arXiv subjects

Simone Marchi

Publications and source records attributed to Simone Marchi.

At least 19 recordsLinked to original sources

arXiv2025

Evidence of Possible Spectral Variability in the Patroclus-Menoetius Binary System

We present new visible-wavelength spectroscopic observations of the Patroclus-Menoetius binary system in the Jupiter Trojan population. Motivated by previously published spectra from different instruments that showed evidence of significant longitudinal variability, we obtained two spectra spanning 440-680 nm at near-opposite rotational phases with the Gemini Multi-Object Spectrograph on the Gemini South telescope during the late 2024 apparition. The same solar analog was used for both observations to remove one source of inconsistency. We measured spectral slopes of 2.51% $\pm$ 0.05%/100 nm and 8.13% $\pm$ 0.05%/100 nm at the two different rotational phases. The first of these measurements was serendipitously obtained during an occultation of Menoetius by Patroclus. Although the statistical significance of the spectral slope discrepancy persists even after considering possible systematic errors stemming from differences in slit position angles and air masses between the asteroid and solar analog exposures, we consider this report of variability to be tentative. We briefly explore several scenarios that could explain the measured spectral slope variability. Additional follow-up observations are necessary to definitively confirm and characterize any inhomogeneities across the surface, which will have major implications for the 2033 flyby of Patroclus-Menoetius by the Lucy spacecraft.

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arXiv2025

The formation and structure of iron-dominated planetesimals

Metal-rich asteroids and iron meteorites are considered core remnants of differentiated planetesimals and or products of oxygen-depleted accretion. Investigating the origins of iron-rich planetesimals could provide key insights into planet formation mechanisms. Using differentiation models, we evaluate the interior structure and composition of representative-sized planetesimals (approx. 200 km diameter) while varying oxygen fugacity and initial bulk meteoritic composition. Under the oxygen-poor conditions that likely existed early in the inner regions of the Solar System and other protoplanetary disks, core fractions remain relatively consistent across a range of bulk compositions (CI, H, EH, and CBa). Some of these cores could incorporate significant amounts of silicon (10-30 wt percent) and explain the metal fractions of Fe-rich bodies in the absence of mantle stripping. Conversely, planetesimals forming under more oxidizing conditions, such as beyond snow lines, could exhibit smaller cores enriched in carbon, sulfur (more than 1 wt percent), and oxides. Sulfur-rich cores, like those formed from EH and H bulk compositions, could remain partly molten, sustain dynamos, and even drive sulfur-rich volcanism. Additionally, bodies with high carbon contents, such as CI compositions, can form graphitic outer layers. These variations highlight the importance of initial formation conditions in shaping planetesimal structures. Future missions, such as NASA's Psyche mission, offer an opportunity to measure the relative abundances of key elements (Fe, Ni, Si, and S) necessary to distinguish among formation scenarios and structure models for Fe-rich and reduced planetesimals.

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arXiv2025

Prospects of a New $L_5$ Trojan Flyby Target for the Lucy Mission

NASA's Lucy spacecraft is en route to conduct the first close encounter with Jupiter's Trojans. While most scheduled flybys lie in the $L_4$ cloud, the only $L_5$ target is the Patroclus-Menoetius binary. Since each flyby offers unique insights into target and population properties unattainable from Earth, we examine the feasibility of including an additional, yet unknown, $L_5$ target while minimizing the impact on Lucy's primary mission. We use the background $L_5$ Trojans brighter than the completeness limit to model their absolute magnitude, spatial, and orbital distributions. A semi-analytical approach estimates the number of Trojans accessible to Lucy for a given $\Delta v$ budget in both pre- and post-Patroclus scenarios. Our results indicate that, while it is unlikely that any suitable Trojan lies on Lucy's nominal path, a moderate $\Delta v$ investment ($35-50\,\mathrm{m/s}$) could enable a sub-kilometer ($500-700\,\mathrm{m}$) flyby prior to the Patroclus encounter. Post-Patroclus, the likelihood of a similar flyby is $\sim60\%$ for $\Delta v\sim$ 50 m/s. Simulations with synthetic Trojans reveal that potential targets cluster near the node opposite to the encounter window, producing an optimal search period in late 2026 for both scenarios. Surveying the densest $10\%$ of this region would require under 5 nights with Subaru/HSC or under 2 nights with Rubin, using shift-and-stack techniques. A successful sub-kilometric flyby would expand Lucy's Trojan target size range and provide new constraints on collisional evolution and the long-standing asymmetry in the $L_4/L_5$ clouds. This nodal-clustering strategy could guide target searches in future Lucy extensions or other planetary flyby missions.

