A planet roughly the size of Mars is on a collision course with the Earth. Eventually, the two planets collide and the Moon and the Earth are created in the outcome. Or at least that's what the Moon formation model says that happened some 4.5 billion years ago. But there is something missing. The Moon is here, the Earth is here, but where is the additional debris if there was any?

A new model based on the current Moon formation theory says that additional debris or satellites may have been orbiting around Earth as late as a few tens of millions of years after the catastrophic collision in the Earth-Moon two Lagrangian points, locations in space where the gravitational effects produced by the two cosmic bodies are canceled out. These moonlets, called by scientists Trojans, could still be visible on the night sky if left undisturbed with the passage of time.

"The giant impact that likely led to the formation of the Moon launched a lot of material into Earth orbit, and some could well have been caught in the Lagrangian points", says Jack Lissauer, study team member from NASA's Ames Research Center.

According to their model, the moonlets may have remained as much as 100 million years in their original orbits, albeit gravitational influences from the other planets in the solar system altered their orbital trajectories and sent them either wandering through the solar system or crashing down towards the Moon and Earth.

"The perturbations from the other planets are very, very tiny." However, when it comes to gravity and large objects even the smallest influences can have catastrophic results in the future. The interactions determined changes in Earth's orbit, modifying the gravitational effects of the Sun on the Trojans. "That is what ultimately destabilizes the Trojans", says Lissauer.

University of British Columbia researcher Matija Cuk, working on a similar model, believes that Trojan satellites only a few tens of kilometers across could have orbited the Earth as much as a billion years before being ejected out of the system or being destroyed through collisions. "They would have looked more like Jupiter or Venus in the sky than a satellite. They would have resembled vary bright stars", Cuk said.