This is a schematic showing how atmospheres form.
Click on image for full size
The Origin of an Atmosphere
There are four ideas for the origin of a planetary atmosphere. Those four ideas are: 1. that the planet-elements of which a planet was made released the atmosphere, 2. that the atmosphere was drawn to the planet from the gaseous cloud out of which everything came, 3. that comets hit the planet and brought molecules of air with them, 4. that volcanoes erupted and made an atmosphere from gases inside the planet.
The one that applies to Neptune is hypothesis #2, in which the original material, which Neptune drew out of the primitive nebula stayed, and forms the atmosphere today.
You might also be interested in:
Scientists think that the solar system formed out of a spinning cloud of hydrogen and helium gas. Because the cloud was spinning, it flattened into a frisbee shape, just like a ball of pizza dough becomes...more
The giant planets have definitely changed since their formation. But how much remains to be seen. Most of the original air of the giant planets remains in place. (The earth-like planets lost most of their...more
This image shows the new Great Dark Spot of Neptune, which was discovered using the Hubble Space Telescope. The image shown here, shows a "hole" in the clouds of Neptune in pink, in the northern hemisphere,...more
This image shows some clouds known as "cirrus" clouds, extending for many kilometers across the face of Neptune. These clouds are very high up, for they can be seen to cast shadows on the lower clouds,...more
This image of Neptune uses false colors to show where the smog is. The smog of Neptune can be seen in red along the edge of the image. These hazes of smog are found at very high altitudes, over the clouds...more
Like Jupiter and all the giant planets, Neptune's appearance shows a striped pattern of clouds. Other cloud shapes seen over time include a small dark spot, the "scooter" and the Great Dark Spot. The Great...more
If you had a quiz question in school that asked what year Neptune was discovered, you'd probably choose 1846. But Neptune wasn't discovered the way all the other planets in our solar system were. Astronomers...more
The picture shows places on Jupiter which are hot. Jupiter is a very warm body in space, as shown in the picture, and this warmth is associated with the energy of Jupiter. Neptune has also been found to...more