A recent study led by the University of Michigan has shed new light on the debate surrounding the origin of water on Earth. The research suggests that a significant portion of Earth's water may have come from 'dark comets,' a type of near-earth object that exhibits nongravitational accelerations due to outgassing but lacks a visible coma.
According to the study, up to 60 percent of near-earth objects could be classified as dark comets, containing or having contained ice that could have contributed to Earth's water content. These findings imply a larger presence of volatiles and organics in the inner Main Asteroid Belt than previously known.
Dark comets differ from ordinary comets in that they do not display a visible coma and are more akin to asteroids in terms of their orbits. Despite their asteroid-like appearance, dark comets exhibit nongravitational accelerations indicative of degassing from their icy surfaces.
The study examined seven dark comets and estimated that there could be between 50 and 6000 additional dark comets among near-earth objects. These objects, though small in size (tens to hundreds of meters), play a potential role in delivering water to Earth.
Researchers created dynamical models to trace the origins of dark comets, suggesting that the Main Asteroid Belt is a likely source for these objects. The study also highlighted the challenge of detecting fully devolatilized comet fragments in near-earth space.
Looking ahead, the upcoming Hayabusa2 mission to asteroid 1998 KY26 in 2031 is expected to provide valuable insights into the origins and composition of dark comets. By studying these objects further, scientists aim to better understand their role in Earth's water history.
As the search for dark comets continues, researchers emphasize the importance of observing these objects for signs of activity, particularly when they are closest to the sun. Discovering more dark comets could offer crucial clues about their composition and origins, unlocking new knowledge about the sources of Earth's water.
