|
||||||||||||||||||||||||
How many planets are there in our solar system?
When we were all young we were taught there are 9 planets, the last being Pluto. I have read reports of another planet found far beyond Pluto and I do not know if that is the same planet as Eris.
http://www.gps.caltech.edu/~mbrown/planetlila/
That is about Eris. I am not totally sure why they took Pluto off the planet list. I heard they found some objects rotating around our sun that are bigger than Pluto so, instead of naming them planets, they took Pluto off the list. Nonetheless, I want to know if someone knows exactly what we take as our solar system as of today. How many planets? Their names? What is Pluto classified as now and what other objects are classified along with that? Do you agree with Pluto being taken off the list?
http://www.gps.caltech.edu/~mbrown/planetlila/
That is about Eris. I am not totally sure why they took Pluto off the planet list. I heard they found some objects rotating around our sun that are bigger than Pluto so, instead of naming them planets, they took Pluto off the list. Nonetheless, I want to know if someone knows exactly what we take as our solar system as of today. How many planets? Their names? What is Pluto classified as now and what other objects are classified along with that? Do you agree with Pluto being taken off the list?
| Bryan_Bezzle wrote: |
| When we were all young we were taught there are 9 planets, the last being Pluto. |
And when your grandparents were young, they were probably taught that there were 8 planets, the last being Neptune. ^_^;
Science grows and changes. C'est la vie.
| Bryan_Bezzle wrote: |
| I am not totally sure why they took Pluto off the planet list. I heard they found some objects rotating around our sun that are bigger than Pluto so, instead of naming them planets, they took Pluto off the list. |
That's roughly correct.
It was actually a sticky and controversial decision - not because astronomers were particularly married to the idea of Pluto being a planet (i honestly don't get what all the fuss among lay persons over Pluto's reclassification is), but because if they didn't make a clear, unambiguous definition very carefully we could have had a hundred planets in our solar system before too long. Not long after Pluto was discovered, we realized that there was a lot of crap out where Pluto was, and Pluto - while bigger than most of the junk out there - wasn't that much bigger. The discovery Eris was pretty much the final straw - this was a long time coming.
| Bryan_Bezzle wrote: |
| Nonetheless, I want to know if someone knows exactly what we take as our solar system as of today. How many planets? Their names? |
Obviously, the Sun, usually named Sol (not an official name).
Four terrestrial planets - the "inner planets": Mercury, Venus, Earth and Mars (in order of increasing distance from the Sun).
The asteroid belt.
Four gas giants - the "outer planets": Jupiter, Saturn, Uranus, and Neptune.
The Kuiper belt.
The scattered disc.
The heliopause (where the Sun's solar winds no longer have the strength to beat the surrounding solar winds of other stars, called the stellar medium).
i'm not sure if the Oort cloud would count as the extent of our solar system... i'd stop at the heliopause myself... and no one knows for sure if the Oort cloud exists.
And of course a whole host of moons (Jupiter and Saturn have like 50 each, and more will probably be discovered by the time i finish this sentence).
| Bryan_Bezzle wrote: |
| What is Pluto classified as now and what other objects are classified along with that? Do you agree with Pluto being taken off the list? |
Pluto is a "dwarf planet", which means:
- It is massive enough to be shaped round by its own gravity.
- It orbits the sun (it's not a moon of some other planet).
- There is other crap in its orbital path of comparable size (planets have cleared their "neighbourhood", dwarf planets have not).
Do i agree? Yes. It was a mistake born out of ignorance to classify Pluto as a planet in the first place. Once we discovered the Kuiper belt, it was over for Pluto's planethood, in my opinion. Of course, inertia made it difficult to change what had already been decided - however wrong. But when Eris was found, that was it - any objection at this point was silly.
I agree that the concern among the lay public doesn't make much sense, but the concern among scientists makes even less sense to me.
| Gagnar The Unruly wrote: |
| I agree that the concern among the lay public doesn't make much sense, but the concern among scientists makes even less sense to me. |
Oh, the concern among the scientists is reasonable... but it's not about Pluto. ^_^;
The concern about IAU's decision in 2006 that resulted in the reclassification of Pluto is one of precision. They wanted precise definitions of planets/asteroids/whatever, so that when they found something there would be no ambiguity whatsoever over whether or not what they had found was a planet or not. The 2006 definitions are... vague. Read a certain way, Earth is not a planet, badum-ching! See the problem? ^_^;
Pluto should still be a planet in my opinion as it rotates, revolves and has its own satellites.
