• Question: How many planets are there in total of the whole space?

    Asked by to Dre, Charli, Heather, Oliver, Becky on 19 Jun 2014. This question was also asked by .
    • Photo: Charlotte Flavell

      Charlotte Flavell answered on 19 Jun 2014:

      Hi raiden9080,

      This is a tough question! I think the honest answer is that we don’t know because we haven’t counted them.

      There are 8 planets in our solar system (when I was at school there used to be 9 but poor Pluto got downgraded), but these are just the ones that orbit around our Sun. The sun is a star and there are an estimated 2-4 hundred BILLION stars in our galaxy, the Milky Way, each of which could have planets orbiting it. If you were to multiply the number of stars by the number of planets you’d get 2-3 TRILLION planets. That’s a lot!

      That’s just for our galaxy. Some people say there are 100-200 BILLION galaxies, each with their own stars and planets….

      So I think it’s fairly safe to say that the answer is A LOT!

    • Photo: Oliver George

      Oliver George answered on 19 Jun 2014:

      Charlotte beat me to this question so I’m going to go a little off topic and relate her answer to aliens. 😉

      Based on how many planets we think there are in the universe some very smart people put together an equation to suggest how many planets might have intelligent life (ALIENS!!!) on them. This equation is called the Drake equation (https://en.wikipedia.org/wiki/Drake_equation). Using the available data they deduced that there could be as many as 100,000,000 alien civilisations just in the Milky Way!

      There’s something else called the Fermi paradox (https://en.wikipedia.org/wiki/Fermi_paradox) which relates to this too. Enrico Fermi was a physicist way back in the 1950s who spent a lot of time thinking about how likely we were to find life. Based on similar ideas to the Drake equation he thought that we should have met aliens by now. Maybe they walk among us. 😉

      I know I didn’t really answer your question but I hope you find these things interesting.

    • Photo: Rebecca Williams

      Rebecca Williams answered on 19 Jun 2014:

      Hi Raiden9080,
      I think Charli has answered your question really well.

      I was at a talk recently given by a famous physicist (not Brian Cox, but the american version!) who said that there were 100 billion galaxies in our universe. Each galaxy has 100 billion stars in it. And that the universe is 100 billion years old in dog years!! I think that physicists really like the number 100 billion and aren’t very good at counting! 😉

    • Photo: Andrea Cristini

      Andrea Cristini answered on 20 Jun 2014:

      I don’t think we will ever be able to count how many planets there are. Like Charli says though, it’s a LOT!

      What’s interesting though is even if telescopes could see to the edge of the universe, what they would see might not actually be there.

      This is because everything we see with our eyes is just the light that is reflected (or is not absorbed) by that object, so when we see a planet in a telescope it is just the light from stars reflecting off that planet into the telescope.

      Light takes time to travel (although it travels REALLY fast – the fastest anything can possibly travel which is the speed of light), so by the time light reaches us on earth from a planet really far away, that planet might not be there anymore, say if it was destroyed by a dying star or swallowed up in a black hole.

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