As many of you already know, the Earth's atmosphere is in fact a very powerful anti-asteroid shield. Theoretically, tens of meteorites and other similar objects should impact the ground each day, but their vast majority burns up high above the planet, on account of the friction force it generates when it enters the atmosphere. In addition to this defense mechanism, astronomers have recently identified another one. It would appear that asteroids moving too close to the Earth tend to experience quakes, or tremors, all caused by the gravitational pull our planet exerts upon them, Space reports.

Experts explain that asteroids should never appear to have a smooth and clean surface. Since more than four billion years ago, when they were formed shortly after the Sun appeared, they have been wondering the solar system, experiencing solar winds and severe beatings from particles and other space rocks. Their surface should therefore bear the signs of devastation, and not look pristine. However, in the case of near-Earth objects that scientists have identified thus far, this does not appear to be the case, and this fact has led researchers to hypothesize the existence of these quakes.

“Any part of the surface that's facing into the Sun is hit by the solar wind, which damages the mineral grains and turns them red. An analogy is a sunburn,” Massachusetts Institute of Technology (MIT) expert Richard Binzel, who has been the lead researchers on the new study, explains. He goes on to show that the reddened surface of an asteroid is not permanent, in the sense that only the rocks on the surface have their mineral composition so devastated by solar winds that it turns red. Underneath this surface, a layer of fresh material lies, just ready to show itself when the situation arises.

And the perfect opportunity arises when the asteroids move too close to our planet, without actually trying to hit it. The Earth's gravitational pull induces small quakes in the space rocks, shaking the uppermost layer of pebbles, and forcing the reddened surface underground. This all makes sense, scientists say, when understanding that most asteroids are actually a collection of loosely connected pieces of space debris, rather than a single chunk of rock. “All of the particles that got reddened are going to flip over and you're going to have new material that's fresh now out facing the sun. So it's going to change the color of the asteroid from red to a brighter gray,” Binzel adds.

“We put two and two together and found that asteroids that come very close to the Earth have very fresh undamaged surfaces, and so something about coming close must have resurfaced them. The simplest explanation is that the bodies got shaken up as they came close,” the team leader further explains. Details of the investigation appear in the January 21 issue of the respected scientific journal Nature. In an essay accompanying the study, Southwest Research Institute planetary scientist Clark Chapman, who has not been part of the investigation, concludes that, “The correlation between NEO [near-Earth object] colors and near-Earth passes is excellent.”