2012 TC4: NASA's Planetary Defense Systems Put to the Test Over Near Miss Asteroid

Animation showing asteroid 2012 TC4, which will fly-by Earth on 12 October.

On 12 October, an asteroid will pass by Earth at an astronomical stone's throw from the surface of Earth, whizzing past us at a distance of as little as 4,200 miles. And NASA is using this opportunity to test out some of its planetary defense systems.

2012 TC4 is a small asteroid, measuring between 30 and 10 feet wide. This is just a little bigger than the Chelyabinsk meteor that impacted over Russia in February 2013. During this close approach, there is no risk to the planet: "We know the orbit of 2012 TC4 well enough to be certain that it won't hit Earth," Paul Chodas, manager of the Center for Near-Earth Object Studies, explained earlier this month.

The asteroid, however, presents NASA with an opportunity to test out some of the systems it has in place for protecting the planet from dangerous Near Earth Objects.

"Scientists have always appreciated knowing when an asteroid will make a close approach to and safely pass the Earth because they can make preparations to collect data to characterize and learn as much as possible about it," Michael Kelley, who led the observations of 2012 TC4, said in a statement. "This time we are adding in another layer of effort, using this asteroid fly-by to test the worldwide asteroid detection and tracking network, assessing our capability to work together in response to finding a potential real asteroid threat."

Planetary defense systems currently used by NASA focus on observations and monitoring via a network of observatories. Testing their capabilities on an asteroid that is coming so close to Earth means scientists can refine their techniques and better understand the strengths and limitations of their capabilities.

At present, the size of 2012 TC4—and the distance it will pass Earth—is poorly constrained. While the closest distance it will come to us is 4,200 miles, it could be up to 170,000 miles, which is about two-thirds of the distance between the Earth and the Moon.

Vishnu Reddy, from the University of Arizona's Lunar and Planetary Laboratory, said: "This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications."

Scientists plan to use telescopes to establish the asteroid's trajectory. "This is the perfect target for such an exercise because while we know the orbit of 2012 TC4 well enough to be absolutely certain it will not impact Earth, we haven't established its exact path just yet," Chodas said. "It will be incumbent upon the observatories to get a fix on the asteroid as it approaches, and work together to obtain follow-up observations [that] make more refined asteroid orbit determinations possible."

Protected orbit of the asteroid 2012 TC4. NASA/JPL-Caltech

As well as observation networks for monitoring asteroids, NASA is also working on developing more direct approaches to planetary defense, including deflection. In June, the space agency announced its first asteroid deflection mission—Double Asteroid Redirection (DART) had entered the next phase of design.

This plan involves hitting the asteroid to shift its orbit, pushing it out of Earth's path. The first target for DART is a binary asteroid (an asteroid with two bodies) that has a distant approach to Earth in 2022 and 2024. NASA will hit one of the bodies to see how much it veered off course compared to the other body in the system.

"DART is a critical step in demonstrating we can protect our planet from a future asteroid impact," said Andy Cheng, co-leader on the mission. "Since we don't know that much about their internal structure or composition, we need to perform this experiment on a real asteroid. With DART, we can show how to protect Earth from an asteroid strike with a kinetic impactor by knocking the hazardous object into a different flight path that would not threaten the planet."