# Mineral Quantum Dots on the Moon

Arijit Roy, R Ramachandran, S V Singh, K K Marhas, W Khan, J K Meka, M Ambresh, Sahil Rathi, V Thiruvenkatam, P Janardhan, et al.

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Arijit Roy, R Ramachandran, S V Singh, K K Marhas, W Khan, et al. Mineral Quantum Dots on the Moon. 2025. [hal-05354527](https://hal.science/hal-05354527v1)

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Distributed under a Creative Commons Attribution 4.0 International License
Mineral Quantum Dots on the Moon

Arijit Roy,¹, * R Ramachandran,¹,², * S V Singh,¹ K K Marhas,¹ W Khan,¹,³ J K

Meka,¹ M Ambresh,⁴ Sahil Rathi,¹ V Thiruvenkatam,³ P Janardhan,¹ Satyendra

Nath Gupta,¹ N J Mason,⁵ Anil Bhardwaj,¹ S Vijayan,¹ and B Sivaraman¹, †

¹Physical Research Laboratory, Ahmedabad 380059, India

²Institute of Astronomy Space and Earth Sciences, Kolkata 700054, India

³Indian Institute of Technology Gandhinagar, Gandhinagar 382055, India

⁴Micro Nano Characterization Facility, Indian Institute of Science, Bengaluru 560012, India

⁵Centre for Astrophysics and Planetary Science, School of Physical Sciences,
University of Kent, Canterbury, CT2 7NH, United Kingdom

(Dated: November 7, 2025)

Naturally occurring extraterrestrial Quantum Dots (QDs) have been elusive, despite QDs of synthetic origin being well studied and documented. Here, we present the first identification of mineral-based quantum dots (mQDs) in the pristine lunar regolith samples returned by the Luna 16 mission. Sample 1630, collected from a core depth of 20 - 28 cm in the Mare Fecunditatis region of the moon, when analyzed using high-resolution transmission electron microscopy (HR-TEM), revealed discrete, crystalline nanoparticles ranging from 2 - 15 nm, exhibiting clear lattice fringes with interplanar spacings of 0.21 nm and 0.22 nm. On comparison with the literature, we confirmed these correspond to MgO and FeO phases, respectively, with additional α-Fe⁰ nanocrystals identified. The quantum confined dimensions (2 - 10 nm) of these mineral phases classify them as mQDs. We attribute their formation to impact events on the Moon that are evident by the abundance of craters present.

# I. INTRODUCTION

Quantum Dots (QDs), the nm-sized structures possessing quantum confinement properties and exhibiting unusual electrical and optical properties, have been a hot topic of discussion in recent times for several reasons, including their ability to transport electrons and emit light of various colours when exposed to UV light [1]. While QDs have been extensively studied since their first synthesis in the 1980s [2–4], studies of their natural occurrence (no artificial synthesis process involved) have been fairly recent (honey, humic substances, coconut water, etc). All the naturally occurring terrestrial QDs discovered/found to date have been carbon-based. To the best of our knowledge, extraterrestrially occurring QDs have not been reported to date. Even though nanostructures like (nano)diamonds have been known to be present in meteorites for more than a century now [5], none of them have been characterized as QDs. Even in the case of such nanostructures, the debate still continues as to whether they are an outcome of the terrestrial event (entry into Earth/impact on Earth) or if they were formed extraterrestrially. Hence, a more reliable source for an undisputed confirmation of the extraterrestrial (ET) origin of such structures would be the ET bodies themselves or the pristine samples brought back from there (sample return missions).

Since the “one giant leap for mankind” over half a century ago, there have been several sample return missions, and these ET materials have been continuously studied

and have yielded several insights into various aspects of the bodies they were brought back from, as well as universal astrochemistry/astrobiology. Specifically with respect to the moon, to date, there have been 8 successful sample return missions and first among them being Apollo 11, 12 and Luna 16. Despite the extensive analyses of the returned samples [6], no confirmed reports exist of naturally occurring QDs in such ET materials. As mentioned previously in the context of meteorites, even in the case of returned samples, while several nanomaterials have been found [7–9], none of them have been characterised as QDs.

