Caption: 
A new SwRI-led paper highlights the scientific progress made in understanding the evolution of terrestrial planets, including the effects of late large impacts on pre-existing modes of tectonics. For instance, the Earth experienced transient subduction, when one tectonic plate slides beneath another. Because Venus’ surface is covered by a single plate, a high-velocity impact led to a superheated core and long-lived volcanism. On Mars, a large, low-velocity impact facilitated variations in its hemispheres. Impacts also modify the atmospheres of terrestrial planets in profound ways, including eliminating or supplementing existing gases.