How does a single sensor help change your outlook on a planet? A single small seismometer on Mars can help understand Mars' past, present and future. What do an ultrasound and Mars have in common? Both can use a single sensor to peer deep inside. Listening to the echoes of marsquakes helps researchers understand what's in Mars' core. Modelling the inside of Mars' core helps researchers understand its past and future. Mars is often thought to be volcanically dead, but there are signs of some activity. A cluster of marsquakes can help researchers find evidence of vulcanism on Mars.