Search

Anghel, S., et al., The increase in detector sensitivity and availability in the past three decades has allowed us to derive knowledge of the meteoroid flux and impact energy into the Earth's atmosphere. We present the multi-instrument detected 2018 December 22 fireball over Western Pyrenees, and compare several techniques aiming to obtain a reliable method to be used when measuring impacts of similar scale. From trajectory data alone, we found a bulk density of 3.5 g cm-3 to be the most likely value for the Pyrenean meteoroid. This allowed to further constrain the dynamic mass, which translated into a kinetic energy of 1 ton TNT (4.184 × 109 J). For the second energy derivation, via the fireball's corrected optical radiation, we obtained a more accurate empirical relation measuring well-studied bolides. The result approximates to 1.1 ton TNT, which is notably close to the nominal dynamic result, and agrees with the lower margin of the seismic-based energy estimation, yet way lower than the infrasound estimate. Based on the relation derived in this study, we consider the nominal estimate from both the dynamic and photometric methods to be the most accurate value of deposited energy (1 ton TNT). We show that the combination of these two methods can be used to infer the meteoroid density. Among the methods presented in this paper, we found that the optical energy is the most reliable predictor of impact energy near the ton TNT-scale., S. Anghel and D. A. Nedelcu were supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0226/16PCCDI/2018, within PNCDI III. EP-A and JMT-R acknowledge funding from PGC2018-097374-B-I00 (MCI-AEI-FEDER, EU). M. Birlan work was partly supported by SEEING-IEA CNRS program. R. Hueso and A. Sánchez-Lavega were supported by Diputación Foral de Bizkaia and Gobierto Vasco IT1366-19.

The biological activity of proteins is partly due to their secondary structures and conformational states. Peptide chains are rather flexible so that finding ways inducing protein folding in a well-defined state is of great importance. Among the different constraint techniques, the interaction of proteins with inorganic surfaces is a fruitful strategy to stabilize selected folded states. Surface-induced peptide folding can have potential applications in different biomedicine areas, but it can also be of fundamental interest in prebiotic chemistry since the biological activity of a peptide can turn-on when folded in a given state. In this work, periodic quantum mechanical simulations (including implicit solvation effects) at the PBE-D2* level have been carried out to study the adsorption and the stability of the secondary structures (α-helix and β-sheet) of polypeptides with different chemical composition (

Water is the most abundant molecule in the solid state of the interstellar medium, and its presence is critically important for life in space. Interstellar water is thought to be effectively synthesised by reactions occurring on the surfaces of interstellar grains, as gas-phase reactions are not efficient enough to justify its high abundance. In the present work, DFT simulations have been performed to investigate the formation of interstellar water through the O + H

Water is the most abundant molecule in solid state of the interstellar medium, and its presence is critically important for life in space. Interstellar water is thought to be effectively synthesised by reactions occurring on the surfaces of interstellar grains, as gas-phase reactions are not efficient enough to justify its high abundance. In the present work, DFT simulations have been performed to investigate the formation of interstellar water through the O + H2 → H2O reaction on olivinic silicate surfaces that contain Fe2+ cations. The surfaces have been modeled adopting both a periodic and cluster approach. The study focuses on: i) the stability of the surface models as a function of the electronic states (i.e., quintuplet, triplet and singlet) arising from the presence of the Fe2+ centers, ii) the adsorption of H2 on the silicate surfaces and its likely activation due to the Fe2+/H2 interactions, and iii) characterising the energy profiles of the H2O formation reaction complemented with kinetics that include tunneling effects. Results indicate that quintuplet is the most stable electronic state in all the bare surface models. H2 adsorption, however, do not show a clear trend on the relative stabilities of the H2/surface complexes with the electronic states, which is in general more favourable on singlet state surfaces. Finally, reactions simulated on the periodic surfaces show elementary high energy barriers but the reaction is kinetically feasible (considering the long lifetime of interstellar clouds) due to the dominance of tunnelling. In contrast, on the nanocluster models, tunneling effects cannot contribute due to the presence of endoenergetic elementary steps. It is predicted that the reactions on the nanoclusters is only possible if the energy released during the adsorption of the O atom is used to overcome the energy barriers.

