How many planets are there?I herd pluto ceres huya nibiru sedna are planets too?

Answer 1

Pluto was "demoted" to "dwarf planet" status last year when the IAU (International Astronomical Union) adopted a formal definition of "planet" that included the requirement that a planet clear its orbit of other objects. Pluto is the largest of many "Plutinos" that orbit in a 3:2 resonance with Neptune. Huya is another such object. This leaves the planet count at 8.

Sedna is a Kuiper Belt object, orbiting beyond Neptune, and may also qualify as a dwarf planet.

Ceres was initially classified as a planet when it was discovered in 1801, but was later demoted when it became clear that it was just one of many objects in the asteroid belt. The draft proposal before the IAU last year would have considered Ceres a planet too, based on the fact that it orbits the sun and is roughly spherical, but Ceres lost out when the orbit-clearing requirement was added, and it is now considered a dwarf planet like Pluto.

Nibiru is an imaginary planet popularized in the pseudo-scientific writings of Zecharia Sitchin and others.

Answer 2

Go see wikipedia for a history and some modern definitions (see link below).

In 1801. when Ceres was discovered, it was called a planet. Then they found a second of the same nature and on similar orbit. Then a third, etc. After a while, when they saw that it was a collection of pieces (it was thought, at one time, that they were the pieces of a planet that blew up), they demoted them to "minor planets" (also called asteroids).

Same thing happened to Pluto. When it was discovered, it was called a planet. It was thought that it was bigger than the Earth. Now we know that it is much smaller and we are finding all kinds of objects that are similar and on similar orbits. So, again, a planet is "demoted" but a new sub-class is created from it (dwarf planets). These particular ones are TNO (Trans Neptunian Objects).

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Originally (when it was thought that the Earth was the centre of the universe), the Sun and the Moon were planets (but not the Earth, as it was not moving). The word planets came from a Greek expression -- aster planetes --meaning "wandering star" as these "stars" appeared to move among the fixed stars.

When Copernicus and Kepler showed that the Sun was a the centre of our system, then the Sun was no longer a planet, the Earth became a planet and the Moon lost its status as planet and became a satellite, just like the 4 brand new satellites of Jupiter that had just been discovered (when they were first seen by Galileo in 1610, he called them planets, even though he knew they were moving around Jupiter).

Galileo begins his description with:
"“Superest ut, quod maximum in praesenti negotio existimandum videtur, quatuor planetas ..."

It is only later, when, again, similar objects around other planets were discovered, that the moons of Jupiter lost their status of "planets" and became satellites.

So, we are now up to 4 times in our history when some "planets" have lost their status.

Answer 3

There are currently only 8 planets by definition. Pluto was demoted last year.

Answer 4

The current view is 8 major planets.

Answer 5

Officially there are now just 8 planets in our solar system. Pluto has been demoted to 'sub-planet.'

Answer 6

8 pluto is not a planet anymore.. there are on 8 PLANETS and lots of stars

Answer 7

There are more planets than we can count. When you look up at the stars at night every dot is a sun with it's own planets orbiting around it.

Answer 8

i agree with everyone else, there are 8 planets. Pluto was removed because it belongs to the cypher belt (i think)

Answer 9

8 the rest are minor planets, poor pluto, sniff i loved that dog and now his a minor.