A crewed mission to Mars would rank among the most complex and costly undertakings in human history -- and US President Donald Trump has vowed to make it a national priority.

That political momentum, coupled with SpaceX chief Elon Musk's zeal, has breathed new life into a cause long championed by Red Planet advocates -- even as major obstacles remain, including Trump and Musk's latest feud.

- Why go? -

As NASA writes in its Moon to Mars blueprint, "exploration of the cosmos remains a great calling for humanity."

A mission to Mars would pursue scientific objectives like determining whether Mars ever hosted life and charting the evolution of its surface, as well as answering broader space physics questions -- such as the history of the Sun through studying Martian soil.

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