arXiv subjects

Francesca E. DeMeo

Publications and source records attributed to Francesca E. DeMeo.

At least 19 recordsLinked to original sources

arXiv2026

Dark asteroids exhibiting intermediate characteristics between C and X types

Large main-belt asteroids with visible geometric albedos below 0.1 are predominantly classified within the C- and X-complex spectroscopic classes. C-type and dark X-type asteroids typically exhibit flat to slightly negative and positive spectral slopes, respectively. They are further distinguished by the presence (for C-types) or absence (for dark X-types) of a shallow absorption feature near 1.0-1.3 micron. We serendipitously discovered that the asteroids 1093 Freda and 1390 Abastumani display spectral characteristics intermediate between these two classes, combining a positive visible-to-near-infrared spectral slope with a shallow absorption band. A search in the literature reveals additional asteroids with similar properties. The existence of such objects, spanning a continuum of spectral shapes between C- and dark X-types, may point to a common genetic origin. Their spectral behavior could be explained by the presence of cronstedtite, an Fe-rich serpentine, on their surfaces.

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arXiv2024

The Massalia asteroid family as the origin of ordinary L chondrites

Studies of micrometeorites in mid-Ordovician limestones and Earth's impact craters indicate that our planet witnessed a massive infall of ordinary L chondrite material 466 million years (My) ago (Heck et al. 2017, Schmieder & Kring 2020, Kenkmann 2021) that may have been at the origin of the first major mass extinction event (Schmitz et al. 2019). The breakup of a large asteroid in the main belt is the likely cause of this massive infall. In modern times, material originating from this breakup still dominates meteorite falls (>20% of all falls) (Swindle et al. 2014). Here, we provide spectroscopic observations and dynamical evidence that the Massalia collisional family is the only plausible source of this catastrophic event and of the most abundant class of meteorites falling on Earth today. It is suitably located in the inner belt, at low-inclination orbits, which corresponds to the observed distribution of L-chondrite-like near-Earth objects (NEOs) and of interplanetary dust concentrated at 1.4 degrees (Sykes 1990, Reach et al. 1997).

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arXiv2023

Near-IR Spectral Observations of the Didymos System -- Daily Evolution Before and After the DART Impact, Indicates Dimorphos Originated from Didymos

Ejecta from Dimorphos following the DART mission impact, significantly increased the brightness of the Didymos-Dimorphos system, allowing us to examine sub-surface material. We report daily near-IR spectroscopic observations of the Didymos system using NASA's IRTF, that follow the evolution of the spectral signature of the ejecta cloud over one week, from one day before the impact. Overall, the spectral features remained fixed (S-type classification) while the ejecta dissipated, confirming both Didymos and Dimorphos are constructed from the same silicate material. This novel result strongly supports binary asteroid formation models that include breaking up of a single body, due to rotational breakup of km-wide bodies. At impact time +14 and +38 hours, the spectral slope decreased, but following nights presented increasing spectral slope that almost returned to the pre-impact slope. However, the parameters of the $1~μm$ band remained fixed, and no "fresh" / Q-type-like spectrum was measured. We interpret these as follow: 1. The ejecta cloud is the main contributor ($60-70\%$) to the overall light during the $\sim40$ hours after impact. 2. Coarser debris ($\geq 100~μm$) dominated the ejecta cloud, decreasing the spectral slope (after radiation pressure removed the fine grains at $\leq10$ hours after impact); 3. after approximately one week, the ejecta cloud dispersed enough to make the fine grains on Didymos surface the dominating part of the light, increasing the spectral slope to pre-impact level. 4. a negligible amount of non-weathered material was ejected from Dimorphos' sub-surface, suggesting Dimorphos was accumulated from weathered material, ejected from Didymos surface.

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arXiv2022

Spectral evolution of dark asteroid surfaces induced by space weathering over a decade

The surface of airless bodies like asteroids in the Solar System are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In December 2010, the T-type asteroid 596 Scheila underwent a collision with a few-tens-of-meters impactor. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10-year period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the Solar System. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203 Pompeja). New observations show that 203 Pompeja has a X-type-like surface, with some local surface areas exhibiting a very red spectrum.