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arXiv2025

Size-Frequency Distribution of Terrestrial Leftover Planetesimals and S-complex Implanted Asteroids

The isotopic composition of meteorites linked to S-complex asteroids has been used to suggest that these asteroids originated in the terrestrial planet's region, i.e., within 1.5 au, and later got implanted into the main asteroid belt (MAB). Dynamical models of planet formation support this view. Yet, it remains to be demonstrated whether the currently observed size-frequency distribution (SFD) of S-complex bodies in the MAB can be reproduced via this implantation process. Here we studied the evolution of the SFD of planetesimals during the accretion of terrestrial planets with the code LIPAD self-consistently accounting for growth and fragmentation of planetesimals. In our simulations we vary the initial surface density of planetesimals, the gaseous disk lifetime, and the power slope of the initial planetesimals' SFD. We compared the final SFDs of leftover planetesimals in the terrestrial planet region with the SFD of observed S-complex MAB objects (D $>$ 100km). We found that the SFDs of our planetesimal populations and that of S-complex MAB objects show very similar cumulative power index (i.e., q $\approx$ 3.15 in N($>$D)$~\propto$ D$^{-q}$) for slopes in the diameter range 100 km $<$ D $<$ 400 km by the end of our simulations. Our results support the hypothesis of S-complex MAB implantation from the terrestrial planet forming region, assuming implantation is size-independent, and implies that implantation efficiency is smaller than $\mathcal{O}$(10$^{\rm -2}$--10$^{\rm -4}$) to avoid over-implantation of (4) Vesta-sized objects or larger.

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arXiv2025

A pre-flyby view on the origin of asteroid Donaldjohanson, a target of the NASA Lucy mission

The NASA Lucy mission is scheduled to fly-by the main belt asteroid (52246) Donaldjohanson on April 20, 2025. Donaldjohanson (DJ hereafter) is a member of the primitive (C-type class) Erigone collisional asteroid family located in the inner main belt in proximity of the source regions of asteroid (101955)~Bennu and (162173)~Ryugu, visited respectively by OSIRIS-REx and Hayabusa2 missions. In this paper we provide an updated model for the Erigone family age, and discuss DJ evolution resulting from non-gravitational forces (namely Yarkovsky and YORP), as well as its collisional evolution. We conclude the best-fit family age to be $\sim 155$~Myr, and that, on such timescales, both Yarkovsky and YORP effects may have affected the orbit and spin properties of DJ. Furthermore, we discuss how the NASA Lucy mission could provide independent insights on such processes, namely by constraining DJ shape, surface geology and cratering history.

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arXiv2024

A Contact Binary Satellite of the Asteroid (152830) Dinkinesh

Asteroids with diameters less than about 5 km have complex histories because they are small enough for radiative torques, YORP, to be a notable factor in their evolution. (152830) Dinkinesh is a small asteroid orbiting the Sun near the inner edge of the Main Asteroid Belt with a heliocentric semimajor axis of 2.19 AU; its S type spectrum is typical of bodies in this part of the Main Belt. Here we report observations by the Lucy spacecraft as it passed within 431 km of Dinkinesh. Lucy revealed Dinkinesh, which has an effective diameter of only $\sim$720 m, to be unexpectedly complex. Of particular note is the presence of a prominent longitudinal trough overlain by a substantial equatorial ridge, and the discovery of the first confirmed contact binary satellite, now named (152830) Dinkinesh I Selam. Selam consists of two near-equal sized lobes with diameters of $\sim$210 m and $\sim$230 m. It orbits Dinkinesh at a distance of 3.1 km with an orbital period of about 52.7 hr, and is tidally locked. The dynamical state, angular momentum, and geomorphologic observations of the system lead us to infer that the ridge and trough of Dinkinesh are probably the result of mass failure resulting from spin-up by YORP followed by the partial reaccretion of the shed material. Selam probably accreted from material shed by this event.

