Astronomers Discover Graveyard for 'Lazarus Comets' Near Mars and Jupiter

First Posted: Aug 02, 2013 09:45 AM EDT

Astronomers have made a surprising discovery. They've found a veritable graveyard for comets in our solar system. These objects have been inactive for millions of years. Yet some of the comets have returned to life, causing researchers to name them "Lazarus comets."

Comets are some of the smallest objects in the Solar System. Only a few miles across, they're usually made up of a mixture of rock and ice. When they journey close to the sun during their travels through space this ice can turn to gas which forms a characteristic tail, such as the one seen on the Comet ISON.

In order to examine these objects a bit more closely, the researchers looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter. This area contains more than one million objects that range in size between 1 to 500 miles across. Asteroids are essentially the building blocks of planets that never formed. In this particular area, though, researchers found 12 active comets--something of a surprise for the astronomers.

"We found a graveyard of comets," said Ignacio Ferrin, one of the researchers, in a news release. "Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few percent."

It's actually surprisingly easy for these comets to rise from the dead. The orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter, which means that the shapes of their orbits change. This can lead to a decrease in the minimum distance between the object and the Sun and a slight increase in average temperature.

"These objects are the 'Lazarus comets,' returning to life after being dormant for thousands or even millions of years," said Ferrin. "Potentially any one of the many thousands of their quiet neighbors could do the same thing."

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.

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