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arXiv2022

Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy

We identify spectral similarities between asteroids and meteorites. We identify spectral matches between 500 asteroid spectra and over 1,000 samples of RELAB meteorite spectra over 0.45-2.5 microns. We reproduce many major and previously known meteorite-asteroid connections and find possible new, more rare or less-established connections. Well-established connections include: ordinary chondrites (OC) with S-complex asteroids; pristine CM carbonaceous chondrites with Ch-type asteroids and heated CMs with C-type asteroids; HED meteorites with V-types; enstatite chondrites with Xc-type asteroids; CV meteorites with K-type asteroids; Brachinites, Pallasites and R chondrites with olivine-dominated A-type asteroids. We find a trend from Q, Sq, S, Sr to Sv correlates with LL to H, with Q-types matching predominately to L and LL ordinary chondrites, and Sr and Sv matching predominantly with L and H ordinary chondrites. Ordinary chondrite samples that match to the X-complex, all measurements of slabs and many labeled as dark or black (shocked) OCs. We find carbonaceous chondrite samples having spectral slopes large enough to match D-type asteroid spectra. In many cases the asteroid type to meteorite type links are not unique. While there are well established matches between an asteroid class and meteorite class, there are less common but still spectrally compatible matches between many asteroid types and meteorite types. This result emphasizes the diversity of asteroid and meteorite compositions and highlights the degeneracy of classification by spectral features alone. Recent and upcoming spacecraft missions will shed light on the compositions of many of the asteroid classes, particularly those without diagnostic features, (C-, B-, X-, and D-types), with measurements of Ceres, Ryugu, Bennu, Psyche, and C-, P-, and D-types as part of the Lucy mission.

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arXiv2022

The debiased compositional distribution of MITHNEOS: Global match between the near-Earth and main-belt asteroid populations and excess of D-type Near-Earth Objects

We report 491 new near-infrared spectroscopic measurements of 420 near-Earth objects (NEOs) collected on the NASA InfraRed Telescope Facility (IRTF) as part of the MIT-Hawaii NEO Spectroscopic Survey (MITHNEOS). These measurements were combined with previously published data (Binzel et al. 2019) and bias-corrected to derive the intrinsic compositional distribution of the overall NEO population, as well as of subpopulations coming from various escape routes (ERs) in the asteroid belt and beyond. The resulting distributions reflect well the overall compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The close compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against any strong composition change with size in the asteroid belt between ~5 km down to ~100 m. A notable exception comes from the over-abundance of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and nu6 ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate preferential spectral evolution from D-type surfaces to C- and P-types as a consequence of space weathering, or to the fact that D-type objects fragment more often than other spectral types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.

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arXiv2021

The appearance of a 'fresh' surface on 596 Scheila as a consequence of the 2010 impact event

Dust emission was detected on main-belt asteroid 596 Scheila in December 2010, and attributed to the collision of a few-tens-of-meters projectile on the surface of the asteroid. In such impact, the ejected material from the collided body is expected to mainly comes from its fresh, unweathered subsurface. Therefore, it is expected that the surface of 596 was partially or entirely refreshed during the 2010 impact. By combining spectra of 596 from the literature and our own observations, we show that the 2010 impact event resulted in a significant slope change in the near-infrared (0.8 to 2.5 μm) spectrum of the asteroid, from moderately red (T-type) before the impact to red (D-type) after the impact. This provides evidence that red carbonaceous asteroids become less red with time due to space weathering, in agreement with predictions derived from laboratory experiments on the primitive Tagish Lake meteorite, which is spectrally similar to 596. This discovery provides the very first telescopic confirmation of the expected weathering trend of asteroids spectrally analog to Tagish Lake and/or anhydrous chondritic porous interplanetary dust particles. Our results also suggest that the population of implanted objects from the outer solar system is much larger than previously estimated in the main-belt, but many of these objects are hidden below their space-weathered surface.

