On July 23, 2012, a coronal mass ejection (CME) passed through the Earth's orbit. If it had occurred just one week earlier, it would have struck our planet - and been as potentially devastating as a massive asteroid.
A CME is the result of an extreme solar storm. In 2012, the CME was the worst recorded in more than 150 years.
Had it hit Planet Earth, it would have likely begun as solar flares that could have knocked out GPS (affecting planes, trains and automobiles, as well as cell phones and mobile devices) and also resulted in radio blackouts.
Anywhere from a few minutes to a few hours later, satellites would have been affected. Next, anything powered by an electric grid could have been fried. Even people living in certain areas of the world would have been unable to even flush a toilet, as many more modern toilets rely on electric pumps.
Had all of this occurred, we still would not have recovered - two years later.
Where did it hit? The storm cloud hit the STEREO-A spacecraft. It was the perfect place, because STEREO-A was ideally equipped to calculate everything in the debris field, providing scientists with more information than they'd ever been able to accumulate before. The spacecraft was not damaged because it was designed for use outside the protective Earth shield, so it was ideally suited for this catastrophe.