Scientists have discovered seven new “dark comets,” celestial objects that blur the boundary between asteroids and comets, bringing the total number of known dark comets to 14. These objects resemble asteroids but move like comets and could provide valuable insights into the origins of Earth’s water and the development of life.
Unlike traditional comets, dark comets do not have visible tails, but they exhibit non-gravitational acceleration, meaning their movement is influenced by forces beyond gravity.
The newly discovered dark comets fall into two distinct groups: outer dark comets and inner dark comets.
Interestingly, dark comets may contain water ice even within the inner solar system, challenging the traditional “snow line” theory. Their potential ice reservoirs suggest they might have played a crucial role in delivering water to Earth, offering key clues about the origins of life.
The search for dark comets will expand with advanced tools like the Vera C. Rubin Observatory, which will begin identifying more of these objects starting in 2025.
A fascinating study published in the Proceedings of the National Academy of Sciences reveals the discovery of seven new dark comets, exciting astronomers worldwide.
This latest discovery brings the total number of known dark comets to 14, marking a significant step in unraveling their mysteries. These enigmatic objects, which resemble asteroids but travel like comets, could hold critical information about Earth’s water origins and the evolution of life.
Researchers have classified dark comets into two groups: those in the outer solar system and those in the inner solar system. This finding not only deepens the mystery surrounding these objects but also opens new avenues for understanding their role in shaping our solar system and delivering essential materials to Earth.
Dark comets represent a relatively new category of celestial objects that challenge traditional understandings of comets and asteroids.
Unlike typical comets, often described as “dirty snowballs” composed of ice, dust, and rock, dark comets lack the characteristic tails formed when solar radiation vaporizes their icy layers. Instead, they appear as faint, point-like objects, much like asteroids.
However, dark comets exhibit non-gravitational acceleration, meaning their trajectories are influenced by forces beyond gravity. In regular comets, this additional push comes from ice sublimating into gas, creating thrust that propels them forward. Dark comets, however, show no visible signs of evaporation, leaving scientists questioning the source of their acceleration.
The first hints of dark comets emerged in 2016 when researchers observed that the object 2003 RM was deviating from its expected orbit. This anomaly couldn’t be explained by conventional forces affecting asteroids, such as the Yarkovsky effect, which describes how sunlight subtly alters an asteroid’s trajectory.
Then, in 2017, the interstellar object ʻOumuamua further fueled interest in these enigmatic bodies. Like 2003 RM, ʻOumuamua displayed non-gravitational acceleration without visible signs of evaporation, sparking widespread scientific curiosity.
The discovery of seven new dark comets has allowed scientists to classify them into two primary groups based on their location, size, and orbital characteristics.
- Outer Dark Comets reside in the outer solar system, beyond Jupiter’s orbit. They are larger, with diameters ranging from hundreds of meters to several kilometers, and follow elliptical orbits similar to those of traditional comets. Their orbital properties suggest a connection to Jupiter-family comets, which originate from the outer solar system and enter orbits influenced by Jupiter’s gravity.
- Inner Dark Comets exist within the inner solar system and are much smaller, measuring just a few dozen meters or less. They follow nearly circular orbits, similar to planets, and are believed to originate from the inner region of the asteroid belt.
Despite their small size, these objects also exhibit non-gravitational acceleration, indicating the presence of volatile substances—likely ice—beneath their surfaces.
One of the most intriguing aspects of dark comets is their potential to contain water ice. When the solar system formed 4.5 billion years ago, a boundary known as the “snow line” separated regions where water could exist as ice from those where it remained in gas or liquid form.
The snow line is located just beyond Jupiter’s current orbit, meaning that objects in the inner solar system were traditionally thought to be too warm to retain ice. However, the non-gravitational acceleration of inner dark comets suggests they must contain some volatile material—possibly ice—generating the thrust needed for their unusual movement. This raises fascinating questions about how these objects acquired their ice and whether they played a role in delivering water to Earth.
The discovery of dark comets has profound implications for our understanding of Earth’s history. Scientists have long debated how water, a fundamental ingredient for life, arrived on our planet.
One leading theory suggests that icy comets and asteroids delivered water during the early stages of the solar system’s formation. With their potential ice reservoirs, dark comets could be a missing piece of this puzzle.
Daryl Seligman, a physicist at the University of Michigan and the lead author of the study, suggests that dark comets may have been a crucial source of life-sustaining materials. “The more we learn about them, the better we can understand their role in shaping our planet,” he explained.
Finding dark comets is no easy task. Unlike their bright counterparts, they do not produce glowing tails that make them easy to detect. Instead, astronomers rely on the faint sunlight they reflect, using powerful telescopes to identify their presence.
The recent discovery of seven new dark comets was made possible thanks to the Dark Energy Camera (DECam) in Chile, which captures high-resolution images of the night sky. The search for dark comets is expected to accelerate in the coming years.
Starting in 2025, the Vera C. Rubin Observatory—equipped with the largest digital camera ever built—will begin scanning the sky. This state-of-the-art facility is expected to identify even more dark comets, potentially doubling or tripling the number of known objects in this category.
The discovery of dark comets is a reminder of how much we still have to learn about our solar system. These mysterious objects challenge existing classifications of comets and asteroids and provide compelling clues about the origins of Earth’s water.
With each new finding, scientists come one step closer to understanding how these enigmatic objects reached us—perhaps delivering the most vital resource for life on our planet: water.
