Planets

efron_24 · Apr 11, 2006

In Robert Roy Britt's Blog it is said that Pluto should no longer be called a planet and new found worlds even further away should not be concidered planets either. The problem would be the size. But Pluto is closer in size to Earth than Earth is to Jupiter and Saturn. Besides.. Both Pluto and Earth have relative small atmospheres compared to the Gas Giants So if Pluto is not a planet, why should the rock worlds between the Sun and the Astroid belt be called Planets, like Jupiter, Saturn, Uranus and Neptune. If one would say that Planets should have more than one moon. Pluto would join Mars and the Gas Giants and Earth, Mercury and Venus would not be planets. If one would say that Planets should have a ring, Pluto would proberbly join the Gas Giants and again Earth would not be a planet. If Planets should have a certeign size.. Mercury and Mars are very very small as well.. But if we say that Earth and Luna are a double planet (making Luna planet nr. 10), the largest moons of Jupiter and Saturn are also Planets. We could say that only the worlds that are visual by naked eye (without Telescope) are planets or In order to stop this nonsense, there should indeed be new names. Earth (Mars, Venus, Mercury) should not be in the same category as the Gas Giants. Call Earth, Mars, Venus, Mercury and the Giant moons of Jupiter and Saturn Planets Give Jupiter, Neptune, Saturn, Uranus an other category name and do the same with worlds smaller than our moon. <div class="Discussion_UserSignature"> </div>

Saiph · Apr 11, 2006

well, you've got two groupings of planets, jovian, and terrestrial. The question is, does pluto qualify as a terrestrial planet? It's really small (half the size of mercury), has an unusual composition, and a very, very eccentric orbit for a planet. It is also the same general features as other Kupier Belt objects. These differences are significant enough to question pluto's status as a planet. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

robnissen · Apr 11, 2006

Pluto became a planet by mistake in that it was originally thought to be MUCH larger than it is. It is time to fix the mistake. There should be two criteria for a planet: 1) it is at least the size of Mercury; 2) it orbits the sun (or another star). End of story. Other criteria are irrelevant, i.e. what its made of; its orbital inclination, etc. If somewhere out in the Kuiper belt, there is a something the size of Mercury, its a planet. But other than that, there are 8 planets.

harmonicaman · Apr 11, 2006

(Repost) The International Astronomical Union (IAU), which is a member of the International Council of Science (ICSU), is responsible for maintaining a unified system of astronomical classification. Within the IAU is the Working Group for Planetary System Nomenclature (WGPSN) which maintains the astronomical naming conventions and planetary nomenclature for orbiting bodies. This is the seminal authority which will decide on a system to disambiguate the Solar System. Just like Ceres has been reclassified as a mere asteroid, rather than a major planet; it is my opinion that Pluto will also have to be redesignated as a Kuiper Belt Object to fit the new realities caused by recent discoveries! This isn't a bad thing. In the end it will help us get a clearer picture of the structure of the Solar System and in the future there may have to be several sub-classifications as new objects are discovered. The Kuiper Belt and Oort Cloud may someday have to be separated into several sub-sets such as inner and outer belts and/or areas far removed from the plane of the elliptic; to suggest a few examples. The same thing was done for the rings of Saturn when we discovered new ring divisions! It's just too cumbersome to call everything under the Sun a "Planet". I think new names such as mesoplanet, planetesimal, microplanet, planetoid and the like, will have to become a part of the Solar Systems' lexicon and in the end it will help our scientific understanding of the universe. "Fear of a name increases fear of the thing itself." - J. K. Rowling, Harry Potter and the Sorcerer's Stone, 1997

dragon04 · Apr 11, 2006

The term "planet" is pretty arbitrary. As Saiph pointed out, Pluto's orbit and composition could perhaps make us revisit what constitutes a "planet" Or perhaps reclassify "planets" by types. For an example, let's say that Clyde Tombaugh discovered Sedna and "Xena" at the same time he discovered Pluto. They almost assuredly would have been classified as planets. I think rather that we should look at bodies orbiting our Sun in terms of classification. Terrestrial bodies, Gas bodies, and ice bodies, for example. Of all the known "planets", perhaps Mercury is the most enigmatic. It's the first body from the Sun. But it's tiny, has an eccentric and inclined orbit (second only to Pluto), and seems to be far more metallic than the next 3 rocks out. To me, "planet" is rapidly becoming an archaic term. It might have been okay when we could only observe 5 other ones, but doesn't quite fit the bill as we discover new bodies. For example, Titan would easily fit the bill of "planet" were it in its own discreet orbit around the Sun. And one could put forth the argument that Titan (among other "moons") is far more "planetary" a body than Pluto. I don't think it serves us to get really hung up on nomenclature. And now I have confused the issue even more. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

