A radar survey of M- and X-class asteroids

A radar survey of M- and X-class asteroids II. Summary and synthesis

Context. Basaltic V-type asteroids are leftovers from the formation and evolution of differentiated planetesimals. They are thought to originate from mantles and crusts of multiple different parent bodies. Identifying the links between individual V-type asteroids and multiple planetesimals is challenging, especially in the inner part of the main asteroid belt, where the majority of V-type asteroids are expected to have originated from a single planetesimal, namely, (4) Vesta. Aims. In this work, we aim to trace the origin of a number of individual V-type asteroids from the inner part of the main asteroid belt. The main goal is to identify asteroids that may not be traced back to (4) Vesta and may therefore originate from other differentiated planetesimals. Methods. We performed a 2 Gyr backward numerical integration of the orbits of the selected V-type asteroids. For each asteroid, we used 1001 clones to map the effect of orbital uncertainties. In the integration, we use information on physical properties of the considered V-type asteroids such as pole orientation, rotational period, and thermal parameters. Results. The majority of the studied objects can be traced back to the Vesta family within 2 Gyr of integration. The number of objects of the low-inclination V-types did not reach the boundary of the Vesta family during the integration time. Two asteroids, namely, (3307) Athabasca and (17028) 1999 FJ5, do not show a dynamic link to (4) Vesta. Increasing the integration time for these objects leads to further separation from (4) Vesta. Conclusions. The majority of V-types in the inner main belt outside the Vesta family are clearly Vesta fugitives. Two objects, namely, (3307) Athabasca and (17028) 1999 FJ5, show no clear dynamical link to (4) Vesta. Together with (809) Lundia (from our previous work), these objects could represent the parent bodies of anomalous HED meteorites such as the Banbura Rockhole. Furthermore, some objects of the low-inclination population cannot be traced back to (4) Vesta within the 2 Gyr integration.

The identification of meteorite parent bodies provides the context for understanding planetesimal formation and evolution as well as the key solar system dynamical events they have witnessed. We identified that the family of asteroid fragments whose largest member is asteroid (161) Athor is the unique source of the rare EL enstatite chondrite meteorites (Avdellidou et al. 2022), the closest meteorites to Earth in terms of their isotopic ratios. The Athor family was created by the collisional fragmentation of a parent body 3 Gyr ago in the inner main belt (Delbo et al. 2019), however the diameter of the Athor family progenitor was much smaller than the putative size of the EL original planetesimal (Triellof et a. 2022). Therefore, we deduced that the EL planetesimal that accreted in the terrestrial planet region underwent a first catastrophic collision in that region, and one of its fragments suffered a more recent catastrophic collision in the main belt, generating the current source of the EL meteorites.  We investigated the possible ways that could have brought the Athor family progenitor in its current position in the inner main belt. To do so, we used an interdisciplinary methodology where we combined laboratory meteorite thermochronometric data, thermal modelling, and dynamical simulations.  We showed that planetesimal fragments from the terrestrial zone must have been implanted into the main asteroid belt at least 60 Myr after the beginning of the solar system. We concluded that the giant planet instability is the only dynamical process that can enable such implantation so late in the solar system timeline.  Acknowledgements. We acknowledge support from the ANR ORIGINS (ANR- 18-CE31-0014). This work is based on data provided by the Minor Planet Physical Properties Catalogue (MP3C) of the Observatoire de la Côte d’Azur (mp3c.oca.eu).

