A recent study by the University of Michigan has opened new perspectives in understanding how water reaches Earth. Scientists have discovered that up to 60% of near-Earth objects could be dark comets (asteroids that contain or previously contained ice). This discovery could hold the key to answering the age-old question of how water reaches our planet.

Dark comets combine the characteristics of asteroids and comets. Asteroids are icy rocky bodies that orbit closer to the Sun, usually in the region called the snow line. Comets, on the other hand, are icy bodies with a coma, a cloud of sublimating ice and dust. In addition, comets have small accelerations that are not due to gravity but rather due to ice sublimation, these are called non-gravitational accelerations.

Scientists have studied seven dark comets and estimated that between 0.5% and 60% of near-Earth objects could be dark comets, which have no coma but have non-gravitational acceleration. The researchers also suggest that these dark comets come from the asteroid belt, which suggests that objects in the asteroid belt contain ice.

The study also suggests a potential route for delivering ice to near-Earth space. How Earth gets its water is an old question. “We don’t know if these dark comets brought water to Earth, but there’s still debate about exactly how water from Earth got here. Our study showed that that’s another possible scenario,” said Aster Taylor, a graduate student in astronomy at the University of Michigan and lead author of the study.

Because the near-Earth environment is chaotic, near-Earth objects do not remain in their current orbits for long (more than 10 million years). The fact that the solar system is much older means that near-Earth objects came from another source.

To determine the origin of this dark comet population, Taylor and his co-authors created dynamical models that attributed non-gravitational accelerations to objects from different populations. They then modeled the paths of these objects over a period of 100,000 years, taking into account the non-gravitational accelerations. The researchers observed that many of these objects ended up where dark comets are found today, and found that of all the potential sources, the main asteroid belt was the most likely place of their origin. Other dark comets likely came from the inner belt of the asteroid belt.

This discovery could hold the key to understanding the distribution of water on Earth and help answer the age-old question of the origin of water on our planet.