What is the planet after Neptune?

Answer 1

Pluto used to be the ninth planet and the one farthest from the sun, but it was declassified as a planet due to lack of mass and gravity in August 2006 and so Neptune is now the planet farthest from the solar system.

Pluto was declassified as a planet because it lacked the new requirements for the classification of a planet introduced in 2006. Neptune, being four times the size of the Earth, is unlikely to be declassified any time soon.

Although there are no more planets after Neptune (unless you still count Pluto), there's still a whole bunch of stuff. There's a huge doughnut-shaped disc of comets, asteroids and other icy bodies stretching from just beyond Neptune's orbit out to about twice as far from the Sun, known as the Kuiper Belt (it was predicted in the 1950s by the Dutch-born American astronomer Gerard Kuiper, but it wasn't discovered until the 1990s.) There are thought to be over 70,000 Kuiper Belt objects (or KBOs) over 100km (60 miles) in diameter, and probably billions of smaller ones, but do far we've only discovered the thousand or so biggest/brightest/easiest to observe.

Although most of the thousands and thousands of known objects in the Kuiper Belt are tiny frozen comets or asteroids, a few dozen of the very biggest are massive enough to behave like small planets, with enough gravity to pull them into a rounded sphere, internal layers, atmospheres, surface features, etc. These KBOs are known as dwarf planets or plutoids and Pluto is now considered to be one of the largest plutoids/KBOs rather than a true planet. Three other plutoids are confirmed: Haumea, Makemake and Eris (which is more massive than Pluto.) A few dozen other KBOs may turn out to be plutoids too, once we've observed them more carefully and confirmed they are round like planets.

All the KBOs, whether they're comet nuclei, asteroids or plutoids/dwarf planets, are very, very cold. Most of them contain water ice, but it's so cold that that water is frozen as hard as steel, and it's so cold that other substances which are gases on Earth like methane, ammonia, carbon dioxide, carbon monoxide, and even nitrogen and oxygen (air itself!) are frozen solid. From the surface of a KBO, the Sun would be little more than a bright star.

What's beyond the Kuiper Belt? Astronomers don't know, but our observations of comets suggest many of them come from a huge, spherical shell of comets called the Oort Cloud. The distance from the Earth to the Sun is called an astronomical unit, or AU, and it's about 150 million km/93 million miles.

On this scale:

• Earth is 1AU from the Sun
• Neptune is 30AU from the Sun
• The Kuiper Belt stretches from 30-50AU from the Sun
• Some KBOs have orbits that take them out to 100AU from the Sun
• The Oort Cloud would be 30,000-100,000AU from the Sun!

The Oort Cloud seems to exist, based on our calculations, but it's so far away and the objects are so small and faint that nobody's ever seen it. Perhaps they never will. But the Oort Cloud, if it exists, extends out about a quarter of the way to the nearest star, marking the edge of the Solar System.

Answer 2

were not sure yet, it was Pluto until they dissmissed it as a planet in 2006, as far as we know neptune is the last planet

Pluto. But Neptune is weirder.

Answer 3

Pluto is no longer classified as a planet as there are other bodies out in the Kuiper belt of similar shape and characteristics. It is now called a "dwarf planet".

Answer 4

The old planet ploto