Question: Hi steven I was think the other night whilst i was gazing at the stars and i thought of a question and it is how many undiscovered planets are there and do you believe in extra terrestrial creatures.

  1. This is a very interesting question. Because the planets are undiscovered, we don’t know how many there are going to be, but we can make some educated guesses.

    Firstly, the estimate of stars in the Milky Way galaxy, that is our galaxy, is between 100 billion and 400 billion stars. This is a huge number so here is a slightly easier way to think of it.
    100 million seconds is equal to about 110 days.
    But 100 billion seconds is about 3000 years. So it is a huge number, and those are just the stars in our galaxy. There are more than a 100 billion galaxies, each with hundreds of billions of stars. The numbers are just so big.
    So it is likely that there are more planets in the universe than there are grains of sand on all the beaches on Earth.

    This leads to your second question. Given that there are so many planets in the universe, I think it is very likely that there is extra-terrestrial life somewhere in our galaxy. Whether they are intelligent or have technology or if they could ever travel here are all very interesting questions also. It may be that the galaxy has billions of planets with life, but because it is such a big place, we may never meet.

    Here are some good links for you to read more about other planets
    The Kepler mission is looking for other planets and has found more than a 1000 candidate planets and it has only been going for about a year now.
    Also here is a video interview I did with Dr Lineweaver who is an astrobiologist and thinks about these things all the time.


  2. The Kepler mission, a telescope in Earth orbit, is finding many planets. Thousands in fact. It appears that about 5% of stars have planets the size of Earth and about 15 – 20% of stars have multiple planets. So, considering the billions of stars in each galaxy and the billions of galaxies, that adds up to a lot of planets. Kepler has found a few Earth-sized planets orbiting Sun-like stars. Obviously that is interesting because these are systems that potentially look a bit like our planet. However, it gets most interesting when we find planets in what is called the habitable zone. The habitable zone describes planetary orbits that are not too close (too hot) and not too far (too cold) from the star, where water can exist in liquid form. There are not too many planets known in habitable zones. One of them, GL 581, is the subject of a study that I’m doing with one of my PhD students. We have used radio telescopes to search for transmissions from this particular planet. We haven’t been able to find any signals – so not ETs yet? Begs the question of who do you tell first if you ever found something? Ever see the film Contact? But yes, I’d be shocked if “advanced” life forms did not exist somewhere else in the Universe. And I hope it is like Futurama.


  3. Hi Jamesy, I thought I would jump in on part of the extra terrestrial creatures part of this question.
    Around 1960 a scientist called Francis Drake came up with an equation that might predict the number of extra terrestrial civilisations that might exist. He wasn’t thinking about bacteria and such on other planets but extra terrestrials capable of communicating with us. His equation is called the Drake Equation, which lacks creativity as a label but is really interesting as a thought experiment.

    His equation looks like this: N = R* x fp x ne x fl x fi x fc x L
    where N = the number of civilisations in our galaxy with which communication might be possible
    R* = the average rate of star formation per year in our galaxy
    fp = the fraction of those stars that have planets
    ne = the average number of planets that can potentially support life per star that has planets
    fl = the fraction of the above that actually go on to develop life at some point
    fi = the fraction of the above that actually go on to develop intelligent life
    fc = the fraction of civilisations that develop a technology that releases detectable signs of their existence into space
    L = the length of time for which such civilisations release detectable signals into space

    Currently N = a number between 0 and nearly 200 million which is a very wide set of possible answers but thats because we simply do not know what some of the bits in the equation should be!

    As a biologist i would say that there is probably life on other planets but it may not resemble the characteristics of life as we understand it so unless its obvious we might never notice it.

    Great question!


  4. Hi jamesy,
    This is a very interesting question. There are probably so many undiscovered planets out there that it is very likely that some of them may have conditions that are favourable for supporting life. What type of life that is is another question… they could resemble bacteria or perhaps could be more advanced creatures. I guess that would depend on the type of conditions as well. Great answers by Dustin, Steven and James. This stuff is completely unrelated to my work so it is definitely good for me to be able to learn about things like this in IAS! πŸ™‚
    And it would be cool if there were civilisations like in Futurama, or Stargate!



  1. Thank You πŸ™‚


  2. I have seen the contact along with a few people in my class