Watching the heavens for NEOs
A few months ago after I was privileged to see an early evening bolide (much like the one in the photo), I wondered what the ancients and not-so-ancients thought about such sights. After all, the heavens are full of objects that enter our atmosphere and threaten to harm us, and one only has to look at the Barringer/Meteor Crater in Arizona or the photos from the 1908 Tunguska event in Siberia to begin to understand the depth of destruction that could result if—or make that when—a large object should hit our planet.
When Comet Shoemaker-Levy 9 crashed into Jupiter in 1994, the prospect of Earth being hit by an object from space became more real to the average person, even capturing the imagination of Hollywood, which offered up two competing movies in 1998: Deep Impact and Armageddon.
The former involved a comet colliding with the earth, and the latter, an asteroid. Both scenarios involved attempts by scientists (and oil drillers, in the case of Armageddon) to deflect the trajectory of the object to eliminate, or at a minimum, decrease the impact. In these movies, of course, humanity was saved; but in a real future scenario, would we be so lucky?
Until the last few decades, we could only watch the sky and wonder what doom might come raining down on us from the heavens, catching us unawares and unprepared. It wasn't until the 1970s that scientists were better able to track objects in space due to advancements in radiometry, photometry, and spectroscopy.
The 1980s saw the emergence of the Spacewatch program, designed to detect and track NEOs, or near-Earth objects. Starting in 1984, the 0.9-meter Newtonian Spacewatch telescope was used at Kitt Peak in Arizona for surveying comets and asteroids. It was the first telescope to detect comets using electronic detectors (charge-coupled devices, or CCDs) instead of photographic plates. In 1993, a 1.8 meter telescope was added for detecting NEOs.
Some of the notable achievements of Spacewatch include being the first to detect a near-Earth asteroid with CCD technology (1989); the first CCD discovery of a comet (1991); and the discovery of two new asteroid populations.
Another discovery of the Spacewatch program is that there are many more small near-Earth asteroids (those less than 100 meters in diameter) than was previously thought. The largest near-Earth asteroids are about 10 kilometers in diameter. Scientists have estimated that the impact of an asteroid the size of only 1 kilometer in diameter would have a global catastrophic effect. Those that are smaller, like the ones in Siberia and Arizona, would cause regional devastation, but leave the rest of the world intact—though not unaffected.
There are about 900 near-Earth objects more than 1 kilometer in diameter. While statistically, one of these objects impacts the Earth every 330,000 years, realistically, the chance is just as great that it could happen tomorrow.
With the efforts of Spacewatch and similar programs at other observatories around the globe, it is hoped that the 900 potentially catastrophic NEOs will be found within the next few decades.