In 2012, Dr. Stewart and Matija Cuk, then a postdoctoral researcher, proposed a variation, that Theia slammed into Earth at high speed, scrambling up the materials of the two bodies. The resulting Earth would also have been spinning fast, and they explained how the gravitational interactions with the sun would have then slowed everything.

“We changed the impactor,” Dr. Stewart said. “We changed the energy. We’re changing momentum. We’re changing the way the moon forms. We’re now changing the whole dynamical sequence. Everything is different except the words, ‘giant impact.’”

Dr. Stewart and Dr. Cuk said the revised calculations explained most everything about the moon.

But there was still a nagging discrepancy — a five-degree tilt of the moon’s orbit compared with the orbits of the planets and most everything else in the solar system. It’s what astronomers call the plane of the ecliptic.

The motion of moons and planets follow an orderly set of rules, Dr. Stewart said. “It makes very clean predictions, and when something goes against the orderly set of rules, it requires something special happening,” she said. “The clean prediction is the moon is in the ecliptic. Period. That’s where it should be.”

At its birth, the moon was quite close to Earth, probably within 20,000 miles. Because of the tidal pulls between Earth and moon, the moon’s orbit has been spiraling outward ever since, and as it does, Earth’s pull diminishes and the pull of the sun becomes more dominant.

By now, with the moon a quarter of a million miles from Earth, the sun’s gravity should have tipped the moon’s orbit to lie in the same plane as the ecliptic. Last year, two astronomers proposed that planetesimals perhaps as big as the moon itself buzzing through the inner solar system tipped the moon’s orbit through repeated close passes.