Why are gas planets considered planets?

Question

Why don't they consider planets to be only those made of rock like Earth?

Brian, I didn't know that, so then if Earth were any further from teh Sun it too could very well be a giant gas???

Thanks Venus and everyone else, makes sense now.. :-]

Answer 1

the word planet comes from the greek word for "wanderer" and this is because when ancient greek astronomers watched the stars move across the sky, they saw a few stars that didn't move along with all the others and moved backwards and forwards against the backdrop of all the other stars. These were the planets and this weird motion was caused because they revolve around the Sun and are not fixed with respect to the stars in the sky. So in part, they are considered planets because of ancient history.

In general, planets are objects that are not stars of a certain size that formed out of a planetary disk around our star. The gas giants, though very different from the inner planets, still fall into this category. Pluto is perhaps the weird planet and there is currently debate as to whether or not it should be considered a planet at all since there are many things about it that aren't very planetary. All of the other planets orbit in a plane and it appears Pluto is a part of a sort of second asteroid belt of objects called Kuiper Objects.

As someone mentioned earlier, the gas giants are thought to perhaps have solid cores like earth. But because they were further from the sun and the gases around them were cooler when they were forming, the gas giants were able to gravitationally attract and hold on to a lot more gas than the inner planets. If you were to move earth out beyond the asteroid belt now, it wouldn't become a gas giant because there is no longer a gaseous planetary disk for it to attract gas from. But if you moved it out there when the planets were still forming, then yes, it could have been a gas giant.

Answer 2

Let's just put it this way - the gas giants are made up of the same stuff that the earth is. This interstellar dust came together to form planets, both solid and gas. Each of these bodies still have a core of highly dense material (some think it to be rock or liquid metal) that holds the body together. In fact, the "gas" giants are not really gas at all, since throughout most of the volume of these planets, there is no distinction between liquids and gases, since all the components (other than solid materials in the core) are above the critical point, so that the transition between gas and liquid is smooth.

Anyway, the smaller mass of the planets near the sun suggests that the sun actually pulled most of the debris into itself or expelled it to futher distances. Thus, small, dense balls were created, their energies low enough to create solids. But further from the sun, more material remained. Those planets still had a solid, dense, core, but had too much material to make a solid form (too much energy still remains; though planets like Neptune and Uranus are thought to have ice, nonetheless). In all other ways, they behave just as the other planets do, thus their classification as planets.

Answer 3

I think the answer deals with historical convention. People began calling things "planets" long before they knew there were such differences as "gas giants" and "rocky" planets. Evidence for this viewpoint can be found in the fact that Pluto is not considered a true planet by most astronomers, yet popular opinion holds that it is.

Answer 4

Even though the Gas giants are very big and have their own miniature planetary system but they do not produce or generate energy through fusion and the circle around the star as other smaller Rockey planets do.Therefore they can not be called stars and as such they all are called planets.Now a days a new name is designated to planets like Jupiter- "Brown Dwarf".These are also called as failed stars.

Answer 5

There are astronomers who want to reclassify planets. They would call Mercury, Venus Earth and Mars Terrans, Jupiter, Saturn, Uranus and Neptune Gas Giants and pluto would be a Kupier Belt object. They want to abolish the word "Planet" altogether.

Answer 6

For some unknown reasons astronemers call the objects that are in circular or elliptical motion as planets. Smaller ones they call derbies. Other objects including some commets also orbit around our sun with precision orbit. So it is only our definition nothing else.

Answer 7

they're gaseous plumes with sizes that eclipse earth - they possess gravitational pull - if they were any closer to the sun, their gaseous exteriors would begin to dissolve and minerals at their cores would harden and they could become a rocky planet

Answer 8

Actually, Pluto's moon isn't bigger than Pluto. Pluto is 2274 km and the moon, Charon is only 1172 km.

Answer 9

why is pluto a planet there are astroids bigger its own moon is bigger the exact definition iof a planet is still under discussion

Answer 10

Because they are not massive enough to have become suns.