Discoveries of giant comets roaming outside of our solar system has scientists worrying about encounters with the Earth that could potentially be devastating, according to an article in the Daily Mail.

The National Aeronautics and Space Administration (NASA) has primarily focused on asteroids located in belt between Mars and Jupiter and the agency has identified and is tracking almost 13,000 near-Earth objects within our solar system.  NASA has classified about 1,600 as Potentially Hazardous Asteroids (PHAs) that they are monitoring closely.

These giant comets, known as centaurs, are balls of ice and dust that have unstable orbits that begin out past Neptune.  Hundreds of them have been discovered in the last few decades and more are being spotted each year.

They can be as wide as 61 miles across and contain more mass than all the asteroids with Earth-crossing orbits discovered so far.  These giant centaurs’ orbits cross paths with Jupiter, Saturn, Uranus and Neptune, and the concern is what happens when they get too close to one of these planets.

Some research suggests Saturn’s moon, Phoebe, was once a centaur that was captured by the planet’s gravitational field as it passed by sometime in the past.

The researchers say about every 40,000 to 100,000 years, a centaur will ricochet off the gravity field of one of those planets and be directed towards the Earth.  As they get closer to the Sun, they begin to disintegrate and break up into smaller pieces and debris trails, and that would make contact with the Earth inevitable.

The team wrote in its report the disintegration of such a comet would produce a prolonged period of strikes on the planet that could last as much as 100,000 years.  Many scientists believe such an event brought about the extinction of the dinosaurs, and could be responsible for other such extinctions across history.  It is possible the first life on our own planet could have been brought here by one of these centaurs, depositing water and organic molecules as it struck the Earth.

They also added that the focus on near-Earth asteroids causes an underestimation of the impact an encounter with a centaur would have on Earth, and life as we now know it.  They say their work suggests we need to look beyond the Earth’s immediate neighborhood and closely monitor the giant comets lurking outside of Jupiter’s orbit.

The team presented their findings in the Royal Astronomical Society journal, Astronomy and Geophysics.