A miniature black hole, dropped into the centre of the Earth (possibly as some sort of weapon).
An asteroid impact sufficiently large to turn the Earth into another asteroid belt.
An asteroid impact sufficiently large to divert the Earth’s orbit, sending it falling into the Sun (admittedly, this would have an effect on a Martian colony as well, but not necessarily a fatal one)
A miniature black hole, dropped into the centre of the Earth (possibly as some sort of weapon).
An asteroid impact sufficiently large to turn the Earth into another asteroid belt.
An asteroid impact sufficiently large to divert the Earth’s orbit, sending it falling into the Sun (admittedly, this would have an effect on a Martian colony as well, but not necessarily a fatal one)