If that's not a planet then what is?
If that's not a planet then what is?
| _AVG_ wrote: |
| Pluto should still be a planet in my opinion as it rotates, revolves and has its own satellites.
If that's not a planet then what is? |
Pluto has its own satellites? Maybe we sent some to check it out but it is incapable as far as we know of having its own satellites. Maybe you mean moon because Pluto does have a moon.
| Indi wrote: | ||
Oh, the concern among the scientists is reasonable... but it's not about Pluto. ^_^; The concern about IAU's decision in 2006 that resulted in the reclassification of Pluto is one of precision. They wanted precise definitions of planets/asteroids/whatever, so that when they found something there would be no ambiguity whatsoever over whether or not what they had found was a planet or not. The 2006 definitions are... vague. Read a certain way, Earth is not a planet, badum-ching! See the problem? ^_^; |
Kind of. If there's some discrete variation in celestial bodies that makes planets, dwarf planets, moons, planetoids, whatever more or less distinct, either in how they formed or what their makeup is like, then labels help. Otherwise, they just make it seem like discrete variation exists where none does. It's a problem in ecology, where people like to use labels to sort and identify things, but those labels aren't necessarily all that helpful. If it's that hard to figure out what a planet should be, it's probably not worth worrying about. On the other hand, maybe it's not that hard. To me there's nothing about Pluto per se that makes it not planet-like, but that's just a profession of ignorance.
| _AVG_ wrote: |
| Pluto should still be a planet in my opinion as it rotates, revolves and has its own satellites.
If that's not a planet then what is? |
Everything in space rotates, revolves, wobbles and moves. ^_^; Even our sun us just a satellite of the galactic core.
And there is not much out there of any appreciable mass that doesn't have satellites. Large asteroids can have satellites, from a few miles across to the size of pebbles.
You see what i mean? ^_^; When you get down to the details, it's not easy to make a precise definition. Everything appears to be black and white as long as you stand a few paces back and squint, but when you take a closer look... what really makes Pluto any different from any of the other rocks in the Kuiper belt, other than it's fairly big (but not that much bigger, really)? The Moon is six times the mass and one and a half times the size (this is from memory, so i might be wrong). Pluto is in a field of other asteroids (unlike the other planets, which have all cleared their neighbourhoods). What really makes it anything more than a big ass rock in a field of rocks?
| Bryan_Bezzle wrote: |
| Pluto has its own satellites? Maybe we sent some to check it out but it is incapable as far as we know of having its own satellites. Maybe you mean moon because Pluto does have a moon. |
(A moon is a satellite.)
Ah, but does Pluto have a moon?
Charon is about half the size of Pluto, and a tenth of the mass (by comparison, the Moon is about a quarter of the size of Earth, and 1/100 of the mass - and some people consider the Earth and the Moon to be a double planet rather than a planet and a moon). One thing you have to understand is that the Earth is not fixed with the Moon revolving around it - both the Earth and the Moon orbit a point between them. It just so happens that that point is below the surface of the Earth. In the Pluto-Charon system, the point is not below the surface of Pluto, so the two both orbit around a point between them. That would make them a double planet, not a planet and a moon, ne?
So if Pluto is a planet, why not Charon? It's nearly as big as Pluto, and they're both parts of a double system that is orbiting the Sun.
(The Pluto-Charon system then have other, smaller moons orbiting around them both, of course.)
Indeed, what's a moon? How big does an orbiting rock have to be before we call it a moon? The Moon is not the only large body of rock orbiting the Earth, you know. (Actually, the Moon is huge, compared with the moons of most planets. Some people even consider the Earth-Moon system to be a double planet. Most moons are way smaller than their parent bodies.)
| Gagnar The Unruly wrote: | ||||
Kind of. If there's some discrete variation in celestial bodies that makes planets, dwarf planets, moons, planetoids, whatever more or less distinct, either in how they formed or what their makeup is like, then labels help. Otherwise, they just make it seem like discrete variation exists where none does. It's a problem in ecology, where people like to use labels to sort and identify things, but those labels aren't necessarily all that helpful. If it's that hard to figure out what a planet should be, it's probably not worth worrying about. On the other hand, maybe it's not that hard. To me there's nothing about Pluto per se that makes it not planet-like, but that's just a profession of ignorance. |
Yeah, exactly, it's a labelling thing - which i've never really held much stock in, because slapping arbitrary labels on points along a continuum is not really helpful (the same problem exists in evolutionary biology with determining where one species ends and the other begins). Mathematically and physically speaking, there's really no difference in the astronomical properties between a pebble, an asteroid, a gas giant and a star except for the scale of those properties. All follow the same equations of motion, and all influence each others motions - even a pebble in scattered disc effects the motion of the Sun... just not perceptibly.
