It Came From Beyond the Kuiper Belt

Sorry about two threads in one day, but there sure is a lot of news going on out there. Anyway, it looks like astronomers have discovered a new planetoid farther out than Pluto. Some argue that it is the 10th planet. Others argue that even Pluto shouldn;t be considered a planet...

Source: BBC
Source: CNN

My only regret is that they didn;t call it Rupert or Persephone. :P

Wikipedia article on Sedna.

Also, according to one definition (which seems pretty sensible and non-arbitrary to me), Pluto and Charon are in fact not planet and moon but a double planet. Or a double astronomical object.

So this is Nibiru. The NASA problably could not stop the truth!

OMG WORLD IS GONNA END THEY FOUND PLANET X

Zoost said:

So this is Nibiru. The NASA problably could not stop the truth!

Oh no, aren;t those the people who said that a planet twice the size of Jupiter would fly through the solar system in the matter of minutes (thus breaking the rules of physics by going faster than the speed of light), rearranging the face of Earth back in May 2003?

Yeah, that sure did happen.

It was a bit dissapointing really, the only thing it moved was a few thousand biros..but that happens every day

Scientists have been theorizing about the existence of extra planets to the point where they believe there may be as many as 12 in our solar system. One planet supposedly is in orbit nearer the sun than Mercury, hidden by the star's solar flares(although this is old information; they may very well have discarded that theory years ago). In truth there are no defined "borders" to our solar system, so who's to say there aren't hundreds of planet/oids out there?

NASA, along with other astronomical research installations, have to make discernations between errant chunks of rock and planets. I'd like to see some kind of source explaining the difference.

Numbermind said:

One planet supposedly is in orbit nearer the sun than Mercury, hidden by the star's solar flares(although this is old information; they may very well have discarded that theory years ago).

The Vulcan theory was abandoned as Einstein's theory of relativity entered the scene, almost a century ago.

Well, there you go. The science textbooks in my high school were most likely older than that.

heh...what it this Quaorar planet then that i heard about before?

Quaoar

Thats where saddam was really hiding...

we know so very little about the outer solar system, when are we gonna send another prope out there? the last ones were the voyager probes, and that was quite some time ago

Danarchy said:

Oh no, aren;t those the people who said that a planet twice the size of Jupiter would fly through the solar system in the matter of minutes (thus breaking the rules of physics by going faster than the speed of light), rearranging the face of Earth back in May 2003?

Yeah, that sure did happen.

No. These people believe there there is a 12th (including the sun and moon) planet (see here for more info). that orbits around our sun. And is close to earth only once every 3600 years. These people believe that humans are decendents of the inhabitors of this 12th planet.

Read the internet for more info ;-)

MaximusNukeage said:

we know so very little about the outer solar system, when are we gonna send another prope out there? the last ones were the voyager probes, and that was quite some time ago

Uh, the Voyager probes are only barely getting there, after 20 years in space. Don't expect immediate results if new ones are sent out :P

Zoost said:

No. These people believe there there is a 12th (including the sun and moon) planet (see here for more info). that orbits around our sun. And is close to earth only once every 3600 years. These people believe that humans are decendents of the inhabitors of this 12th planet.

Read the internet for more info ;-)

Yeah, I admit I just scanned the articles you linked to, but I thin I heard that story before as well.

Fredrik said:

The Vulcan theory was abandoned as Einstein's theory of relativity entered the scene, almost a century ago.

The search for Vulcanoids is still going on. There was an article about it in March'04 issue of Astronomy magazine.

And there are few hundred KBO's (Kuiper Belt Objects) already discovered, first of them in 1992, and now it is obvious that if Pluto was discovered recently, it was assigned to Kuiperoids, cause its properties are just the same as of other KBO's.

including the sun and moon

The moon is not a planet, its a moon..if you wanted to include moons as planets there would be about 50 in the solar system (saturn and jupiter have tons..)

Earth's moon is unlike any other in the solar system (except Pluto's), as it is relatively large compared to the planet it orbits. I'm no expert on this stuff, but it is possible to conceive of definitions of "planet" and "moon" that define our moon as a planet.

From the page Fredrik linked to, the Earth and Moon fail the definition of "double planet" based on the fact that the barycenter is inside the Earth (though nowhere near the Earth's centre). The moon causes the Earth quite a major "wobble".

Grazza said:

Earth's moon is unlike any other in the solar system (except Pluto's), as it is relatively large compared to the planet it orbits. I'm no expert on this stuff, but it is possible to conceive of definitions of "planet" and "moon" that define our moon as a planet.

From the page Fredrik linked to, the Earth and Moon fail the definition of "double planet" based on the fact that the barycenter is inside the Earth (though nowhere near the Earth's centre). The moon causes the Earth quite a major "wobble".

No. The moon is a satellite that orbits Earth, meaning it's not a planet. It's only about 1/4 the size of the earth -- Pluto's Charon is virtually half the size of Pluto and it orbits incredibly closely. Jupiter's Ganymede is the largest satellite in the solar system (way bigger than the moon), but it doesn't make it a planet.

Psyonisis said:

No.

Is that an agreeing or disagreeing "no"?

Fredrik said:

Is that an agreeing or disagreeing "no"?

I'm no expert on this stuff, but it is possible to conceive of definitions of "planet" and "moon" that define our moon as a planet.

Er, disagreeing with that.

Grazza gave an example (albeit implicit) of a valid such definition: defining Earth and the moon as a double planet.

Psyonisis said:

No. The moon is a satellite that orbits Earth, meaning it's not a planet.

The correct definition of "planet" is not at all clear - do a web search to see what I mean. And by the definition you seem to be using, the moon would be a planet, since the sun exerts a stronger gravitational pull upon it than the Earth does.