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arXiv2021

A new approach to feature-based asteroid taxonomy in 3D color space: 1. SDSS photometric system

The taxonomic classification of asteroids has been mostly based on spectroscopic observations with wavelengths spanning from the VIS to the NIR. VIS-NIR spectra of $\sim$2500 asteroids have been obtained since the 1970s; the SDSS MOC 4 was released with $\sim$4 $\times$ 10$^{5}$ measurements of asteroid positions and colors in the early 2000s. A number of works then devised methods to classify these data within the framework of existing taxonomic systems. Some of these works, however, used 2D parameter space that displayed a continuous distribution of clouds of data points resulting in boundaries that were artificially defined. We introduce here a more advanced method to classify asteroids based on existing systems. This approach is simply represented by a triplet of SDSS colors. The distributions and memberships of each taxonomic type are determined by machine learning methods in the form of both unsupervised and semi-supervised learning. We apply our scheme to MOC 4 calibrated with VIS-NIR reflectance spectra. We successfully separate seven different taxonomy classifications with which we have a sufficient number of spectroscopic datasets. We found the overlapping regions of taxonomic types in a 2D plane were separated with relatively clear boundaries in the 3D space newly defined in this work. Our scheme explicitly discriminates between different taxonomic types, which is an improvement over existing systems. This new method for taxonomic classification has a great deal of scalability for asteroid research, such as space weathering in the S-complex, and the origin and evolution of asteroid families. We present the structure of the asteroid belt, and describe the orbital distribution based on our newly assigned taxonomic classifications. It is also possible to extend the methods presented here to other photometric systems, such as the Johnson-Cousins and LSST filter systems.

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arXiv2021

Discovery of two TNO-like bodies in the asteroid belt

Two extremely red main-belt asteroids: 203 Pompeja and 269 Justitia, were identified from combined visible and near-infrared spectroscopic observations collected at the IRTF and SAO observatories. These two asteroids have a redder spectral slope than any other D-type body, which are the reddest objects in the asteroid belt, and similar to RR and IR-class objects found in the outer Solar System among trans-Neptunian objects and Centaurs. Spectroscopic results suggest the presence of complex organic materials on the surface layer of these asteroids, implying that they could have formed in the vicinity of Neptune and been transplanted to the main belt region during a phase of planetary migration. 203 Pompeia is the only very red asteroid known so far among the ~250 bodies with diameter larger than 110 km (i.e. presumably structurally intact) found in the asteroid belt. These discoveries add another piece of evidence that the main asteroid belt hosts a population of bodies that were formed in the outskirt of the Solar System.

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arXiv2020

Twenty years of SpeX: Accuracy limits of spectral slope measurements in asteroid spectroscopy

We examined two decades of SpeX/NASA Infrared Telescope Facility observations from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate uncertainties and systematic errors in reflectance spectral slope measurements of asteroids. From 628 spectra of 11 solar analogs used for calibration of the asteroid spectra, we derived an uncertainty of 4.2%/micron on slope measurements over 0.8 to 2.4 micron. Air mass contributes to -0.92%/micron per 0.1 unit air mass difference between the asteroid and the solar analog, and therefore for an overall 2.8%/micron slope variability in SMASS and MITHNEOS designed to operate within 1.0 to 1.3 air mass. No additional observing conditions (including parallactic angle, seeing and humidity) were found to contribute systematically to slope change. We discuss implications for asteroid taxonomic classification works. Uncertainties provided in this study should be accounted for in future compositional investigation of small bodies to distinguish intrinsic heterogeneities from possible instrumental effects.

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arXiv2019

Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to Families

Differentiated asteroids are rare in the main asteroid belt despite evidence for ~100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope. We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of ~600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

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arXiv2018

How Many Hydrated NEOs Are There?

Hydrated minerals are tracers of early solar system history, and have been proposed as a possible focus for economic activity in space. Near-Earth objects (NEOs) are important to both of these, especially the most accessible members of that community. Because there are very few identified hydrated NEOs, we use the Ch spectral class of asteroids as a proxy for hydrated asteroids, and use published work about NEO delivery, main-belt taxonomic distributions, NEO taxonomic distributions, and observed orbital distributions to estimate the number of hydrated asteroids with different threshold sizes and at different levels of accessibility. We expect 53 $\pm$ 27 Ch asteroids to be present in the known population of NEOs $>$ 1 km diameter, and using two different approaches to estimate accessibility we expect 17 $\pm$ 9 of them to be more accessible on a round trip than the surface of the Moon. If there is no need to define a minimum size, we expect 700 $\pm$ 350 hydrated objects that meet that accessibility criterion. While there are few unknown NEOs larger than 1 km, the population of smaller NEOs yet to be discovered could also be expected to contain proportionally-many hydrated objects. Finally, we estimate that hydrated NEOs are unlikely to bring enough water to account for the ice found at the lunar poles, though it is possible that asteroid-delivered hydrated minerals could be found near their impact sites across the lunar surface.

