Could Dark Comets Be the Key to Earth's Water? - Mystery Hunter

If you peer into the space around Earth's orbit, you'll discover a vast collection of rocks. To date, astronomers have identified more than 35,000 near-Earth objects (NEOs). These NEOs include asteroids and comets that occasionally enter our Solar System's vicinity before swooping away again.

However, it's believed that many more are yet to be discovered. A recent study suggests that up to 60 percent of these NEOs could be "dark comets," a fascinating type of celestial body that might hold crucial clues about the origins of Earth's water.

Understanding Dark Comets

Dark comets are intriguing objects that once contained or still contain ice within their rocky bodies. This discovery, led by Aster Taylor from the University of Michigan, provides an important insight into the mystery of how Earth acquired its water in the early days of the Solar System.

Taylor explains, "We don't know if these dark comets delivered water to Earth. We can't say that. But we can say that there is still debate over how exactly the Earth's water got here." This research shows another possible pathway for ice to travel from other parts of the Solar System to Earth's environment.

The Nature of Space Rocks

Space rocks within the Solar System can take several forms. Asteroids and comets are the two most well-known types. Asteroids are dry, rocky bodies, while comets are icy rocks that release material when they approach the Sun and heat up. Meteors, on the other hand, are rocks that enter a planetary atmosphere, and meteorites are the chunks that fall to a planetary surface.

There is a significant variation within these categories, with some crossover between them. Dark comets are believed to be a hybrid type, but much about them remains unknown.

Characteristics of Comets

A comet's distinctive features include a fuzzy 'coma' or atmosphere of gas and a tail produced by the sublimation of ice. Another key characteristic is acceleration. As a comet ejects material, this ejection provides additional propulsion beyond what is expected from gravitational forces alone. This outgassing can also increase the comet's spin.

A dark comet lacks a visible coma or tail but exhibits non-gravitational acceleration. Taylor and colleagues studied seven known dark comets to better understand how many more could be lurking near Earth.

Estimating the Prevalence of Dark Comets

The team's estimates suggest that between 0.5 and 60 percent of all NEOs could be dark comets. This wide range indicates the need for further research, but the current findings imply that there could be a substantial amount of frozen material in the Solar System, not just near Earth but also in the asteroid belt between Mars and Jupiter.

Taylor notes, "We think these objects came from the inner and/or outer main asteroid belt, and the implication of that is that this is another mechanism for getting some ice into the inner Solar System." This finding suggests there may be more ice in the inner main belt than previously thought.

The Lifecycle of Near-Earth Objects

Near-Earth objects don't remain in our planet's vicinity for long, cosmically speaking. The inner Solar System is gravitationally active, leading to a typical lifespan of around 10 million years for these objects. Given the Solar System's age of approximately 4.6 billion years, this implies a constant replenishment of NEOs.

The research team conducted simulations to determine the origins of dark comets, assigning non-gravitational accelerations to objects from various populations within the Solar System. The results indicate that most dark comets near Earth likely originated from the main asteroid belt.

The Role of Centrifugal Force

A comet's accelerated spin can cause it to break apart under centrifugal force. The fragments, which are also icy and gassy, continue to move under non-gravitational acceleration, resulting in multiple rocks from a single comet.

Among the seven dark comets analyzed by the team, one, named 2003 RM, appears to be a larger rock ejected from the main belt. The other six are products of centrifugal fragmentation from a large rock that left the main belt and broke apart near the Sun.

Future Research and Discoveries

The researchers suggest that ground- and space-based observations of dark comets may help measure outgassing rates and compositions, potentially revealing their dynamic origins. Future survey missions may also identify more dark comets, refining our understanding of these objects and their source populations.

Understanding dark comets and their potential role in delivering water to Earth remains a fascinating and ongoing area of study, promising to shed light on the mysteries of our Solar System's history.


The research has been published in Icarus/sciencealert