• Grades: 6–8, 9–12

The following questions were answered by astronomer Dr. Cathy Imhoff of the Space Telescope Science Institute.

What is Neptune made of?
Neptune, like the other gas giant planets, is made of very cold gases of hydrogen, helium, and methane. It has wispy white clouds, which we think are made of methane crystals. (On Earth, the wispy white cirrus clouds are made of ice crystals.) It is almost as cold as Pluto: –330° Fahrenheit.

What is the surface of Neptune like?
Very cold, about –350° Fahrenheit! The surface is not solid — it consists of clouds. The sun is very far away — it would look rather dim from Neptune. Brrrrrrrrr!

Does Neptune have rings around it? What are they like?
Yes. The Voyager spacecraft took some pictures of them. They are not big rings like Saturn's. They are thin and some may not be complete circles. Now we know that four planets have rings — Jupiter, Saturn, Uranus, and Neptune!

Does Neptune have more than two moons?
Yes. Voyager found six new moons. Two were known before — Triton and Nereid — so we know of eight so far. The six new moons are all smaller and closer to the planet, so they would be really hard to see from Earth. The smallest is only 30 miles across.

Are Neptune's two dark spots the same as Jupiter's red spot?
They are similar. Neptune's dark spots and Jupiter's red spot are all big storms, with winds blowing at a thousand miles per hour. They also spin, like a hurricane.

Is Pluto one of Neptune's escaped moons rather than an actual planet?
Recently some astronomers have shown that this is probably not so. They calculated where each of the planets was in their orbits in the past. It turns out that their orbits are such that they never were close to each other. So it now seems unlikely that Pluto was ever a moon of Neptune.

When Neptune and Pluto were orbiting did they change places?
No, they didn't change places. Their paths crossed. This is like two kids running, one in a circle, and the other in an oval. Pluto is orbiting in an oval and for a while has come closer to the sun than Neptune (which is going in a circle). But most of the time Pluto is further away.

Why is Neptune further from the sun than Pluto?
Most of the planets go around the sun in nice, orderly, nearly circular orbits. But not Pluto. It has an oval-shaped orbit, known as an ellipse. We aren't sure why Pluto is different. But when it comes closest to the sun, as it is now, it comes a little closer than Neptune. But most of the time it is further from the sun than Neptune or any other known planet.

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