The solar system is full of massive chunks of rock and ice, and some of them are even big enough to follow their own orbital paths around the sun. According to a report from Discovery News, a new study warns that these massive space rocks whizzing past the Earth pose a much higher risk to life than previously thought.

The greatest area of concern is undoubtedly the asteroid belt between Mars and Jupiter, which is home to millions of chunks of space debris that can often fall out of orbit and come hurtling towards the surface of another planet.

In recent decades, however, scientists have noticed hundreds of massive comets with extremely large orbits, which they decided to call “centaurs.” The discovery of these new comets has led astronomers to reconsider their risk management strategies for preventing a collision with Earth.

The centaur comets are primarily made of ice and dust, and measure between 50 and 100 kilometers in diameter. Their orbits are highly elliptical, beginning past the planet Neptune.

The orbits follow a path around Jupiter, Saturn, Uranus, and Neptune, but it remains possible that one of these giant planets’ gravitational fields could knock a centaur out of orbit, potentially headed straight for the Earth. Researchers estimate that this can happen once every 40,000 to 100,000 years.

The real risk posed by incoming centaurs would be the debris that forms as they break up on their approach toward the sun. According to the study, “The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years. Assessment of the extraterrestrial impact risk based solely on near-Earth asteroid counts, underestimates its nature and magnitude.”

Scientists blame the mass extinction that wiped dinosaurs from the face of the Earth 65 million years ago was the work of a comet striking the planet. The mass of one centaur comet is greater than the combined mass of all of the asteroids counted in the Mars-Jupiter belt to date.

There is no present indication that a centaur comet is making its way for Earth, but the study offers a more balanced assessment of the impact risks within the solar system.

A press release from the Royal Astronomical Society describing the details of the study can be found here.