Most Howardite-Eucrite-Diogenite (HED) meteorites (analogs to V-type asteroids) are thought to originate from asteroid (4) Vesta. However, some HEDs show distinct oxygen isotope ratios and therefore are thought to originate from other asteroids. In this study, we try to identify asteroids that may represent parent bodies of those mismatching HEDs. In particular, the origin of the anomalous Bunburra Rockhole meteorite was traced back to the inner main asteroid belt, showing that there might be asteroids that are not genetically linked to the asteroid (4) Vesta (the main source of V-type asteroids and HED meteorites) in the inner main belt. In this work we identify V-type asteroids outside the dynamical Vesta family whose rotational properties (retrograde vs prograde rotation) suggest the direction of Yarkovsky drift that sets them apart from typical Vestoids and Vesta fugitives. Specifically Nesvorny et al. 2008 simulated escapes paths from the Vesta family and showed that typical Vesta fugitives in the inner main asteroid belt at semi-major axis a < 2.3 AU have to have retrograde rotations and physical and thermal parameters that maximize the Yarkovsky force in order to evolve to scattered orbits within 1-2 Gyrs (age of the Vesta collisional family). Therefore large asteroids outside the Vesta family and with a < 2.3 AU and having thermal and rotational properties minimizing the Yarkovsky drift or showing Yarkovsky drift direction towards (4) Vesta are the best candidates for non-Vestoids V-type asteroids and therefore parent bodies of anomalous HED. In this study, we have performed accurate photometric observations and determined sense of rotation for several asteroids testing their links to Vesta and anomalous HED. We have found several potential non-Vestoid candidates. Those objects have to be studied in more detail to fully confirm their link to anomalous HEDs.

Phobos and Mars orbit as a base for asteroid exploration and mining

16 Psyche is one of the most massive asteroids in the asteroid belt. This object has a diameter of over 200 km and contains about 1% of the mass of the entire asteroid belt. It is believed to be the exposed iron core of a protoplanet and is the most massive metallic M-type asteroid. It was discovered by the Italian astronomer Annibale de Gasparis on March 17, 1852, in Naples and named after the Greek mythological figure Psyche. The prefix "16" means that it was the sixteenth minor planet in the order of discovery. 16 Psyche is the most massive metallic asteroid of type M. Radar observations indicate a fair pure iron-nickel composition. For a long time, scientists have imagined the possibility of fishing for metals from asteroids, or meteorites, close to our planet. Today, those predictions may come true. NASA is going to build a robot, called "Psyche", which will have the mission to explore an asteroid in the main asteroid belt between Mars and Jupiter. The asteroid "16 Psyche" has a diameter of 226 kilometers and is made of metals such as iron, nickel and gold. The metals that make up this unique asteroid could be worth more than $ 10 trillion. Radar observations indicate that Psyche has a dense and mostly metallic composition, consistent with one of the highest radar albedos in the asteroid belt (0.37±0.09). The psyche appears to have a surface that is 90% metallic and 10% silicate rock, with 6±1% orthopyroxene. Scientists believe that these metals can be mostly iron and nickel. NASA's infrared telescope installation at Mauna Kea Observatories reported evidence (~ 3 μm absorption characteristics) of hydroxyl ions on the asteroid in October 2016 that could suggest water ice. Because the psyche is believed to have formed in dry conditions without the presence of water, hydroxyl could have reached the psyche through previous impacts of low-carbon asteroids. The psyche appears to be an exposed metal core or a fragment of a metal core in a larger differentiated parent body, about 500 kilometers in diameter. If the Psyche is really one, there could be other asteroids in similar orbits. However, Psyche is not part of any identified asteroid family. One hypothesis is that the collision that formed the Psyche occurred very early in the history of the Solar System and all other remains were transformed into fragments by subsequent collisions or had their orbits beyond recognition. However, this scenario is considered to have a probability of only 1%. An alternative is that the psyche has been broken by impacts, but not catastrophically. In this case, it may be a candidate for the parent body of mesoseiderites (a class of meteorites with stony stones). Another possibility is that the Psyche is the end of the various relic bodies left by the formation of the inner planet. The asteroid's mantle may have been stripped not of a single collision, but of multiple (> 3) relatively slow side collisions with bodies of comparable or larger size. What is left is a metal core covered by a thin layer of silicates, which is revealed spectrally. In such a case, the Psyche would be analogous to Mercury, but much less massive.