Saiph · Apr 12, 2006

Unfortunately, using Mercury as a size yardstick for what constitutes a planet is rather...arbitrary. There are moons larger than mercury for example, as Dragon pointed out. Generally, I expect there to be a major category: planets, with some sub-categories in the future. Some general, not quite so arbitrary guidelines for planets: Large enough to be spherical. The earth is "smoother than a billiard ball". While it doesn't have to be perfectly smooth, significant deviations should count against the object. Differentiation of the mantle and crust. Iron core, silicate crusts, etc, for "terrestrial" objects. Orbits a star...but we get a little funny here. Our moon technically orbits the sun, more than it orbits earth...well, not technically, in reality. If in a "binary relationship" if the barrycenter is inside one object, that object is the planet, the other the moon. If the barrycenter is outside both objects, then you've got a "binary planet." Jovians are much easier to spot, they've just got an upper limit of: no sustained core fusion (deuterium or otherwise). If they've got it/had it, they're brown dwarfs or full blown stars. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newmoon · Apr 12, 2006

As reported here, most of the IAU committee voted to keep Pluto a planet. Only six people on the committee wanted to demote Pluto. Setting the threshold of planethood at Pluto makes sense. Despite all the talk about Pluto's smallness, it is larger than 99.8 percent of all the known members of the Edgeworth-Kuiper belt. The fact that 62 years elapsed from the discovery of Pluto to the discovery of the next object in the Edgeworth-Kuiper belt tells you that Pluto is indeed a very special (and abnormally large) object. So is 2003 UB313.

mikeemmert · Apr 12, 2006

Robert Roy Britt's blog I thought was kind of out there...like Xena. He says Mike Brown is on a crusade. I'll believe that if his secret planet name is Beelzebub, a Palestinian god. I like the name Xena, myself. I hope it goes permanent. It comes from the traditions of the New Lands. Her attitude towards human rights is markedly different from the old traditions. This "controversy" comes from the new findings from Hubble. To tell you the truth, I thought Space.com's headline announcing this, "Proposed 10th Planet Shrinks Under Hubble's Gaze" was kind of confrontational. It lends a kind of authority to Hubble vs. other instruments that it really doesn't have. But if you look at the image (posted below, whenever it gets approved), I find it hard to believe that an authoritative diameter can be deduced from 1 1/2 pixels. Not to a four percent accuracy, at any rate. The measurement that I was really looking for was Xena's mass, which should be determinable from an examination of Gabrielle's orbit. Nothing was said about this in the Space.com article, the Hubble website, or, despite promises which have kept me on the edge of my seat for months, Mike Brown's website. Mike Brown came closest, he said we'd know by the end of the year. I had a pronouncement that hinged on that finding. I predicted that Xena's mass would be within 15% of Triton's. This post is already too long, so I'll deal with that in my next post...

mikeemmert · Apr 12, 2006

Ooops, the image didn't post. Oh, well, I'll try again. But since you can only post one image per post, I'll have to deal with my prediction that Xena would be within 15% of Triton's mass in my next post.

mikeemmert · Apr 12, 2006

About that prediction... I have felt for a long time that Pluto and Triton, and now Xena and Santa (2003 EL61), are not planets. "Obviously" Triton is a moon. It orbits Neptune, right? Backwards... It must be a captured object, right? Captured from where? I think that place would be from the Sun/Neptune Lagrange points L4 and L5. In fact, I think substantial objects formed at every Lagrange point in the solar system. Capture of such objects in an orbit is, however, unusual. Spacecraft must fire their rocket engines to slow down enough to get into orbit around a planet. Now, an object formed in a Lagrange point approching the object whose Lagrane point formed it will be approaching at a particularly slow velocity. Yet and still, there must be some mechanism for the object to shed angular momentum with respect to the planet (or moon, the Jovian moons have Lagrange points, too). Since there's no rocket motor, then there either has to be a collision or some gravitational interaction to get the object into orbit. I thought a long time ago that Triton must have hit one of the original moons of Neptune. But then, moons are tiny, space is vast, and the chances of such a collision are small. At the time, Pluto was thought to be a binary with Charon. If Triton was a binary, it had a much better chance of shedding angular momentum with respect to Neptune. It would just transfer such momentum to it's partner, which would leave the system with more energy than it came in. Having thought that Triton is an ex-binary member led to me thinking that the two objects must be the same size. However, it now appears that Xena is smaller, about the same size as Pluto. So I've had to reanalyze the Triton capture scenario. I still don't think it hit an original Neptunian moon on the first pass, since Xena's far out aphelion needs to be explained. But once in orbit, Triton would make pass aft

jatslo · Apr 12, 2006

A planet sized comet? Comets may be extra-solar, so planets may be extra-solar too. elliptic orbits, in which a planet creates chaos every 26-million years causing mass extinction on worlds like our own?!??! <--- Thinking Out Loud.

robnissen · Apr 13, 2006

"Unfortunately, using Mercury as a size yardstick for what constitutes a planet is rather...arbitrary." I don't agree. Mercury was one of the five planets known to the ancients and was a "planet" when planets were first defined (unlike Pluto). Thus, we have a definition of a planet, that is thousands of years old, there is no reason to change. Especially considering that the only reason Pluto was even named a planet was because of a major error regarding its size.

beshinaman · Jul 5, 2007

Can enyone tell me who are the new planets found in our sollar sistem and give a picture of them?

