This is exactly how.

The Terminator started.

The first scalable robot to have built an exact copy of itself could herald a fundamental rethink of how robots may be used to explore other planets.

I like how they played it out as "a fundamental rethink of how robots may be used to explore other planets." And not, "a fundamental rethink of how robots will enslave humankind on earth." But that's just good P.R. I guess.

Hod Lipson and colleagues at Cornell University in Ithaca, New York, built their self-replicating device using small mechanical building blocks that can swivel, and also attach themselves to one another using electromagnets.

I also like how they left out the part where they get together to form a "SUPERBOT" but they probably haven't worked out the kinks in that just yet.