Neptune is one of the giants of the solar system. But it’s so far away that it’s tough to study. We know little about its interior. And much of what scientists think they know comes from lab experiments and computer models.

Neptune is the Sun’s most remote major planet. So although it’s almost four times Earth’s diameter, it’s a tiny target for telescopes. And only one spacecraft has ever visited the planet – Voyager 2, in 1989.

From those observations, along with those from telescopes on the ground and in space, scientists have developed a model of how Neptune is put together. It probably has a dense, rocky core, surrounded by an “ocean” of super-heated water, ammonia, and methane. The pressure squeezes this layer so tightly that the compounds act like ice.

Around that is a layer of hydrogen, which is topped by a methane-rich atmosphere. The methane absorbs red light, giving the planet a blue-green color.

It’ll be decades before another mission can approach Neptune. Until then, we’ll have to rely on a lot more calculations to understand this remote giant.

Neptune is at its best right now. It’s in view all night and it’s brightest for the year. Even so, you need a telescope to spot it. But you can easily spot its location. As night falls, look for Saturn, which looks like a bright star, low in the east. Neptune is to the left of Saturn, by a bit more than a finger held at arm’s length.

Script by Damond Benningfield