The first breakthrough study has just more than doubled the number of known “dark comets”-those mysterious, shadowy creatures of our solar system displaying both asteroid-like and cometary behaviors. A paper just published in Proceedings of the National Academy of Sciences shows that these mysterious bodies come into two clear categories and that their role in the solar system possibly even life may be far from benign.
The first dark comet was discovered in 2016 when astronomers noticed something odd coming from the near-Earth asteroid 2003 RM. Its path was bent as if it was ejecting volatile material off its surface. However, unlike true comets, 2003 RM did not develop a visible tail, which led researchers to refer to the object as a “dark comet.” Then, in 2017, another interstellar visitor, ‘Oumuamua, was discovered exhibiting comet-like acceleration without developing a tail. That finding prompted the realization that dark comets were, in fact, a new class of objects that further blurred the line between asteroids and comets.
In 2023, the discovery of six other similar objects with hybrid features gave further credence to dark comets. With these seven more, a total of 14 such objects are now known as dark comets. The investigation so far by the researchers has shown that based on their size and orbit, the objects can be further divided into two classes: outer dark comets and inner dark comets.
The outer dark comets are larger and have highly eccentric, elliptical orbits much like the Jupiter-family comets. On the other hand, inner dark comets, being smaller, make their journeys within the inner solar system in approximately circular orbits. This might eventually enable scientists to find out their source and origin.
Dark comets can also yield important clues regarding life on Earth. A recent study hypothesized that many near-Earth objects are fragments of larger bodies that once had homes in the asteroid belt between Mars and Jupiter. Such fragments might hold great importance in the transport of the building blocks of life to Earth.
And so, as researchers continue to learn about dark comets, they could well unlock secrets about the solar system’s formation and the essential processes that led to life on our planet.
