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You are probably somewhat familiar with our Solar System. At least you most likely know that there are eight planets in it, including the Earth, the Sun, moons, and a number of other objects like Pluto and asteroids. However, there is a lot more beyond the Solar System of which you may not be aware.
Our galaxy is the Milky Way Galaxy, but there are also other ones including the Andromeda Galaxy. Each galaxy is a system composed of different star systems, stellar remains, and interstellar medium. Although astronomers are not certain, they estimate that there are one hundred billion galaxies in the universe. Between the galaxies is intergalactic space, which has a thin gas in it. It is no wonder that the universe is considered to be infinite when you consider how large our Solar System is and that this Solar System is just one of many in our galaxy. This really puts into perspective exactly how small the Earth, and we, are in the big picture.
The Milky Way galaxy has many stars in it. Beyond our Solar System is interstellar medium and more stars along with their star systems. Interstellar medium is the vacuum of space between different star systems, although the space is not actually an empty vacuum. It has dust and other particles in it in addition to cosmic rays and magnetic fields.
Astronomers have already discovered many extrasolar planets – planets beyond our Solar System that orbit stars other than our own. The first extrasolar planet’s existence was not confirmed until 1995, because technology was not advanced enough to detect these distant planets. Since then, 357 extrasolar planets, also known as exoplanets, have been discovered. It is estimated that only a small percentage of stars have planets, and most of these stars are similar to our own Sun.
At first, the only extrasolar planets that astronomers could find were gas giants similar to Jupiter. However, in recent years, they have found planets similar to Neptune. This strengthened the hope of astronomers who were looking for Earth-like planets. In fact, some astronomers believe that they have found Earth-like planets in the past few years. Astronomers are still trying to find a way to determine whether there is life on these planets.
While there is still much more to learn in our own Solar System - the Moon is the only place besides Earth humans have actually set foot - there are also many things to discover beyond our Solar System. Not just other stars, but also other galaxies if we can reach them.
Universe Today has articles on finding a cyclops galaxy and astronomers could detect oceans on extrasolar planets.
For more information, try lightest exoplanet discovered and top 10 most intriguing extrasolar planets.
Astronomy Cast has an episode that deals with the extrasolar planets.