Well, its small mass certainly contributed to it losing heat more efficiently. But Mercury (much less massive than Mars) and Ganymede (around the same mass as Mars) both have a magnetic field, so there are a lot of other factors at play. Something to do with a change in the chemical composition of Mars’ mantle, and the possible lack of plate tectonics, I’m not so familiar with the causes though.
Wasn’t that because Mars isn’t heavy enough?
Well, its small mass certainly contributed to it losing heat more efficiently. But Mercury (much less massive than Mars) and Ganymede (around the same mass as Mars) both have a magnetic field, so there are a lot of other factors at play. Something to do with a change in the chemical composition of Mars’ mantle, and the possible lack of plate tectonics, I’m not so familiar with the causes though.