Over half of near-Earth objects could be dark comets, shows study

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Up to 60% of the objects near Earth could be dark comets, according to a new study by the University of Michigan.

Dark comets are strange asteroids that orbit the sun and might have ice inside them. These objects could have played a role in bringing water to Earth.

Asteroids are usually rocky and don’t have ice because they orbit close to the sun, where any ice would turn into gas.

Comets, on the other hand, are icy and form a fuzzy cloud called a coma as the ice turns into gas.

Dark comets are a mix of both—they don’t have a coma, but they do have small accelerations not caused by gravity, hinting they might still have some ice.

The study, led by U-M graduate student Aster Taylor, suggests that many of these dark comets come from the asteroid belt, a region between Mars and Jupiter filled with rocky asteroids.

This belt has been suspected of containing ice since the 1980s. The research shows that dark comets could bring this ice into the inner solar system, possibly even to Earth.

“While we can’t say for sure that these dark comets brought water to Earth, our work shows that it’s possible,” Taylor said. “There’s still a lot of debate about how Earth got its water.”

Taylor’s team studied seven dark comets and estimated that between 0.5% and 60% of all near-Earth objects could be dark comets.

They believe these dark comets likely come from the asteroid belt and have small amounts of ice that cause their unique accelerations.

The researchers used dynamical models to trace the origins of these dark comets. They found that the main asteroid belt is the most likely source. One dark comet, called 2003 RM, has an orbit that takes it close to Earth and then out to Jupiter, similar to comets influenced by Jupiter’s gravity.

This suggests it might have been pushed inward from its original orbit.

The study also explored why these dark comets are so small and spin so quickly. Comets are like dirty ice cubes, made of rocks and ice. When they get closer to the sun, the ice turns into gas, causing them to accelerate and spin faster.

This spinning can make the comet break into smaller pieces, which continue to spin and break apart further.

Taylor explained, “These pieces still have ice, so they spin faster and faster until they break into even smaller pieces. This process can keep going, making tiny, fast-spinning objects.”

The researchers believe the larger dark comet, 2003 RM, was once part of the outer asteroid belt but got kicked inward. The other six dark comets likely came from the inner asteroid belt, breaking apart after getting knocked inward.

In previous work, Taylor and their team identified nongravitational accelerations in near-Earth objects and named them “dark comets.” They determined these accelerations were due to small amounts of sublimating ice.

Their current work aims to understand where these dark comets come from and how they might have brought ice into the inner solar system.

In conclusion, dark comets are mysterious objects that could have delivered ice, and possibly water, to Earth.

They come from the asteroid belt and have unique characteristics that set them apart from regular asteroids and comets.

This study opens up new questions about the role of dark comets in our solar system and their potential impact on Earth.

Source: University of Michigan.