Elon Musk is putting his dreams of colonizing Mars on hold and said his SpaceX rocket company will instead focus on building a city on the moon.

Whether its pioneering spirit and an urge to explore or a chance to make a fortune or new life out in space, colonization of our solar system may pursue many strategies across many new worlds.

Humanity is on the verge of a new frontier—colonizing the solar system. But what’s actually stopping us? From the challenges of long-term space travel to the need for genetic modifications, this video ...