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Dark comets: Hidden, near-Earth ice giants can be both friend and foe

Did you know that up to 60% of near-Earth objects could be dark comets? These mysterious celestial bodies orbit our sun and might have been one of the sources of water to our blue planet.

They likely contain or previously contained ice, and new exciting findings from a study conducted by the University of Michigan serve to reinforce this theory.

Aster Taylor goes deep

Leading the study was Aster Taylor, a vibrant U-M graduate student in astronomy. With the cosmos as their playground, Taylor’s curiosity led them to dig deeper into the frosty mysteries of the asteroid belt.

For those of you who are new to the term, the asteroid belt is a region of the solar system tucked between Jupiter and Mars, acting as the host to a multitude of rocky asteroids.

Taylor’s findings echo the suspicion since the 1980s, that these asteroids may possibly harbor subsurface ice.

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.”

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

There you have it. This thrilling detective work by Taylor and their dedicated team has played a huge role in shedding light on dark comets, the elusive and mysterious water-bringers of our solar system.

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.

So, the next time you find yourself gazing at the night sky, remember; there’s always more than meets the eye. Each star, planet, and comet holds secrets waiting to be discovered, fueling our eternal curiosity and wonder about the cosmos.

The full study was published in the journal Icarus.


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