The Astronomy Thread

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Re: The Astronomy Thread

Post by GeoModder »

I guess that's where the barycenter comes into play. :lol:
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Re: The Astronomy Thread

Post by icekatze »

hi hi

Big news in the world of astronomy: New Horizons passed its closest approach to Pluto today!

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Re: The Astronomy Thread

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Unfortunately, it will take more than a year to download all of the data from the probe, to say nothing of analyzing it.

It is neat to finally have a picture of what Pluto looks like, though.

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Re: The Astronomy Thread

Post by GeoModder »

I wonder if next 'Pluto year' the dwarf planet would look different from space. I assume some of those surface 'features' we see now are a result of atmospheric condensing (or the start of that proces since Pluto is still in local 'Summer').
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Re: The Astronomy Thread

Post by icekatze »

hi hi

Since Charon has a lot more visible surface features and cratering, I think the general hypothesis is that Pluto probably has some sort of process that is refreshing its surface.

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Re: The Astronomy Thread

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GeoModder wrote:I wonder if next 'Pluto year' the dwarf planet would look different from space. I assume some of those surface 'features' we see now are a result of atmospheric condensing (or the start of that proces since Pluto is still in local 'Summer').
It was also my thought that the dark equatorial areas could be condensation of some kind of organic compounds... but Pluto's axial tilt is so extreme that right now it should be the north pole that is warmer, not the equator.

Pluto has a lot of surface ice (it's very bright), while Charon seems darker and more rocky at first glance. All of Pluto's 5 moons are in the same weird plane, which suggests they are the remnants of a massive collision.

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Re: The Astronomy Thread

Post by GeoModder »

Now I can only hope that during my lifetime there'll be at least a flyby mission to Eris to see if an object a quarter more massive is indeed smaller then Pluto.
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Re: The Astronomy Thread

Post by Arioch »

I did find it amusing that they made a big deal about Pluto now being the largest KBO... when the diameter was revised from 2302 km to 2370. As if the estimate for Eris (~2300 km, last I heard) is now suddenly more accurate.

I get the feeling that the New Horizons team suffers a bit from Pluto Inferiority Complex. I notice during the briefings they seem to conspicuously avoid the use of the term "dwarf planet."

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Re: The Astronomy Thread

Post by Mr Bojangles »

I watched "Direct From Pluto" on the Science Channel and if it was in anyway accurate, then the New Horizons team is firmly in the camp of "Pluto's still a planet!" I mean, they showed clips of the NH PI at a local school that held a mock protest to have Pluto be called a planet again. Basically, the impression that I got was that they were pretty unhappy with the IAU.

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Re: The Astronomy Thread

Post by GeoModder »

Its bound to happen. After all, Pluto is their baby so to speak.
Whether we call it a planet, KBO, dwarf planet, or whatever, I'm happy there's this resurgence of wonder about the mysteries of those objects we still haven't seen from up close.
Its been a good couple years now, with Vesta, Ceres, and now the Pluto/Charon binary revealed as interesting worlds in their own right.
If I could make a list for the next objects to visit, Eris, Chiron, and the moons of Uranus and Neptune would be on it.
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Re: The Astronomy Thread

Post by Arioch »

The IAU planet definition is pretty nonsensical; the bit about having to clear its orbit of similar objects is absurd, as I don't see how that has anything to do with the qualities of being a planet. It seems quite common that multiple proto-planets can form in the same orbit (Earth supposedly had a planet called Theia in the same orbit), and though they usually eventually collide, it's possible that with the right orbital resonances with surrounding planets, such a dual-planet orbit could be stable. And, as far as I'm aware, such planets could potentially be extremely massive. How can such an object, potentially more massive than Earth, be classified as a "dwarf planet?" The classification also puts Ceres and Pluto in the same category, when Ceres is a rocky asteroid, and Pluto is an icy Kuiper Belt Object that's more than 100 times more massive.

It's also a distinction without any real scientific value. It's purely for academic bookkeeping; planetarium curators would rather subtract one "planet" from the list than have to constantly be adding new ones.

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Re: The Astronomy Thread

Post by Mr Bojangles »

I certainly wasn't surprised to know how the NH team feels towards Pluto's status. Nor am I surprised by how people in general feel about it. Personally, whether we ultimately classify it as a dwarf planet or a regular planet, I don't much care. What I care most about is the apparent lack of scientific rigor applied to the existing definition by the IAU; the decision was rushed and certainly lacked real consensus.

So long as the definition is strong and unambiguous, I'm fine with eight planets or potentially scores of them. :)

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Re: The Astronomy Thread

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On the one hand, defining a planet in rigid terms is like trying to define "How long is a piece of string", and Pluto is generally small enough, distant enough, and eccentric enough for them to nudge it off and avoid irritants like adding dozens of new planets because other KBO's are larger and such.

On the other hand, the New Horizons team have been working on this for ten years and long before Pluto was left out in the cold, so it's completely understandable that they're in the Pluto is a Planet camp.

Personally, I'm of the opinion that Pluto should have been grandfathered in. The Voyager and Pioneer plaques both bear a model of our solar system with the nine planets there. Generations of children grew up learning that Pluto was a planet. Yes, there is no scientifically sound reason to do so, but the definition the IAU uses is equally unscientific, since Earth orbit crossing asteroids would deem Earth not to be a planet, since that essentially means Earth has yet to clear its orbit. :roll:

Grandfathering Pluto in as a planet and designating all subsequent objects found as KBO's would have been the better solution. It would've been the exception that proved the general rule, would have avoided the awkwardness of redesignation, and would've kept the cantankerous eccentric planet that is Pluto in the family instead of locking it in the attic and hoping it starves.
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Re: The Astronomy Thread

Post by Namaphry »

I dunno. If we grandfather it in, then we have to keep explaining it to children hundreds of years down the line, including those born on other worlds and around other stars, and we Terrans would end up looking like sentimental nitwits in the process.

