Why are the outer planets so much more gaseous than the inner terrestrial ones?

Answer 1

Many of the original theories of the formation of our solar system postulated that a proto-planetary disk of dust and gas that surrounded our sun some 4.5 billion years ago, and this disk rotated around the sun, just as we orbit the same star now. The most popular theory put forth the idea that within this spinning disk, the heavier, metallic elements (silicates and so forth) would fall in towards the star, and the lighter elements, mainly Hydrogen and Helium, would be spun out towards the outer edge of this disk. Thus, the inners planets grew to become small, rocky bodies, while the planets farther out were able to feed off of, and grow exponentially from, this abundance of lighter elements farther out from the sun's orbit.

In recent years, it must be noted, this general concept of planetary formation has come into question, mainly due to the large volume of planetary systems discovered thus far that do not fit with this model of formation. Many Extrasolar or Exoplanets, those being planets found outside of our solar system, that have been discovered in the last 20 years have been found to be large, gas giant-type planets, very similar in makeup to our own Jupiter. The main difference, however, is that a significant portion of these planets have been found to orbit very close to their host star (usually at a fraction of the distance from which we orbit the sun), and can exhibit extremely small orbital periods, often on the order of less than a week. This type of Exoplanet is known as a Hot Jupiter.

The biggest problem with these findings as it pertains to our original theories is that having such large bodies orbiting in so close to a host star precludes the star from being able to support smaller, more terrestrial planets such as our own. An idea currently put forth, called the Planetary Migration Theory -PMT-, is thus far best able to explain this difference in what we believed we'd fine, and what we have actually observed. This theory puts forth the idea that these large gas giant planets did indeed form in a farther orbit from their star than we now observe them, and for reasons we are yet unable to fully explain, migrate in towards their star, eventually settling into a fairly stable orbit very close in.

If this theory proves to be true, than it does not necessarily invalidate our original theories on what causes the make-up of our own solar system. If we find that we have a hard time proving the PMT, this forces us to continue to re-think our ideas on planetary formation and orbital position. If we learn anything from each new discovery of new planets and stars, it is that our solar system is hardly a standard model or template for galactic planetary system formation, but rather, one more snowflake in the storm...Unique and awe-inspiring.

Answer 2

The early solar system comprised of a disk of gas which was hot near the newly formed protosun (about 2000 degrees Kelvin) and cooler at further distances. Rocky substances condensed at the higher (inner) temperatures, while icy substances condense at much lower temperatures further out (about 200 degrees Kelvin) and hydrogen and helium at lower temperatures still - just above absolute zero. So in the early stages, the inner solar system was rocky, while the planets forming in the outer regions of the sola rsystem were made from (and accumulated) ice and gas. Things have pretty much remained this way since.

Answer 3

Because there was probably more gas than rock in space when our solar system was made (so inner planets are rocky and small) and rocks are probably more easily captured by gravity (so rocky planets are closer to the sun than gas planets). Also, it was probably rocks that began to grab the gasses, which may be why the core of gas planets are rock (either that or because when gas is compressed, it becomes rock), and rocky planets probably have a liquid core because the friction of the rocks being pulled together caused so much heat, that the rock in the middle melted, and the rock continues to keep it hot because it would take a LONG time to get cold temperatures to move through the crust. Besides, because the rocky planets are closer to the sun than gas planets, then besides at night time, the planet's surface would be really hot!

Answer 4

The cloud of gas and dust that formed the solar system was mostly hydrogen and helium. These gasses were driven out of the inner solar system by heat and solar wind of the young sun, leaving behind mostly rocky material. The outer solar system was far enough from the sun to escape this fate.

Answer 5

The outer planets are rocky inside also, their rocky part is larger than the inner planets and can attract lighter gaseous elements like helium, hydrogen, etc. The earth's gravity is not strong enough to capture lighter gasses as with all the other inner planets. Jupiter is almost considered a brown dwarf star; it captures everything because its gravity is so immense.

Answer 6

The outer planets are more gaseous because they formed beyond the frost line, where it was cold enough for volatile gases like hydrogen and helium to condense into solid ice grains. As a result, the outer planets were able to accrete these gas-rich ices early in their formation, leading to their larger sizes and gaseous compositions compared to the inner terrestrial planets, which formed closer to the sun where volatile gases existed in gaseous form.

Answer 7

They are made of gas.

Answer 8

because they are colder and farther