Question about planets what I don't understand..?

Question

Earth is a planet and It has a surface, right? So does Mars!

Then why is Jupiter a planet when it doesn't have a surface as it's all gas?

Then they say that Pluto isn't a planet anymore - even though it has a surface and goes around the sun like all the others.

Can anyone explain this to me? And there are other planets with no surface!

What is the qualifications you need to become a planet?

Answer 1

This question is highly debatable. It all comes down to how you want to categorize celestial objects. Other gas planets: saturn, uranus, neptune. These planets, Jupiter especially, can be thought of as baby suns. They are composed of gas, like the sun, but lack the gravity to get those chemical reactions going. Without the chemical reaction, they cannot shine like the sun.

Pluto is too small to be a planet. It even has a moon, a moon that is nearly the same size as Pluto. The moon (Charon) doesn't really revolve around Pluto. They kind of co-revolve around one another. The problem with Pluto arose when several objects of comparable size to Pluto were found further out than Pluto from the sun. Some were even bigger than Pluto. Either you had to say Pluto wasn't a planet, or you would have to add all these other objects to the list of planets. And chances are, more are going to be discovered. I think they did the right thing by demoting pluto. Otherwise, the list of planets was going to be out of control.

Obviously, having a rocky surface is not a requirement to be a planet as planets have come to be defined. It most likely has to do with size, it must revolve around a star, and I'm sure they (astronomers) have thrown in a few more requirements just to be safe.

However, astronomers have discovered a pair of objects that are revolving around one another that are bigger than Jupiter, but too small to be a star. They are not revolving around a star, they may be too big to be planets, but too small to be a star. So, again, we run into a problem with categorizing celestial objects. As more discoveries are made, more definitions will have to be redefined.

Hope this helps.

Answer 2

Even though the gas giants do not have a hard crust like the earth, doesn't mean they don't have a surface. The surface doesn't have to be solid. A planet does not need to contain any solid material.

As far as Pluto being a planet or not really doesn't matter. The whole thing is arbitrary. They are trying to define what is a planet by a set of rules, and the newly adopted set removed Pluto from the planet class.

In reality it doesn't matter what you call Pluto. Regardless of what you call it, or what title you give it, it is what it is. These Astronomers are really just wasting their time arguing a mute point.

Answer 3

In 2006, the International Astronomical Union created an official definition of a planet in the solar system, something that had never technically existed before. This definition states that a planet is a body that orbits the Sun, has sufficient mass to assume a spheroidal shape by hydrostatic equilibrium (that is, gravity makes it round), and has cleared the neighborhood of its orbit.

Jupiter is a planet because it is round and it has forced other objects away from its orbit. Main belt asteroids, for example, get bounced away if they approach resonance with Jupiter. Pluto is not a planet because its orbit is regulated by Neptune. Whether or not the object has a surface is not a factor.

Answer 4

Jupiter actually does have a surface, just not a solid rocky surface like earth , mercury , mars etc.It has a thick layer of frozen gases and which finally leads to a liquid or solid hydrogen mantle. Beneath that Jupiter probably has a core of rocky material with a mass 10–15 times that of the earth.
A planet is defined as nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, around which it revolves.

Answer 5

Jupiter and Saturn are planets, as well as being gas giants.

The term "planet" has gone through several changes over the years. You can check the link below to see.

Basically, a planet needs to meet three criteria:

1. Is in orbit around the Sun
2. Has reached hydrostatic equilibrium (enough mass to assume a round shape)
3. Has cleared its orbit of similar sized objects.

Pluto doesn't meet the third criteria because it shares its orbit with Charon, another body which satisfies the first two criteria, but not the third. Hence, both are now classed as "dwarf" planets, and pending a "binary dwarf planet" system.

But in the end, a planet is any body in orbit around the sun which satisfies the above three criteria. A planet does not HAVE to be solid, just have enough mass where its gravity and angular momentum allow it to have a spherical shape, and this includes gas giants. If, for example Jupiter were to acheive enough mass to ignite nuclear fusion in its core, it would become a second sun, and our system would only have seven planets in a binary star system, although for how long with that kind of gravity and radiation, no one knows! ;)

Answer 6

Venus does have a surface. It just can not be seen.

The pressure of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans). It is composed mostly of carbon dioxide. There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite be Venus in ultra-violet light There are strong (350 kph) winds at the cloud tops but winds at the surface are very slow, no more than a few kilometers per hour.

Venus probably once had large amounts of water like Earth but it all boiled away. Venus is now quite dry. Earth would have suffered the same fate had it been just a little closer to the Sun. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.

The International Astronomical Union (IAU) Working Group on Extrasolar Planets made a position statement on the definition of a planet that incorporated a working definition:

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

This definition has been widely used by astronomers when publishing discoveries in journals since this time, although it remains a temporary, working definition until a more permanent one is formally adopted. It also did not address the controversy over the lower mass limit.

Answer 7

The International Astronomical Union is the organization that can officially decide what qualifies a body as a planet. Below is their official decision --

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.
(...http://www.iau.org/iau0603.414.0.html...)

Pluto doesn't qualify because of item 'c,' but the gas giant planets like Jupiter, etc., do.

Answer 8

Jupiter, Saturn, Uranus and Neptune don't have easily defined surfaces. As one goes deeper in the planet's atmosphere, pressure and density would increase until the gases began to act more like liquids and slushes. It would be a surface but you couldn't "land" on it (other obvious problems aside). The rocky planets just have more recognizable types of surfaces.

The Pluto ejection is largely a political decision. (It went back and forth at the conference and could again.) Essentially, they didn't like Pluto's small size and odd orbit. But their decision hasn't changed it's size, shape, orbit or position. It's still out there.

Answer 9

To be a planet, you need sufficient mass to shape yourself into a sphere under your own gravity and to clear your orbit of asteriods and such. You don't need a surface, technically. Just because Earth has something, doesn't mean every planet has to. And Jupiter is solid at the surface - it's metallic hydrogen way down under all that deep atmosphere.

Answer 10

The International Astronomical Union defines "planet" as a celestial body that, within the Solar System,[1]
(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;

Jupiter isnt just a big ball of gas. It has an atmosphere, a core, and the gas that it does have is really thick as you go deeeper down.

And for pluto. Pluto is now a dwarf planet and the meaning for a dwarf planet follows;

The International Astronomical Union (IAU), the official scientific body for astronomical nomenclature, defines a "dwarf planet" as a celestial body that, within the Solar System,[1]
(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 (near-spherical) shape;
(c) has not cleared the neighbourhood around its orbit; and
(d) is not a satellite
The term "dwarf planet" was adopted in 2006 as part of a three-way classification of bodies orbiting the Sun. Objects that are large enough to have cleared the neighbourhood of their orbit are defined as "planets", while those which are too small to be in hydrostatic equilibrium are defined as "small solar system bodies". As defined, the term "dwarf planet" does not apply to other planetary systems.[2]
Three dwarf planets are currently recognised: Ceres, Pluto and Eris. Other bodies might be added to the list once it has been determined whether criterion (b) is fulfilled