No Man's Sky might be all about exploring your personal universe, but there's also a big crafting and element-collecting side to the game as well — often prompting you to pool your resources before you can move forward in your adventure.
Among these elements is Thamium9, one of the most important elements in the game, as well as one of the elements of which you'll be needing the most early on.
Thamium9 is used for a variety of purposes, such as powering your life support systems, mining equipment and various weapons — and most importantly, it is the energy source needed for your Pulse Engine, which allows you to travel at high speeds through space, thus shortening the time it takes for you to go from planet to planet.
For what it's worth, it's actually quite easy to find Thamium9 on the surface of various planets — just look for plants that have three or four stalks, but the problem is that it is impossible to try and point out specific locations from where it can be found because everyone's game is unique.
Fortunately, while it is easy to find Thamium9 on the appropriate planet, it is even easier to find it in space during your travels. As you travel from planet from planet, you'll come across an assortment of objects that can be interacted with in some way, and among them are the many asteroids that you can easily find floating around. Instead of trying to avoid them, shoot them down (the small, metallic ones, in this case) using your ship's Photon Cannon, and they will break into Thamium9.
In the video below, courtesy of Arekkz Gaming, you can see this trick being put into practice.
As you can see, the amount of Thamium9 you get from destroying the appropriate objects is quite plentiful, and it shouldn't take players all that long to amass a solid amount of it. Once you do have enough of the isotope, you can fill up your Pulse Engine's tank with it and launch yourself in any direction to continue your journey.
Of course, there is also the option of trading with other ships that you come across at various space stations, but it's not guaranteed that they'll have any Thamium9 to offer you. Even if they do, it's not likely to be as much as you can get by simply shooting down various asteroids using this simple trick.
