Can SC judges be impeached?
In theory, yes, but in reality it has never happened.
“Can SC judges be impeached?”
Yes and it is easier to do than repealing the law of gravity but only SLIGHTLY easier.
They can be impeached, but only one Justice has ever been so - Samuel Chase back in 1800 or so. Wikipedia has the details, but the short version is, he was resoundingly acquitted, and that it sort of set a precedent that SCOTUS Justices were untouchable, as a practical matter.
So, basically, we’re stuck with the Roberts court and its supremely political decisions for the near future. One hopes a GOP win in 2016 will lead to some Alito-like replacements for Ginsburg and Breyer (the most likely lefties to step down, IMHO), but I’m not holding my breath anymore.