An international team led by NASA has tested the International Asteroid Warning Network, which successfully tracked a potentially dangerous asteroid as it made a close flyby of the Earth in October. Billed as the first global exercise using a real asteroid to test global response capabilities, the TC4 Observation Campaign observed and plotted the orbit of the asteroid 012 TC4 as it passed within 27,200 mi (43,780 km) of the Earth.
The odds of the Earth being struck by a large asteroid are small, but given the fact that even a small asteroid can deliver the impact of a tactical nuclear weapon, preventing or at least predicting such impacts is a high priority in the space community. However, like teams of Second World War bomber spotters, asteroid tracking requires practice and, since it isn't possible yet to create dummy asteroids, astronomers are using the real thing.
In this case, the target was asteroid 2012 TC4, which is a small, elongated asteroid approximately 50 ft (15 m) long and 25 feet (8 m) wide. It was originally spotted by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii as part of the NASA Planetary Defense Coordination Office's (PDCO) NEO Observations Program. Though it passed out of observational range quickly, astronomers managed to plot its orbit well enough to predict its return this year. In April of this year, it was selected to test the International Asteroid Warning Network.
In July 2017, TC4 was reacquired by the European Southern Observatory's Very Large Telescope, and observatories around the world joined in as it approached the Earth and made its closest pass in October. The goal of the exercise was to not only track the asteroid, but to learn more about its properties, assess whether it will one day hit the Earth, and, most important, to see how well the network could communicate with the observers in the United States, Canada, Colombia, Germany, Israel, Italy, Japan, the Netherlands, Russia and South Africa.
According to NASA, the exercise was a success and resulted in a better understanding of the target asteroid and its potential threat. The Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory (JPL) in Pasadena, California was able to precisely calculate the asteroid's trajectory, including the effects of solar radiation pressure, using both optical and radar telescope, allowing astronomers to conclude that 2012 TC4 does not pose a hazard to Earth.
In addition, scientists were able to deduce the asteroid's shape and clock its rotation, giving it a "day" of 12 minutes as it tumbles as well as spins. Unfortunately, adverse weather conditions prevented observers from determining the physical composition of TC4, which may consist of either dark, carbon-rich or bright igneous material.
Because the network is intended for the practical purpose of Earth defense rather than pure science, an important component of the exercise was to see how well the observers could communicate with one another as well as with the US government up to the executive branch in the event of an actual emergency.
"We are much better prepared today to deal with the threat of a potentially hazardous asteroid than we were before the TC4 campaign," says Michael Kelley, TC4 exercise lead at NASA Headquarters.