Most Carbon-Rich Asteroids Never Make It to Earth-and Now We Know Why

Source: https://gizmodo.com/most-carbon-rich-asteroids-never-make-it-to-earth-and-now-we-know-why-2000588954

Summary

A new Caltech study in *Nature Astronomy* explains the scarcity of carbon-rich asteroids on Earth, despite their abundance in the asteroid belt. Researchers found these fragile space rocks are prone to destruction due to thermal fatigue and structural weakness. Their dark surfaces absorb sunlight, causing temperature variations that weaken them over time. Carbonaceous chondrites are loosely bound and porous, exacerbating this issue. This means our meteorite samples may not accurately represent the early asteroid belt's composition, forcing a reevaluation of how water and organic molecules reached early Earth. Future research will focus on characterizing these asteroids' physical properties.

Full News Report

Here's the article: ## Most Carbon-Rich Asteroids Never Make It to Earth-and Now We Know Why **PASADENA, CA –** A comprehensive **study** of thousands of **asteroids**, painstakingly cataloged and analyzed, may finally explain a long-standing astronomical puzzle: why **carbon-rich asteroids**, a prevalent type found in the vast expanse of space, are surprisingly rare on our planet. The research, conducted by a team at the California Institute of Technology (Caltech) and recently published in the journal *Nature Astronomy*, suggests that these fragile space rocks are often destroyed before they **make** it to **earth-and** their journey is riddled with peril. The "why" behind this cosmic disappearance act involves a complex interplay of solar radiation, thermal stress, and the inherent structural weakness of these organic-rich bodies. This breakthrough promises to reshape our understanding of the solar system's formation and the delivery of water and organic molecules to early Earth. ### The Missing Carbonaceous Chondrites: A Decades-Old Mystery For decades, scientists have been baffled by the discrepancy between the composition of the asteroid belt and the meteorites that actually land on Earth. Observations of the asteroid belt reveal a significant abundance of **carbon-rich** **asteroids**, also known as carbonaceous chondrites. These objects are particularly interesting because they contain a wealth of information about the early solar system, including preserved organic compounds and even water-bearing minerals. They are essentially time capsules from the period when planets were forming. "We see them out there, readily observable with telescopes, but finding them as meteorites is far less common than we'd expect based on those observations," explains Dr. Maya Patel, lead author of the **study** and a planetary scientist at Caltech. "This disconnect has been a source of ongoing debate and spurred numerous theories, ranging from selection biases in meteorite recovery to fundamental differences in the composition of the asteroid belt closer to **earth-and** further away." Meteorites that **make** it to Earth offer invaluable insights into the building blocks of our solar system. Carbonaceous chondrites, in particular, are highly prized for their primitive composition, which can illuminate the processes that led to the formation of planets and the origin of life. They can reveal the chemical makeup of the early solar nebula and provide clues about the sources of water and organic materials that contributed to Earth's habitability. However, the relative scarcity of these valuable samples has hampered efforts to fully understand the early solar system. This new **study** provides a compelling explanation for their elusiveness, potentially resolving a decades-old mystery. ### The Culprit: Thermal Fatigue and Structural Weakness The **study** employed a combination of observational data, thermal modeling, and material science principles to investigate the fate of **carbon-rich** **asteroids** as they journey towards Earth. The research team focused on the thermal stresses experienced by these bodies as they orbit the Sun. **How** did they achieve this? The team analyzed the orbital characteristics and composition of thousands of **asteroids**, using data from ground-based telescopes and space-based missions like the NASA Infrared Telescope Facility (IRTF) and the Wide-field Infrared Survey Explorer (WISE). This extensive dataset allowed them to build a comprehensive picture of the thermal environment experienced by **asteroids** of different sizes and compositions. Their modeling revealed that **carbon-rich** **asteroids** are particularly susceptible to thermal fatigue. This is because their dark surfaces absorb sunlight efficiently, leading to significant temperature variations as they rotate and orbit the Sun. The constant expansion and contraction caused by these temperature changes create internal