But I heard there were organizations that would do this for you. There are organizations that will take your money and send you a certificate, but those documents have no validity and are not recognized by anyone else. It will be just as valid. The various businesses that claim that you can have a star named after you or a friend are only going to separate you from your money.
Planetary names come from Greek and Roman mythology.
This is also true of the names of many planetary satelites, although some of the moons of Uranus were named after characters from Shakespeare. Star names come to us via historical convention. Most of the stars that have individual names were named thousands of years ago and were first catalogued by Ptolomey in ancient Egypt. All stars are also given a numerical designation based on the constellation in which they're found and their relative brightness. The brightest are given a Greek letter designation followed by the name of the constellation such as Alpha Centauri, Sigma Draconis, etc.