"Pluto is dead" - Mike Brown, It's official Options

[Guest_PhilCo126_*]

Don't know if anybody brought this up yet ...

But ...

Does the UMSF logo on the top left of the page needs any adjustment ?

[djellison]

It's been mentioned before

If someone goes and changes the logo on the plaque on the Pioneer spacecraft....then I'll change the logo

Doug

[Guest_PhilCo126_*]

Great thinking Doug ... back in 2004, Pluto was still considered a planet ...

[Alan Stern]

Pluto is a planet and perhaps the most historic object discoverd of the past 150 years in solar system science.

-Alan

[GregM]

.

[helvick]

Besides, if nothing was done about this issue, I predict that we would end up with a Solar System containing 20 or more "planets" – and IMO that would have been as least as crazy as keeping Pluto's status as a "true" planet.

I find most of your arguments very well founded and your position is clearly one of the calmer ones in this debate but this last item doesn't make much sense. Why not 20 planets if needs be? There are certainly many more than 20 planets provided we don't limit ourselves to our Solar System so why not have 20 or more here? I'll accept that it doesn't make much sense to include most "satellites" in the same bucket as most "planets" but in my book Titan (as an entity in itself) has much more in common with Venus and Earth than it does with our Moon so why arbitrarily lump it into a group that would imply that it was other than it is?

[Jyril]

Why not 20 planets if needs be?

Why some objects that clearly belong to debris belts should be considered planets? If only some of them, then why not all?

If Pluto is considered a planet, any remotely meaningful definition would mean dozens of planets. When asked, "Should Pluto be demoted?" most people said "no" but if asked "Should there be dozens of planets?" the answer would have been "no" again. Of all potential definitions, the "leave no iceball behind" definition was the least popular.

Like it is already said several times before, the whole term 'planet' is dumb. There is no good definition that is both scientific (i.e. not arbitrary) and exclusive. There is not much common between Jupiter and Earth; both are round, dominate their neighborhoods and have circular, low-inclined orbits. Still they both are 'planets'. Physically Earth is much more similar to the Galilean moons and Titan. Titan, a would-be planet, and Atlas, a tiny chunk of ice, are both just 'Saturnian satellites'.

I think the best thing to do is to ditch history and culture-loaded terms like 'planet' and classify objects by their physical properties and orbital properties separately.

[helvick]

I think the best thing to do is to ditch history and culture-loaded terms like 'planet' and classify objects by their physical properties and orbital properties separately.

Yep - leave "planet" as a cultural term that is decided by common use and get the IAU to come up with a sensible classfication for all bodies within all solar systems and then map our bodies into that. Such a system should be of some _use_ in defining the broad physical characteristics and dynamics of the bodies. Ideally in my book it would be represented by an unpronouncable "word" so we could forever prevent a repeat of the spurious arguments based as the confusion of schoolchldren and society's attachment to a scientific definition that become obsolete.

[David]

Those who have a historical interest in the question of the definition of a planet, may be interested in reading a discussion of the same written by William Herschel shortly after the discovery of Ceres and Pallas (1802), at which time these bodies are rejected as potential planets, and it is suggested that they require a new name, neither planet or comet, for which the name asteroid is proposed: the intention being that "planets, asteroids, and comets, will in future comprehend all the primary celestial bodies that either remain with, or only occasionally visit, our solar system."

Observations on the two lately discovered celestial Bodies
Abstract
Article
See especially pp. 223 of the article et seq.

The criteria Herschel uses for his definition of planet very nearly anticipate all the definitions that have been suggested since. They are, verbatim:

1. They are celestial bodies, of a certain very considerable size.
2. They move in not very excentric [sic] ellipses round the sun.
3. The planes of their orbits do not deviate many degrees from the plane of the earth's orbit.
4. Their motion is direct. (Herschel means "prograde")
5. They may have satellites, or rings.
6. They have an atmosphere of considerable extent, which however bears hardly any sensible proportion to their diameters.
7. Their orbits are at certain considerable distances from each other.

It would seem there is nothing new around, as well as under, the Sun.