The majority of basaltic objects in the main belt are dynamically connected to Vesta, the largest differentiated asteroid known. Others, due to their current orbital parameters, cannot be easily dynamically linked to Vesta. This is particularly true for all the basaltic asteroids located beyond 2.5 au, where lies the 3:1 mean motion resonance with Jupiter. In order to investigate the presence of other V-type asteroids in the middle and outer main belt (MOVs) we started an observational campaign to spectroscopically characterize in the visible range MOV candidates. We observed 18 basaltic candidates from TNG and ESO - NTT between 2015 and 2016. We derived spectral parameters using the same approach adopted in our recent statistical analysis and we compared our data with orbital parameters to look for possible clusters of MOVs in the main belt, symptomatic for a new basaltic family. Our analysis seemed to point out that MOVs show different spectral parameters respect to other basaltic bodies in the main belt, which could account for a diverse mineralogy than Vesta; moreover, some of them belong to the Eos family, suggesting the possibility of another basaltic progenitor. This could have strong repercussions on the temperature gradient present in the early Solar System, and on our current understanding of differentiation processes.

In their model for the origin of the parent bodies of iron meteorites, Bottke et al proposed differentiated planetesimals that were formed in the region of 1-2 AU during the first 1.5 Myr, as the parent bodies, and suggested that these objects and their fragments were scattered into the asteroid belt as a result of interactions with planetary embryos. Although viable, this model does not include the effect of a giant planet that might have existed or been growing in the outer regions. We present the results of a concept study where we have examined the effect of a planetary body in the orbit of Jupiter on the early scattering of planetesimals from terrestrial region into the asteroid belt. We integrated the orbits of a large battery of planetesimals in a disk of planetary embryos, and studied their evolutions for different values of the mass of the planet. Results indicate that when the mass of the planet is smaller than 10 Earth-masses, its effects on the interactions among planetesimals and planetary embryos is negligible. However, when the planet mass is between 10 and 50 Earth-masses, simulations point to a transitional regime with ~50 Earth-mass being the value for which the perturbing effect of the planet can no longer be ignored. Simulations also show that further increase of the mass of the planet strongly reduces the efficiency of the scattering of planetesimals from the terrestrial planet region into the asteroid belt. We present the results of our simulations and discuss their possible implications for the time of giant planet formation.

Carbonaceous asteroids, including Ryugu and Bennu, which have been explored by the Hayabusa2 and OSIRIS-REx missions, were probably important carriers of volatiles to the inner Solar System. However, Ryugu has experienced significant volatile loss, possibly from hypervelocity impact heating. Here we present impact experiments at speeds comparable to those expected in the main asteroid belt (3.7 km s−1 and 5.8 km s−1) and with analogue target materials. We find that loss of volatiles from the target material due to impacts is not sufficient to account for the observed volatile depletion of Ryugu. We propose that mutual collisions in the main asteroid belt are unlikely to be solely responsible for the loss of volatiles from Ryugu or its parent body. Instead, we suggest that additional processes, for example associated with the diversity in mechanisms and timing of their formation, are necessary to account for the variable volatile contents of carbonaceous asteroids.

Context. Understanding the conditions that lead to the formation of planetesimals – the building blocks of planets - and their initial size distribution is a central problem of modern planetology. While most of these original planetesimals were accreted onto the terrestrial planets and the cores of the giant planets, some were also stranded in the main belt, where 4.5 Gyr of collisional evolution broke most of them into families of collisional asteroid fragments. However, some planetesimals survived, and are still hidden amongst asteroid fragments in the main belt. Aims. We make use of astronomical data to identify these leftover planetesimals amongst all other asteroids. Our search is based on separating planetesimal survivors from families of asteroids generated by collisions. Namely, we aim to identify and “clean” the main belt of collisional family members: by doing so, we would be left with the surviving members of the original planetesimals. Methods. We focus here on the inner portion of the main belt for asteroids with intermediate to high albedo. It is known that current asteroid family catalogs are not suitable for the aforementioned cleaning; they are conservative and only one-quarter of the known asteroids are associated with the approximately 120 distinct asteroid families. We therefore developed methods to inclusively link asteroids to known collisional families in order to better capture their extent. Namely, we apply a hierarchical clustering method (HCM) on asteroids filtered according to the V-shape of the Yarkovsky drift of each family in order to reassess family membership (V-shape-constrained HCM). The identified families were removed and the remaining background population was searched for previously undetected collisional families. Results. We succeed in using our V-shape-constrained HCM to link family “halos” to their cores. After removing these reassessed families from the asteroid population, our V-shape search reveals a previously unknown collisional family of S-type asteroids in the inner main belt with an age of 4.3 ± 1.7 Gyr and a significance level of 3.4σ. When this ancient collisional family is removed, 34 planetesimals are identified and their size-frequency distribution is presented. Conclusions. The asteroid belt has two components: planetesimals and collisional fragments. The cumulative size-frequency distribution of planetesimals has a steep power-law index for bodies larger than 100 km in diameter and a much smaller power-law index for planetesimals smaller than 100 km.