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arXiv2018

The Mission Accessible Near-Earth Objects Survey: Four years of photometry

Over 4.5 years, the Mission Accessible Near-Earth Object Survey (MANOS) assembled 228 Near-Earth Object (NEO) lightcurves. We report rotational lightcurves for 82 NEOs, constraints on amplitudes and periods for 21 NEOs, lightcurves with no detected variability within the image signal to noise and length of our observing block for 30 NEOs, and 10 tumblers. We uncovered 2 ultra-rapid rotators with periods below 20s; 2016MA with a potential rotational periodicity of 18.4s, and 2017QG$_{18}$ rotating in 11.9s, and estimate the fraction of fast/ultra-rapid rotators undetected in our project plus the percentage of NEOs with a moderate/long periodicity undetectable during our typical observing blocks. We summarize the findings of a simple model of synthetic NEOs to infer the object morphologies distribution using the measured distribution of lightcurve amplitudes. This model suggests a uniform distribution of axis ratio can reproduce the observed sample. This suggests that the quantity of spherical NEOs (e.g., Bennu) is almost equivalent to the quantity of highly elongated objects (e.g., Itokawa), a result that can be directly tested thanks to shape models from Doppler delay radar imaging analysis. Finally, we fully characterized 2 NEOs as appropriate targets for a potential robotic/human mission: 2013YS$_{2}$ and 2014FA$_{7}$ due to their moderate spin periods and low $Δv$.

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arXiv2017

The compositional diversity of non-Vesta basaltic asteroids

We present near-infrared (0.78-2.45 μm) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type. The remainder of the sample are classified as V- or R- type. All of these asteroids are dynamically detached from the Vesta collisional family, but are too small to be intact differentiated parent bodies, implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system. The 1- and 2-μm band centers of all objects, determined using the Modified Gaussian Model (MGM), were compared to those of 47 Vestoids and fifteen HED meteorites of known composition. The HEDs enabled us to determine formulas relating Band 1 and Band 2 centers to pyroxene ferrosilite (Fs) compositions. Using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids. We also conduct a careful error analysis of the MGM-derived band centers for implementation in future analyses. The six outer belt V- and R-type asteroids show more dispersion in parameter space than the Vestoids, reflecting greater compositional diversity than Vesta and its associated bodies. The objects analyzed have Fs numbers which are, on average, between five and ten molar percent lower than those of the Vestoids; however, identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result. Given the gradient in oxidation state which existed within the solar nebula, these results tentatively suggest that these objects formed at either a different time or location than 4 Vesta.

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arXiv2016

Near-infrared thermal emission from near-Earth asteroids: Aspect-dependent variability

Here we explore a technique for constraining physical properties of near-Earth asteroids (NEAs) based on variability in thermal emission as a function of viewing aspect. We present case studies of the low albedo, near-Earth asteroids (285263) 1998 QE2 and (175706) 1996 FG3. The Near-Earth Asteroid Thermal Model (NEATM) is used to fit signatures of thermal emission in near-infrared (0.8 - 2.5 micron) spectral data. This analysis represents a systematic study of thermal variability in the near-IR as a function of phase angle. The observations of QE2 imply that carefully timed observations from multiple viewing geometries can be used to constrain physical properties like retrograde versus prograde pole orientation and thermal inertia. The FG3 results are more ambiguous with detected thermal variability possibly due to systematic issues with NEATM, an unexpected prograde rotation state, or a surface that is spectrally and thermally heterogenous. This study highlights the potential diagnostic importance of high phase angle thermal measurements on both sides of opposition. We find that the NEATM thermal beaming parameters derived from our near-IR data tend to be of order 10's of percent higher than parameters from ensemble analyses of longer wavelength data sets. However, a systematic comparison of NEATM applied to data in different wavelength regimes is needed to understand whether this offset is simply a reflection of small number statistics or an intrinsic limitation of NEATM when applied to near-IR data. With the small sample presented here, it remains unclear whether NEATM modeling at near-IR wavelengths can robustly determine physical properties like pole orientation and thermal inertia.

