There are about seven times more large comets at the outer edge of our solar system than once thought, according to NASA. While these comets spend most of their time billions of miles away from the sun, when they do edge into our region of the solar system, they have the potential to collide with planetsincluding Earth.

Scientists used the Wide-field Infrared Survey Explorer(WISE) spacecraft to work out the size and numbers of short- and long-period comet populations. This refers to the orbital periodlong refers to comets that take more than 200 years to orbit the sun, while short-period comets take less than 200 years.

Their findings, published inThe Astronomical Journal, show there are vastly more long-period comets than previous estimates had indicated. The number of comets speaks to the amount of material left over from the solar systems formation, lead author James Bauer said in a statement. We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought. The Oort Cloud is a shell of icy objects that surrounds the solar system, far beyond Neptune.

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In the study, scientists looked at long-period comets and Jupiter-family cometscomets that have an orbital period of less than 20 years and are controlled by Jupiter. Comets are formed from material that was left over from the formation of the planet, so studying them helps us understand the evolutionary history of the solar system.

In total, in the area of the sky surveyed, scientists found56 long-period comets and 108 short-period comets. Over the course of the eightmonths of the survey, our results indicate that the number of long-period comets passing within 1.5 au [about 140 million miles] are a factor of several higher than previous estimates, they wrote.

This illustration shows how scientists used data from NASA's Wide-field Infrared Survey Explorer spacecraft to determine the nucleus sizes of comets. NASA/JPL-Caltech

By getting a better understanding of how many long-period comets there are and how they differ from Jupiter-family comets, researchers are able to gain a key insight into how and why the solar system appears to us as it does.

Researchers found that there are far more long-period comets than Jupiter-family cometsand that long-period comets are on average twice as big, measuring at least 0.6 miles across. Our results mean theres an evolutionary difference between Jupiter-family and long-period comets, Bauer said.

They also discovered that long-period comets passed the sun far more often than had been thought. This finding is important, as it has implications for the risk of comets hitting Earth and indicates more of them have probably affected planets, such as delivering icy materials to them. Comets travel much faster than asteroids, and some of them are very big, study co-author Amy Mainzer said. Studies like this will help us define what kind of hazard long-period comets may pose.

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NASA: There Are Far More Massive Comets Hiding at the Edge of the Solar System Than We Thought - Newsweek