MeteorWayne · Jul 5, 2007

There have been no new planets discovered in our solar system in over a century, unless you include Pluto..And it's status as a planet is a matter of some dispute at this time. In any case, Pluto was discovered in 1930, and nothing qualifying as a planet has been discovered since; in fact it is unlikely (but possible) that any more planets could be discovered. Eris, seems to fit in the "dwarf planet" category, even though it is larger and more massive than Pluto. And it is not visible to the naked eye, which is what the term planet really means. We've searched our local neighborhood pretty thoroughly, though not completely. The word "planet" means wanderer, i.e. objects that move against the background stars. The chances of us discovering any such objects since the late 1800's is vanishingly small. Wayne <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

3488 · Jul 5, 2007

I suppose the closest after Pluto is KBO Eris. But see MeteorWayne's post above for real explanation. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

kelvinzero · Jul 5, 2007

Hi beshinaman, I guess you are meaning Kupier Belt Objects and Dwarf Planets. Technically they are not planets, but that mainly because astronomers had to draw a line somewhere between jupiter and an orbiting speck of grit. Many of them are big enough to be spherical. Im not too familiar with the exact definition of either. As usual, the easiest source is wikipedia http://en.wikipedia.org/wiki/Kuiper_belt http://en.wikipedia.org/wiki/Dwarf_planet I also found this cool list of objects sorted by radius: http://en.wikipedia.org/wiki/List_of_solar_system_objects_by_radius.

beshinaman · Jul 6, 2007

thanks! <img src="/images/icons/laugh.gif" />

nimbus · Jul 6, 2007

Kelvin's last wikipedia link doesn't work for me, so here's another similar page, just in case. This one's off topic, but I guess someone might find it neat. <div class="Discussion_UserSignature"> </div>

spacecrusader · Sep 5, 2007

Why is Saturn so light?

fatal291 · Sep 5, 2007

because its made of gas

CalliArcale · Sep 5, 2007

Obligatory semantic nitpick: Saturn is not light, as weight is not something that can be measured in its free-floating situation. It is less massive than you might expect, however. <img src="/images/icons/wink.gif" /> A nice layperson's quick-reference guide to the planets is The Nine Planets (which kept its domain name even after Pluto got demoted). From their appendix of physical data, Saturn has a mass of 568,000,000,000,000,000,000,000,000 kg (or 5.68 x 10^26). This makes it the third most massive object in our solar system, after Jupiter and the Sun. But because it is so gaseous, it has an average density of only 0.69 g/cm3. (For comparison, 1.0 is the density of water. Earth, the densest single object, is 5.52 g/cm3. This is because it contains a lot of iron, and is large enough that its gravity compresses it to be a bit denser than it would otherwise be.) If you could put it in a sufficiently large tank of water, and it weren't in freefall, it would float. This makes it the least dense of all the major planets. That's not to say that it's so diffuse all the way across. It's core is predicted to be extremely dense, possibly dense enough to produce liquid metallic hydrogen (which requires compressing the hydrogen until the atoms are less than the Bohr radius apart -- really freakin' dense, in other words). But the outer layers are obviously not very dense at all. All of the gas giants are relatively "light". Jupiter is 1.33 g/cm3, Uranus is 1.32 g/cm3, and Neptune is 1.64 g/cm3. Saturn was long believed to be the least dense object in the solar system. But it was recently dethroned by a very surprising object: one of its satellites, the chaotic moon Hyperion. Hyperion has a strange, spongey appearance and despite being apparently made mostly of ice and a little rock, it has a density of only 0.56 g/cm3. (The physical properties appendix at Nine Planets stil <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

heyscottie · Sep 5, 2007

You can think of hyperion as something like volcanic rock, some of which can float, at least until their pores fill with water, causing them to sink like a ... well, like a rock.

alokmohan · Sep 5, 2007

It is latest guinnes book of world in solar record in solar system.

willpittenger · Sep 6, 2007

Since Calli mentioned Hyperion's appearance, I have attached the image of Hyperion from Wikipedia. Note: Uplink will not accomodate the full res image. It is too large. Sorry. Also, I want to add a slight note to the comment about Saturn floating in water. It would do so only if it was wrapped in a massless and volumeless container. Otherwise, the gas would simply move out of the way. Also, Saturn's own gravity would affect the water. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

spacecrusader · Sep 6, 2007

well if saturn is just made of gasses, then how are the gasses staying in a circular motion. shouldnt they just move into space?

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