WHEN you need to save Earth from an incoming asteroid, try shooting at its bright spots. A new analysis of fragments of the Chelyabinsk meteor, which exploded over Russia in 2013, suggests that firing something at an asteroid鈥檚 lighter areas may be the best way to deflect it.
The Chelyabinsk object arrived without warning, injuring around 1500 people. If would-be planetary protectors do spot something similar en route, they could use a projectile to shift it off course. But figuring out how is tricky, and not something to be trying for the first time with an asteroid hurtling toward us.
The perfect shot transfers maximum momentum to the target without breaking it apart completely. To achieve that, we need to know its composition and internal structure, and then take aim accordingly. 鈥淏efore firing the projectile, we would need to study carefully the surface of the body and select the best location,鈥� says at the Institute of Space Sciences in Barcelona, Spain.
Advertisement
Work led by , Trigo-Rodr铆guez鈥檚 graduate student, looked at the three rocks making up the Chelyabinsk object: a pale and relatively pristine material with a grainy texture, a darker substance with opaque veins, and another dark material filled with droplet-shaped bits of metal. The team made tiny indentations in each with a diamond-tipped probe, to measure hardness and stiffness ().
Those properties influence the choice of target and how much the asteroid鈥檚 path could be shifted. 鈥淭here are pieces that fly off a little bit like the droplets of fluid if you throw a rock into a pond,鈥� says Paul Miller of Lawrence Livermore National Laboratory in California. 鈥淸Aiming at] that material actually gives you bonus push, bonus momentum.鈥�
As a target, the pale material won out: it was softer, so can 鈥渟plash up鈥� as Miller describes more easily. That same rock is common in near-Earth asteroids, and can be detected from afar using spectral analysis.
One issue is that the three materials were mingled in the sample, which was only about a square centimetre in cross section. 鈥淚t鈥檚 not currently obvious how well we can extrapolate from small scales to asteroid scale,鈥� says at the Johns Hopkins Applied Physics Lab in Laurel, Maryland. For example, we don鈥檛 know of asteroids where the different rocks form a patchwork of metre-sized or larger pieces that could be targeted. At best, we could look for an area with a high proportion of the paler rock.
Right now, our analyses are 鈥渓iterally skin-deep鈥�, says at the University of Arizona in Tucson. 鈥淲hat we need to know in the end is what is inside an asteroid.鈥� To help us find out, a is supposed to crash into a small asteroid in the 2020s, and another called will study that impact. But the status of both is in doubt (see 鈥�Keep an eye on space鈥�).
鈥淪ooner or later we will convince our politicians that these pioneer missions to test impact deflection in asteroids are needed right now,鈥� Trigo-Rodr铆guez says. 鈥淭he next asteroid to hit the Earth is probably not known yet. We should be ready.鈥�
Leader: 鈥�No room for complacency over threats from space鈥�
This article appeared in print under the headline 鈥淎pocalyptic asteroids have chink in armour鈥�
