A team of astronomers from the University of Anitoquia in Medellin, Columbia has discovered a graveyard of comets, some of which, they say, could become active again after remaining dormant for millions of years. The newly discovered comets are located in the main asteroid belt between Mars and Jupiter, which contains at least 85,000 dead and dormant comets. The study, by astronomer Prof. Ignacio Ferrin and his colleagues, will appear in the upcoming issue of Monthly Notices of the Royal Astronomical Society.
Comets fizzle out when most of their water content has evaporated. However, they may become active again with an increase of solar energy by only a few percent, according to Ferrin. This can occur fairly easily, he says, if they are pushed closer toward the sun by Jupiter’s gravity. When this happens, the shape of a comet’s orbit can change, drawing them nearer to the sun. When heated by the sun, the dormant comet’s water content begins to sublimate and causes it to become active again as long as its energy lasts, the authors write. They dubbed these comets ‘Lazarus comets’ after the biblical figure Lazarus who was resurrected several days after his death by Jesus Christ.
The asteroid belt, which astronomers believe originated many millions of years ago, is estimated to contain at least 500,000 celestial objects ranging in size from 1 kilometer (3,280 feet) to 800 kilometers (497 miles) in length, according to the Royal Astronomical Society. Asteroids are thought to be the leftover building blocks of a planet that never formed due to disruption by Jupiter’s strong gravitational pull. Comets differ from asteroids in that they are located farther from the sun and produce a temporary atmosphere in the form of a tail as they are pulled closer to the massive, burning star.
According to astronomers, the main asteroid belt was once populated by thousands of active comets, which ultimately burned out as they aged. Over the past ten years, however, researchers have found 12 active comets in the asteroid belt. Because this came as somewhat of a surprise, the Medellin team decided to investigate their origin. What they discovered suggested that these re-activated comets came back to life after moving closer to the sun, which gave them a sufficient energy boost to cause them to rejuvenate.
“These objects are the ‘Lazarus comets,’ returning 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 observed.
To date, only a dozen spacecraft have investigated the asteroid belt. Additional research may determine the number of comets that were once active there and perhaps identify potential Lazarus comets.