omg... A temp as hot as the sun? Do you even realize just how hot that is? More than enough to melt any earth-bound solid, I'll tell you that. The sun gives off enough energy to power this planet for thousands of years easily. The heat is something like in the tens of thousands.
No alien weapon burns like this, and plasma scientifically does not operate like this. To be completely fair, plasma can't be used as a weapon; it's more likely that the so-called plasma-weapons of the Halo series are a product of brain bugs and are actually another type entirely.