A team of researchers from NASA announced the discovery of seven dark comets — objects that look like asteroids but behave like comets. It turned out that they are divided into two different populations.
Anomalous acceleration
Scientists first learned of the existence of dark comets in March 2016, when they discovered that the trajectory of asteroid 2003 RM had deviated slightly from its intended orbit. This deviation could not be explained by typical asteroid behavior, such as the slight acceleration known as the Yarkovsky effect. It consists in the appearance of a weak jet pulse due to thermal radiation from the surface of the asteroid heated during the day and cooling at night, giving it additional acceleration.
In 2017, astronomers first discovered a celestial body coming to the Solar System from interstellar space. The object, named Oumuamua, also showed anomalous acceleration similar to the behavior of 2003 RM, giving rise to much speculation that it was an alien spacecraft.
By 2023, researchers had discovered seven solar system objects that looked like asteroids but accelerated like comets without forming any visible tail. This was enough for the astronomical community to put them in a separate category: “dark comets”.
Two types of dark comets
A team of researchers from NASA’s Jet Propulsion Laboratory has attempted to find an answer to the question of the origin of dark comets. While analyzing the data, they were able to find seven more such objects, thus doubling their known population. This sample was enough to begin to determine if there was anything that set them apart.
As it turns out, the answer to that question is yes. By analyzing the reflectivity of their surface and orbits, scientists have discovered that there are two different types of dark comets in our Solar System. The first, dubbed outer dark comets, have similar characteristics to the Jupiter family of comets. Their main distinguishing features are very elongated orbits and larger sizes (hundreds of meters or more across).
The second group (inner dark comets) inhabit the inner part of the Solar System. They move in nearly circular orbits and are noticeably smaller, measured in tens of meters.
Like many other astronomical discoveries, this finding not only expands our knowledge of dark comets, but also raises a number of additional questions about where they originate and what causes their anomalous acceleration. Scientists are also interested in whether they contain water and organic compounds. Dark comets may be previously unknown suppliers of “ingredients” that contributed to the emergence of life on Earth.
Provided by NASA