In applying his criteria, Herschel finds that the asteroids differ from the planets in criteria 1, 3, 5 (incorrectly, as it turns out; he assumed that no body as small as an asteroid could have a satellite), and 7, and agreed in 2 (he was unaware of the more eccentric asteroids) and 4. On 6 he was really aiming at distinguishing planets and asteroids from comets (interpreting the "coma" of the comet as an atmosphere). His "7", is basically the "orbit clearing" idea expressed in a somewhat different way; though he seems to have had Bode's Law in the back of his mind, saying that allowing two "planets" in crossing orbits would upset the regular arrangement of planetary orbits, whereas it could be retained if they were placed into a "different species".

Applying Herschel's criteria to Pluto and Eris, we find the following responses:
1. Unknown, because we do not know where to draw a line in the large gap between Mercury and Ceres.
2. May exclude Pluto, certainly excludes Eris.
3. Excludes Pluto and Eris.
4. Includes Pluto and Eris.
5. Includes Pluto and Eris.
6. Includes Pluto, Eris?
7. Excludes Pluto. probably excludes Eris too.

So whereas by Herschel's criteria, asteroids might meet from 1 to 3 planetary criteria, Eris and Pluto meet three or four.

[Guest_Kevin Heider_*]

Pluto is a planet and perhaps the most historic object discoverd of the past 150 years in solar system science.

-Alan

Why do dynamically challenged KBOs get all the respect and glory? Perhaps this is the reason I hope that Ceres is still considered an asteroid. Ceres orbits in the asteroid belt, is a member of the asteroid belt, and should be known as an asteroid AND a 'dwarf planet'.

Ceres apparently lives in the ghetto of the solar system and just because it is now a 'dwarf planet' let's hope that people don't forget where it comes from! If Ceres is not an asteroid then smaller asteroids will truly never get any public respect.

Asteroids like (152) Atala (100+km in dia; low albedo and a featureless reddish electromagnetic spectrum) deserve to be part of something bigger, ie: a group of objects that include (1) Ceres.

-- Kevin Heider

[David]

I should add that Herschel had a less-than-noble reason for opposing the admission of Ceres and Pallas as planets in 1802; if they were planets, then his discovery of the "Georgian Planet" (Uranus) only 21 years earlier would shine a little less lustrously.

But I prefer to absolve him of such a motive; it appears from his writing that his gut objections were aesthetic: these tiny asteroids -- thought there were then only two of them, but Herschel, with laudable prescience, foresaw that many more would be discovered -- were making his solar system untidy. Herschel's distress at the messiness of the asteroids mirrors exactly modern astronomers' distress at the messiness of the KBOs.

In addition to attempting to define the term planet, Herschel also provides a definition of asteroid (a term that he seems to have invented), which he intended to be "sufficiently extensive to take in future discoveries". It is as follows:

"Asteroids are celestial bodies, which move in orbits either of little or of considerable excentricity [sic] round the sun, the plane of which may be inclined to the ecliptic in any angle whatsoever. Their motion may be direct, or retrograde; and they may or may not have considerable atmospheres, very small comas, disks, or nuclei."

(Herschel's instruments had misled him into perceiving Ceres and Pallas as having faint comae surrounding them.)

It would appear that if Herschel had still been alive in 1930, and had not changed his mind, he would likely have classified Pluto as an asteroid, and would certainly have considered the other KBOs to be asteroids as well.

[Gsnorgathon]

C'mon guys! There are five planets: Mercury, Venus, Mars, Jupiter, and Saturn. The rest of 'em are - I dunno quite what - poseurs? - but they ain't planets.

[Jyril]

If you think that way, you should accept the Sun and the Moon as planets.

[Alan Stern]

Now we are relying on the perspectives of a man living two centuries ago to justify a bad definition
of planets?

With all due respect, I am disappointed by the discussion above. It is as if, owing to the diveristy of life, one concluded there is no common thread to living things, no tree of life with all its diversity, so we might as well simplify by just defining organisms as objects which control their ecological niche.

Yes, planets are diverse, but they do make up a class of bodies larger than rocks and smaller than stars.
They are found in many dynamical niches, colors, compositions, and sizes, but they all share the traits
that they neither do fusion in their interiors as stars do, nor retain arbitrary shapes, as rocks do.

-Alan

[JRehling]

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
I find it absolutely remarkable that a group of science minded people (people who often relegate the “human” aspect of “science” behind that of logic, facts, measurements, and figures) are now placing those “human aspects” as reasoning to resist this decision.
[/quote]

It's a mistake to think that this planet-definition issue has anything to do with science.

