How the Sun Protects Earth From Getting Clobbered By an Asteroid
Marat Ahmetvaleev / Duck: The Chelyabinsk meteor lights up the Russian sky, in 2013
A trick of heat and light makes space rocks self-destruct
The Earth grew up in an awfully rough neighborhood and it’s always needed the help of powerful friends. This was specially true in the early days of the solar system, during the so-called heavy bombardment phase, when asteroids and comets turned the region near the sun into something of a free-fire zone.
One of the things that prevented us from getting blown to smithereens was the fortuitous location of Jupiter which, with its powerful gravity, intercepts some of the incoming ordnance before it can reach us. That still leaves a lot of debris on the loose—witness the 66-ft (20 m) meteor that exploded in the skies over Chelyabinsk, Russia in 2013. All the same, according to a new study in Nature, it appears that we’re more protected than we knew—thanks to the powers of the sun.
Astronomers around the world keep a close watch on what they call near-Earth objects (NEOs)—asteroids that orbit through the solar system within 121 million miles (224 million km) of the sun, which brings them dangerously close to the Earth’s own 93 million mile (172 million km) orbit. Much of that census-taking is done by the Catalina Sky Survey, a program conducted principally by NASA’s Jet Propulsion Laboratory and the University of Arizona.
Recently, a team of investigators led by research scientist Mikael Granvik of the University of Helsinki began looking at the population of known NEOs and noticed something strange: While the mix of dark asteroids and brighter, more reflective ones is more or less even throughout the solar system, in the vicinity of the sun, many of the dark ones go missing. What’s more, in this case, the solar “vicinity” can be pretty huge. Smaller bodies often get torn apart gravitationally as they approach what’s known as the Roche limit of a larger body like the sun or a planet—a distance of about 2.5 times the radius of that body. But the dark asteroids start falling apart at about ten times the solar radius, or about 4.3 million miles from the sun.