In 2010, Richard Binzel, a professor of planetary sciences at MIT, identified a likely explanation: Asteroids orbiting in our solar system's main asteroid belt, situated between Mars and Jupiter, are exposed to cosmic radiation, changing the chemical nature of their surfaces and reddening them over time.
By contrast, Binzel found that asteroids that venture out of the main belt and pass close to Earth feel the effects of Earth's gravity, causing "asteroid quakes" that shift surface grains, exposing fresh grains underneath. When these "refreshed" asteroids get too close to Earth, they break apart and fall to its surface as meteorites.
Since then, scientists have thought that close encounters with Earth play a key role in refreshing asteroids. But now Binzel and colleague Francesca DeMeo have found that Mars can also stir up asteroid surfaces, if in close enough contact.
The team calculated the orbits of 60 refreshed asteroids, and found that 10 percent of these never cross Earth's orbit. Instead, these asteroids only come close to Mars, suggesting that the Red Planet can refresh the surfaces of these asteroids.
DeMeo said that they don't think Earth is the only major driver anymore, and it opens our minds to the possibility that there are other things happening in the solar system causing these asteroids to be refreshed.
The idea that Mars may shake up the surface of an asteroid is a surprising one: As Binzel points out, the planet is one-third the size of Earth, and one-tenth as massive -- and therefore exerts a far weaker gravitational pull on surrounding objects. But Mars' position in the solar system places the planet in close proximity with the asteroid belt, increasing the chance of close asteroid encounters.
DeMeo, who suspected that Mars may have a hand in altering asteroid surfaces, looked through an asteroid database created by the International Astronomical Union's Minor Planet Center. The database currently consists of observations of 300,000 asteroids and their orbits; 10,000 of these are considered near-Earth asteroids.
The study has been published in the journal Icarus.
--ANI (Posted on 19-11-2013)