A Recent Spectral Analysis of Primitive Asteroids

A recent study improved our understanding of the composition of primitive asteroids and their origins by analyzing the visible near-infrared (VNIR) spectra of primitive asteroids within the Main Belt and the Jupiter Trojan clouds, according to a recent study published in arXiv (1).

Primitive asteroids are thought to be remnants of the early solar system's formation (1–3). These asteroids are located in the outer main-belt region, and they are characterized by low albedos and red slopes in the VNIR (1,3). Because primitive asteroids are theorized to be subject to weaker thermophysical processing, they offer astronomers and spectroscopists a good opportunity for learning about galaxy formation (2). These primitive asteroids are made of rock and stone, and contain carbon-rich compounds, aqueous alteration, and sometimes surface ice (3–5). Many primitive asteroids in the main belt have a strong spectral signature of olivine-rich silicate regoliths, which are like those found in the Trojans (3–5). However, some asteroids, such as 368 Haidea, lack strong evidence of olivine when looking at their mid-infrared (MIR) spectrum (5).

A comet, an asteroid, a meteorite falls to the ground against a starry sky. | Image Credit: © Aliaksandr Marko - stock.adobe.com

In this study, a team of four researchers (Oriel A. Humes, Audrey C. Martin, Cristina A. Thomas, and Joshua P. Emery) from Northern Arizona University and the University of Central Florida explores the diverse origins of primitive asteroids within the Main Belt and the Jupiter Trojan clouds. In their research, the team aimed to determine whether the spectral similarities observed in the VNIR spectra of primitive Main Belt asteroids and Jupiter Trojans reflect a true compositional resemblance (1).

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To determine whether spectral similarities exist, the research team examined data from the Spitzer Space Telescope’s IRS spectrograph and from the Stratospheric Observatory for Infrared Astronomy's (SOFIA) FORCAST instrument (1). For both instruments, the researchers analyzed the mid-infrared to far-IR (5–40 µm or 2000 to 250 cm^-1) spectra of thirteen primitive Main Belt D- and P-type asteroids (1).

The researchers concluded based on their findings that many primitive asteroids in the Main Belt share spectral signatures with their Trojan counterparts (1). However, the researchers did call out a couple key differences between the two, particularly when the silicate compositions were examined (1). Differences in the silicate compositions suggest a diversity of origins for these primitive asteroids.

In their study, the researchers spent a significant amount of time studying the spectra of asteroid 368 Haidea. Its spectrum is interesting because it is lacking strong evidence of olivine in its mid-IR spectrum (1). Despite being classified as a D-type asteroid, 368 Haidea's spectrum does not resemble that of D-type Jupiter Trojans, highlighting the complexity and variability within these asteroid populations (1).

The study also highlights differences in the shapes of the 10-µm features between Main Belt and Trojan asteroids, including lower continuum slopes and leftward skewing among Main Belt asteroids (1). The researchers, by examining asteroids across multiple spectral regions, was able to reveal more information about their true composition and origin (1).

By combining new observations with archival data, this study contributes to advancing our understanding of primitive asteroid composition and origins, paving the way for further exploration and research in the field of planetary science.

References

(1) Humes, O. A.; Martin, A. C.; Thomas, C. A.; Emery, J. P.Comparative Mid-Infrared Spectroscopy of Dark, Primitive Asteroids: Does Shared Taxonomic Class Indicate Shared Silicate Composition? arXiv 2024, 2404.19388. DOI: 10.48550/arXiv.2404.19388

(2) De Pra, M. N.; Pinilla-Alonso, N.; Carvano, J.; et al. A Comparative Analysis of the Outer-Belt Primitive Families. Astronomy & Astrophysics. 2020, 643. DOI: 10.1051/0004-6361/202038536

(3) Campins, H.; de Leon, J.; Licandro, J. Chapter 5 – Compositional Diversity Among Primitive Asteroids, in Primitive Meteorites and Asteroids. 2018, 345–369. DOI: 10.1016/B978-0-12-813325-5.00005-7

(4) Takir, D.; Emery, J. P. Diversity of Primitive Asteroids in the Heliocentric Region Between 3 AU and 4 AU. Presented at the 54th Lunar and Planetary Science Conference 2023, at The Woodlands, Texas, on March 13–17, 2023.

(5) Tillman, N. T. Asteroid Belt: Facts & Formation. Space.com. Available at: https://www.space.com/16105-asteroid-belt.html (accessed 2024-05-01).