Mars is primarily composed of oxygen, silicon, iron, magnesium, sulfur, calcium, aluminum, and other trace elements. The average elemental composition shows that oxygen is the most abundant element, making up about 45.9% by mass of the planet. Silicon comes second at 21.2%, followed by iron at 13.4%, magnesium at 11.8%, sulfur at 3.6%, calcium at 2.7%, aluminum at 2.2%, and the rest of the trace elements make up about 9.2% of Mars' mass.