Nero said:
Is it dangerous to do mantras for outer planets?
I think it can be. It requires a high level of spiritual understanding and advancement to handle such intense energies. They are called the transcendental planets for a reason, and not only because they are the upper octaves of personal planets.
That being said, anything can be dangerous depending on how you use it. Some things are more touchy and take a more careful touch to handle properly than other things. You can think of it like handling a stable sulfur compound versus handling nitroglycerin - one is going to be easier to handle than the others, but if you do something foolish with the sulfur compound then maybe it could be a little dangerous. It's all relative levels of safety/danger. Another example would be making an ordinary rock dangerous by throwing it at someone, whereas the sun can fry you in so many different ways if you're not careful. Most people can handle the danger level of a rock, but it takes a little more teaching first for people to understand how to be safe from the sun. Like for example, a child might not know not to carelessly fall asleep in the sun unless someone told them. But even a child will likely be able to handle a rock on their own.