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المغرب الذي كان
يتألف كتاب \"المغرب الذي كان\" من أربعة أجزاء. يحمل الجزء الأول عنوانا : \"البلاط المغربي\"، ويصف فيه علاقته بالسلاطين، خاصة السلطانين مولاي عبد العزيز ومولاي عبد الحفيظ، وما عرفه المغرب إبان فترات حكمهم من أحداث ووقائع وثورات... هذا الجزء يتضمن سبعة فصول في الجزء الثاني المعنون ب \"الريسوني\" يروي هاريس علاقته بهذا الثائر المعروف وكيف تحولت علاقتهما بعد عملية الاختطاف الشهيرة إلى إعجاب متبادل وصداقة راسخة، على الرغم من أنه كان لا يحلو له إلا أن يصفه بأنه لص وقاطع طريق. في الجزء الثالث المعنون ب \"أولياء وشرفاء وآثمون\" يتحدث هاريس عن أهمية الطرق الصوفية في المغرب وعلاقته ببعض أهم أقطابها وأهمهم شرفاء وزان مثل مولاي العربي ومولاي محمد ومولاي التهامي أولاد شريف وزان الأكبر سيدي عبد السلام، يتناول هاريس في الجزء الرابع المعنون ب ”فرص التغيير ”كيف تغير الوضع في المغرب في عهد الحماية الفرنسية، من وجهة نظره، حيث صار أفضل حالا وأكثر أمانا واستقرارا مما كان عليه في السابق، الكتاب يتضمن أيضا في نهايته فصلا مقتطفا من كتاب هاريس: \"أرض سلطان إفريقي\" وهو بعنوان \"رحلتي إلى شفشاون\" يصف فيها هاريس رحلته المحفوفة بالمخاطر إلى هذه البلدة المغربية التي كانت محظورة حينها على الزائر المسيحي، حيث يقال \"إن ثلاثة مسيحيين فقط زاروا مدينة شفشاون المسورة : أحدهم مات مسموما، والثاني جاء لمدة ساعة متنكر في زي حاخام… والآخر كان والتر هاريس\"... وهناك كلمة ختامية نقدية جد مهمة للكاتب جيمس شاندلر اختتمنا بها الترجمة.
Book
Investigating the Relationship between (3200) Phaethon and (155140) 2005 UD through Telescopic and Laboratory Studies
The relationship between the near-Earth objects (3200) Phaethon and (155140) 2005 UD is unclear. While both are parents to meteor showers (the Geminids and Daytime Sextantids, respectively) and have similar visible-wavelength reflectance spectra and orbits, dynamical investigations have failed to find any likely method to link the two objects in the recent past. Here we present the first near-infrared reflectance spectrum of 2005 UD, which shows it to be consistently linear and red-sloped, unlike Phaethon’s very blue and concave spectrum. Searching for a process that could alter some common starting material to both of these end states, we hypothesized that the two objects had been heated to different extents, motivated by their near-Sun orbits, the composition of Geminid meteoroids, and previous models of Phaethon’s surface. We thus set about building a new laboratory apparatus to acquire reflectance spectra of meteoritic samples after heating to higher temperatures than available in the literature to test this hypothesis and were loaned a sample of the CI chondrite Orgueil from the Vatican Meteorite Collection for testing. We find that while Phaethon’s spectrum shares many similarities with different CI chondrites, 2005 UD’s does not. We thus conclude that the most likely relationship between the two objects is that their similar properties are only by coincidence as opposed to a parent-fragment scenario, though the ultimate test will be when JAXA’s DESTINY+ mission visits one or both of the objects later this decade. We also discuss possible paths forward to understanding Phaethon’s properties from dynamical and compositional grounds.
