On 13 April 2029, asteroid 99942 (heretofore known as Apophis) is estimated to come within 18,300 miles of the Earth. This alarming distance is even more shocking when one takes into consideration that modern geosynchronous satellites orbit the Earth at approximately 26,000 miles. Once the shock has cleared, there is another fact you need to take into consideration: astronomers across the globe are tracking Apophis every day. It is currently labeled as a “0” on the Torino Scale. The Torino Scale is used to categorize the likeness of an asteroid impact on Earth.
The impact of Apophis on Earth is improbable but it is more marketable in today’s society that it will hit. The question at hand is how do astronomers track asteroids such as Adophis? Furthermore, what have been the technological developments that have led to modern asteroid tracking practices? A brief journey through this development follows. It should open the door to understanding just how astronomers across the globe track potential world-killing asteroids like Apophis.
The first asteroid ever discovered was Ceres. Italian astronomer, Giuseppe Piazzi located it in the night sky in 1801. Piazzi’s method to discover Ceres predominated astronomy for some time. Discovery was performed by differentiating an asteroid’s motion from that of the stars. This was conducted through telescopic observation and careful documentation of the asteroid’s position over a period of 4-10 days. It was a painstakingly slow process and required the coordination of dozens of astronomers across the globe.
In the 1890s the revolution of photography made it much easier for astronomers to identify objects in space. Through a relatively “simple” process, astronomers attached cameras to their telescopes. This allowed them to develop an exposure which allowed them to differentiate the movement of an object against the background of stars.
Hubble Telescope. Image Credit: NASA/ESA
Nineteenth century astronomers utilized two different approaches to produce this exposure. The first was to take one very long exposure and then visually inspect the picture for any trails left by moving objects. The second approach required a much more complex process and much more time to reach the same end. The second approach required the astronomer to take multiple exposures. The exposures would be compared utilizing either a blink comparator or a stereoscope to identify minor movements in objects between the separate exposures. In 1891, Max Wolf discovered the first asteroid utilizing photography: 323 Brucia.
In the 1950s the world was full swing into the “Space Race” and the United States and Soviet Union were launching satellites into orbit on almost a weekly basis. These satellites ushered in a new era for asteroid research. Astronomers across the globe competed to include their small space-based telescopes and photo-telescopes on these orbiting space machines. For the most part, the photographic technology had not changed in the sixty years since its initial use. However, by placing the telescopes and cameras aboard satellites, astronomers discovered a whole new universe. While on Earth these telescopes and photo-telescopes had to compensate for the degradation imposed on their observations by the atmosphere, but once in orbit the atmosphere was no longer an issue.
Prior to the launch of the Hubble Space Telescope (HST) in the 1990s, the Infrared Astronomical Satellite (IRAS) revolutionized asteroid research. When IRAS became fully operational in 1983, scientists were able to point its instruments at the asteroid belt and establish an infrared map of the entire thing. The infrared exploration of asteroids in space continues to this day. The roots of this exploration can be traced back to IRAS.
While IRAS was paving the way into infrared studies of asteroids, another technology was being introduced that would forever change how asteroid research would be conducted. In 1984, the Spacewatch system demonstrated a new technology known as charged couple devices (CCD). CCDs utilized computer processing to determine if an object was moving in the sky. A drift-scan technique; where the readout rate is clocked to the sidereal drift rate across the CCD; created an image that displayed the movement of objects in the sky. The technology quickly proved its worth. It produced far better results than photographic technology and earth-based telescopic observation. The CCD revolution had begun. Since the late 1980s CCDs have become the technology of choice when conducting asteroid observation.
Current CCD cameras are similar to those used in digital camcorders. They record images digitally. Separated by several minutes, multiple images are taken of the same region of the sky and then fed into a computer system. The system then differentiates any movement by objects in the sky, presenting a digital readout to the astronomer. The astronomer completes the process by verifying the movement and documenting it.
These CCD cameras have since been installed on terrestrial-based telescopes and orbital telescopes. This has revolutionized asteroid tracking once again. Furthermore, CCD cameras have been installed on solar system probes, to include some that have landed on asteroids. These having taken surface pictures of asteroids and beamed them back to Earth. These probes have also rocketed regolith (surface material) samples back to Earth. This allows for the study of the chemical make-up of asteroids.
Beyond CCD satellites, telescopes, and probes, new radar telescopes have been placed strategically across the globe and in orbit; allowing astronomers to develop radar images of the shape and structure of asteroids far off in the asteroid belt between Mars and the outer planets. This radar technology is in its infancy but the possibilities of what it can do are endless.
Since the first asteroid was discovered over two centuries ago, the technology to continue discovery has gone under many changes. Piazzi used a simple telescope and mathematical equations to verify the existence of Ceres. This was the norm until the invention of photographic technologies over 90 years later. Photographic observation of asteroids evolved as photography equipment evolved. It was the mainstay technology for astronomers until the invention of infrared telescopes and CCDs in the 1980s. For the last 25 years or so, infrared telescopes, CCD cameras, and now radar telescopes have been paving the way to the future for asteroid researchers.
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