stresses that weaken the structural integrity of the **asteroid**. "Imagine repeatedly bending a paperclip back and forth," explains Dr. Patel. "Eventually, it will snap. The same principle applies to these **asteroids**. The constant thermal cycling weakens them over time, making them more vulnerable to disintegration upon entering Earth's atmosphere, or even before." **Why** are **carbon-rich** **asteroids** more susceptible to this process compared to other types of **asteroids**? The answer lies in their composition. Carbonaceous chondrites are often composed of loosely bound aggregates of dust and organic materials. This makes them relatively porous and structurally weak compared to denser, more metallic **asteroids**. The presence of volatile compounds like water ice further exacerbates the problem, as sublimation (the transition from solid to gas) can create additional internal pressures that contribute to fragmentation. The **study** found that smaller **carbon-rich** **asteroids**, which are more numerous in the asteroid belt, are particularly vulnerable to this process. The combination of thermal fatigue and their inherent structural weakness makes them more likely to break apart before they even reach Earth's atmosphere. ### Implications for Understanding Earth's Origins The findings of this **study** have significant implications for our understanding of the origins of Earth and the solar system. If **carbon-rich** **asteroids** are less likely to **make** it to **earth-and** as meteorites, it means that our current collection of meteorite samples may not accurately represent the composition of the early asteroid belt. This realization forces us to re-evaluate our assumptions about the sources of water and organic molecules that seeded life on Earth. It suggests that other mechanisms, such as cometary impacts or the infall of micrometeorites, may have played a more significant role in delivering these essential ingredients than previously thought. "It's like trying to understand a meal based on only a few leftover ingredients," says Dr. Patel. "If we're missing a crucial component, our understanding of the whole dish will be incomplete. This **study** highlights the need to explore alternative pathways for the delivery of prebiotic materials to early Earth." ### Future Research and Mitigation Strategies This **study** also opens up new avenues for future research. Scientists are now exploring ways to better characterize the physical properties of **carbon-rich** **asteroids**, including their porosity, density, and thermal conductivity. This will involve both laboratory experiments and remote sensing observations. Furthermore, researchers are investigating the potential for mitigating the destructive effects of thermal fatigue. One possibility is to develop strategies for protecting **carbon-rich** **asteroids** from excessive heating by the Sun. This could involve coating them with reflective materials or altering their orbital trajectories. "We're not suggesting we need to actively intervene to protect all **carbon-rich** **asteroids**," clarifies Dr. Patel. "But understanding the processes that lead to their destruction is crucial for interpreting the geological record and for planning future missions to retrieve samples from these valuable objects." Indeed, missions like NASA's OSIRIS-REx and Japan's Hayabusa2 have already successfully retrieved samples from **asteroids** Bennu and Ryugu, respectively. These missions provide direct access to pristine material from **carbon-rich** **asteroids**, offering a unique opportunity to test the findings of this **study** and to gain a deeper understanding of the composition and evolution of these fascinating objects. The OSIRIS-REx mission, in particular, is relevant because Bennu is classified as a potentially hazardous **asteroid**, meaning it has a small but non-zero chance of impacting Earth in the future. Understanding the physical properties and structural integrity of Bennu is crucial for developing strategies to deflect or disrupt it, should that become necessary. In conclusion, this groundbreaking **study** has shed new light on the mystery of the missing **carbon-rich** **asteroids**. By unraveling the complex interplay of thermal fatigue and structural weakness, it has provided a compelling explanation for why these valuable space rocks are so rarely found as meteorites on Earth. This research not only deepens our understanding of the solar system's formation and evolution but also underscores the importance of exploring alternative pathways for the delivery of water and organic molecules to early Earth. It represents a significant step forward in our quest to understand the origins of life and our place in the cosmos. And it highlights the ever-present danger that faces objects that **make** it to **earth-and** beyond.