An international team of astronomers from the United States, the Czech Republic and Italy has concluded that more than half of objects in near-Earth space could be called dark comets, a little-studied type of asteroid. The study was published in the scientific journal magazine Icarus.
Dark comets are something of a mystery because they combine features of both asteroids and comets.
Asteroids are ice-free rocky bodies that orbit close to the Sun, usually in a region called the ice line. This means that they are close enough to the Sun that any ice that may have been carried by the asteroid will sublimate, or change from solid ice directly to gas.
Comets are icy bodies that exhibit a diffuse coma, or comet-like cloud, of ice and dust particles. In addition, comets often have small accelerations, called non-gravitational accelerations, that are caused by the sublimation of ice, not by gravity.
The team studied seven dark comets and calculated that between 0.5% and 60% of near-Earth objects could be dark comets, which have no coma but have non-gravitational accelerations.
To determine the origins of this dark comet population, the scientists created dynamical models that attributed non-gravitational accelerations to objects from different groups. They then modeled the paths these objects would follow given the non-gravitational accelerations determined over a period of 100,000 years.
Experts noticed that many of these objects were found in the same places as dark comets today, and found that of all the potential sources, the main asteroid belt was the most likely place for their origin.
The study also found that the remaining dark comets likely came from the inner asteroid belt.
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