For a good period of time, scientists were puzzled by the number of asteroids that were being flung into the inner solar system. Normally, asteroids float along in lonely orbits between Mars and Jupiter. Scientists thought that asteroids only left the orbit when they got whacked by other asteroids. This would move the asteroid closer to the nearby planets, where it would get slingshotted clear away from its brethren. Most of the models that scientists had constructed predicted a much lower incident of this instability that was actually observed. The solution came when two scientists created a new simulation, incorporating a phenomenon described more than 100 years earlier.

In the late 1800's, a Russian engineer named I.O. Yarkovsky developed a theory. He summized that a body, having absorbed heat from external sources, would radiate this heat asymmetrically, and a corresponding acceleration would result. Yarkovsky's Effect was thought to be negligible, and in most cases was acknowledged, then ignored. And even when it was experimentally observed acting upon manmade Earth-orbiting satellites, it wasn't factored into calculations.

Last year, scientists Paolo Farinelli and David Vokrouhlicky, adding to work done by Charles Peterson in the 1970's, wrote their own simulation, taking into account the Yarkovsky Effect. The numbers they produced from the sim matched those observed in the real solar system. They discovered that the Yarkovsky Effect has a profound effect on asteroids.

Photons from the sun strike an asteroid in the belt. The asteroid absorbs the photon's energy (and undergoes acceleration due to an even lesser force known as Poynting-Robertson Drag). The asteroid becomes warmer on the side facing the sun, and radiates the heat in the opposite direction, creating a sort-of tiny heat jet. Over a period of time (several million years), the Yarkovsky Effect pushes the asteroid into what's known as a resonance orbit, where it becomes unstable and is eventually flung by the gravity of larger bodies into the inner solar system.

Farinella and Vokrouhlicky calculated that over a long period of time (10 million to 1 billion years), the orbit of an asteroid can be altered by several million kilometers, pushing a significant number of asteroids into near-earth trajectories.

Time to call in the world's best deep-core driller.

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