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Exoplanets: How Many Exoplanets have been found? What is the Kepler Mission? Is there Life Outside the Solar System?

Updated on July 18, 2012

An exoplanet, or extra-solar planet, is a planet outside our solar system. Astronomers are interested in exoplanets because of the possibility that such planets could support extra-terrestrial life. It is also interesting to compare other solar systems to our own to see just how unique or commonplace our solar system is.

At the time of writing, 562 exoplanets have been discovered.

How Are Exoplanets Discovered?

The first exoplanets were identified by noticing anomalies in the orbits of binary stars. The gravitational pull exerted by an exoplanet causes the orbit of a binary star to be disrupted. Astronomers can make detailed measurements of the star's radial velocity (its velocity towards or away from Earth) by looking for a Doppler shift in the spectrum of the light radiated by the star - if the spectrum is blue-shifted then the star is moving towards us, and it is red-shifted if the star is moving away. By looking for tiny anomalies in these radial velocity measurements, astronomers can deduce the presence of an exoplanet.

It is also possible to "see" a exoplanet as it passes in front of the star, by measuring a very slight decrease in how bright the star appears.

Kepler Mission

The Kepler telescope was launched into orbit around the Earth in 2009. Its purpose is to continuously monitor over 100,000 stars to look for variations in their brightness that could indicate an exoplanet passing in front of the star. It has already detected signs of over 1200 exoplanets, and that is by watching only a tiny fraction of the sky. Although some of these results may be false positives, it appears that there is a huge number of exoplanets out there.

Is there another one out there?
Is there another one out there?

Extra-Terrestial Life on Exoplanets

The discovery of so many exoplanets is exciting because of the possibility that some of them could support extra-terrestrial life.

Most of the early exoplanet discoveries turned out to be gas giant planets, similar to Jupiter and Saturn in our solar system. Our solar system appeared to be unusual in that the closest planets to our Sun are small, rocky planets rather than gas giants. However, there may be a selection bias at work: larger planets are easier to detect, so it makes sense that we would see more of these compared to Earth-like rocky planets.

Sixty-eight of the exoplanets detected by Kepler are Earth-sized. Could one of these have the correct atmosphere and planetary conditions to support life?


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    • alian346 profile image


      7 years ago from Edinburgh, Scotland

      It seems to me that from all the recent discoveries made in a short space of time and in a very small 'area of the sky' that stars with planets are the norm. If we do the maths then that adds up to an incredible number of planets in the Universe (very conservative estimate 10000000000000000000000) if we assume only one planet per star. Therefore the chances of other life forms existing are pretty high. Whether they are anything like us would be up for debate. It would depend on many variables. Life may not depend on water or any of the other things we need to survive. It may be based on an entirely different chemistry due to different conditions of temperature and pressure and chemical composition on other planets.

      Sorry, this is turning into a Hub!

      This is one of the most exciting, fascinating and mind-blowing subjects there is.

      Thank you for writing the Hub, topquark - a good job, well done.


    • topquark profile imageAUTHOR


      7 years ago from UK

      Hi puzzled. There are two things that make exoplanets much more difficult to see than stars. The most important factor is that stars emit light, whereas planets don't. The other reason is that exoplanets are much, much smaller than stars. It's theoretically possible that you could see a planet in silhouette as it passed in front of the star, but as the stars themselves are usually only tiny dots seen through a telescope, and the planet is many thousand times smaller, in practice it's generally not possible to make them out. That's why astronomers have to detect them by looking for the tiny wobbling motion they cause the star to make, due to their gravitational pull.

      Hope that helps :)

    • profile image


      7 years ago

      But what i don't understand is why can we see stars and not exoplanets?

      My teacher is asking me to find it out but i don't know the answer!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    • sparkster profile image

      Marc Hubs 

      7 years ago from United Kingdom

      With all these planets being discovered I believe it's only a matter of time before we discover life on one of them. Great hub.

    • topquark profile imageAUTHOR


      8 years ago from UK

      Thanks Spirit Whisperer. I plan to read more of your hubs too.

    • Spirit Whisperer profile image

      Xavier Nathan 

      8 years ago from Isle of Man

      This is the first of your hubs that I have read and I found it very interesting, I like your writing style and the way you make your knowledge accessible to everyone. I will definitely be a more frequent visitor and look forward to learning from you. Thank you.

    • topquark profile imageAUTHOR


      8 years ago from UK

      According to Andrei Finkelstein, we'll find extra-terrestrial life within 20 years, and yes it will look like us:

      I don't necessarily believe him, but it's interesting to throw an expert opinion into the debate.

    • Simone Smith profile image

      Simone Haruko Smith 

      8 years ago from San Francisco

      What a fascinating thing! I had never heard of exoplanets before. Now I'll have to do some more reading on them! Thanks so much for writing this informative introduction.

    • Slarty O'Brian profile image

      Ron Hooft 

      8 years ago from Ottawa

      Well I don't mean they necessarily look like us. Just that they would all have to have similar organs for similar purposes, as well as appendages, etc. I'm just wondering to what extent we would be similar by nature of the laws governing biological beings, and if there are such laws.

      I imagine that a world exactly like our would be rather rare. So I would expect to see something different.

      So wouldn't it be strange if they did look like us? What would that tell us about nature?

      Wouldn't it also be strange if there was no other life out there? I think it highly unlikely but since we have not found any yet it is not impossible. Or is it? We will have to wait and see.

    • BlissfulWriter profile image


      8 years ago

      Most likely life on other planets would not resemble us. The chance of them evolving the same way as we did are slim. Mostly likely, they will evolve differently and hence be quite different from us.

    • Slarty O'Brian profile image

      Ron Hooft 

      8 years ago from Ottawa

      What I am wondering about is whether we should expect life on other planets to resemble our own with the same kinds of structures like hearts and lungs etc, or if it is more likely that such life would be vastly different from our own?

    • topquark profile imageAUTHOR


      8 years ago from UK

      That's a good question Wreshyn. I would hope we'd take it as an opportunity to share knowledge and learn about each other and not try to annihiliate each other like in the movies.

    • Wreshyn profile image


      8 years ago from Stockholm


      Thank you for stoping by my hub. Means alot to me to hear that it is a nice hub. Your hub is exactelly what I like to read about. The exoplanets. Makes me wonder how many planets we actually already spotted that inhabits life. But life that we don´t know about yet. The thing about humans is that when they look for life on other planets they look for life that needs the exact formula like us to exist. I know there are many scientists that don´t look for that exact formula.

      What we know about life is that it needs a lot of different coincidences in order for life to grow.

      Everyday scientists find out new things about our universe.

      There´s one thing I need to ask: What would really happen that day when we DO find intelligent life? How would humanity react? We´ve seen the movies, but as we know, the movies are just that. A movie. :o)

    • topquark profile imageAUTHOR


      8 years ago from UK

      Awful or awesome, which one's the typo? :P

    • Sun Pen 50 profile image

      Sun Pen 50 

      8 years ago from Srilanka

      There is no doubt that the number of planets in the universe can be more than the number of stars. We do not see them because they do not have their own light for us to see. How many of them can hold intelligent life forms ... or many other wonders that we cannot even imagine.

      Topquark, you write awful hubs. Thanks. up/awsome


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