Astronomers discovered a "graveyard of comets." Some of the objects returned to life after lying dormant for millions of years, prompting researchers to dub them "Lazarus comets."

Comets are small in comparison to other extraterrestrial objects, they are made up of rock and ice, a Royal Astronomical Society press release reported.

The objects' notorious "tails" are composed of gas and dust.

"If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail.." the press release stated.

Comets typically take thousands of years to complete one revelation around the sun, there are also about 500 short-period comets.

Some researchers believe a comet colliding with the Earth may have been the origin of terrestrial water.

A study examined the asteroid belt between Mars and Jupiter, a common theory is the asteroids are would-have-been planets that were disrupted by Jupiter's strong gravitational pull.

Scientists were surprised to find 12 comets in the asteroid belt.

"We found a graveyard of comets", Professor Ignacio Ferrin, an astronomer with the University of Anitoquia, said. "Imagine all these asteroids going around the Sun for eons, 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 per cent."

The researchers believe the comets' orbits are disrupted by Jupiter's gravity. The change can bring the objects closer to the sun.

If this theory is true, the belt once held "thousands of active comets," but is now only a "graveyard."

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