The adsorption of 11 amino acids (Gly, Leu, Met, Phe, Ser, Cys, Glu, Gln, Arg, Lys, and His) on the TiO2(110) rutile surface is investigated adopting a theoretical approach, using the PBE-D2* functional as implemented in the periodic VASP code. The adsorption of the amino acids is considered in their canonical, deprotonated and zwitterionic forms. For all cases, the most stable adsorption mode adopts a bidentate (O,O) binding with surface undercoordinated Ti atoms, in agreement with previous experimental and computational studies using glycine as a test case. Such a binding mode is possible due to the surface morphology, because the Ti-Ti distances match very well with the carboxylic O-O distance. The most stable adsorption states are the deprotonated and the zwitterionic ones, the canonical one lying significantly above in energy. The relative stability between the deprotonated and the zwitterionic states results in a delicate trade-off among dative interactions (O, N, and S atoms of the amino acids with Ti atoms of the surface), H-bond interactions, dispersive forces and, to a lesser extent, steric hindrance of the amino acidic lateral chains. Finally, the difference in the amino acid adsorption between the (110) rutile and the (101) anatase surfaces is discussed both from the energetic and surface morphological standpoints, highlighting the larger reactivity of the rutile polymorph in adsorbing and deprotonating the amino acids compared with the anatase one.

The formation of the interstellar complex organic molecules (iCOMs) is a hot topic in astrochemistry. One of the main paradigms trying to reproduce the observations postulates that iCOMs are formed on the ice mantles covering the interstellar dust grains as a result of radical--radical coupling reactions. We investigate iCOMs formation on the icy surfaces by means of computational quantum mechanical methods. In particular, we study the coupling and direct hydrogen abstraction reactions involving the CH$_3$ + X systems (X = NH$_2$, CH$_3$, HCO, CH$_3$O, CH$_2$OH) and HCO + Y (Y = HCO, CH$_3$O, CH$_2$OH), plus the CH$_2$OH + CH$_2$OH and CH$_3$O + CH$_3$O systems. We computed the activation energy barriers of these reactions as well as the binding energies of all the studied radicals, by means of density functional theory (DFT) calculations on two ice water models, made of 33 and 18 water molecules. Then, we estimated the efficiency of each reaction using the reaction activation, desorption and diffusion energies and derived kinetics with the Eyring equations. We find that radical--radical chemistry on surfaces is not as straightforward as usually assumed. In some cases, direct H abstraction reactions can compete with radical--radical couplings, while in others they may contain large activation energies. Specifically, we found that (i) ethane, methylamine and ethylene glycol are the only possible products of the relevant radical--radical reactions; (ii) glyoxal, methyl formate, glycolaldehyde, formamide, dimethyl ether and ethanol formation is likely in competition with the respective H-abstraction products, and (iii) acetaldehyde and dimethyl peroxide do not seem a likely grain surface products., 46 pages, 15 figures. Accepted for publication in ApJs

The biological activity of proteins is partly due to their secondary structures and conformational states that may change in the presence of mineral surfaces.

Imai et al., The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH3OH, HCOOCH3, and CH3OCH3, are detected toward the protostar. The rotation temperature and the emitting region size for CH3OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C18O, CH3OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M⊙ and, This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01376.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The authors acknowledge financial support from JSPS and MAEE under the Japan–France Integrated Action Program (SAKURA: 25765VC). D.J. is supported by NRC Canada and by an NSERC Discovery Grant. E.B. and G.B. acknowledge funding from the European Research Council under the European Union's Horizon 2020 research and innovation program, for the project "The Dawn of Organic Chemistry," grant agreement No. 741002. G.B. acknowledges support from the PID2020-117710GB-I00 grant funded by MCIN/AEI/10.13039/501100011033 and from the Unit of Excellence María de Maeztu 2020–2023 award to the Institute of Cosmos Sciences (CEX2019-00918-M). I.J.-S. has received partial support from the Spanish State Research Agency (AEI) through project Nos. PID2019-105552RB-C41 and MDM-2017-0737 Unidad de Excelencia "Maria de Maeztu" - Centro de Astrobiologia (CSIC-INTA). This study is supported by grants-in-aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (18H05222, 18J11010, 19H05069, 19K14753, and 21K13954).

