Asteroids
Science fiction, or fact?
The events depicted in the story, Orbital Maneuvers, have not happened (I sincerely hope they never happen!), but there is ample evidence that our tiny planet has experienced such cataclysmic impacts in the past. As we have ventured out into our solar system we have seen more evidence of such impacts on the rocky inner planets and the many moons of the gaseous outer planets. In fact, during the period in 1994, from July 16th through the 22nd, we had a ringside seat as comet Shoemaker-Levy fractured into more than twenty fragments and collided with the planet Jupiter. The largest fragment – G, estimated to be about 1.2 miles across (2 km), impacted at a velocity of approximately 37 miles per second (59 km/sec). That’s about 133,200 miles per hour (213,120 km/hr)! The energy released was equivalent 6,000,000 megatons of TNT – about 600 times the estimated arsenal of the world. The fireball from fragment G rose about 1800 miles (3000 km) above the Jovian cloud tops, leaving a scar in Jupiter’s atmosphere that was almost 25,000 miles across (40,000 km) – approximately three times the diameter of Earth. There are many links to this event on the Internet if you have a desire for more information.
The damage resulting from the impacts in the story was probably not depicted as severely as it would be in reality. Debris thrown into orbit about the Earth would most likely damage satellites orbiting lower than several thousand miles. The space station would not have escaped severe damage at an orbit of five hundred miles. Having experienced the tsunami in Indonesia on December 26, 2004, either first hand, or as most of us did, via the Internet and television, we got a taste of a major catastrophe – albeit, this event only represented a very small portion of what an asteroid impact would bring. Waves from that event were recorded as far away as Nova Scotia and Peru. The waves generated, and the degree and scope of the damage by that event would pale in comparison to the destruction caused by an ocean impact of a moderate to large size asteroid.
Recent And Not So Recent Events
The possibilities of an impact of the proportions depicted in the story are far from zero. However, they are smaller than the chances of an impact from a smaller extraterrestrial body, only because the smaller ones are more numerous. To see directly the destructive force of a smaller asteroid, all one has to do is visit Meteor Crater in Arizona. Fifty thousand years ago, a meteor about 150 feet (46 meters) in diameter impacted the Earth and released an amount of energy equivalent to 2.5 million tons of TNT. Compare that to the destruction caused by the atomic bomb that was dropped on Hiroshima, Japan in 1945, which was equivalent to 18 thousand tons of TNT. The results of this impact produced a crater that is almost a mile wide (1.6 km) and about 500 feet (151 meters) deep.
“All life within a radius of three to four kilometers [1.8 –3.4 miles] was killed immediately. The fireball that formed would have scorched everything within a radius of ten kilometers [6 miles]. A shock wave moving out at 2,000 km/hr [1200 mph] leveled everything from 14 to 22 kilometers [8-13 miles], dissipating to hurricane-force winds that persisted to a radius of 40 kilometers [24 miles].” Wikipedia
Not something that one would want to witness first-hand! The dust produced by the impact most likely did not affect Earth’s climate to any great degree. Contrary to the event that occurred some 65 million years ago, when a large asteroid (5-9 miles or 9-14 km) across collided with Earth in the region that is now known as the Yucatan Peninsula. The residual crater was over one hundred miles (160 km) in diameter. This cataclysm is believed by many to be the cause of the dinosaur extinction at the end of the Cretaceous period, although there is current debate raging (Proposed by professor Gerta Keller from Princeton University.) that this event occurred about 300,000 years after the impact.
An impact calculator is available that allows one to select various impact parameters such as asteroid diameter, density, impact velocity and angle, as well as the nature of the impact site—water or rock and then see what the damage is at a specified distance from the impact. The results can be very chilling in the least!
A more recent event occurred over Siberia in June of 1908. This 10-megaton air-explosion leveled trees over an area almost 1000 square miles (2500 sq km). There have been other recent high altitude explosions over the Amazon in the 1930’s, Central Asia in the 1940’s, Greenland in 1996 and a significant event over the Mediterranean in 2002. The last event occurred during a period of extremely high tension between India and Pakistan, and had it happened over one of these nuclear-armed countries it could have been the trigger to an all out nuclear exchange. So we not only have to fear what Mother Nature can throw at us but our response to such an event!
Searching The Skies
Today we are aware of the potential lethal effects of such impacts and have been casting a wary eye towards the heavens, trying to identify these marauding interlopers before they appear unannounced. There are several programs that have been undertaken by different countries, groups and agencies: The NEA (Near Earth Asteroids), NEO (Near Earth Objects) surveys and the currently active, Spaceguard survey, LINEAR (LIncoln Near-Earth Asteroid Research), Catalina Sky Survey, Pan-Starrs and the Large Synoptic Survey Telescope, to be constructed in 2010 with first light in 2015. These programs have been focused on locating objects that cross Earth’s path and are as large or larger than 1 kilometer (.6 miles) in size. The newer projects, Pan-Starrs and LSST, have telescopes with very large CCD’s (the imaging device at the heart of your digital camera) that cover a much larger area of the sky, allowing them to scan the entire sky several times a month and at sensitivities down to the 25th magnitude. This increased sensitivity will allow cataloging of asteroids of the size of 100 to 140 meters in diameter. Note that current surveys (as of June, 2009) can’t detect objects on the order of 300 meters in diameter.
We may eventually map all of the NEO’s but the fact that several relatively close passes (less than the distance from Earth to the Moon) have only been discovered after they have passed by our planet should make one realize that this threat should be taken seriously!
© 2010, RC Davison