We can set everything beyond Neptune's orbit into its own group... and so long as we're anthropomorphizing Pluto, I've gotta say that giving it the same status as Neptune is pretty demeaning to the big blue thing. Even Neptune's moon Triton is bigger than Pluto.

I prefer the 'Kuiper Belt Object' definition, just like I'd call Ceres an asteroid. The whole 'dwarf planet' thing just seems like it's a half-baked conciliatory gesture. Classifying Pluto as a 'plutoid', though, is pretty funny. I'd let them get away with that as an official definition, if I were hypothetically in a position to intervene.

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Re: The Astronomy Thread

Post by icekatze »

hi hi

Speaking of grandfathering things in, we're still going to have to explain to children hundreds of years down the line why the solar system has a completely different classification system for planets than any other system in the universe.

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Re: The Astronomy Thread

Post by Mr Bojangles »

icekatze wrote:hi hi

Speaking of grandfathering things in, we're still going to have to explain to children hundreds of years down the line why the solar system has a completely different classification system for planets than any other system in the universe.
Wouldn't we just apply our classification system to other solar systems? Or are you saying that you know that we're using a classification system that other sapient life doesn't? In the future, no less.

Are you some sort of time-traveling alien, icekatze??

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Re: The Astronomy Thread

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Namaphry wrote:I dunno. If we grandfather it in, then we have to keep explaining it to children hundreds of years down the line, including those born on other worlds and around other stars, and we Terrans would end up looking like sentimental nitwits in the process.
At which point we explain the story of how Pluto was discovered using the power of mathematics, science and observation, how it was named, and the important astronomers who contributed to its discovery. The reason we call it a planet? The same reason we call certain hills on Earth mountains and why it varies from country to country, there is no strict definition. It's consideration as a planet comes as part and parcel of being the first object of its kind to be discovered and in recognition of the historical and cultural impact it had and of the imaginations it captured, it's something that the other KBO's, as momentous as their ongoing discoveries are, simply don't really share withe the foremost member of their population.

This would of course apply just as well to our descendants living in far flung star systems centuries down the road too. If they feel strongly enough that a decently sized object in their system should be called a planet for whatever reason, then perhaps they too can share the story of why and how it came to be designated as such.
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Re: The Astronomy Thread

Post by icekatze »

hi hi
The official definition of "planet" used by the International Astronomical Union (IAU) only covers the Solar System and thus does not apply to exoplanets. As of April 2011, the only defining statement issued by the IAU that pertains to exoplanets is a working definition issued in 2001 and modified in 2003. That definition contains the following criteria:

Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in the Solar System.

Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed or where they are located.

Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).
Categorizing something does not inherently add information. Science is about observing, not in deciding what the universe is, either by dictate or vote. People still haven't come to a consensus about whether Europe and Asia are separate continents, or if Australia is a continent or a large island, and scientifically, it doesn't matter.

They should have asked linguists to come up with definitions, because linguists at least can understand that words are allowed to have multiple definitions.

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Re: The Astronomy Thread

Post by Namaphry »

Pluto is what it is. Twentieth century cultural baggage doesn't make it more significant than Eris, Haumea, or Makemake, not any more than centuries of revisionism makes Christoforo Columbo more significant than all the explorers of the Americas that came before and after him. There's a lot of sentiment invested, but it's not from my generation.

'It was important to us, so it should be important to you' is a really bad attitude to have toward education, it can be used to justify almost anything. When our understanding changes, we need to review where we afford our reverence. Otherwise, we're resisting the change, trying to hold on to the way we thought things were rather than grasping the way things are.

Of course, there's a lot of subjectivity involved in discerning 'the way things are' and we still don't know everything. Still, it's pretty obvious that we were missing information when Pluto was discovered, and for many years afterward. 'The Search for Planet X' was based on an inaccurate estimate of the mass of Neptune. Nothing like that ever fit into the cosmic scheme. Pluto was searched for and discovered with overinflated expectations, and yet most people never realized it didn't meet them, or that the premise itself was false.

It reminds me of a story I heard, that an overambitious explorer called the island north of Montreal 'Lachine' because he thought he'd found China. This isn't quite true. He was overambitious, and searching for a route to China, but his land was called 'Lachine' as a joke at his expense, when he failed.

For Pluto, I'd say we're missing an admission that it's not 'Planet X', and that there never was one. But if we can call an island on the St. Lawrence River 'Lachine', I can understand calling an ice dwarf in a trans-Neptunian orbit 'the 9th planet'. It just seems a bit mean, from this perspective.

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Re: The Astronomy Thread

Post by icekatze »

hi hi

Twentieth century cultural baggage doesn't make any of the planets significant, but significance itself is completely subjective to begin with.

Why is the Earth even considered a planet? Planet means "wanderer," and was derived from the points of light that wandered through the night sky, rather than staying in place like stars. But the Earth doesn't wander through the night sky when people look up at night. Talk about cultural baggage, trying to impose astronomical significance on an object just because it's the place where someone lives, or because it isn't the center of the universe anymore.

What sort of cultural baggage do you suppose the term "trans-neptunian" orbit carries with it? Why does being further out than neptune have any significance? Why not call all the objects sunward of Jupiter "sub-jovian" objects, and all the objects beyond Jupiter, "trans-jovian" objects? After all, the only objects in the solar system are the Sun, Jupiter and assorted debris. ;)

The major difference between Pluto and China is that China is inhabited by people that can say that any other place is not actually where they live. If there had been no China to begin with, there would be nothing stopping someone from naming a newly discovered land China.

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