They believe ancient lunar patterns, resembling a face, were caused by a large object hitting the far side of the Moon. A shock wave then passed all the way to the Earth-facing side, causing the crust to crack and allowing molten magma to bubble to the surface.
When the magma cooled, it left the Moon with scars that still show today.
Early space missions showed the Moon was not perfectly spherical. Its surface is warped in two spots - an Earth-facing bulge and a complementary depression on the far side.
Scientists have long wondered if these features were caused by Earth's gravity tugging on the Moon early in its history, when the surface was still molten.
But a team at Ohio State University in the United States decided the features were remnants of an ancient impact after using gravity fluctuations measured by two NASA probes to map the Moon's interior.