heard the issue raised a number of times today (including by my colleague Sean over on CV) that it is somehow to be thought of as a bad thing that there’s more coverage in the press of the Pluto demotion than there is of the new results giving new direct evidence of Dark Matter. The former is supposed to be all about the politics of science while the latter is supposed to be covered more since it is a profound new result. [...]

By: What You’re Doing Is Rather Desperate » Planet defined - now there are eight

Thu, 24 Aug 2006 22:21:21 +0000

[...] The votes are in and the community has spoken - Pluto is not a planet. Clifford explains all at his new blog, Asymptotia. At the end of the day, it looks like the IAU have a pretty good democratic process in place. There was much wailing on our local radio station this morning - textbooks to be rewritten! Confusion in high school science class! How will the kids digest this new and confusing information? I suspect that they’ll take it in their stride. It’s not difficult - eight, not nine. That’s science - it’s not static, ideas change with new information. Science teachers should see this as a great opportunity to discuss the nature of science, but I suppose most school science is more concerned with rote learning of facts just like “how many planets”. [...]

By: astromcnaught

astromcnaught — Thu, 24 Aug 2006 21:11:41 +0000

ksh95. Yes indeed, almost.
The first set of proposed rules allowed a planet in another solar system which had an eccentric orbit around another planet to be a moon then a planet then a moon, as it orbited, if you see what I mean.

Now we have planets which have to have cleared their neighbourhood, sort of. Since Neptune has Pluto in the way it has not cleared the local space of junk therefore Neptune is not a planet. haha.

How rude, calling Pluto junk. Apologies.

By: So Do We Need a New Planetary Mnemonic? - Asymptotia

So Do We Need a New Planetary Mnemonic? - Asymptotia — Thu, 24 Aug 2006 20:42:24 +0000

[...] « Eight Planets! [...]

By: ksh95

ksh95 — Thu, 24 Aug 2006 20:25:55 +0000

Pluto and Neptune have intersecting orbits, therefore Pluto has not yet cleared it’s orbit and is a dwarf.

Doesn’t the reciprocal argument make Neptune also a dwarf????

I guess the astronomers are not explaining themselves clearly, or perhaps I didn’t pay sufficient attention.

By: astromcnaught

astromcnaught — Thu, 24 Aug 2006 19:12:06 +0000

Must say it all strikes me as somewhat simpleminded. A bit like botanists declaring that everything with roots over 6 feet high is a tree, everything less than 2 feet high is a plant and all the rest are bushes.

Still, it’s better than what we had before, and the unseemly bunfight has caught the publics imagination in a scientific way.

Incidentally, 81 percent of 13,000 AOL members think that Pluto should still be a planet. How many of that number are astrologers is not divulged

Back to mneumonic production…

By: astromcnaught

astromcnaught — Thu, 24 Aug 2006 16:09:37 +0000

Hooray !!!!

Makes mnemonic writing even easier now

By: John Branch

John Branch — Thu, 24 Aug 2006 15:17:58 +0000

There’s a conceptual clarity in these resolutions that I appreciate, and that I prefer over the habits of speech and of feeling that incline some of us oldies to say “I want to keep calling Pluto a planet.” It seems to me one could teach a machine, or a Martian, the meaning of these definitions, which is another way of saying we can use them like a razor to decide which object goes into which pile. (I admit I haven’t considered the implications fully; maybe there will be difficulties.) Since science is a human activity, there may be more to consider than just what we could rigorously formalize and teach to a machine, but at least that approach is apt to be self-consistent, isn’t it?

By: Twelve Planets! - Asymptotia

Twelve Planets! - Asymptotia — Thu, 24 Aug 2006 15:01:44 +0000

[...] It’s official!* There are twelve planets in our Solar System (so update all the posters, such as the ESA one on the right). [Update1…. Oh no it’s not official! See here.] [Update2: The vote is in… see here.] [...]