Earth’s cousin: Scientists have made these rough estimates about life on Kepler 452b.

Scientists are about to confirm the discovery of the 4,000th planet outside of our own solar system. What are these mysterious worlds, and will we find alien life on them?

  • What is an exoplanet?

    An exoplanet is any planet outside of our solar system. Exoplanets come in all shapes and sizes, from gas giants double the size of Jupiter to tiny, rocky Moon-sized worlds.

    Some planets orbit two stars. Other rogue planets don’t orbit any star at all, but roam around the universe in darkness.

  • How many are there?

    The number of exoplanets discovered by NASA is about to hit 4,000.

    However, this is just a drop in the ocean compared to what is probably out there.

    Most stars in the Milky Way are orbited by at least one planet, and there are 400 billion stars in the Milky Way.

    Across the universe, astronomers estimate there are one billion trillion stars (that’s one with 21 zeroes). The number of planets waiting to be found is truly unimaginable!

  • How do we find them?

    Scientists use many different telescopes and sensors on the ground and in space to find exoplanets — but it is not easy!

    Exoplanets are hundreds of times fainter and smaller than the bright stars they orbit. It is very rare that an exoplanet can be seen directly through a telescope. Instead, most are detected by measuring when a star dims as a planet passes in front of it.

  • Will we find alien life on exoplanets?

    No sign of aliens so far. However, we have found dozens of planets that could potentially be home to life. Astronomers think there could be 40 billion Earth-sized, habitable planets across the universe.

    To find them, scientists first look for planets in what they call the “Goldilocks zone”.

  • Like the fairy tale?

    Pretty much. Just like Goldilocks’s porridge, most planets are too hot or too cold. If a planet is too close to its star, water will evaporate. Too far away, and it will freeze. Planets need to be just the right distance from their star, like Earth.

    Planets in the Goldilocks zone are not necessarily habitable. They also need an atmosphere to protect them from space radiation.

    So far, only one planet definitely has an Earth-like atmosphere, but it is far too hot for life. In fact, its entire surface may be covered in lava. The strongest contender for life found so far is Kepler 452b, nicknamed “Earth’s cousin”.

  • Will we ever visit an exoplanet?

    Not for a very long time, if ever. Our nearest exoplanet, Proxima Centauri b, is 4.24 light years away. NASA’s super-fast New Horizons probe, which is currently approaching the very edge of our solar system, would take over 54,000 years to get there. Besides, we still haven’t visited Mars, the closest planet in our solar system.

You Decide

  1. Do you think alien life exist?


  1. Design a “second Earth”: an ideal new home for humans to live on in the future. Think about all of the things that make life possible on this planet, and make sure you include them!

Word Watch

Circle an object in space. For example, the Moon orbits Earth.
Something which lives apart from others and behaves unpredictably.
Objects which make far away things look bigger.
Good enough to live on.
Turn into gas.
A layer of gases around a planet. In Earth’s case, it also contains gases which animals can breathe.
Potential option.
Light years
One light year is 5.88 trillion miles — or the distance that light can travel in one year.

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