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arXiv2023

JWST near-infrared spectroscopy of the Lucy Jupiter Trojan flyby targets: Evidence for OH absorption, aliphatic organics, and CO$_{2}$

We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft -- the Patroclus-Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7-5.3 $\mu$m reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 $\mu$m that is most prominent on the less-red objects Eurybates, Patroclus-Menoetius, and Polymele. An additional absorption feature at 3.3-3.6 $\mu$m, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 $\mu$m that we attribute to bound or trapped CO$_2$. Comparisons with other solar system small bodies reveal broad similarities in the 2.7-3.6 $\mu$m bands with analogous features on Centaurs, Kuiper belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7-3.6 $\mu$m absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans' surfaces at the higher temperatures of the Jupiter region. The CO$_2$ band manifested on the surface of Eurybates suggests that CO$_2$ may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.

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arXiv2023

The Collisional Evolution of the Primordial Kuiper Belt, Its Destabilized Population, and the Trojan Asteroids

The tumultuous early era of outer solar system evolution culminated when Neptune migrated across the primordial Kuiper belt (PKB) and triggered a dynamical instability among the giant planets. This event led to the ejection of approximately 99.9\% of the PKB (here called the destabilized population), heavy bombardment of the giant planet satellites, and the capture of Jupiter's Trojans. While this scenario has been widely tested using dynamical models, there have been fewer investigations into how the PKB, its destabilized population, and the Trojans experienced collisional evolution. Here we examined this issue for all three populations with the code Boulder. Our constraints included the size-frequency distributions (SFDs) of the Trojan asteroids and craters on the giant planet satellites. Using this combination, we solved for the unknown disruption law affecting bodies in these populations. The weakest ones, from an impact energy per mass perspective, were 20 m in diameter. Overall, collisional evolution produces a power-law-like shape for multikilometer Trojans and a wavy-shaped SFD in the PKB and destabilized populations. The latter can explain (i) the shapes of the ancient and younger crater SFDs observed on the giant planet satellites, (ii) the shapes of the Jupiter family and long-period comet SFDs, which experienced different degrees of collision evolution, and (iii) the present-day impact frequency of superbolides on Jupiter and smaller projectiles on Saturn's rings. Our model results also indicate that many observed comets, most which are smaller than 10 km in diameter, are likely to be gravitational aggregates formed by large-scale collision events.

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arXiv2023

Early Bombardment of the Moon: Connecting the Lunar Crater Record to the Terrestrial Planet Formation

The lunar crater record features $\sim 50$ basins. The radiometric dating of Apollo samples indicates that the Imbrium basin formed relatively late -- from the planet formation perspective -- some $\simeq 3.9$ Ga. Here we develop a dynamical model for impactors in the inner solar system to provide context for the interpretation of the lunar crater record. The contribution of cometary impactors is found to be insignificant. Asteroids produced most large impacts on the terrestrial worlds in the last $\simeq 3$ Gyr. The great majority of early impactors were rocky planetesimals left behind at $\sim 0.5$--1.5 au after the terrestrial planet accretion. The population of terrestrial planetesimals was reduced by disruptive collisions in the first $t \sim 20$ Myr after the gas disk dispersal. We estimate that there were $\sim 4 \times 10^5$ diameter $d>10$ km bodies when the Moon formed (total planetesimal mass $\sim 0.015$ $M_{\rm Earth}$ at $t \sim 50$ Myr). The early bombardment of the Moon was intense. To accommodate $\sim 50$ known basins, the lunar basins that formed before $\simeq 4.35$--4.41 Ga must have been erased. The late formation of Imbrium occurs with a $\sim 15$--35\% probability in our model. About 20 $d>10$-km bodies were expected to hit the Earth between 2.5 and 3.5 Ga, which is comparable to the number of known spherule beds in the late Archean. We discuss implications of our model for the lunar/Martian crater chronologies, Late Veneer, and noble gases in the Earth atmosphere.

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arXiv2023

Successful Kinetic Impact into an Asteroid for Planetary Defense

While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact. While past missions have utilized impactors to investigate the properties of small bodies those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.