Ethanol (CH$_3$CH$_2$OH) is a relatively common molecule, often found in star forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). Yet, the formation route of this species remains debated. In the present work, we study the formation of ethanol through the reaction of CCH with one H$_2$O molecule belonging to the ice, as a test case to investigate the viability of chemical reactions based on a "radical + ice component" scheme as an alternative mechanism for the synthesis of iCOMs, beyond the usual radical-radical coupling. This has been done by means of DFT calculations adopting two clusters of 18 and 33 water molecules as ice models. Results indicate that CH$_3$CH$_2$OH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with H$_2$O on the water ice clusters can be barrierless (thanks to the help of boundary icy water molecules acting as proton transfer assistants) leading to the formation of vinyl alcohol precursors (H$_2$CCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. We finally discuss the astrophysical implications of these findings., 30 pages, 6 figures Accepted for publication ACS Earth and Space Chemistry

Binding energies (BEs) are one of the most important parameters for astrochemical modeling determining, because they govern whether a species stays in the gas-phase or is frozen on the grain surfaces. It is currently known that, in the denser and colder regions of the interstellar medium, sulphur is severely depleted in the gas phase. It has been suggested that it may be locked into the grain icy mantles. However, which are the main sulphur carriers is still a matter of debate. This work aims at establishing accurate BEs of 17 sulphur-containing species on two validated water ice structural models, the proton-ordered crystalline (010) surface and an amorphous water ice surface. We adopted Density Functional Theory (DFT)-based methods (the hybrid B3LYP-D3(BJ) and the hybrid meta-GGA M06-2X functionals) to predict structures and energetics of the adsorption complexes. London's dispersion interactions are shown to be crucial for an accurate estimate of the BEs due to the presence of the high polarizable sulphur element. While on the crystalline model the adsorption is restricted to a very limited number of binding sites with single valued BEs, on the amorphous model several adsorption structures are predicted, giving a BE distribution for each species. With the exception of few cases, both experimental and other computational data are in agreement with our calculated BE values. A final discussion on how useful the computed BEs are with respect to the snow lines of the same species in protoplanetary disks is provided, Comment: 22 pages, 9 figures, Accepted for publication in The Astrophysical Journal

On February 16, 2021, an artificial object moving slowly over the Mediterranean was recorded by the Spanish Meteor Network (SPMN). Based on astrometric measurements, we identified this event as the reentry engine burn of a SpaceX Falcon 9 launch vehicle’s upper stage. To study this event in detail, we adapted the plane intersection method for near-straight meteoroid trajectories to analyze the slow and curved orbits associated with artificial objects. To corroborate our results, we approximated the orbital elements of the upper stage using four pieces of “debris” cataloged by the U.S. Government’s Combined Space Operations Center. Based on these calculations, we also estimated the possible deorbit hazard zone using the MSISE90 model atmosphere. We provide guidance regarding the interference that these artificial bolides may generate in fireball studies. Additionally, because artificial bolides will likely become more frequent in the future, we point out the new role that ground-based detection networks can play in the monitoring of potentially hazardous artificial objects in near-Earth space and in determining the strewn fields of artificial space debris. [Figure not available: see fulltext.], This research was supported by the research project (Grant No. PGC2018-097374-B-I00, PI: JMT-R), which is funded by FEDER/Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación. This project has also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (Grant No. 865657) for the project “Quantum Chemistry on Interstellar Grains” (QUANTUMGRAIN).

Computational modeling of protein/surface systems is challenging since the conformational variations of the protein and its interactions with the surface need to be considered at once. Adoption of first-principles methods to this purpose is overwhelming and computationally extremely expensive so that, in many cases, dramatically simplified systems (

