 Here's a solar storm that erupted on August 21, 2012. It's like the one on October 14, 2014, that SOHO and other spacecraft tracked across the solar system. This kind of storm is called a coronal mass ejection, or CME for short. CMEs are billion-ton clouds of solar plasma launched by a single explosion. A typical velocity is around 300 kilometers per second. That's 186 miles per second. This 2014 CME washed over spacecraft throughout the inner solar system, including Curiosity on Mars and ESA's Rosetta orbiting comet 67P. Measuring these storms enables scientists to predict a CME's path and strength. This is important because CMEs can disrupt communications and power systems on Earth if we are not prepared.