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arXiv2016

Spectral properties of near-Earth and Mars-crossing asteroids using Sloan photometry

The nature and origin of the asteroids orbiting in near-Earth space, including those on a potentially hazardous trajectory, is of both scientific interest and practical importance. We aim here at determining the taxonomy of a large sample of near-Earth (NEA) and Mars-crosser (MC) asteroids and analyze the distribution of these classes with orbit. We use this distribution to identify their source regions and to study the strength of planetary encounters to refresh asteroid surfaces. We measure the photometry of these asteroids over four filters at visible wavelengths on images taken by the SDSS. These colors are used to classify the asteroids into a taxonomy consistent with the widely used Bus-DeMeo taxonomy based on spectroscopy. We report here on the taxonomic classification of 206 NEAs and 776 MCs determined from SDSS photometry, representing an increase of 40% and 663% of known taxonomy classifications in these populations. Using the source region mapper by Greenstreet et al. (2012), we compare the taxonomic distribution among NEAs and main-belt asteroids of similar diameters. Both distributions agree at the few percent level for the inner part of the Main Belt and we confirm this region as a main source of near-Earth objects. The effect of planetary encounters on asteroid surfaces are also studied by developing a simple model of forces acting on a surface grain during planetary encounter, which provides the minimum distance at which a close approach should occur to trigger resurfacing events. By integrating numerically the orbit of the 519 S-type and 46 Q-type asteroids back in time and monitoring their encounter distance with planets, we seek to understand the conditions for resurfacing events. The population of Q-type is found to present statistically more encounters with Venus and the Earth than S-types, although both types present the same amount of encounters with Mars.

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arXiv2015

The Compositional Structure of the Asteroid Belt

The past decade has brought major improvements in large-scale asteroid discovery and characterization with over half a million known asteroids and over 100,000 with some measurement of physical characterization. This explosion of data has allowed us to create a new global picture of the Main Asteroid Belt. Put in context with meteorite measurements and dynamical models, a new and more complete picture of Solar System evolution has emerged. The question has changed from "What was the original compositional gradient of the Asteroid Belt?" to "What was the original compositional gradient of small bodies across the entire Solar System?" No longer is the leading theory that two belts of planetesimals are primordial, but instead those belts were formed and sculpted through evolutionary processes after Solar System formation. This article reviews the advancements on the fronts of asteroid compositional characterization, meteorite measurements, and dynamical theories in the context of the heliocentric distribution of asteroid compositions seen in the Main Belt today. This chapter also reviews the major outstanding questions relating to asteroid compositions and distributions and summarizes the progress and current state of understanding of these questions to form the big picture of the formation and evolution of asteroids in the Main Belt. Finally, we briefly review the relevance of asteroids and their compositions in their greater context within our Solar System and beyond.

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arXiv2014

Observations of "Fresh" and Weathered Surfaces on Asteroid Pairs and Their Implications on the Rotational-Fission Mechanism

The rotational-fission of a rubble-pile asteroid can result in an "asteroid pair", two un-bound asteroids sharing similar orbits. This mechanism might exposes material that previously had never have been exposed to the weathering conditions of space. Therefore, the surfaces of asteroid pairs offer the opportunity to observe non-weathered fresh spectra. We report near-IR spectroscopic observations of 31 asteroids in pairs. We analyze their spectral slopes, 1 μm absorption band, taxonomy, and estimate the time elapsed since their separation. Analyzing the 19 S-complex objects in our sample, we find two fresh Q-type asteroids that are the first of their kind to be observed in the main-belt over the full visible and near-IR range. This solidly demonstrates that Q-type objects are not limited to the NEA population. The pairs in our sample present a range of fresh and weathered surfaces with no clear evidence for a correlation with the ages of the pairs. However, our sample includes old pairs (1 to 2 My) that present low spectral slopes. This illustrates a timescale of at least ~2 My before an object develops high spectral slope that is typical for S-type asteroids. We discuss mechanisms that explain the existence of weathered pairs with young dynamical ages and find that the "secondary fission" model (Jacobson & Scheeres 2011) is the most robust with our observations since: 1) the secondary members in our sample present fresh parameters that tend to be fresher than their weathered primaries; 2) most of the fresh pairs in our sample have low size ratios between the secondary and the primary; 3) 33% of the primaries in our sample are fresh, similar to the prediction set by this model; 4) known satellites orbit two of the pairs in our sample with low size ratio and fresh surface; 5) there is no correlation between the weathering state and the primary shape as predicted by other models.

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