The gravitational pull of a large number of asteroids perturbs a pulsar’s motion to a degree that is detectable through precision timing of millisecond pulsars. The result is a low-frequency, correlated noise process, similar in form to the red timing noise known to affect canonical pulsars, or to the signal expected from a stochastic gravitational-wave background. Motivated by the observed fact that many millisecond pulsars are in binary systems, we describe the ways in which the presence of a binary companion to the pulsar would affect the signal produced by an asteroid belt. The primary effect of the companion is to destabilize the shortest-period orbits, cutting off the high-frequency component of the signal from the asteroid belt. We also discuss the implications of asteroid belts for gravitational-wave search efforts. Compared to the signal from a stochastic gravitational-wave background, asteroid-belt noise has a similar frequency and amplitude, and is similarly independent of radio frequency, but is not correlated between different pulsars, which should allow the two kinds of signal to be distinguished.

The identification of meteorite parent bodies provides the context for understanding planetesimal formation and evolution as well as the key Solar System events they have witnessed. However, identifying such links has proven challenging and some appear ambiguous. Here, we identify that the family of asteroid fragments whose largest member is (161) Athor is the unique source of the rare EL enstatite chondrite meteorites, the closest meteorites to Earth in terms of their isotopic ratios. The Athor family was created by the collisional fragmentation of a parent body 3 Gyr ago in the inner main belt. We calculate that the diameter of the Athor family progenitor was 64 km in diameter, much smaller than the putative size of the EL original planetesimal. Therefore, we deduce that the EL planetesimal that accreted in the terrestrial planet region underwent a first catastrophic collision in that region, and one of its fragments suffered a more recent catastrophic collision in the main belt, generating the current source of the EL meteorites.

\n Context. V-type asteroids in the inner main belt are thought to be genetically related to (4) Vesta as collisional fragments. We investigate their relationship with Vesta observing putative V-type asteroids.\n Aims. The aim of this work is to observe candidate V-type asteroids, selected in different regions of the inner main belt, to characterize them and hence better understand their relationship with (4) Vesta.\n Methods. We present new NIR reflectance spectra of 18 V-type candidate asteroids, selected from datasets of possible V-type asteroids. The data were obtained at the 3.6 m Telescopio Nazionale Galileo, covering the spectral range 0.7 to 2.5 μm. We derive spectral parameters from NIR spectra to infer mineralogical information of the observed asteroids. The spectra of these asteroids are examined and compared to those of Howardite-Eucrite-Diogenite meteorites (HED), of which (4) Vesta is believed to be the parent body, and other V-type asteroids observed during previous campaigns. To enlarge the data set and increase the statistical significance of the analysis, we included the data presented in our previous article, obtaining a final data set of 41 V-type asteroids. \n Results. The V-type asteroids examined here show a higher variability of band parameters with respect to HEDs values, as for (4) Vesta. This result indicates that (4) Vesta and V-type asteroids have mineralogies that are not completely represented in the HEDs collection. \n Conclusions. An important finding is that some of the observed asteroids show spectral characteristics similar to diogenites, a result that may have relevant implications on their origin. Moreover, most of the diogenitic asteroids are not members of the Vesta classical family.\n