Nevertheless, even though there are no direct confirmations of the presence of QDs on the moon or any other ET bodies, our previous works [10, 11] strongly suggest the possibility of their ET formation/existence formed by stellar, impact, and shock processes. Finding naturally occurring QDs in any ET sample would have profound implications for understanding both ET geochemistry and the fundamental processes guiding nanostructure formations in astrochemical environments. Such findings could also shed light on new pathways for QD synthesis, provide insights into space weathering processes, and provide potential resources for future lunar exploration missions. Furthermore, QDs from lunar materials could serve as unique probes for understanding the early solar system environment and the role of quantum confinement effects in spectroscopic observations.

In this work, we report the first evidence of naturally occurring QDs within lunar samples from the Luna 16 mission. Using High-Resolution Transmission Electron Microscopy (HR-TEM), we demonstrate the presence of discrete nanocrystals exhibiting the characteristics of QDs and establish a foundation for

<footnote>* Equal contribution</footnote>

<footnote>† bhala@prl.res.in</footnote>
<figure><img src="image_3.png" /><figcaption>FIG. 1. (a) Lunar Reconnaissance Orbiter - Wide Angle Camera image shows the Luna 16 landing site (yellow star) and the nearby larger craters like Langrenus and Taruntius, whose impact originated ejecta could be deposited at the Luna 16 site. (b) Lunar Reconnaissance Orbiter - Narrow Angle Camera image shows the high-resolution image of the Luna 16 site covered by numerous small craters with diameters ranging from a few meters to several tens of meters. These smaller crater ejecta could have mantled the landing site, and these numerous craters are the main source for the Luna 16 sample used in this study.</figcaption></figure>

understanding quantum dot genesis in extraterrestrial materials.

## II. MATERIALS AND METHODOLOGY

### A. Material and its origin

In this study, we used the sample no. 1630 (core depth 20 - 28 cm) of the returned samples from the Luna 16 mission [12]. These are the lunar ground samples collected by the automatic probe "Luna-16" and returned to Earth. The samples were taken in the northeastern portion of Mare Fecunditatis (at 0°46'S lat. and 56°18'E long.) by drilling from the surface to a depth of 35 cm and filling a container in the tube of the drill. This site, which is similar to the geological settings of Apollo 11 and 12, is located within the basaltic mare-filled units. Absolute radiometric ages obtained from the Luna 16 samples suggest an age of ~3.4 to 3.5 billion years [13, 14], whereas the crater count over the landing site provide an absolute model age of 3.45 billion years [15]. Post these lava emplacements, this landing site region is mantled by distal impact crater ejecta, especially Taruntius and Langrenus craters (Fig. 1). This landing site region is dominated by secondary craters and ejecta rays from other craters. This includes the ejecta ray from 1) the Tycho crater, which is located ~2200 km away in the SSW direction and 2) probably from the 5 million-year youngest crater

Giordano Bruno crater ray located ~1700 km in the NNE direction. The four zones of the Luna 16 drill core sample contain Gabbro, breccias, basalt, agglutinates, and anorthosite [16]. The closest anorthositic terrain from the Luna landing site is ~70 km away. The presence of anorthosite on top of the basaltic lava flow within the landing site is therefore a clear indicator of impact transported anorthosite material.

### B. Methodology

Approximately 3 mg of the Luna 16 sample was mixed with ~20 µL of pure ethanol solution and ultrasonicated for about 15 minutes. Following that, the solution containing the particles suspended was drop-casted onto three Quantifoil TEM grids and allowed to dry overnight in an oven (thermo vac) pre-heated to 30°C. These grids were then cleaned using Ar-O₂ plasma to remove any contamination that could arise during the sample processing before loading the grid into the HR-TEM (Ti-TAN - Themis). The HR-TEM images were taken at an operating voltage of 300 kV. The interplanar spacing of the different crystalline nanostructures present in the sample was calculated using the Image J software [17] and cross-verified using Gatan Inc.'s Digital Micrograph™(DM) software.

Photoluminescence (PL) measurements were done using Renishaw Raman spectrometer equipped with 532
<figure><img src="image_4.png" /><figcaption>FIG. 2. HR-TEM micrographs of the LUNA-16 samples - (A) Large grains, (B) shows the presence of many spherical grains in a particular zone in (A). (C) MgO quantum dot (within the red box), the inset shows its electron diffraction pattern, with a d-spacing is around 0.21 nm. (D) FeO quantum dot (within the orange box), the inset shows its electron diffraction pattern, with a d-spacing of 0.22 nm.</figcaption></figure>

nm laser, air cooled CCD detector and an upright optical microscope. We have used 50X objective for exciting the sample as well as for collecting the PL emission from the QD. The laser spot size on the sample is ~1 µm. As the size of the QDs are very small (< 10 nm), there can be many QDs in this 1 µm area. So, this is a kind of ensemble measurements.

