Simulated space weathering of Fe- and Mg-rich aqueously altered minerals using pulsed laser irradiation

Kaluna, H. M.; Ishii, H. A.; Bradley, J. P.; Gillis-Davis, J. J.; Lucey, P. G.

doi:10.1016/j.icarus.2016.12.028

Cited by 36 publications

(21 citation statements)

References 64 publications

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“…Finally, our results also suggest that weathering of FeS, and possibly other sulfides, via micrometeorite impacts is not responsible for the decrease in spectral slope (bluing) that was observed in previous studies (Gillis-Davis et al, 2017). Thus, other minerals, such as carbonaceous material, may be more important for driving the observed spectral decrease, as well as the two-step spectral trend noted recently (Kaluna et al, 2017). Future studies will focus on studying space weathering effects in these other minor components present in the asteroid regolith.…”

Section: Implication For Space Weathering On Airless Bodies Via Microsupporting

confidence: 79%

Space Weathering of FeS Induced via Pulsed Laser Irradiation

et al. 2020

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Here we present results from pulsed laser irradiation of troilite samples in an effort to simulate space weathering on airless bodies via micrometeorite impacts. We find that the spectral trends observed in directly irradiated samples and samples with a vapor-deposited coating are different than those found in silicate minerals previously studied. For instance, direct laser irradiation causes our troilite samples to initially brighten, but continued irradiation causes darkening and a decrease in spectral slope. In contrast, our samples with a vapor-deposited coating show a continuous increase in spectral slope and overall albedo as the deposit thickness increases. Observation using both digital imaging and electron microscopy of our directly irradiated samples leads us to conclude that topography effects likely become important after a relatively high number of laser pulses in our directly irradiated samples, causing the apparent darkening and decrease in spectral slope. Thus, we conclude that the spectral changes observed relevant to space weathering via micrometeorite impacts are an increase in spectral slope and an increase in the albedo of troilite. Future studies will investigate whether these trends are generally representative of other sulfide-bearing minerals and of weathering trends in other components found in the asteroid regolith.Plain Language Summary Carbonaceous asteroids are the most common asteroid found in our solar system. While it is generally accepted that the surfaces of these objects are altered over time by impacts via energetic particles, it is not currently understood how this alteration will change the spectral properties of the surface. In this study, we investigated how the spectral reflectance of troilite (FeS), one component that will likely be found on the surface of these types of asteroids, was altered by pulsed laser irradiation, which is used to mimic micrometeorite impacts that are regularly occurring on asteroid surfaces. The main finding in our study that is different from what has been found in previous studies with other relevant minerals, such as silicates, is that the overall reflectance spectrum brightens as the sample is altered. These results, combined with previous ones, will help astronomers interpret reflectance spectra taken of carbonaceous asteroids and possibly other extraterrestrial objects containing troilite.

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Section: Implication For Space Weathering On Airless Bodies Via Microsupporting

confidence: 79%

Space Weathering of FeS Induced via Pulsed Laser Irradiation

et al. 2020

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“…The laser was incident at 60°measured with respect to the sample normal, operated at 20 Hz with a 10 ns pulse length, and the power density was varied from about 10 to 250 μJ/cm 2 /pulse. This power is about 10 6 times less intense than what is typically used for laser simulations of micrometeorite impacts (Kaluna et al, 2017;Loeffler et al, 2008;Matsuoka et al, 2015). The experiments were carried out at room temperature (25°C) which, although cooler than typical dayside surface temperatures, is within expected temperature ranges on Mercury.…”