Ethanol (CH

Introduction In Spain, the Spanish Meteor Network (SPMN) has been operating for 25 years, recording meteoric events and re-entries over the Iberian Peninsula, Morocco, and the insular territory [1]. This is a pro-am project involving a scientific team specialized in areas such as astronomy, geology, geophysics, and chemistry. Obtaining the trajectory of meteoroids impacting the atmosphere is crucial both for the recovery of possible meteorites and for studying their origin in the Solar System. Some of these objects can be dynamically associated with their parent bodies, being part of meteoroid streams [2]. Herein lies the importance of monitoring the sky constantly and completely from multiple monitoring stations. The SPMN network has 34 stations equipped with all-sky cameras or wide-angle lenses, and we recently upgraded the software to reduce the ever-increasing amount of data. Here we present our automated Python (called 3D-FireTOC) pipeline for meteor detection from digital systems, astrometric measurements, photometry, atmospheric trajectory reconstruction and heliocentric orbit computation, all in all quantifying the error measurements in each step [3]. Analytical procedures of the 3D-FireTOC software A key step to achieve proper reduction is the development of automated astrometry to ensure the measurement of meteors appearing in the field of view of video-detection systems. To do this, we use computer vision techniques to obtain the pixel coordinates corresponding to the moving meteor in each frame. Each image is processed and compared with a reference image (without detection) allowing us to extract the pixels that have been activated by the meteor. In this way, the centroid of the detected pixel area corresponds to the position in the image of the meteoroid (see Figure 1). Due to the changing nature of this type of recordings as well as possible light reflections and obstacles in the field of view, we have implemented three methods to avoid false positives: 1) discriminating by the size of the detected area excluding excessively small and large contours, 2) predicting the next position of the meteor with a Kalman filter, and 3) post-processing the detected points and applying clustering algorithms to check if the trajectory is consistent with a more or less straight line. Figure 2 shows an example of false positive avoidance. To transform the pixels into real coordinates is necessary to identify stars in the image to obtain their position in the sky for the date of the event. To do this, we use corner detection algorithms since the stars appear randomly distributed in the sky and far from each other. Again, we use clustering algorithms but this time selecting the points identified as noise, as can be seen in Figure 2. Once the stars have been identified, thanks to JPL's Horizons ephemerides, we can model the deformation produced by the lens by finding the correspondence between pixel and real position. In particular, we apply a polynomial variant [4] of the method proposed by [5] for all-sky camera astrometry. Fig.1 Fig. 2 The result we obtain from each observation is an apparent trajectory projected on the celestial sphere. Naturally, two or more observations sufficiently far apart are required to triangulate the real position of the meteoroid. Because these fragments reach the Earth at very high velocities, air resistance practically does not bend their trajectories so that they can approximate a straight line. This allows the plane intersection method to be applied to reconstruct the atmospheric flight [6]. Finally, the trajectory is projected backwards to obtain the radiant, i.e. the position of origin in the sky. From the atmospheric flight, the α-β criterion can be applied approximating the chances that the event produced meteorites [7,8]. Recent example: SPM010521 event On May 1, 2021, a bolide flew over Aragón reaching a magnitude of -11. It was recorded by 6 stations of the SPMN network (Table 1 and Figure 3). The luminous phase started at 107 km altitude and ended at 43 km. The flight angle with respect to the horizontal was 24º degrees. With a geocentric velocity of 30 km/s, its orbital parameters indicate a possible association with a IAU working list of meteor showers called Southern May Ophiuchids. Unfortunately, it was not a meteorite-dropper event as reveals the α-β criterion result: α=315.4, β=1.2, an estimated initial mass of 0.1 kg and an estimated final mass less than one gram. Figure 4 shows the 3D representation and scale of the reconstructed atmospheric trajectory, as well as the calculated heliocentric orbit. Fig. 3 Fig. 4 Conclusions With the implementation of this new software, the SPMN increases its capacity to rapidly generate new knowledge about the origin of large meteoroids, and their capacity to generate hazard. Multi-station analyses also provide valuable information about their bulk physical properties and, from their heliocentric orbits, the dynamic association with comets, asteroids, or even planetary bodies can be inferred [3]. In addition, the automation of the meteor detection and the entire analysis process allows immediate preparation of meteorite search campaigns. Our software developments will be soon applied to increase our close cooperation with FRIPON [9]. As an example of application, we present the results obtained on SPMN010521, a recent fireball recorded and analyzed by the SPMN, which did not produce meteorites and seems to be dynamically associated with an unestablished meteor shower. Acknowledgements This research has been funded by the research project PGC2018-⁠097374-⁠B-⁠I00, (MCI-⁠AEI-⁠FEDER, UE). Funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme for the project “Quantum Chemistry on Interstellar Grains” (QUANTUMGRAIN, grant agreement No. 865657) is acknowledged. References [1] Trigo-Rodríguez J.M. et al. (2006) Astronomy & Geophysics 47, 6.26 [2] Hughes, D. W.(1990) MNRAS 245, 198-203. [3] Peña-Asensio, E., Trigo-Rodríguez, J. M., Gritsevich, M., & Rimola, A. (2021) MNRAS 504(4), 4829-4840. [4] Bannister, S. M., Boucheron, L. E., & Voelz, D. G. (2013) ASP125(931), 1108. [5] Borovička, J. (1992) AICAS, 79. [6] Ceplecha, Z. (1987) BAIC, 38, 222-234. [7] Gritsevich M., 2009, Advances in Space Research, 44, 323. [8] Sansom E. K., et al., 2019, The Astrophysical Journal, 885, 115. [9] Colas, F. et al. (2020) Astronomy & Astrophysics 644, id.A53, 23 pp.

