Earlier this week, the HAARP antenna array in Alaska transmitted a series of longwave radio signals to an asteroid passing behind the moon just two distances from Earth. It is believed that the signals penetrated the asteroid, giving scientists information about the asteroid’s interior, and equipping them with another piece of information that could be crucial to protecting the planet from collision.

Most asteroid-observing programs here on Earth use shortwave radio frequencies, including visual asteroid surveys such as those provided by NASA’s worldwide Center for Near-Earth Object Studies (CNEOS) observatories, or those provided by the NASA Deep Space Network. size, location and paths of asteroids. While these programs provide extremely valuable data on any potential asteroid impact hazards, they are limited in that they can only “see” the surface of the asteroid.

HAARP, run by the University of Alaska Fairbanks, has traditionally been used to analyze our ionosphere (and has even been included in several conspiracy theories). It is also capable of sending long wave radio signals. Such signals can penetrate objects, allowing observers to gain insight into their internal structure. In that case, studying an asteroid’s interior architecture may one day give scientists a way to blast or deflect a space rock that comes too close to Earth.

The target of the observation was the asteroid 2010 XC15, which is about 500 feet (152 meters) in diameter, making it small by asteroid standards. It now passes the Earth at a distance of two Moons, or twice the distance from the Earth to the Moon.

The HAARP experiment joins other asteroid research efforts, such as NASA’s DART mission, which crashed a spacecraft into an asteroid in September, and the OSIRIS-REx mission, which captured a piece of land from asteroid Bennu in 2020.

While no one expects the asteroid to cause any trouble to Earth anytime soon, astronomers have taken a close look at an asteroid known as Apophis, which will pass near Earth on April 13, 2029, at a distance of about 20,000 miles (32,187 km). In terms of context, it’s closer than many satellites currently orbiting the planet. All this said, while Apophis was once thought to be dangerous, researchers using updated observations now believe it won’t be a threat for at least a century, giving scientists plenty of time to figure out how to deal with it.