Journal Article
Ice, Ice, Maybe? Investigating 46P/Wirtanen’s Inner Coma for Icy Grains
The release of volatiles from comets is usually from direct sublimation of ices on the nucleus, but for very or hyperactive comets other sources have to be considered to account for the total production rates. In this work, we present new near-IR (NIR) imaging and spectroscopic observations of 46P/Wirtanen taken during its close approach to Earth on 2018 December 19 with the MMIRS instrument at the MMT Observatory to search for signatures of icy or ice-rich grains in its inner coma that might explain its previously reported excess water production. The morphology of the images does not suggest any change in grain properties within the field of view, and the NIR spectra do not show the characteristic absorption features of water ice. Using a new Markov Chain Monte Carlo–based implementation of the spectral modeling approach of Protopapa et al., we estimate the areal water ice fraction of the coma to be <0.6%. When combined with slit-corrected Af ρ values for the J, H, and K bands and previously measured dust velocities for this comet, we estimate an icy grain production rate of less than 4.6 kg s−1. This places a strict constraint on the water production rate from pure icy grains in the coma, and in turn we find that for the 2018–2019 apparition approximately 64% of 46P’s surface was actively sublimating water near perihelion. We then discuss 46P’s modern properties within the context of other (formerly) hyperactive comets to understand how these complex objects evolve.
Journal Article
Near-infrared Spectroscopy of the Nucleus of Low-activity Comet P/2016 BA14 during Its 2016 Close Approach
The near-Earth comet P/2016 BA14 (PanSTARRS) is a slow-rotating, nearly dormant object, a likely dynamical twin of 252P/LINEAR, and was recently shown to have a mid-infrared spectrum very dissimilar to other comets. Comet BA14 was also recently selected as one of the backup targets for the ESA’s Comet Interceptor, so a clearer understanding of BA14's modern properties would not just improve our understanding of how comets go dormant but could also aid in planning for a potential spacecraft visit. We present observations of BA14 during its 2016 Earth close approach taken with the NASA Infrared Telescope Facility on two dates, both of which are consistent with direct observations of its nucleus. The reflectance spectrum of BA14 is similar to 67P/Churyumov–Gerasimenko, albeit highly phase-reddened. Thermal emission contaminates the reflectance spectrum at longer wavelengths, which we correct with a new Markov Chain Monte Carlo thermal modeling code. The models suggest that BA14's visible geometric albedo is p V = 0.01–0.03, consistent with radar observations; its beaming parameter is typical for NEOs observed in its geometry; and its reflectance spectrum is red and linear throughout the H and K bands. It appears very much like a “normal” comet nucleus despite its mid-infrared oddities. A slow loss of fine grains as the object’s activity diminished might help to reconcile some of the lines of evidence, and we discuss other possibilities. A spacecraft flyby past BA14 could get closer to the nucleus than with a more active target, and we highlight some science questions that could be addressed with a visit to a (nearly) dormant comet.
Journal Article
Surfaces of (Nearly) Dormant Comets and the Recent History of the Quadrantid Meteor Shower
The parent of the Quadrantid meteor shower is the inactive solar system small body (196256) 2003 EH1. EH1 has likely only gone dormant in the past few hundred years, and may be related to the bright comet C/1490 Y1. Compared with the other best-studied inactive meteor shower parent (3200) Phaethon, EH1 has received comparatively minimal characterization of its surface properties. We present the first reflectance spectrum and additional photometry of EH1, as well as new spectra of the nuclei of three nearly dormant comets P/2006 HR30 (Siding Spring), 364P/Pan-STARRS, and 249P/LINEAR for comparison. We also present new short-term high-resolution orbital integrations of these bodies for context. EH1s spectrum is red in color below 0.8 μm in between C and D types, consistent with previous photometric measurements, but is blue beyond 0.8 μm until at least 1.02 μm. 249P and 364P have both red slopes consistent with C taxonomic types and HR30 has a classic comet nucleus D-type slope. If the downturn in EH1’s spectrum is due to an absorption feature, magnetite and olivine are plausible candidates, but more data are needed. 249P and 364P have similar recent and historical dynamical evolutions in addition to their similar surface properties. We discuss the interrelation between the dynamical histories and modern surfaces of these four objects and suggest avenues for further study to better constrain how the Quadrantids and Geminids were created.
