In Attack of the Clones, we see a pursuit of Slave I by Obi-Wan in a 'Jedi Fighter' backfire, leading to Slave I chasing Obi-Wan through an "asteroid field", which is the ring of planet Geonosis. In the midst of this chase, we see a shot from Slave I destroy half of an asteroid. The size of the asteroid is 8 meters, as judged from the ~4 meter wide fighter. This means that Slave I fragmented a mere 3-4 cubic meters of asteroid, without significant vaporization or melting. Calculations will soon follow.
Using Wong's own asteroid calculator (since I explicitly haven't worked that scene yet), and inputting the high-side estimate of 10 meters for the asteroid, one finds that the required cratering energy (i.e. the energy required to make a crater equal to the radius, which is pretty much the effect seen) would be only .2 tons (0.84 gigajoules, or 840 megajoules) for solid granite. Even if we assume that these are magic planetary rings made of nickel-iron (as opposed to common rings made of far lesser materials, usually ice or sometimes collections of dust and dirt clods), we're only up to 19.7 gigajoules for the overestimate asteroid, from a vehicle significantly larger than a fighter.