Space Debris and Other Threats From Outer Space (8 page)

Abstract

The official definition of a “mass extinction event” is one that wipes out over 30 % of the species on Planet Earth. Of the five mass extinction events that have occurred over the last half billion years, the last one is believed to have been caused by a massive asteroid, estimated to have been some 6 miles (10 km) in diameter. It hit the ground with a force equivalent to over 6 billion Hiroshima-sized atomic bombs, or one such bomb for every human on Earth. This massive asteroid created a crater some 62 miles (100 km) in diameter, as shown in Fig. 8.1. It created searing heat equivalent to the surface of the Sun and instantly killed by heat and concussive shock everything for a huge distance around. But this was just the first phase. It created hurricanes with winds of 500 miles (800 km) an hour and raging forest fires.

–Democritus of ancient Greece

The official definition of a “mass extinction event” is one that wipes out over 30 % of the species on Planet Earth. Of the five mass extinction events that have occurred over the last half billion years, the last one is believed to have been caused by a massive asteroid, estimated to have been some 6 miles (10 km) in diameter. It hit the ground with a force equivalent to over 6 billion Hiroshima-sized atomic bombs, or one such bomb for every human on Earth. This massive asteroid created a crater some 62 miles (100 km) in diameter, as shown in Fig. 
8.1
. It created searing heat equivalent to the surface of the Sun and instantly killed by heat and concussive shock everything for a huge distance around. But this was just the first phase. It created hurricanes with winds of 500 miles (800 km) an hour and raging forest fires.

The ultimate killer that managed to wipe out up to 70 % of the plant and animal species on the planet was the deadly cloud of iridium-rich debris that screened sunlight from the surface for many months. This absence of sunlight was the largest killer of all. The strike that was visible for only one second before impact not only ended the age of dinosaurs but also killed off almost everything else. The crater from such a massive hit to Mexico and the Caribbean is still visible today. This is a visible reminder that it can happen here. Asteroid and comet strikes are not just a concept for a science fiction screenplay but a very threatening reality [31].

If a K-T event were to happen today, the destruction to buildings, farmlands, dams, energy, information networks, and more would be vast. Perhaps most of humanity would be quickly returned to the Stone Age. Many plants, wildlife, livestock, and people would die due to the initial heat and energy, but the loss of sunlight would spread death for perhaps the majority of species across the planet. The losses in economic terms would not be in the trillions of dollars but the quadrillions of dollars. As death spread across the world, money would become meaningless as survival began to trump the concept of personal wealth. A repeat of the K-T event would be a very, very, very bad thing indeed. It is thus imperative for astronomical and space programs to do everything possible to detect such threats and to take preventive action against such a dire event.

At this time some 90 % of the asteroids that are greater than 1,000 m in size are thought to have been identified, but only 20 % of the asteroids in the range of 100–1,000 m have been located. A space object of this size is still quite massive. An asteroid, such as a known near Earth object named Apophis measures only about 300 meters in size, a small fraction of the asteroid that triggered the K-T extinction. Yet if Apophis were to hit Earth at 40,000 miles per hour (64,000 km/hour) would still do very substantial harm. NASA’s calculations indicate that it would have the equivalent power of 30,000 atomic bombs exploding. If this giant bolide were to hit the Atlantic Ocean near the East Coast, the ensuing tsunami would literally wipe out Boston, New York City, Washington, D.C., Miami and indeed every other coastal city, town and village in between. But this would only be the initial fatalities. Potentially billions of people could be lost from a direct hit from an Apophis-sized asteroid and the cloud of dust that would enshroud the planet for months to follow. Recently a meteorite the size of an aircraft carrier with an estimate size of 10,000 tons burst above Siberia, Russia with tremendous force. Thousands of people were injured and tens of thousands vehicles, homes and buildings damaged. This of course was like a pebble in relation to potentially hazardous asteroids are out there, but this was a wake up call to those who think this danger is imaginary.

Although the man in the street does not think about the threat from asteroids and comets, space scientists at NASA, ESA, and JAXA certainly do. The WISE space telescope launched by NASA in mid-December 2009 has been carefully as many NEOs as possible during its time in orbit as well as far flung galaxies as well. In the time between its launch and its shut down on February 17, 2011, the Wide-field Infrared Space Explorer had collected millions of images and completed one and a half inventories of Earth’s overhead sky by a systematic scanning process. The WISE satellite infrared sensors during its mission captured some 1.8 million images. These have allowed scientists to detect nineteen previously unseen comets. It also allowed the detection of over 33,500 asteroids and 120 previously unknown near-Earth objects (NEOs) that could become potential hazards to Earth at a future date. The infrared sensors that detect radiation outside the visible light range was able to detect low heat dwarf “brown stars” and detect objects that might be invisible due to dense dust cloud layers and other obscuring elements.

The quarter-of-a-billion-dollar project was certainly successful in living beyond its projected 10-month mission lifetime. Ultimately it was the exhaustion of the coolant for the infrared sensors that was the lifetime limiting factor. By cleverly shifting from a four IR sensor operation to only two the lifetime was extended further than expected. After the coolant was entirely expended, a further program called NEO-WISE was undertaken for three months up until its February 2011 end date. During this NEO-wise phase, the spacecraft was entirely devoted to searching for NEOs. But this task still remains to be completed.

Currently this comet- and asteroid-detecting spacecraft is now in hibernation with its coolant expended. In order to complete this crucial inventory of potentially dangerous asteroids and comets that might eventually hit Earth, additional space telescopes are needed. This would likely mean satellites with the ability to alter their range of view, more IR sensors and sufficient coolants to extend the spacecraft’s lifetime. The question that many would ask is: “Is it really necessary to spend this much money on the very long shot that we might find a killer asteroid?” It turn out there is a fairly good answer to that question.

Asteroid 2011 AG5 was discovered in January 2011 by the WISE imaging process. After initial analysis it was determined that there was a very credible chance that Asteroid 2011 AG5 could indeed collide with Earth in 2040. After further analysis it was decided that this was a long shot indeed unless something very strange happens in terms of the asteroid’s interaction with the Sun’s gravity, known as a “keyhole” event. This “keyhole” gravitation event that would make the asteroid do a “loop-de-loop” in a way that could put this asteroid in a resonance orbit with Earth. If this should happen it could result in about a 15 % chance of a horrific collision in 2040. The problem at this time is that this PHA (potentially hazardous asteroid) is on the other side of the Sun, and thus no precise measurements can be taken until late in 2013 or 2014. Figure 
8.2
indicates the possible “keyhole” event and how this could actually spell trouble down the road.