Journal Article
The Evolution of Activity and Chemical Composition in Rosetta’s Comet Targets across Multiple Apparitions: Complications for CS2 as the CS Parent in Comet Nuclei
Jupiter-family comets are ephemeral small bodies injected into the inner solar system from the Kuiper Belt, doomed to either sublimate all their volatiles and become inert or violently shatter from the activity. We investigate two target candidates of the ESA Rosetta mission, comets 46P/Wirtanen and 67P/Churyumov-Gerasimenko, which had favorable apparitions for Earth-based observations in 2018–2019 and 2021, respectively. Using the Hubble Space Telescope STIS and COS instruments, we observed OH and CS emissions to characterize production rates of H2O and CS, established Af ρ values, and placed upper limits on the production rate of C2 and its parent. We find CS/H2O relative abundances that are significantly (5σ–7σ) larger than previous remote near-UV (NUV) measurements of 46P and 67P at similar heliocentric distances and CS/H2O values larger than those obtained via contemporaneous submillimeter observations for the same apparitions. We also find that for 67P the remote derivations of CS2/H2O ratios are substantially (∼50×) higher than the values measured by the ROSINA mass spectrometer on board the Rosetta spacecraft for all NUV-derived CS2 production rates. The discrepancy points toward an unidentified CS parent or parents with contributing factors from uncertainties with the fluorescence efficiencies of the CS (0,0) band of the A 1Π–X 1Σ+ system around 2580 Å. Given the significance of understanding the chemistry and dissociation physics of sulfur-bearing molecules in comets for tracing planetesimal formation environments, as well as the limited studies in this area, we propose several hypotheses to explain this discrepancy and outline future studies to address these issues.
Journal Article
Contemporaneous Multiwavelength and Precovery Observations of the Active Centaur P/2019 LD2 (ATLAS)
The Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) provides the first opportunity to observe the migration of a solar system small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now. The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multiwavelength observations of LD2 from 2020 July 2–4: Gemini North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO Submillimeter Telescope millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleus’s effective radius to ≤1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g′−r′=0.70±0.07 , r′−i′=0.26±0.07 , a dust-production rate of ∼10–20 kg s−1, and an outflow velocity between v ∼ 0.6–3.3 m s−1. We did not detect CO toward LD2 on 2020 July 2–3, with a 3σ upper limit of Q(CO) < 4.4 × 1027 mol s−1 (⪅ 200 kg s−1). Near-infrared spectra show evidence for water ice at the 1%–10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus, it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long-baseline monitoring effort.
Journal Article
Dust Outburst Dynamics and Hazard Assessment for Close Spacecraft–Comet Encounters
Using the gas drag by sublimating cometary surface ices for the acceleration of dust particles and deceleration by the gravity field of the nucleus combined with basic laws of mechanics, the sizes, velocities, and number densities of escaping particles are calculated and evaluated with respect to the hazard assessment of comet–spacecraft flybys and encounters. We find good agreement between our analytical method and the more elaborate and precise DSMC calculations, but, being simpler, our method can more easily be used to explore a wide range of cometary conditions and can be more easily scaled to specific comets with different nucleus sizes, masses, and gravity potentials and various gas and dust production rates. Our analytical method is applied to outbursts expanding into a cone of ∼60°, where the gas density falls off with height from the surface rather than radial distance from the center of a uniformly outgassing nucleus. In this scenario, larger dust particles can be ejected and attain ballistic trajectories, go into orbit, or escape from the nucleus, thus being potentially more hazardous to a spacecraft. Sample calculations are carried out for potential dust outbursts for the highly active Centaur/Comet 29P/Schwassmann-Wachmann 1 for various assumed active areas and dust particle size distributions. Particle velocity ranges for ballistic trajectories, orbiting particles, and particles escaping into the coma are presented. These calculations are used to estimate the coma particle number densities during outbursts to get an assessment of the hazards and required mitigation for a flyby or orbiting space mission.
Journal Article
FUV Observations of the Inner Coma of 46P/Wirtanen
Far-ultraviolet observations of comets yield information about the energetic processes that dissociate the sublimated gases from their primitive surfaces. Understanding which emission processes are dominant, their effects on the observed cometary spectrum, and how to properly invert the spectrum back to the composition of the presumably pristine surface ices of a comet nuclei are all critical components for proper interpretation and analysis of comets. The close approach of comet 46P/Wirtanen in 2018–2019 provided a unique opportunity to study the innermost parts of a cometary coma with the Hubble Space Telescope Cosmic Origins Spectrograph, rarely accessible with remote observations, at length scales (hundreds of kilometers) and wavelengths (900–1430 Å) previously probed only by the European Space Agency’s Rosetta spacecraft. Our observations show a complex picture for the inner coma; atomic production rates for H and O that show water is the dominant source of both, an abundance of atomic sulfur that is difficult to explain with the lifetimes of common sulfur parent molecules, and a density distribution that is poorly fit with both Haser and vectorial models.
Journal Article