Moon’s tilt may be remnant of giant impact billions of years ago

New York Times : Of all the rocky planets in our solar system, Earth is the only one with a large moon. Although most researchers agree that Earth’s moon probably formed when a Mars-sized object called Theia collided with Earth, modeling has failed to completely explain the Earth–Moon relationship as it exists today. Sarah Stewart of the University of California, Davis, and Matija Cuk of the SETI Institute say that by altering the impactor’s energy and momentum, they have come up with a sequence that better explains the current dynamics and compositions of Earth and the Moon. Further, the researchers’ model also offers an explanation as to why the Moon’s orbit has a five-degree tilt relative to those of the planets and other objects in the solar system. Stewart and Cuk propose that when Theia struck Earth, it knocked Earth over on its side at an angle of 60–80 degrees. Over the next 4 billion years, Earth straightened up, but the Moon is still shifting.