The idea here is that - while Earth formed slowly from planetary embryos colliding - Mars is itself a solitary planetary embryo that formed very early in the history of our solar system.

Although our solar system only has one star, most stars like our sun are not solitary, but are binaries where two stars orbit each other a pair, or multiples involving even more stars.

A similar system might ease the pressure on the solitary round-the-world yachtsmen, he adds.