You might be more familiar with the Imbrium Basin than you think. If you live in the Northern Hemisphere, you probably see the famous Man in the Moon (pictured above) quite often. The face's right eye is actually known as the Mare Imbrium, a dark lava plain within the Imbrium Basin.

Schultz based his study on the markings, which are pronounced enough to be visible from Earth even if you're only using a small telescope, found inside the impact crater. One set of markings that radiate out from the center can be easily explained: that's the protoplanet's point of initial contact. There's another set of markings with a different angle (see below), however, that has always been a source of mystery.

To uncover the truth behind those mysterious grooves, Schultz performed a series of impact experiments using the Vertical Gun Range (PDF) at the NASA Ames Research Center. Scientists can simulate high-speed celestial body impacts within the facility, which boasts a 14-foot cannon that can fire projectiles at up to 16,000 miles per hour. During his tests, he noticed that small pieces would break off the projectile and hit the surface of the object representing the moon at high speed. Those pieces formed marks consistent with the second set of markings in the Imbrium Basin.

After Schultz and his team figured out how those markings or grooves formed, they were able to calculate the size of the asteroid. Their 150-mile estimate is on the lower end, though, and the rock could have actually been larger than 186 miles across. This new estimate and the presence of impact basins even larger than Imbrium could mean that there was an abundance of protoplanets in our solar system 3.8 to 4 billion years ago. As Schultz said, "The large basins we see on the moon and elsewhere are the record of lost giants."

[Image credit: NASA/Northeast Planetary Data Center/Brown University]