Life of the Martian dynamo

► A large embryo collision prevented dynamo activation in Mars for the first 100 Myr. ► A strong dynamo existed for ∼300 Myr, until the 20 impacts that occurred at ∼4 Ga. ► Ares impact constrained the core convection to the upper ∼200 km for ∼28 Myr. ► The pre-existing dynamo retained its strength in subcritical condition after Ares. ► Acidalia impact eventually killed the dynamo.