Invisible "dark comets" account for 60% of all near-Earth objects

By now, you’ve heard of dark matter, but have you heard of dark comets? Probably not. “Dark comets” are comets that don’t reflect much light, making them potential hazards for our planet because they are very difficult to detect with Earth-based telescopes.

According to new research, roughly 60% of all near-Earth objects are “dark” comets.

These mysterious celestial bodies orbit our sun and might have been key sources of water as Earth was forming billions of years ago.

These dark comets likely hold or used to hold ice, which raises some intriguing questions about their role in forming our planet and how water came to be on Earth.

Studying dark comets

Important new findings from a study led by Aster Taylor from the University of Michigan have backed up this fascinating theory. Taylor’s curiosity drove his team to explore the chilly mysteries of the asteroid belt, a region full of potential.

For those unfamiliar, the asteroid belt is located deep in our solar system between Jupiter and Mars. It’s home to a bunch of rocky asteroids, each with its own unique story.

Taylor’s discoveries support a long-held suspicion that has been around since the 1980s: these asteroids might just have subsurface ice.

The implications of these findings are huge, not just for our understanding of the solar system but also for exploring potential resources for future space missions.

Dark comets connected to Earth’s water?

Taylor, through their study, could not confirm if these dark comets indeed delivered water to Earth but highlighted that this could be another path to bring ice from other parts of the solar system to Earth.

“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,” Taylor said.

“The work we’ve done has shown that this is another pathway to get ice from somewhere in the rest of the solar system to the Earth’s environment.”

Despite dozens of studies, some very recent, it boggles the mind that to this day, scientists are still unravelling how Earth got its water?

Dark comets vs. normal comets

Dark comets, somewhat enigmatic bodies, unite features of both asteroids and comets. Asteroids are close enough to the Sun to vaporize any ice they might carry in a process called sublimation, thus categorizing them as rocky bodies sans ice.

They tend to have more stable and predictable orbits and lack the characteristic cometary coma or tail.

Comets, on the other hand, display a distinctive fuzzy cloud enveloping them, known as a coma, which is created as the sublimating ice carries along dust.

This gives them a characteristic glowing appearance when viewed through telescopes or even to the naked eye in some cases. They generally have more elongated orbits that can take them far from the Sun and then close again.

Fun fact, they exhibit slight accelerations not due to gravity, but courtesy of this sublimation process! These non-gravitational forces can cause changes in their orbits over time.

Cracking the code

Taylor’s study took a detailed look at seven dark comets and estimated that anywhere between 0.5 and 60% of all near-Earth objects could be these unique bodies.

They are devoid of comae (or cometary dust clouds) but endowed with nongravitational accelerations, likely resulting from minor amounts of sublimating ice.

According to their findings, these dark comets probably originate from the asteroid belt.

“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,” Taylor said.

“There may be more ice in the inner main belt than we thought. There may be more objects like this out there. This could be a significant fraction of the nearest population. We don’t really know, but we have many more questions because of these findings.”

Cosmic carousel

Taylor explained that our near-Earth environment is a chaotic place, dynamically evolving over a mere ten million years. Near-Earth objects don’t maintain their orbits very long and are continuously replenished by a larger extraneous source.

To figure out the home of these mysterious dark comets, Taylor’s research team developed dynamical models and followed their path for a whopping 100,000 years.

Most ended up right where dark comets are today, with the main asteroid belt being their most probable birthplace.

“Near-Earth objects don’t stay on their current orbits very long because the near-Earth environment is messy,” they said.

“They only stay in the near-Earth environment for around 10 million years. Because the solar system is much older than that, that means near-Earth objects are coming from somewhere — that we’re constantly being fed near-Earth objects from another, much larger source.”

Origins and destinies of dark comets

One of the observed dark comets, 2003 RM, likely came from Jupiter’s family of comets by being drawn inward from its orbit.

The rest possibly emerged from the inner band of the asteroid belt, suggesting that ice is likely present in the inner main belt.

But why are these dark comets so tiny and rapidly spinning? Taylor explains that an acceleration-inducing off-gassing process occurs when comets get bumped within the ice line. This, added with continuous ice loss, results in even smaller, quickly rotating bodies.

“These pieces will also have ice on them, so they will also spin out faster and faster until they break into more pieces,” Taylor said.

“You can just keep doing this as you get smaller and smaller and smaller. What we suggest is that the way you get these small, fast rotating objects is you take a few bigger objects and break them into pieces.”

How dark comets shape our solar system

To sum it all up, dark comets are still a mystery, but the work of Aster Taylor has uncovered more details that could help us spot them in the future, while providing more clues to the origin of Earth’s water.

Dark comets are potentially very dangerous because their low reflectivity (or albedo) makes them harder to spot, yet they could still pose a significant impact threat to Earth.

By utilizing advanced telescopes and cutting-edge technology, they have uncovered crucial information about these mysterious objects, their origins, and their impact on our cosmic neighborhood. It’s a reminder that our knowledge of the universe is still expanding, just like the universe itself.

The full study was published in the journal Icarus.

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