Pluto no longer a Planet

[#juan]

Thursday, Aug 24, 2006
Pluto demoted under new definition of planet



(CBC) - Little Pluto, formerly the solar system's smallest planet, has been stripped of its status by the International Astronomical Union, reducing the number of planets to eight.

The new guidelines - introduced in Prague on Thursday after a week of debate by the 2,500 astronomers at the organization's conference - define what is a planet and what is not. Pluto didn't make the cut.

Pluto has been considered a planet since its discovery in 1930. Pluto is now considered a "dwarf planet," and the eight others - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - are now called "classical planets."


Pluto, which is smaller than Earth's moon, doesn't fit the new criteria for a classical planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighbourhood around its orbit."

Pluto's orbit is inclined relative to the rest of the solar system and crosses over the orbit of Neptune, disqualifying it as a classical planet.

link

 

[#juan]

I think it was a peculiar decision

The "Classical Planets" include: Four Gas giants, Jupiter, Saturn, Uranus, and Neptune, Two smaller planets with substantial atmospheres, Earth and Venus. One hot barren rocky planet, Mercury. One almost barren planet with thin, wispy atmosphere, Mars. All the "classical planets" have moons except Venus and Mecury

Pluto is an icy, rocky, spherical body with a known moon, "Charon", but it misses the cut because it's orbit is crooked.

They never asked me.... :wink:

 

[s_lone]

What's kind of neat about Pluto and Charon is that they orbit each other. Their "gravity center" is not in one body but rather a point in space. On top of that, their are two moons orbiting the dual system Pluto-Charon.

 

[#juan]

Our moon and the Earth

have a similar relationship except the center of mass of the two bodies is just below the surface of the Earth on the side facing the moon. So the Earth does have a pronounced wobble.

 

[#juan]

Here is a rough sketch of Pluto and companions.

 

[hiAll]

ok and what about the X10 planet? It's considered to be the ten'th (well now maby nine'th) planet.

 

[Kreskin]

This is probably a dumb question but if Neptune and Pluto orbits cross each other will it ever be possible that they collide with each other..even billions of years out?

 

[#juan]

I think one day there will be a collision. I think I read in an astronomy journal a few years ago that scientists had calculated that a collision was not going to happen in the next twenty thousand years. The thing is, that the distances involved are so great, it is like two microbes orbiting the Earth at different speeds a hundred miles out. Chances of a collision are very small. Not nil, but small. Pluto takes about two hundred and fifty years to orbit the sun once. Neptune is quicker at about a hundred and sixty five years

 

[gc]

RE: Pluto no longer a Pla

Poor Pluto

 

[Graeme]

Umm okay No, Pluto and neptune do not orbit the sun at the same angle, they will never collide.

Our moon and the Earth

have a similar relationship except the center of mass of the two bodies is just below the surface of the Earth on the side facing the moon. So the Earth does have a pronounced wobble.

wrong again, the earth has a slight wobble, but not in the same way as you think, and in fact the moon helps to stabalize the wobble of the earth. It is believed a lot of the wobble is caused by a large amount of friction and iron deposits deep inside the earth (they are unballanced). The moon's orbit is not parallel nor perpendicular to the earths orbit, or the earths rotation of axis.

The moons center or gravity is off center by 6000ft closer to earth, that is why the moon doesn't spin.

 

[super☆man]

Pluto which was formerly the solar system's smallest planet has now stripped of its status.what do you think the important new? In my opinion, Although the pluto seems to leave the solar system we still define it as a planet of the solar system.
The planet which must has a lot of secrets make me feel its importance.

 

[Dexter Sinister]

Re: RE: Pluto no longer a Planet

Jeez Graeme, what have you been reading? Pluto crosses Neptune's orbit twice in its year, what do you think would happen if Neptune chanced to be at the crossing point when Pluto arrived? Chances of a collision are small, but not zero.

Your comprehension of orbital mechanics is, shall we say, somewhat limited. The earth does indeed have a significant wobble as #jaun stated, the moon's apparent path across our skies is pretty much in the same plane as the earth's orbit around the sun, the location of the moon's centre of gravity really doesn't have anything to do with that, and the moon does spin, just not from the perspective of someone on earth. Tidal friction on the moon has slowed its spin to match its orbital period so it always presents the same face to the earth, but to an observer outside the earth-moon system, both earth and moon orbit a common centre of gravity which happens to be inside the earth but well away from its centre. That's the wobble #juan was talking about.

 

[#juan]

Thanks Dexter

I should have mentioned that Pluto spends about twenty years inside the orbit of Neptune every orbit so it does have two crossings of Neptune's orbit, or two shots at a collision every Pluto/year.(250 Earth years)

 

[Graeme]

haha You guys have got to be kidding me,

so you think that the past what 4.5 billion years have been a fluke and by random chance they never hit.
every 497 years neptune and pluto repeat their relative orbit to each other. It is a very simple concept Pluto has a tilted orbit.

 

[Dexter Sinister]

No Graeme, we're not kidding you. Things aren't as simple as you believe. The orbital resonance of Neptune and Pluto isn't that precise or constant, it's constantly perturbed by other gravitating bodies, and thus there is a non-zero probability of a collision in a finite time. It's those little perturbations that are responsible for the precession of the equinoxes, for instance, which among many other things means no orbiting body traces out exactly the same path on successive orbits. The solar system's a dynamic place; orbits aren't fixed or immutable.

 

[#juan]

I tend to favor practical astronomy as opposed to theoretical astronomy because it is less frustrating. There are fine astronomers out there who believe Pluto was once a satellite of Neptune. Some of the same fine people will tell you that Pluto likely collided with Triton(a moon of Neptune)and tore out enough material to make Charon. I know enough about astronomy to have enjoyed it as a hobby for the last thirty years or so. I also think that given Pluto's long orbit, about 5 billion miles, and relatively low mass, something, perhaps a wayward asteroid, could perturb it's orbit enough to make it fly right down Neptune's gullet on the next close encounter, Never say never.

 

[jimmoyer]

Great discussion.

By the way earlier this month it seemed the
definition of planet status was cleaner and concise
than it is now with this low voter turnout in
Prague (400 out of 2000? ).

 

[#juan]

Probably, the more people

involved in a discussion, the less will get decided. I haven't yet seen the list of properties, features,etc., that makes a planet a planet. I'm sure it has been published but I just haven't seen it. Having said that, my first reaction is that Pluto has more features that make it a planet than vice versa. I have to read the list.

Here is the list:

The full IAU resolution of the definition of a planet reads:

The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A "planet"1 is a celestial body 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, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body 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) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.


link

 

[Gonzo]

It's a sad day for Pluto, and a happy day for pulishing houses who make school books!
I think Plutos orbit did it in for the tiny "dwarf planet".

 

[#juan]

We'll have to make up a new mnemonic,

Old mnemonic devices such as "Mark's Very Extravagant Mother Just Sent Us Ninety Parakeets" helped them recall that the order was Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Or we could just fix the old one: "Mark's Very Extravagant Mother Just Sent Us Nothing" :wink: