Enigma of the Kuiper Belt’s Color Spectrum Resolved by Scientists

by Klaus Müller
Kuiper Belt Color Mystery

A link has been discovered between aromatic structures and unsaturated hydrocarbon chains, and the diverse colors of hydrocarbon-laden surfaces of Kuiper Belt objects. The University of Hawaii at Mānoa deserves credit for this breakthrough.

The Kuiper Belt, a sizable disk beyond Neptune’s orbit filled with icy bodies such as Pluto, exhibits an alluring color spectrum from pure white to deep reddish shades. This unique color diversity, unmatched elsewhere in our solar system, has puzzled scientists for many years. The widely accepted theory has suggested that these varying colors possibly result from the long-term radiation exposure of organic materials to galactic cosmic rays.

Researchers from the Department of Chemistry at the University of Hawaiʻi at Mānoa spearheaded a new study that simulated the conditions in the Kuiper Belt. This study aimed to uncover the cause behind the color variety observed in hydrocarbon-abundant surfaces of Kuiper Belt objects, thus solving a long-standing puzzle in astrophysics. The results of this research have been recently published in the Science Advances journal.

Professor Ralf I. Kaiser led the research team, and the groundbreaking work was conducted at UH Mānoa. The researchers employed ultrahigh vacuum irradiation experiments and carried out exhaustive analyses to scrutinize the source and evolution of color on a molecular level. This was achieved by processing hydrocarbons like methane and acetylene in conditions mimicking the Kuiper Belt, and observing how they interacted with galactic cosmic rays.

The researchers found that the production of reddish colors can be attributed to aromatic structural units (organic molecules with connected benzene rings) that bear up to three rings, such as in chemical compounds like phenanthrene, phenalene, and acenaphthylene. These units were found to be interconnected via bridges lacking hydrogen atoms. The study from UH also illuminated the intricacies at the molecular level when galactic cosmic rays interact with hydrocarbons. Furthermore, it shed light on the crucial role radiation-exposed ices play in the early creation of precursor molecules for biological life.

Professor Kaiser stressed the importance of this study as it paves the way for systematic identification of the molecular carriers causing the rich hydrocarbon surfaces of Kuiper Belt objects. He added, “Given that astronomical detections have also found ammonia, water, and methanol on the surfaces of Kuiper Belt objects, we hope further experiments on cosmic ray processing of these ices will reveal the true nature of the color diversity of Kuiper Belt objects on a molecular level.”

The study, “Processing of methane and acetylene ices by galactic cosmic rays and implications to the color diversity of Kuiper Belt objects” was authored by Chaojiang Zhang, Cheng Zhu, Andrew M. Turner, Ivan O. Antonov, Adrien D. Garcia, Cornelia Meinert, Leslie A. Young, David C. Jewitt, and Ralf I. Kaiser, and published on 31 May 2023 in Science Advances.
DOI: 10.1126/sciadv.adg6936

Frequently Asked Questions (FAQs) about Kuiper Belt Color Mystery

What is the main discovery of the research led by the University of Hawaii at Mānoa?

The research has discovered that the diverse colors of hydrocarbon-rich surfaces of Kuiper Belt objects are driven by aromatic structures linked through unsaturated hydrocarbon chains.

Where is the Kuiper Belt located in our solar system?

The Kuiper Belt is a large disk filled with icy bodies, located just beyond the orbit of Neptune in our solar system.

What has been the long-standing theory about the color variety of Kuiper Belt objects?

The long-standing theory has been that the color variety of Kuiper Belt objects likely arises from the enduring radiation exposure of organic materials by galactic cosmic rays.

Who led the research team in this study?

The research team was led by Professor Ralf I. Kaiser at the University of Hawaii at Mānoa.

What are the implications of this study?

This research is a crucial first step towards systematically identifying the molecular units responsible for the hydrocarbon-rich surfaces of Kuiper Belt objects. It also provides insight into the role played by ices exposed to radiation in the early production of biological precursor molecules.

More about Kuiper Belt Color Mystery

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ChemNerd June 15, 2023 - 8:14 am

As a chemistry student, I’m so excited about this. The complexity of reactions under space conditions… Mind-blowing. gotta love hydrocarbons!

CosmicChaos June 15, 2023 - 9:54 am

colors in space? and here i thought it’s all just black and stars. i gotta read more about this kuiper belt.

SolarExplorer June 15, 2023 - 8:57 pm

Read the paper yesterday. Quite technical but the findings are amazing. Props to Prof. Kaiser and his team!

AstroFan101 June 16, 2023 - 12:12 am

wow, who woulda thought the kuiper belt was so colorful! science never ceases to amaze.

PlutoLover June 16, 2023 - 3:51 am

So that’s why Pluto’s got those reddish spots…aromatic structures, huh…?


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