Scientists have combined data from three NASA satellites to develop a 3D model that simulates how shocks following coronal mass ejections (CMEs) propagate from the Sun. CMEs, often called solar storms or space storms, are a significant release of plasma and magnetic field from the solar corona. The CMEs set off interplanetary shocks when they erupt from the Sun at extreme speeds, propelling a wave of high-energy particles. These particles can spark space weather events around Earth, endangering spacecraft and astronauts. The scientists Ryun-Young Kwon, solar physicist at George Mason University in Virginia, and Angelos Vourlidas, astrophysicist from the Johns Hopkins University, fit the CME data to their models - one called the "croissant" model for the shape of nascent shocks, and the other the "ellipsoid" model for the shape of expanding shocks - to uncover the 3D structure and trajectory of each CME and shock. They used data from the NASA\/ESA Solar and Heliospheric Observatory (Soho) and NASA's twin Solar Terrestrial Relations Observatory (Stereo) satellites. Each spacecraft's observations alone were not sufficient to model the shocks. But with three sets of eyes on the eruption, each of them spaced nearly evenly around the Sun, the scientists could use their models to recreate a 3D view. Their work confirmed long-held theoretical predictions of a strong shock near the CME nose and a weaker shock at the sides. In time, shocks travel away from the Sun. With the 3D information, the scientists were able to reconstruct their journey through space, the study showed. For the first time, the density of the plasma around the shock, in addition to the speed and strength of the energised particles was deduced by scientists. All of these factors are key to assessing the danger CMEs present to astronauts and spacecraft, said the team in a paper published in the Journal of Space Weather and Space Climate. Understanding a shock's structure - particularly how it develops and accelerates - is key to predicting how it might disrupt near-Earth space.