Interesting but only slightly related link.

Grazza said:

The correct definition of "planet" is not at all clear - do a web search to see what I mean. And by the definition you seem to be using, the moon would be a planet, since the sun exerts a stronger gravitational pull upon it than the Earth does.

But you will never hear an astronomer call the moon a planet of the sun it what I'm saying. If the moon had its own independent orbit around the sun, then it would be considered a planet. Because it's locked with earth, it's now one of earth's satellites.

As for the double planet thing... I'd say the earth/moon system could be considered one (because of the wobble). But since the centre of the system is still at earth, calling it a double planet would be somewhat inaccurate.

Psyonisis said:

Jupiter's Ganymede is the largest satellite in the solar system (way bigger than the moon), but it doesn't make it a planet.

Heh, I think several of Jupiter and Saturn's are actualy bigger than the Earth. My favorite moon of all is Europa, because it's the most likely other place to contain life in the solar system, possibly even moreso than Mars.

Danarchy said:

Heh, I think several of Jupiter and Saturn's are actualy bigger than the Earth.

No, the biggest satellite in the solar system is Ganymede, and although it has as big a diameter as Mercury it only has half as much mass. Nowhere near the size of Earth.

Ganymede:
Mass: 1.482×1023 kg
Equatorial Diameter: 5268 km

Earth
Mass: 5.9742×1024 kg
Equatorial Diameter: 12,756.3 km

Europa is the ice moon right?

Grimm said:

Europa is the ice moon right?

Yes.

This is a citation from that same March'04 issue of Astronomy magazine, Ask Astro section:

Defining a planet

How do you differentiate between a star, a planet, and a moon?

On the big end, the answer is pretty easy. Stars are gaseous bodies that generate heat and radiation through nuclear fusion. Planets, asteroids, comets, and moons are solid objects that don't. The situation gets more complicated, however, when you try to draw a line between planets and smaller bodies, or between planets and moons.
To start, let's restrict the discussion to the lower boundary of planetdom. Then the question becomes: Is Pluto a planet? As one of the self-appointed experts on this topic, I have a simple answer - yes, Pluto's a planet. That's the good news, and perhaps I should stop here. But I can't resist telling you the bad news. Being a planet, as I define it, does not mean what most people think it means, and some professional astronomers would call me nuts for saying Pluto's a planet. Indeed, this has been a surprisingly divisive question recently.
The question of what is a planet is a semantic one, and for reasons I don't have room to explain, a politically charged one. Being a semantic issue means that we can do what we want. We can simply declare that there are nine planets, period. Or we can say any object in orbit around the Sun with a diameter larger than 1,460 miles (2,350 kilometers) is a planet. (Pluto's diameter is about 2,360 km.) Both definitions give us the nine classical planets.
However, it's not possible to develop a physically meaningful definition that leads to nine, and only nine, planets. I can think of definitions that say there are eight planets (guess which one isn't included), or ones in which there are roughly twenty planets. The problem is that nobody has come up with a definition that includes Pluto while excluding large asteroids like Ceres and Vesta.
Alan Stern (principal investigator for NASA's New Horizons mission to Pluto) and I, who originally were on different sides of the Pluto question, got together a couple years ago and developed a compromise. It has two parts. First, we define a planet as anything that goes around a star and is big enough so that gravity makes it roughly round. In the solar system, this includes the nine classic planets. But it also includes many of the larger asteroids and Kuiper Belt objects (Pluto's icy cohorts orbiting beyond Neptune). These include Ceres, Pallas, Quaoar, Ixion, Varuna, and many others that few people have heard of.
We then divided the planets into two groups. Planets large enough to clear their neighborhood of small objects we called "über-planets." Those still embedded in a swarm of small objects we labeled "unter-planets." (We could have used "major" and "minor," but that would not have been politically correct.) Thus, we have eight über-planets and a large number of unter-planets. But at least Pluto is a planet, albeit an unter-planet.
Now, there is one sticky problem that Alan and I swept under the rug. What does "go around a star" mean? In most cases, it's obvious. For example, although Jupiter's moon Ganymede (with a diameter of 3,275 miles, or 5,270 km) is much larger than Pluto, it clearly goes around Jupiter and, thus, is not a planet. But there are two places in the solar system where the distinction isn't clear. The first is - surprise - Pluto. Pluto's moon, Charon, is so large compared to Pluto (half its diameter) that rather than going around Pluto, Charon and Pluto both go around a point lying between them. So, in one sense, Pluto goes around Charon. Is Pluto then a planet? Or should we define them as a binary planet? Should we welcome Charon into The Planet Club? Probably.
The other place where the distinction gets dicey is right here at home. Like all objects in orbit around the Sun, the Moon is always falling towards the Sun (i.e., in technical terms, the Moon's orbit is always concave in a Sunward direction). This contrasts with other major satellites in the solar system. In a real sense, therefore, the Moon is primarily going around the Sun, and Earth is a small perturbation on that motion. Another way of expressing this is that the Sun's gravitational pull on the Moon is nearly twice that of Earth's. So by all rights, the Moon should also be considered a planet!
Well, the list of planets is getting longer and longer, and it's getting farther and farther from the standard picture of a solar system containing nine planets. So let me end by addressing one last question: Who cares? Well, not me, really. As I said above, this is a semantic issue. What's truly important is that each of these objects is a world with a personality of its own. And each tells us important information about how worlds work and how we came to be. This is where we should all focus our attention.

--Hal Levison, Southwest Research Institute.

End of citation.

This is no scan, I hope I haven't violated the copyright stuff (I typed the whole text myself), just I think it's a very interesting read. I would like to stress the words: Who cares, it's a semantic issue. Maybe the Moon is a planet, maybe Pluto isn't, it's all in how you define it.