Aumaan doesn't actually have the power to destroy the solar system
Nohman was just power-tripping. Aware that in spite of his enormous power as the pilot of Anubis, that he would soon die from Metatron poisoning, his narcissism and his madness manifested (like Kuja's from FFIX) into an Omnicidal Maniac
urge to destroy everything. The attack would probably have ripped Mars a new one, though.