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arXiv2022

Formation of Lunar Basins from Impacts of Leftover Planetesimals

The Moon holds important clues to the early evolution of the Solar System. Some 50 impact basins (crater diameter D>300 km) have been recognized on the lunar surface, implying that the early impact flux was much higher than it is now. The basin-forming impactors were suspected to be asteroids released from an inner extension of the main belt (1.8-2.0 au). Here we show that most impactors were instead rocky planetesimals left behind at 0.5-1.5 au after the terrestrial planet accretion. The number of basins expected from impacts of leftover planetesimals largely exceeds the number of known lunar basins, suggesting that the first 200 Myr of impacts is not recorded on the lunar surface. The Imbrium basin formation (age 3.92 Gyr; impactor diameter d~100 km) occurs with a 15-35% probability in our model. Imbrium must have formed unusually late to have only two smaller basins (Orientale and Schrodinger) forming afterwards. The model predicts 20 d>10-km impacts on the Earth 2.5-3.5 Gyr ago (Ga), which is comparable to the number of known spherule beds in the late Archean.

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arXiv2022

The Renaissance of Main Belt Asteroid Science

The NASA Dawn spacecraft took off from Cape Canaveral in September 2007 atop a Delta II rocket starting an ambitious journey to Vesta and Ceres, the two most massive worlds in the largest reservoir of asteroids in the Solar System, the Main Belt. Prior to the Dawn launch, Earth-bound observations of Vesta and Ceres revealed intriguing features--from Vesta's rugged shape to Ceres' tenuous water exosphere--, but these objects remained fuzzy speckles of light even through the lenses of the most powerful telescopes. With Dawn's exploration of Vesta (2011-2012) and Ceres (2015-2018) these two worlds came into focus. Breath-taking details emerged of how large collisions sculpted Vesta liberating massive amounts of material in the inner Main Belt, providing the source of an important family of meteorites recovered on Earth. Ceres' complex geology, which may rival that of the Earth and Mars, unveiled recent cryovolcanic activity. This book is dedicated to these highlights, and many more discoveries of the Dawn mission. By the time Dawn completed its mission in 2018, our understanding of the formation of the Solar System had greatly evolved thanks to new theoretical models and to a new trove of meteorite geochemical data, and Dawn observations of Vesta and Ceres provide new, vital constraints to synergistically interpret models and data. The broader implications of the Dawn legacy are presented in a series of dedicated chapters. The editors hope this book will serve as a solid reference for the younger generations as well as for more seasoned researchers to successfully pursue future exploration of the Main Belt. We certainly have learned a lot thanks to Dawn, and yet we know that we have barely scratched the surface of what Main Belt asteroids can tell us about the dawn of our Solar System.

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arXiv2021

Spectroscopic study of Ceres' collisional family candidates

Context: Despite the observed signs of large impacts on the surface of Ceres, there is no confirmed collisional family associated with this dwarf planet. After a dynamical and photometric study, a sample of 156 asteroids was proposed as candidate members of a Ceres collisional family. Aims: Our main objective is to study the connection between Ceres and a total of 14 observed asteroids among the candidate's sample to explore their genetic relationships with Ceres. Methods: We obtained visible spectra of these 14 asteroids using the OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias(GTC). We computed spectral slopes in two different wavelength ranges, from 0.49 to 0.80{\mu}m and from 0.80 to 0.92{\mu}m, to compare the values obtained with those on Ceres' surface previously computed using the Visible and Infrared Spectrometer (VIR) instrument onboard the NASA Dawn spacecraft. We also calculated the spectral slopes in the same range for ground-based observations of Cerescollected from the literature. Results: We present the visible spectra and the taxonomy of 14 observed asteroids. We found that only two of the asteroids are spectrally compatible with Ceres' surface. Further analysis of those two asteroids indicates that they are spectrally young and thus less likely to be members of the Ceres family. Conclusions: All in all, our results indicate that most of the 14 observed asteroids are not likely to belong to a Ceres collisional family. Despite two of them being spectrally compatible with the young surface of Ceres, further evaluation is needed to confirm or reject their origin from Ceres.

