What are Exoplanets?
It is mystifying how many different galaxies are out in our universe, when we can only travel in our own, the Milky Way. Could there be life on other planets? There are so many different stars that planets orbit around, and ours is only one of trillions. There are many planets that orbit stars in other galaxies, too. They are called exoplanets.
Exoplanet is short for extra solar planet, but most people dont use the full term. Exoplanets are planets that orbit stars other than our own sun. Astronomers come up with different names for the planets based off our own planets here in the Milky Way. For instance, when an astronomer finds a very large planet, they call it a Jupiter, because the biggest planet in our solar system is Jupiter. If a Jupiter is also close to its star, like Mercury, they call it a Hot Jupiter, because it is close to its hot sun. They call a planet a Neptune (also based off ours) if it is made of gas and is between the sizes of Earth and Neptune.
The number of planets orbiting each star varies greatly, and it is hard to detect planets outside our solar system, but astronomers believe that there are at least six planets orbiting the star Gliese 581. They also found out, in 2007, that there are at least five more planets orbiting the star 55Cancri. They have discovered many more exoplanets and lots of stars. Earth is tiny compared to most of them, though. One of the smallest planets discovered so far is almost 6 times bigger than Earth! Most planets are about 300 times the size of Earth though, and are in a class with Saturn and Jupiter. Astronomers can rarely see the exoplanets though. They can only see their stars. They find exoplanets by seeing if a star wobbles or if it is still. It wobbles because of the gravitational pull of orbiting planets. The wobble is not too hard to detect on big planets, but with small planets it can be much trickier, because the gravitational pull is weaker. You can also see an exoplanet when it passes between its star and us. The light from the star dims a bit, because the exoplanet is blocking it. It is hard, but they find a lot of exoplanets this way!
The astronomers mostly look for Jupiter-sized exoplanets, but they look for Earth-sized planets, too. It is hard to find an exoplanet as small as Earth, but when astronomers do, they are usually made of rock like Earth. They can sometimes tell what is inside a planet too, but they never know for sure. Astronomers think that Gliese 436 b (named after its star Gliese 436) has a rock center that is surrounded by ocean water with a hydrogen and helium crust. They are still finding ways to find out more, though. Nothing is for sure about other planets outside our solar system.
The oldest planet discovered so far, PSR B1 620-26 b is nicknamed Methuselah for biblical reasons. It is the oldest planet known, and is a little older than 13 billion years old. It was found in the global cluster, and was formed right after the Big Bang. Methuselah is the oldest planet discovered, but it is not the first planet to be discovered. The first planet discovered was a Hot Jupiter, and it only took four days to orbit its star! 51 Pegasi b was the first planet discovered orbiting an ordinary star. People have suspected for years that planets in other solar systems might support life, and astronomers have now found a possible location. They suspect that a moon in a gap close to planet 55Cancri f might have water on it, and that there might be life there. Astronomers also believe that it is possible for another planet like Earth to exist and that it could support life. This idea is one of the main things that keep astronomers on their feet.
We cant go looking for exoplanets, so it is hard to confirm our findings. Exoplanets are way too far away to go looking for one. It would take thousands of years for an Earth ship to reach even the nearest one! Since they couldnt go looking for exoplanets, people started inventing telescopes to go into space taking pictures. The Hubble telescope was one of them, and it took some of the first pictures of exoplanets. It launched in 1990 and has been in space since. The same year was when we first discovered exoplanets. For a long time astronomers didnt believe that exoplanets existed, but then they started doubting themselves. By now, astronomers have discovered more than five hundred exoplanets and we are still looking for more. About 20 years ago, we were only sure one solar system existed. That solar system was our own. Now we know of hundreds of solar systems besides our Milky Way.
It is very important that we keep looking for exoplanets because then we can see which galaxies are coming toward us and which are moving away. It also helps us to know the history of our universe. Many people believe in the Big Bang, but if we were not constantly studying space, no one would have ever thought of the Big Bang Theory. Studying space gives us a better understanding of what is out there. We learn things every day, but there are always more mysteries. The universe is a pretty amazing thing!
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