Author: Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Feb. 14, 2013: For eons, Earth has felt the tremors of asteroids striking our planet. From the extinction of the dinosaurs 65 million years ago to the felled forests around Tunguska in 1908, the space rocks keep coming.
This week, Earth strikes back. When asteroid 2014 DA14 makes a record close approach to our planet on Feb. 15th, the space rock could be the one feeling tremors.
New research by Richard Binzel, a professor of planetary science at MIT, suggests that many near-Earth asteroids experience a seismic jolt when they pass too close to our planet's gravitational field.
"We are going to be looking closely for evidence of seismic activity on 2014 DA14 as it passes by," says Binzel. "This is the first case of an object coming close enough to experience quakes AND where we have enough notice to plan observations."
Binzel first began to entertain the idea of asteroid-quakes a few years ago when he was pondering a mystery about near-Earth asteroids:
"As asteroids move through space, they slowly turn dark-red. This phenomenon, called 'space weathering', is caused by long exposure to cosmic rays and solar radiation. For decades, however, we have known about a handful of small asteroids that looked [light and fresh]; they were not space weathered."
How did this group of space rocks avoid space weathering? To solve the mystery, Binzel and colleagues calculated the asteroids' orbits and found a telling clue: They all had very close encounters with Earth in the past million years.
"We believe they were 'shaken up' by their encounters with Earth," he says. "Gravitational forces during the flybys can stretch, rattle, and torque these asteroids, causing dark, space-weathered material on the surface to be overturned, revealing the fresh stuff underneath."
There is no Richter Scale for asteroids. Instead, Binzel expresses the force of the quakes in units of gravitational acceleration, or gees. 1 g = the acceleration due to gravity on Earth's surface. "These asteroids experience [seismic activity] in the milli- to micro-g range," he says. "That might not sound like much, but remember these are small bodies. Gravity is not very strong, so just a little shaking or stretching goes a long way."
Binzel imagines what an astronaut floating alongside such an asteroid might see: "The surface could slowly sway or rock by a few centimeters. Other things to look for would be puffs of asteroid-dust rising from the surface and gentle avalanches on the steepest slopes of craters." In rare cases, "rubble pile" asteroids might break apart during the encounter and then re-form as Earth recedes into the distance.
On February 15th, 2012 DA14 will thread the gap between Earth and the belt of geosynchronous satellites that orbits our planet. At closest approach, the 50-meter space rock will be just 17,200 miles above Earth's surface, a prime target for radars and telescopes.
MIT postdoc Nick Moskovitz, who works with Binzel, is coordinating observations with worldwide observatories to pin down the color, spin, shape, and reflectivity of the asteroid as it passes by. Changes in any of these quantities might be a sign of a quake. Participating telescopes include La Palma in the Canary Islands, the Siding Spring and Perth observatories in Australia, Mt John in New Zealand, Mt Canopus in Tasmania, WISE in Israel, and the Clay Center Massachusetts.
Also, NASA's Goldstone radar will be pinging 2012 DA14. The radar data can be used to create 3D movies showing the space rock from all sides. Goldstone might be the first to capture an asteroid-quake in action.
"We stand to learn a lot from the observations," says Binzel.
Let the flyby begin.
For more information about 2012 DA14 and other asteroids of interest, visit NASA's Near-Earth Object Program web site: http://neo.jpl.nasa.gov
Last Updated: 14 February 2013