A researcher from NASA has revealed that comets actually pose a bigger threat to Earth than asteroids. Unlike asteroids, the researcher noted that comets are almost impossible to detect before they collide with Earth.

Comets are frozen balls of gas, rock and dust that are known to orbit the Sun. Usually, comets are very massive and can be as big as a small town.

During a previous meeting of the American Geophysical Union, researcher Joseph Nuth of NASA’s Goddard Space Flight Center talked about how dangerous comets can be. Usually, when it comes to Earth-ending scenarios, asteroids are almost always the main topic of the discussion.

“Comets have largely been ignored by people that are interested in defending the planet,” Nuth said, as per Space.com.

According to the NASA researcher, agencies and the public are more interested in asteroids than comets simply because they are far more common. In terms of the number of known asteroids and comets, the former outweigh the latter. In addition, asteroids are easier to detect than comets because they usually occupy Earth’s surrounding regions.

Unfortunately, the mysterious nature of comets is exactly what makes them far more dangerous to Earth than asteroids. Since comets are known to orbit near the dark outer edges of the Solar System, astronomers rarely get the chance to spot and observe them. This means that they can remain undetected for long periods of time until they end up on a collision course with Earth.

 “A comet comes out of nowhere, pretty much,” Nuth said.

Although asteroids are made up of harder materials than comets, the latter can still cause extinction-level events on Earth due to its large size. These objects, which can be as big as entire towns or mountains, could hit Earth while traveling at speeds of tens of thousands of miles per hour.

If Earth gets hit by a comet of this magnitude, the planet could experience the same catastrophic event that wiped out the dinosaurs 66 million years ago. Aside from the massive energy that will be released from a comet’s impact, the planet will also experience a nuclear winter that can last for decades or even longer.