Chambers and Lissauer proposed that a previously unknown terrestrial planet once existed in an eccentric and unstable orbit around the Sun, at least 4,000 mya. They connect this planet, which they name Planet V, and its disappearance with the Late Heavy Bombardment episode of the Hadean era.

"The extra planet formed on a low-eccentricity orbit that was long-lived, but unstable," Chambers reported. About 3.9 billion years ago, Planet V was perturbed by gravitational interactions with the other inner planets. It was tossed onto a highly eccentric orbit that crossed the inner asteroid belt, a reservoir of material much larger than it is today. It spun through the inner belt of asteroids, causing them to fly into Mars-crossing orbits. This temporarily enhanced the population of bodies on Earth-crossing orbits, and also increased the lunar impact rate.

According to Chambers, Planet V most probably was destroyed by being plunged into the Sun.

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