Abstract– Eucrites, which are probably from 4 Vesta, and angrites are the two largest groups of basaltic meteorites from the asteroid belt. The parent body of the angrites is not known but it may have been comparable in size to Vesta as it retained basalts and had a core dynamo. Both bodies were melted early by 26Al and formed basalts a few Myr after they accreted. Despite these similarities, the impact histories of the angrites and eucrites are very different: angrites are very largely unshocked and none are breccias, whereas most eucrites are breccias and many are shocked. We attribute the lack of shocked and unbrecciated angrites to an impact, possibly at 4558 Myr ago—the radiometric age of the younger angrites—that extracted the angrites from their original parent body into smaller bodies. These bodies, which may have had a diameter of approximately 10 km, suffered much less impact damage than Vesta during the late heavy bombardment because small bodies retain shocked rocks less efficiently than large ones and because large bodies suffer near‐catastrophic impacts that deposit vastly more impact energy per kg of target. Our proposed history for the angrites is comparable to that proposed by Bogard and Garrison (2003) for the unbrecciated eucrites with Ar‐Ar ages of 4.48 Gyr and that for unbrecciated eucrites with anomalous oxygen isotopic compositions that did not come from Vesta. We infer that the original parent bodies of the angrites and the anomalous eucrites were lost from the belt when the giant planets migrated and the total mass of asteroids was severely depleted. Alternatively, their parent bodies may have formed in the terrestrial planet region and fragments of these bodies were scattered out to the primordial Main Belt as a consequence of terrestrial planet formation.

IntroductionAsteroid (4) Vesta is a unique object among small solar system bodies: the second largest body in the main belt, a probable remnant protoplanet from the earliest epoch of the solar system formation [3], parent body of the large asteroid family and main reservoir of HED-material. Global albedo mosaic obtained by Dawn&amp;#8217;s Framing Camera confirmed ground-based obvservation facts about heterogenity of vestan surface material. Among all areas with unusual spectral behavior stands out a pattern which was previously described in [2] and [1] as an orange material due to conformity of this deposits to the orange tones on the global false-color Clementine mosaics. Analysis provided in previous studies forced the authors ([2], [1]) to assume a connection of patches with the melts ejected during the formation of Rheasilvia. In this work, a detailed analysis of the all orange material areas (except regions near Claudia and Rubria craters) found in the ([2], [1]) was carried out using color-ratio imagery as applied to data obtained by Dawn spacecraft onboard instrument Framing Camera (FC).MethodsWe use color-ratio imagery method to analyze images obtained by Dawn spacecraft onboard instrument Framing Camera (FC) during HAMO orbital phase (spatial resolution ~70 m/pixel) in all color filters (F2-F8). For deriving color ratio maps in this study, we used Level 1b calibrated images available in free access as a part of Planetary Data System archive (https://sbn.psi.edu/pds/sbib/). We selected images of areas that demonstrate presence of orange material patches according to LeCorre et al. (2013). As the refferent color-ratio maps we used C(438nm/917nm) for spectral slope characterization and C(749nm/917nm) for estimation of the pyroxene band depth. Remaining color-ratio maps give an additional information which helps to interpretate spectral behavior of selected areas more accurate.ResultsAlmost all spots within studied areas demonstrate similar spectral behavior. The pacthes of the orange material tend to have stronger absorption at 438 nm. Outside this area, the orange patches are practically indistinguishable from the typical vestan surface material. Patches also have deeper pyroxene band at 0.9 nm and higher albedo than surroundings. In fact, color ratio C(438nm/749nm) distribution maps demonstrate that the population of orange material spots is diverse in terms of shapes and sizes as well as sharpness of spots&amp;#8217; edges (Fig.1). Additionally, several spots, previously classified as orange material [2], show quite distinct spectral characteristics to traditional. Our results seem to contradict with impact melt hypothesis of orange material origin.Fig. 1 &amp;#8211; Oppia crater (8&amp;#176; S, 309&amp;#176; E, D=37km) and surroundings. Color ratio C(438nm/749nm) (a) and C(749nm/917nm) (b) maps.