the planet fourth in order of distance from the sun, after Earth and before Jupiter

Mars is sometimes called the Red Planet because of its distinctive colour. 因为颜色特别，火星有时也被称为“红色行星”。

So is there life on Mars? 那么火星上有生命吗？

in Roman mythology (= ancient stories), the god of war

The work depicts Mars, the god of war, choosing between Minerva and Venus. 这幅作品描绘的是战神玛尔斯在密涅瓦和维纳斯之间进行选择的故事。