Astronomers at Columbia's Universidad de Antioquia have discovered what have since been dubbed "Lazarus" comets, along with their origin: the comet graveyard. The team's findings may explain why some activity of comet-like objects has been spotted in the solar system.
Described in the Monthly Notices of the Royal Astronomical Society, researchers at the University of Antioquia think they have discovered a place in the solar system where comets are taking on asteroid-like orbits. Called "Lazarus" comets, these huge chunks of ice and rock are not located far out in stretched elliptical orbits, like most comets astronomers know of.
Most comets make regular appearances in the solar system, but because their orbits are so wide and elongated, one only sees them nearby at particular times. Think of Halley's Comet, which is visible from Earth every 75 years or so. Other comets have even longer orbits and periods when they are not in the solar system. But unlike typical comets, Lazarus comets have been lying dormant in the asteroid belt that sits between Mars and Jupiter. The asteroid belt alone, according to the University of Antioquia's press release, contain at least 85,000 dormant and extinct rocky comets.
Comets become extinct when the frozen water content is fully expelled, but dormant comets may become active again, thus rising from the dead like Lazarus, given the right kind of increased solar activity. Both kinds of comets were found in the asteroid belt, and the existence of dormant comets might explain why these comets are found popping up in non-comet-like patterns.
"We found a graveyard of comets", said Professo Ferrín of the Universidad de Antioquia. "Imagine all these 500,000 asteroids going around the Sun in those sidereal spaces, absolutely dark, absolutely cold, and absolutely silent, year after year, eons after eons. Except that we have found that some of those objects are not dead, but are dormant comets that may come to life if the energy that they receive from the Sun increases by a few percent. That is what we are seeing today in the main belt of asteroids."
The current theory about the asteroid belt is that it is the remains of rocky beginnings of a planet that never quite formed. However, given that paradigm, you would not expect to find comet remains, or dormant comets coming back to life, in the belt. The team's new theory is that million of years ago, the asteroid belt had thousands of active comets, but as they lost their ice content, their activity diminished. The extinct comets are what you see in that region - the comet graveyard. The researchers estimate that as much as 17 percent of the asteroid belt's population consists of extinct or dormant comets.
But about 11 comets have become active again, due to solar activity shifting their orbit slightly, and causing the "Lazarus" moniker to be placed on them. And the researchers said that there could be many more Lazarus comets out there that have not been detected yet. The Columbian astronomers published a paper detailing their results and theory at the Monthly Notices of the Royal Astronomical Society, which can be found here.