About 2 billion years ago, an impactor hurtled toward Earth, crashing into the planet in an area near present-day Johannesburg, South Africa. The impactor—most likely an asteroid—formed what is today the biggest crater on our planet. Scientists have widely accepted, based on previous research, that the impact structure, known as the Vredefort crater, was formed by an object about 15 kilometers (approximately 9.3 miles) in diameter that was traveling at a velocity of 15 kilometers per second.