Author: Hrvoje Tkalčić, Professor, Head of Geophysics, Director of Warramunga Array, Australian National University

Mars is home to perhaps the greatest mystery of the Solar System: the so-called Martian dichotomy, which has baffled scientists since it was discovered in the 1970s. The southern highlands of Mars (which cover about two-thirds of the planet’s surface) rise as much as five or six kilometres higher than the northern lowlands. Nowhere else in the Solar System do we see such a large, sharp contrast at this scale. What caused this dramatic difference? Scientists have been split on whether it resulted from external factors – such as a collision with a huge, moon-sized asteroid – or internal ones,…

About 2,890 kilometres beneath our feet lies a gigantic ball of liquid metal: our planet’s core. Scientists like me use the seismic waves created by earthquakes as a kind of ultrasound to “see” the shape and structure of the core. Using a new way of studying these waves, my colleague Xiaolong Ma and I have made a surprising discovery: there is a large donut-shaped region of the core around the Equator, a few hundred kilometres thick, where seismic waves travel about 2% slower than in the rest of the core. We think this region contains more lighter elements such as…