None of the science changes whether Pluto is a planet or not (or whether we define planets as having cleared the neighbourhood or not) - the same equations apply either way. So... what's the point, right?
Maybe it's a prestige thing - the more planets there are, the more scientists get to discover them, but the rarer they are, the more prestigious are the ones that actually find one. i feel kinda sorry for Mike Brown, who discovered Eris which more deserves the title of planet than Pluto, because he lost out on a chance to be the "discoverer of the tenth planet". But, on the other hand - and he agrees - how special does that get to be if the 200 or so new bodies we're finding are all called planets too?
Maybe it's a categorization thing - the bigger a body has to be to be a planet, the easier it is to find, which means the easier it is to characterize a solar system. If we allow small planets, it may screw us over when we start talking about Tau Ceti's third planet - no, wait, fourth... er fifth... sixth. In between the time you write a book and it gets published, you could find that it's obsolete four or five times over.
i'm honestly not sure... but if it does matter that we know what is planet vs. what is not a planet, then it is important to have a clear, precise definition. The controversy among scientists now stems from the fact that the definition is not clear.
| Quote: |
| Everything in space rotates, revolves, wobbles and moves. ^_^; ... |
I'm probably wandering off-topic (again!) here but the 'question of this century' can be summarised as:
Everything in the Universe spins (from leptons, bosons and quarks to quasars and their jets): where does the energy come from for this to be the case?
The current best answer is the structure of a mathematical entity known, since about 1841, (variously) as E8, e8, E[sub]8[/sub], Spin( 8 ). It's going to take much time and effort for this to 'sink-in', imho, but it is a beautiful area of study too.
| Bryan_Bezzle wrote: | ||
Pluto has its own satellites? Maybe we sent some to check it out but it is incapable as far as we know of having its own satellites. Maybe you mean moon because Pluto does have a moon. |
Technically, the things we send up into space to give us Sky Sports are artificial satellites. Moons are satellites.
i think pluto still a planet.
I'm all for the reclassification of Pluto as a dwarf planet, as it (a) makes sense, and (b) has a lot of people taking another look at our system, and learning about the lesser known aspects of the solar system. The other day I mentioned something about the asteroid belt to my 17-year-old brother and he didn't know what it was! I was kind of shocked. The outer, trans-Neptunian areas of the solar system are fascinating, but not very well known in the mainstream. I'm sure Pluto doesn't mind being a sort of sensationalist casualty to the process of learning...
As far as i thought, i think pluto is no longer a planet..
But become a moon in Neptune..
This is what i thought....
You can even find at Google
Then taip Pluto is exploded?
Then it will search around 1000 and above.
But become a moon in Neptune..
This is what i thought....
You can even find at Google
Then taip Pluto is exploded?
Then it will search around 1000 and above.
here's the reason pluto is not a planet anymore but considered a dwarf planet.
A “(solar) planet” must be a celestial object that…
a. is in orbit around the Sun
b. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape
c. has cleared the neighbourhood around its orbit
New classification: A “dwarf planet” is a celestial object that…
a. is in orbit around the Sun
b. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape
c. has not cleared the neighbourhood around its orbit
d. is not a satellite of a planet
Solar planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Dwarf planets: Pluto, Eris (formerly Xena or UB313), Ceres
hope that helps.. this came from my lecture in general physics..astronomy.
A “(solar) planet” must be a celestial object that…
a. is in orbit around the Sun
b. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape
c. has cleared the neighbourhood around its orbit
New classification: A “dwarf planet” is a celestial object that…
a. is in orbit around the Sun
b. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape
c. has not cleared the neighbourhood around its orbit
d. is not a satellite of a planet
Solar planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Dwarf planets: Pluto, Eris (formerly Xena or UB313), Ceres
hope that helps.. this came from my lecture in general physics..astronomy.
to complete the story. i might as well post the reason why there was a controversy in the first place..
Gerald Finkelschmidt: the “planet man” - We suspect that
the site may, possibly, be satirical, but we appreciate the
writer's grasp of the problem. “There isn't a good
definition of what constitutes a planet,” says Gerald
Finkelschmidt. “I've put on a few pounds these past
couple of years, but I'm clearly below the limiting mass for
thermonuclear fusion... And I orbit the sun, obviously. So
technically, I qualify… You know, if this works out, I hope
NASA sends a $500 million mission to learn more about
me," he said. "And I hope they bring beer when they do.”