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arXiv2021

Dark Primitive Asteroids Account for a Large Share of K/Pg-Scale Impacts on the Earth

A dynamical model for large near-Earth asteroids (NEAs) is developed here to understand the occurrence rate and nature of Cretaceous-Paleogene (K/Pg) scale impacts on the Earth. We find that 16--32 (2--4) impacts of diameter $D>5$ km ($D>10$ km) NEAs are expected on the Earth in 1 Gyr, with about a half of impactors being dark primitive asteroids (most of which start with semimajor axis $a>2.5$ au). These results explain why the Chicxulub crater, the third largest impact structure found on the Earth (diameter $\simeq180$ km), was produced by impact of a carbonaceous chondrite. They suggest, when combined with previously published results for small ($D \lesssim 1$ km) NEAs, a size-dependent sampling of the main belt. We conclude that the impactor that triggered the K/Pg mass extinction $\simeq 66$ Myr ago was a main belt asteroid that quite likely ($\simeq 60$\% probability) originated beyond 2.5 au.

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arXiv2021

Lucy Mission to the Trojan Asteroids: Instrumentation and Encounter Concept of Operations

The Lucy Mission accomplishes its science during a series of five flyby encounters with seven Trojan asteroid targets. This mission architecture drives a concept of operations design that maximizes science return, provides redundancy in observations where possible, features autonomous fault protection and utilizes onboard target tracking near closest approach. These design considerations reduce risk during the relatively short time-critical periods when science data is collected. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. The mission design allows for concurrent observations of all instruments. Additionally, two spacecraft subsystems will also contribute to the science investigations: the Terminal Tracking Cameras will obtain wide field-of-view imaging near closest approach to determine the shape of each of the Trojan targets and the telecommunication subsystem will carry out Doppler tracking of the spacecraft to determine the mass of each of the Trojan targets.

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arXiv2021

A new martian crater chronology: Implications for Jezero crater

Crater chronologies are a fundamental tool to assess relative and absolute ages of planetary surfaces when direct radiometric dating is not available. Martian crater chronologies are derived from lunar crater spatial densities on terrains with known radiometric ages, and thus they critically depend on the extrapolation Moon to Mars. This extrapolation requires knowledge of the time evolution of the impact flux, including contributions from various impactor populations, factors that are not trivially connected to the dynamical evolution of the early Solar System. In this paper, we will present a new martian crater chronology based on current dynamical models, and consider the main sources of uncertainties. The new martian crater chronology is discussed using two interesting applications: Jezero crater's dark terrain (relevant to the NASA Mars 2020 mission) and the southern heavily cratered highlands. [abridged]

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arXiv2020

Convex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations

We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018 and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs (Buie et al. 2020) to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3{\deg} (1$\sigma$) from J2000 Ecliptic coordinates ($\lambda=208\deg$, $\beta=+77\deg$) or J2000 Equatorial Coordinates (RA=248$\deg$, Dec=+58$\deg$). The sidereal period is refined to $P_{sid}=445.683\pm0.007$ h. The convex shape model is irregular, with maximum dimensions of (60.8, 39.1, 27.8) km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo $p_V=0.043\pm0.002$. The derived phase curve supports a D-type classification for Leucus.

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arXiv2020

Constraining Prebiotic Chemistry Through a Better Understanding of Earth's Earliest Environments

Any search for present or past life beyond Earth should consider the initial processes and related environmental controls that might have led to its start. As on Earth, such an understanding lies well beyond how simple organic molecules become the more complex biomolecules of life, because it must also include the key environmental factors that permitted, modulated, and most critically facilitated the prebiotic pathways to life's emergence. Moreover, we ask how habitability, defined in part by the presence of liquid water, was sustained so that life could persist and evolve to the point of shaping its own environment. Researchers have successfully explored many chapters of Earth's coevolving environments and biosphere spanning the last few billion years through lenses of sophisticated analytical and computational techniques, and the findings have profoundly impacted the search for life beyond Earth. Yet life's very beginnings during the first hundreds of millions of years of our planet's history remain largely unknown--despite decades of research. This report centers on one key point: that the earliest steps on the path to life's emergence on Earth were tied intimately to the evolving chemical and physical conditions of our earliest environments. Yet, a rigorous, interdisciplinary understanding of that relationship has not been explored adequately and once better understood will inform our search for life beyond Earth. In this way, studies of the emergence of life must become a truly interdisciplinary effort, requiring a mix that expands the traditional platform of prebiotic chemistry to include geochemists, atmospheric chemists, geologists and geophysicists, astronomers, mission scientists and engineers, and astrobiologists.

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