The Chelyabinsk Asteroid

This February, the largest asteroid since 1908 impacted the planet’s surface near the city of Chelyabinsk in the Urals region of Russia (Figure 1). In an article published in Nature, Quirin Schiermeier reported that the asteroid shone 30 times brighter than the Sun and moved through the Earth’s upper atmosphere at an initial speed of around 19 kilometers per second, more than 50 times the speed of sound (1). An asteroid is a termed a meteor when it enters an atmosphere, and is termed a meteorite once it hits the ground.

The Chelyabinsk asteroid was undetected because it approached Earth from a region of the sky inaccessible to ground-based telescopes. According to Schiermeier (1), in the weeks before impact, the asteroid would have been visible above the horizon only during the daytime, but at this time, the sky is too bright to see objects of its size.

As the Chelyabinsk meteor passed through the Earth’s atmosphere it produced destructive blast waves and sonic booms that were powerful enough to shatter windows, dishes, and televisions in thousands of homes (1). To place the destructive force of the asteroid in perspective, it produced a destructive power yield of more than 500 kilotons of TNT, 30 times the blast yield of the U.S. atomic bomb that was dropped on Hiroshima in 1945 (2, 3).

Within our solar system, an asteroid is any of the numerous small celestial bodies that revolve around the sun with diameters that range between a few and several hundred kilometers. Based on its trajectory and by its elemental and mineral composition of silicates, the Chelyabinsk asteroid likely originated from the Mars-Jupiter asteroid belt (Figure 2) (see 4).

While no known large asteroids are currently on a collision course with Earth, much less is known about the millions of smaller objects that roam the Solar System (1). Schiermeier estimates that of the millions of likely near-Earth asteroids of at least ten to twenty meters in diameter, only about five hundred have been catalogued.

According to Peter Brown, a planetary scientist at the University of Western Ontario, models suggest that while an object the size of the Chelyabinsk asteroid hits Earth once every 150 years on average (3, 4); the number of observed impacts of a scale exceeding one kiloton of TNT occurs far more frequently: every 20 or even 10 years. For this reason Brown reports that the residual impact risk analysis from asteroids with yet-unknown orbits is shifting to smaller-sized heavenly objects that still have the potential for damage (3, 4).

This threat does not mean that should expect a highly-populated area such as a city to get hitonce every couple of decades, because seventy percent of the planet is ocean and the majority of the remaining surface is unpopulated regions (2).

Given that Schiermeier (1) and Brown (3, 4) conclude that asteroids with the capability of  producing an impact equivalent to 1 kiloton of TNT or more hit the planet far more frequently than previously thought, how do we detect and prevent damage from asteroids with unknown orbits? NASA is now looking for ways to detect asteroids earlier in their approach towards Earth as well as figure out how to deflect them away from our planet (5).

Emanuelli describes one NASA asteroid detection and early-warning system, ATLAS, which is being established in Hawaii (1). The purpose of ATLAS is to look for large “killer asteroids,” years, decades, and even centuries before impact with Earth, thus giving us time to formulate a plan to intercept and deflect the asteroid (6). According to Emanuelli, the system will offer a one week warning for a 45 meter diameter asteroid and three weeks for a 140 meter diameter asteroid. But based on the damage produced by the Chelyabinsk asteroid, more needs to be done to protect the planet from asteroid impact.

References

1. Schiermeier, Q., 2013, Risk of Massive Asteroid Strike Underestimated,Nature News, doi:10.1038/nature.2013.14114, https://s100.copyright.com/AppDispatchServlet?author=Quirin+Schiermeier&title=Risk+of+massive+asteroid+strike+underestimated&publisherName=NPG&contentID=10.1038%2Fnature.2013.14114&publicationDate=11%2F06%2F2013&publication=Nature+News.

2. Foy, H., 2013, Russian Meteor Explosion vs. Hiroshima Bomb: The Real Comparison, in Focus, http://www.spacesafetymagazine.com/2013/02/23/russian-meteor-explosion-yielded-30-times-destructive-power-hiroshima-bomb/.

3. Brown, P. G., et al., 2013, A 500-kiloton Airburst over Chelyabinsk and an Enhanced Hazard from Small Impactors, Nature, Vol. Volume: 503, Pages: 238–241.

4. Brown, P. G., 2013, (Abstract) Fireballs Producing Meteorites: From Chelyabinsk to Tagish Lake, 76th Annual Meteoritical Society Meeting, http://www.hou.usra.edu/meetings/metsoc2013/pdf/5263.pdf.

5. Burk, R., 2013, Earth is at Higher Risk for Asteroid Impact, http://www.dvice.com/2013-11-7/earth-higher-risk-asteroid-impact.

6. Emanuelli, M., 2103, ATLAS, the Asteroid Terrestrial-Impact Last Alert System, in Focus, http://www.spacesafetymagazine.com/2013/02/27/atlas-asteroid-terrestrial-impact-alert-system/