Objects in space are often the subject of scientific investigation. That doesn't mean that every human endeavor pertaining to them is science. This is a good example of one that isn't.

If someone tried to figure out if Pluto was at sometime in the past a satellite of Neptune and they set about collecting data and testing models... that would be science: an investigation to determine something about reality.

2006's planet-definition debate has not involved any questions whatsoever about the inherent nature of things. It's more of an aesthetic debate. It isn't science any more than the contest to name the MER rovers was science.

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
Tell you what: since the books that I have on my shelf say that Jupiter has only 12, and from my sentimental historical perspective I feel more comfortable with that idea, I move that the remaining objects orbiting Jupiter not be considered moons.
[/quote]

If there were a significant "line" to draw between #12 and #13, you might have something there. By and large, I think the ongoing discoveries have trickled in over the years, although chronological gaps without discoveries have surely come and gone. There is a highly significant line between #4 and #5, and we do have a name to reflect that, crediting the discoverer.

The notion of defining planet is almost as silly as it would be to define Galilean in case Jupiter turned out to have a large previously-undiscovered satellite (sure, it would have to be very dark and of very low density) to see if it should be called a Galilean. Or to draw a line between Io and Europa and say that the fourth-largest of them isn't truly a Galilean because it is too much smaller than Ganymede. Impossible: the term Galilean is purely historical. There are four of them and that can never change. New measurements cannot possibly be brought to bear on the matter.

Nobody's convinced me that the term "planet" isn't similar. How would they convince me -- by fiat?

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
Adjust to reality guys.
[/quote]

Nobody's anti-reality, but we are trying to decide which constraints to apply in this aesthetic, non-scientific endeavor.

For me, reality includes the observation that "river" has no formal definition, people write scientific papers using the word "river" without apparent difficulty, and people interact daily with rivers without apparent difficulty. I grew up near a stream about ten feet wide that people (and maps) call "Center Run". Is it a river? I don't think many people would say so, although if you polled enough people someone eventually would. Do we need a committee to define standards of riverhood? I haven't yet seen a problem that that would solve.

And "planet" is no different except very few people ever interact with the objects past Saturn, whereas thousands of people drive cars on bridges over Center Run every day.

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
Pluto isn’t what it was originally thought to be. That doesn’t make it insignificant, just different than our traditional viewpoint. Some people feel that adjusting viewpoints to better fit observation is somehow degrading poor Pluto.
[/quote]

Pluto isn't what it was thought to be in 1965, but as far as this debate goes, it's much the same as our knowledge of it in 1979 -- excepting that it's also a bit more "planetlike" in having three satellites instead of one and a dynamic atmosphere.

The real thing that's changed is that in 1965, it was believed that the largest nonplanet orbiting the Sun was 19% the size of the smallest planet. Now it is certain that no such gap exists in the distribution of sizes. The biggest wake-up call that reality has handed us is that there is no natural category of planet (vs things in the next size bracket down -- there is no size bracket!).

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
From the broadest perspective, to say that Pluto is in the same league as Saturn or even Mars is in my mind being just a little delusional.
[/quote]

From the broadest perspective, to say that Mars belongs more in the category of Saturn rather than Pluto is flagrantly off.

Mars is 1/17th the size of Saturn... and 2.9 times the size of Pluto.

[quote name='GregM' date='Oct 15 2006, 10:29 AM' post='72675']
Maybe the new definitions are not perfect - or even that good for that matter, but at least there is an attempt being made to recognise that newly understood diversity and complexity in the Solar System – instead of hanging dogmatically onto a outdated perspective.
[/quote]

Actually, this is the worst kind of dogmatic hanging-on: the failure to recognize that "planet" is not a natural category and the delusion that it lends itself to formal definition. River-scientists have no such delusion.

What came before 2006 was not delusion (except, of course, when Pluto was assumed, without evidence to be so large). "Planet" was a know-it-when-you-see-it category. That is precisely what the evidence in nature supports: there simply is no gap or natural property distinguishing Jupiter and Mercury on the one hand from Ceres on the other. Jupiter and Mercury are lumped into a category that excludes Ceres for one reason only: history. Calling it science and trying to reverse-engineer it into being reasonable is absurd.