Question: how many planets do u think there are in the unverse?

Douglas Blane answered on 23 Jun 2010:

For most of past history people thought there were only five planets – Mercury, Venus, Mars, Jupiter and Saturn – because they’re the ones you can see in the night sky without a telescope.

They didn’t know what a planet was, but they knew they were there. Then scientists worked out what planets were and how they should be moving.

Their calculations showed there must be other planets whose gravity was affecting the ones we could see. So guys with telescopes started looking where guys with pencils and paper said they should.

They found Uranus, Neptune and Pluto.

Then again for a while the nine were the only ones we knew about.

But scientists had always wondered if other stars might have planets. Was our solar system the result of some freak accident? Had another star passed close to the sun and drawn out a big cigar-shaped piece from it, that became the planets?

Or did planets form around most stars as they were being born?

It was very hard to know because stars are very bright and so far away they are just pinpoints in even the biggest telescopes. Any planets they have are much smaller and not at all bright, so very hard to spot.

But astronomers developed some clever ways of working out if planets were there even if they couldn’t see them.

Then in 1992 astronomers found the first exoplanet – the word they use for a planet round another star.

Since then they’ve found 461 others and are finding more all the time. It’s only a matter of time before they start finding Earth-like planets.

So how many planets in the universe?

Well astronomers estimate there are between 10000000000000000000000 and 1000000000000000000000000 stars in the universe.

And it’s starting to look like just about every star has several planets.

So there seem to be somewhere around 10000000000000000000000000 planets in the universe.

Take a look here to find out more about exoplanets: http://www.planetary.org/exoplanets/