I have to conclude "lens flare" also. There is no way that a planet can move positions, relative to the sun, from shot to shot. That is a physical impossibility, whereas some coloration of roundish lens flare is probably not impossible. Besides that Mercury and Mars are in Pices and conjunct the sun, so even if you could get past the lens flare issues with polarizing filters you will end up shooting which planet? I think this takes a bit of sophistication.