• Question: How big is the percentage of planets that have already been discovered?

    Asked by nielsdebruin to Colm, Eoin, Joseph, Lauren, Stephen on 13 Nov 2013.
    • Photo: colm bracken

      colm bracken answered on 13 Nov 2013:

      Hi nielsdebruin,
      Great question. Up until 1995 we only knew of the planets in our own solar system. However since the discovery of the first exoplanet (planet around another star) in 1995 astronomers have discovered over 800 exoplanets.
      But in terms of what percentage this is of all the planets out there, well, almost zero %. There are over 100 Billion stars in our galaxy and we are certain now that most of them have planets around them. So even if each star only had one planet then the percentage of the planets that we have discovered in this galaxy is about (800/100,000,000,000)x100/1 = 0.0000008%. However there are over 100 billion other galaxies in the known universe, so the real percentage is about 0.000000000000000008%. As I said, almost zero. But it is still hundreds of new planets! 🙂

    • Photo: Stephen Scully

      Stephen Scully answered on 14 Nov 2013:

      Not sure but every time we point a telescope at the sky to have a look for some we find lots more, so I think it is much less than 1%.

    • Photo: Eoin O Colgain

      Eoin O Colgain answered on 16 Nov 2013:

      A tiny percentage.

      Each star can be expected to have a few exoplanets and there are 100 billion x 100 billion of them. There is no reason to believe that our solar system is unique in having planets, since star formation here and elsewhere in the universe should be the same.

    • Photo: Joseph Roche

      Joseph Roche answered on 16 Nov 2013:

      We have found lots of planets. But we think its only a tiny percentage of all the planets that are out there. There are probably as many planets as stars. Billions and billions.

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