Thus came the resolution that the planet must be redefined on August 24 2006.
Gerald Finkelschmidt: the “planet man” - We suspect that
the site may, possibly, be satirical, but we appreciate the
writer's grasp of the problem. “There isn't a good
definition of what constitutes a planet,” says Gerald
Finkelschmidt. “I've put on a few pounds these past
couple of years, but I'm clearly below the limiting mass for
thermonuclear fusion... And I orbit the sun, obviously. So
technically, I qualify… You know, if this works out, I hope
NASA sends a $500 million mission to learn more about
me," he said. "And I hope they bring beer when they do.”
Thus came the resolution that the planet must be redefined on August 24 2006.
I agree with the reclassification of Pluto. The new definition makes sense and are no doubt the clearest way of wording things without refering to minimum masses or things.
well it sure is clear to me now thanks to INDI who seems to know a lot about our solar system.. (or is it just copy-pasted ??)
any way as far as i'm concerned i don't really matter .. what difference does it make if we call it a:
- Planet
or a
- DWARF planet
it's not like the entire planet is going to change it's size just because we put it in a different catagorie
as far as for the scientific part if they can spend their day catagorizing our planets. and it help to make other people understand how it all works then that's great.. but i don't need to have pluto in another catagorie just because it fit better there.. it's probably the final last thing we meet before we finally exit our solar system... so what does it matter ..
any way as far as i'm concerned i don't really matter .. what difference does it make if we call it a:
- Planet
or a
- DWARF planet
it's not like the entire planet is going to change it's size just because we put it in a different catagorie
as far as for the scientific part if they can spend their day catagorizing our planets. and it help to make other people understand how it all works then that's great.. but i don't need to have pluto in another catagorie just because it fit better there.. it's probably the final last thing we meet before we finally exit our solar system... so what does it matter ..
| J-M-site wrote: |
| well it sure is clear to me now thanks to INDI who seems to know a lot about our solar system.. (or is it just copy-pasted ??) |
No, Wikipedia and Encyclopaedia Britannica copy-pasted from me. ^_^
| J-M-site wrote: |
| any way as far as i'm concerned i don't really matter .. what difference does it make if we call it a:
- Planet or a - DWARF planet it's not like the entire planet is going to change it's size just because we put it in a different catagorie as far as for the scientific part if they can spend their day catagorizing our planets. and it help to make other people understand how it all works then that's great.. but i don't need to have pluto in another catagorie just because it fit better there.. |
Well, i'm an engineer at heart, so i tend to think in terms of practicality. There are practical reasons for the distinction, but they're kinda in the realm of science fiction. If you are thinking of building a long term base, you definitely want to build one on a planet, not a dwarf planet... because a dwarf planet is - essentially - a planet in the middle of an asteroid field.
And, by the way, size matters not. A dwarf planet is not necessarily smaller than a planet. It will usually be smaller, but not always, and it might even be bigger. The only difference is that dwarf planets are in an asteroid belt, not in a clear orbit like planets.
Now, Pluto won't care either way what you call it. Recategorizing is not going to change its characteristics in any way. Frankly, it's not really going to effect your life either. However, it does make a big difference to the people writing the astronomy books, because if we don't change the classification of Pluto, we could have a hundred or more planets in a few decades, as our instruments get more sensitive and find more small, dark planets hidden in the asteroid belt or scattered disc. Most people who complain to me about Pluto's downgrade change their tune when i point out that if we hadn't done it, we would have at least two other planets in our solar system already, with many more coming. It makes more sense to me to bite the bullet and kick Pluto out of the club than it does to open the floodgates to dozens more planets.
| J-M-site wrote: |
| it's probably the final last thing we meet before we finally exit our solar system... so what does it matter .. |
Not hardly. ^_^
Beyond Pluto (which is in the Kuiper belt) is the scattered disc, which includes the dwarf planet Eris (which is bigger than Pluto), Beyond that is the heliopause - which is where i'd draw the line of the solar system, but that's just me. Beyond that? Probably the Oort cloud. And beyond that??? ^_^
There's nothing remarkable about Pluto, really. It's not the smallest "planet" in the solar system - Ceres is - it's not the furthest out - Eris is. It's neither the first nor the last dwarf planet discovered - Ceres is older and Eris is more recent. Really... Pluto's not that interesting. Hardly worth being called the sign post of the solar system.
 |