Section: Methodsmentioning

confidence: 99%

Photon‐Stimulated Desorption of MgS as a Potential Source of Sulfur in Mercury's Exosphere

et al. 2020

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Mercury has a relatively high sulfur content on its surface, and a signal consistent with ionized atomic sulfur (S+) was observed by the fast ion plasma spectrometer (FIPS) instrument on the MESSENGER spacecraft. To help confirm this assignment and to better constrain the sources of exospheric sulfur at Mercury, 193 nm photon‐stimulated desorption (PSD) of neutral sulfur atoms (S0) from MgS substrates was studied using resonance‐enhanced multiphoton ionization (REMPI) spectroscopy and time‐of‐flight (TOF) mass spectrometry. Though the PSD process is inherently nonthermal, the measured velocities of ejected S0 were fit using flux‐weighted Maxwellian distributions with translation energies expressed as translational “temperatures” Ttrans = /μkB. A bimodal distribution consisting of both thermal (Ttrans = 300 K) and suprathermal (Ttrans > 1,000 K) components in roughly a 2:1 ratio was found to best fit the data. The PSD cross‐section was measured to be approximately 4 × 10−22 cm2 and, together with the velocity distributions, was used to calculate the PSD source rate of S0 into the exosphere of Mercury. Exosphere simulations using the calculated rates demonstrate that PSD is likely the primary source of S0 in Mercury's exosphere at low (<1,000 km) altitudes.

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“…In the laboratory, several experiments have been performed on carbonaceous chondrites and analog materials to simulate the effects of micrometeoroid bombardment (via laser irradiation) and solar wind exposure (via ion irradiation). A common result of these simulations is the production of opaque materials (Gillis‐Davis et al, ; Gillis‐Davis et al, ; Matsuoka et al, ; Lantz et al, ; Thompson et al, ), notably carbonized materials (Kaluna et al, ; Moroz et al, ); these experiments and results are summarized briefly in the section S5. In particular, Lantz et al () demonstrated that the initial composition of a material plays an important role in determining whether it becomes bluer or reddens upon weathering.…”

Section: Links With Space Weatheringmentioning

confidence: 99%

C‐Complex Asteroids: UV‐Visible Spectral Characteristics and Implications for Space Weathering Effects

Hendrix

Vilas

2019

Geophysical Research Letters

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Space weathering effects on the rocky S-class asteroids are well understood. However, on the low-albedo C-complex asteroids, such as spacecraft targets Bennu and Ryugu, the situation is more complicated, especially due to a lack of spectral features throughout the visible-near infrared spectral region. Here we show, through a combination of observational data and laboratory data of carbonaceous chondrites, phyllosilicates, and mixtures, that the UV-visible spectral region is a diagnostic regime for studying space weathering effects on C-complex asteroids. We show that space-weathering-produced opaque constituents, such as graphitized carbons, darken mixtures with phyllosilicates and produce a bluing the UV-visible spectrum, consistent with what is seen on the asteroids compared with carbonaceous chondrites. Furthermore, we demonstrate that the UV upturns in the spectra of Bennu and Ryugu are consistent with the presence of graphitized carbon on those surfaces, the result of surface processing. Plain Language SummaryWe suggest that the relatively weak UV absorptions of C-complex asteroids compared with carbonaceous chondrite meteorites could be due to the increased presence of carbonized species on the asteroid surfaces, the result of space weathering processes. In fact, carbonized materials could be the source of the UV-visible spectra of Ryugu and Bennu, which appear to show UV upturns rather than UV absorptions. Though iron-rich and carbon-rich opaques have similar spectral effects in the UV-VIS, many laboratory experiments indicate that carbonaceous materials are the products of space weathering processes and thus carbonaceous materials could dominate spectral trends. Furthermore, we show that carbons may exhibit spectral features that change with processing and thus can help us to understand exposure age of some low-albedo targets.

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Simulated space weathering of Fe- and Mg-rich aqueously altered minerals using pulsed laser irradiation

Cited by 36 publications

References 64 publications

Space Weathering of FeS Induced via Pulsed Laser Irradiation

Space Weathering of FeS Induced via Pulsed Laser Irradiation

Photon‐Stimulated Desorption of MgS as a Potential Source of Sulfur in Mercury's Exosphere

C‐Complex Asteroids: UV‐Visible Spectral Characteristics and Implications for Space Weathering Effects

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