Spectroscopy is telling us the extraterrestrial history of space objects, helping us learn about planetary origins.
Scientific research is increasingly utilizing advanced spectroscopy and machine learning (ML) to decode the complex histories of extraterrestrial materials. By employing methods like Raman imaging and reflectance spectroscopy, scientists can distinguish between native minerals and terrestrial weathering, as seen in the analysis of recent meteorites.1–5 These non-destructive techniques allow for the detection of organic molecules and rare mineral phases, providing vital clues about the formation of C-type (carbonaceous) asteroid) asteroids and the evolution of the early solar system. Additionally, new logistic regression models are being used to categorize asteroid compositions based on existing meteorite data, reducing the subjectivity of traditional classification.
In this Q&A overview, we explore how spectroscopy is helping uncover more information about the histories and chemical makeups of extraterrestrial objects.
Space weathering refers to the chemical and physical transformations that occur on the surfaces of airless bodies because of their exposure to the harsh conditions of deep space.1 Because asteroids lack protective magnetic fields or atmospheres (due to their weak gravitational fields and lack of molten cores), they are constantly bombarded by solar wind, comprised of primarily high-energy ions, and micrometeorites.1 To study these effects on Earth, researchers analyzed the CM2 carbonaceous chondrite NWA 12184 (a type of primitive carbonaceous meteorite) using a suite of seven spectroscopic techniques, including visible-to-mid-infrared (vis-to-MIR) reflectance and Raman spectroscopy.1 By irradiating the meteorite with 200 keV He⁺ ions to simulate solar wind, scientists observed distinct spectral changes: darkening, reddening, and shifts in hydration bands.1 These alterations result from the amorphization of surface minerals like olivine, a process that creates a "spectral fingerprint" matching data returned from the Ryugu asteroid by the Hayabusa2 mission.1 Understanding these shifts allows astronomers to more accurately decode the mineralogical history of C-type asteroids, which are primitive, carbon-rich bodies considered the early building blocks of our Solar System.
The primary challenge in Martian research is accurately identifying organic molecules. Organic molecules are usually the vital biosignatures for potential past life when they are embedded in a complex matrix of inorganic minerals.2 The challenge, though, is that they are sometimes hard to detect. The reason for this challenge is primarily because of overlapping spectral signatures.2
As a result, one of the main priorities for researchers is either using or developing new tools that can help them distinguish the individual compounds despite the overlapping spectra. One of the tools scientists are using is pairing Raman imaging with chemometric tools like principal component analysis (PCA) and multivariate curve resolution–alternating least squares (MCR-ALS).2
For example, a recent study that examined the Martian Nakhlite NWA 6148 demonstrates this in action. In the study, researchers used these tools to perform "spectral unmixing," separating complex data into "pure" spectral profiles and relative abundances.2 To preserve the integrity of these rare samples for future missions like the Mars Sample Return (MSR), measurements are taken using low-power lasers (often set to only 10% of maximum power) such that there is no destructive polishing or surface alteration.2 This data-driven approach ensures that no compound is assigned a "negative concentration," providing a chemically meaningful map of organics in their native context.2
Traditionally, asteroid classification has relied on remote sensing data that often lacks detailed mineralogical information and is prone to human subjectivity. A new methodology addressed this by training machine learning (ML) models on a vast data set of 1,422 meteorite spectra from the Reflectance Experiment Laboratory (RELAB).3 Among various algorithms, the Logistic Regression (LR) model proved most effective, achieving a classification accuracy of approximately 92%.3 A key breakthrough involved normalizing the spectral data at 0.70 µm, which enhanced the model's ability to differentiate between classes compared to the historically used 0.55 µm solar maximum.3 This ML approach has successfully linked meteorite types to their parent bodies, such as confirming the connection between howardite-eucrite-diogenite (HED) meteorites and V-type asteroids, believed to be pieces of the asteroid Vesta or Vesta-like bodies.
Aubrites are a rare class of igneous meteorites that formed under highly reducing (oxygen-depleted) conditions, similar to the environments found on Mercury.4,5 The Ribbeck meteorite, which fell in Germany in 2024, provided a pristine look at this class, revealing pure enstatite (a magnesium-rich silicate mineral [MgSiO₃]) with no iron impurities, which is a hallmark of extremely low-oxygen formation environments.4 Spectroscopy also identified rare sulfides like oldhamite (CaS) and brezinaite (a rare chromium sulfide mineral [Cr₂S₃]), which are stable only in these reduced states.4 Interestingly, the Tiglit meteorite from Morocco expanded our understanding of aubrite history by revealing unexpected phases like nanodiamonds, quartz, and cristobalite (a crystalline polymorph of silicon dioxide [SiO₂]).5 Since free silica is typically unstable in highly reducing environments, the presence of these high-temperature polymorphs suggests the meteorite underwent intense post-formational processes, including shock metamorphism and rapid cooling.5 These findings indicate that aubrites (enstatite [MgSiO₃] -rich achondrite meteorite) have a far more complex geological and impact history than previously realized.
Distinguishing between extraterrestrial material and changes caused by Earth's environment is essential for accurately reconstructing the history of the early Solar System.1,5 When meteorites land in environments like the Sahara Desert, they immediately begin to react with the Earth's atmosphere. For example, in the Tiglit meteorite, researchers detected calcite, which they determined was not a native mineral but a product of terrestrial weathering of the calcium sulfide oldhamite (CaS).5 Similarly, the study of the CM2 chondrite NWA 12184 used vis-to-MIR reflectance to identify native phyllosilicates and olivine [(Mg, Fe)₂SiO₄], specifically to distinguish them from secondary products formed on Earth.1 Recognizing these "spectral fingerprints" of contamination ensures that scientists do not mistake Earth-based chemical reactions for evidence of water or thermal activity on the original parent asteroid.1,5