### III. RESULTS AND DISCUSSION

The micrographs obtained via transmission electron microscope analysis of the Luna-16 sample showed the presence of crystalline particles of varying sizes from 1 nm to a few microns (Fig. 2(A)). We also observed crystalline sheets along with particles. Upon examining the
<figure><img src="image_5.png" /><figcaption>FIG. 3. Alpha iron nanocrystal, inset shows its selected area electron diffraction pattern with a d-spacing is around 0.21 nm.</figcaption></figure>

smaller particle sizes, from 1 nm to 30 nm, we could see spherical to nearly spherical particles ranging from ~2 nm to ~15 nm (Fig. 2(B)). These particles display atoms arranged in crystalline phases and are stable at the 300 kV operating voltage.

We calculated the d-spacing of the sheets and the particles, taking into account the known chemical composition of the Luna-16 sample from previous studies. The d-spacings of 0.21 nm and 0.22 nm particles were seen in many places in the sample (Fig. 2(C&D)). While a d-spacing of 0.22 nm can correspond to the (200) plane of iron oxide (FeO) [18], the d-spacing of 0.21 nm can be from either magnesium oxide (MgO) or the nano phase alpha-iron (np-Fe⁰). Although the d-spacing can be similar, the diffraction pattern for a few particles matched with MgO [11] and the others with (np-Fe⁰) (Fig. 3). The presence of the minerals FeO and MgO is known in lunar samples returned from the Moon and in lunar meteorites [19]. Also the np-Fe⁰ is an abundant element present as a component lunar regolith [19–21]. Based on the known chemical composition of the lunar soil and the d-spacing measurements, we hence assign those tiny particles to mineral Quantum Dots (mQDs), ranging from 2 nm to 10 nm. The measured PL spectra is shown in Fig. 4. The presence of very sharp and intense peaks (three peaks) between 550 nm to 570 nm provides optical support [22] to the conclusions drawn from HRTEM images. However, because of the heterogeneous nature of the sample, we cannot determine the chemical nature of the QD using

the PL spectra.

The source of mQDs on the moon could be from the impact events that had heavily cratered the moon's surface. Laboratory experiments have shown that shock processing of the mineral ingredients makes mQDs [11]. In the case of the Luna-16 sample, it is already reported that one of the dominant components of the sample is impact breccia [23]. The impact origin deposition and breccia reveal that, on the Moon, transport of the impact materials is common, and that all these materials have undergone a diverse amount of shock pressures. The studied sample is from the ejecta that are thrown out as a result of the hypervelocity impacts excavating craters near the sample collection area. Such impact events, generating more heat and pressure, produce impact melts where the physico-chemical changes take place. Therefore, the major source of the mQDs on the moon is the impact events.

## IV. CONCLUSION

We have examined the samples from the lunar subsurface brought back by the Luna-16 mission using HR-TEM and have found compelling evidence for the presence of mQDs, MgO and FeO in them. Although the presence of MgO and FeO is known in the lunar soil, their presence as mQDs is not known before. The results reported here help in better understanding the physico-chemical nature of such nanoparticles, including their origins. Our results suggest that impact events in the solar system are a highly likely source of QDs, and extrapolating this argument, we can cautiously contemplate the QDs' widespread presence in the solar system objects. These findings establish the first evidence for naturally occurring extraterrestrial QDs and demonstrate that impact processes represent a viable pathway for quantum nanostructure formation on the Moon and elsewhere, with significant implications for astrochemistry, space weathering studies, and potential *in-situ* resource utilization in future lunar exploration.

## ACKNOWLEDGMENTS

The authors would like to acknowledge the PRL repository for the Luna-16 samples used in this study. We acknowledge Mr. Abhay Gogineni, Mallya Aditi International School for his help in the literature survey. AR, RR and BS acknowledge the Centre for Nanoscience and Engineering (CeNSE), Indian Institute of Science, Bengaluru, India, for providing the HR-TEM facility. RR and BS thank the Sir John and Lady Mason Academic Trust (UK).

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<figure><img src="image_6.png" /><figcaption>FIG. 4. (A) Photoluminescence spectrum of Luna 16 sample in 540 - 590 nm range. Its inset shows the sample. (B) Deconvolution of the spectrum in the 553 - 570 nm range ($R^2$ = 0.9908).</figcaption></figure>

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