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Plasma is a STATE of MATTER so energetic that at least some of the particles present have ionized;
examples range from neon signs at the very cool end to stars at the very hot end.

Saying that the sun isn't composed of plasma is to say that it IS composed of a solid, liquid, or gas.

And additionally:

“so if this mandametal is the star wars equivalent to adamantium, and you say that superman is tougher than any forged metal, then your saying that he is stronger than ndestructible?”

This statement presumes that adamantium is indestructible, which Marvel comic books don't seem to hold to (e.g. Sedating the Hulk fails to work because the adamantium needle breaks), because the writers use it as a means to easily show off how ridiculously strong/powerful a character is. And of course, Superman is a DC comics character, so one would expect his writers to LEAP at the opportunity to show him tearing apart things made of adamantium. On the other hand, Wolverine's claws can apparently eviscerate the Sentry, Marvel's Superman parody, but that may be due to their shape.

And to adress this whole crap about stars being made of plasma? They are actually made of the same center of what our sun has, which is burning Hydrogen Atoms. Which is not plasma. Plasma is what lightining is made of, which is free-flowing electrons in the air. and if light sabers aren't made of Plasma, then there is a chance that it can cut through super man. plus, you know, the whole kryptonite focusing crystal thing? Yea, im pretty sure if a jedi had a light saber with one of those, he could definatly own superman in a fight.

~A query of Chaos
(quick edit, this was obviously noted already… hm… but the fact of there being three focusing chambers there are many things that could affect the blade of the saber to make it much more capable of killing Superman, such as the two types of kryptonite red and green, perhaps huing the blade silver… that color thought aside what ever alse you added could while not giving it mass make it have “weight” such as gravity, I don't know if a crystal like that “exists in the pseudo reality of star wars but it matters little. but you can consider that against a dangerous opponent like superman that the force itself could be used to hone the blade enough to make it have a grave and deadly effect on super man…)

However, I believe the canon explanation of the lightsaber is very different, and to some degree quasimystical (see p98-99 of Jedi vs. Sith: The Essential Guide to the Force) to differentiate a lightsaber from the basic technology used in mundane blaster weaponry. Page 94 of the afforementioned book claims that “Lightsaber technology operates on the complex principle of tightly-controlled arc-wave energy,” and explicitly states that the blade has NO mass, precluding the possibility of plasma.

In short, the science behind the Lightsaber is complete fantasy, just like the science behind the telekinetic powers a Kryptonian unconsciously wields (which, as an aside, a force user might be able to turn off). So, the question is, whose nonsense trumps whose nonsense? And the answer would largely depend on who the writer wanted to win.

Personally, without considering use of the Force, I would STILL bet on Superman. First, he should certainly be able to dodge any jedi not using some sort of precognitive powers, but more practically, consider how much effort Qui-Gon had to exert to poke a hole in that door in Ep I… Doesn't it seem likely that Superman is at least an order of magnitude more resilient than that door? Furthermore, lightsabers can't cut through beskar (i.e mandametal; the Star Wars equivalent to adamantium), and I would presume that Superman is more resilient than any forged metal.