Introduction The constant influx of new material from space to Earth provides an opportunity to delve into the processes that took place in the formation of the Solar System [1]. Some fragments of asteroids or comets have been wandering through space remaining practically unaltered, ending their journey upon impact with our atmosphere producing the spectacular luminous phenomenon known as a meteor or fireballs [2,3]. These almost meter-sized fragments, also called meteoroids, may be dynamically associated with the decay of comets or asteroid impacts [4]. In addition, their study provides us with valuable information about one of the major potential cosmic sources of near-term danger [5]. In order to achieve this goal, 25 years ago the Spanish Meteor and Fireball Network (SPMN) began monitoring the sky by recording and analyzing large fireballs [6]. Today, the network has 34 stations distributed throughout the Iberian Peninsula, and now also in the Canary Islands. This expansion of stations has resulted in the first detection of a fireball over these islands and analyzed entirely by a national team. Thanks to the new 3D-FireTOC software [7], we have been able to reconstruct the atmospheric trajectory and heliocentric orbit of the bolide SPMN30032021 from CCD video recordings. Methodology To correct for the large distortions produced by fisheye lenses, especially near the edges, we calibrated the cameras with the method proposed by [8], which is a polynomial variant of [9]. Once we obtained the apparent trajectories for each station, we applied the plane intersection method to obtain the atmospheric trajectory [10]. We solve the astrometric system combining the Simplex algorithm [11] and Powell's methods [12]. Finally, projecting this trajectory backwards and correcting for diurnal aberration and zenith attraction, we compute the radiant position and the heliocentric orbit. For the error calculation we have applied Monte Carlo methods. Using the calibration uncertainties, we generate random variations with a normal distribution for each bolide coordinate. In this way, we used 1000 clones to obtain the average values and the standard deviation of each computed parameter. Case Study: Bolide SPMN30032021 On Mars 30, 2021, a bright bolide catalogued as SPMN30032021 event occurred over the Canary Islands (see Table 1). It was an event of considerable importance because it has been the first to be recorded and analyzed by two stations of the SPMN network over the archipelago. One of the cameras is located at sea level, in Playa Blanca, on the island of Lanzarote. The other camera is located at the Roque de los Muchachos observatory, in the GranTeCan facilities, which can be seen in Figure 1. Fig. 1 The meteoroid began its luminous phase at an altitude of 77.9 ± 0.4 km with a velocity of 14.07 ± 0.15 km/s. It penetrated the atmosphere to a height of 35.3 ± 0.3 km, indicating that it likely did not produce meteorites. The point of maximum brightness reached a magnitude of -11 ± 1, it could have been seen with the naked eye from Morocco. The flight angle with respect to the horizontal was 40.45 ± 0.11 degrees. Due to its low geocentric velocity its atmospheric trajectory was greatly affected by gravitational attraction. Its orbital elements indicate that it originated from the inner asteroid belt. Figure 2 shows the 3D and scaled reconstruction of the SPMN event using the 3D-FireTOC software. Figure 2. Reconstruction of the atmospheric flight of the SPMN30032021 event with its apparent trajectory as seen from GranTeCan (left) and as seen from Playa Blanca (right). Conclusions The SPMN network continues to expand, providing global coverage throughout the Iberian Peninsula, the Balearic Islands and now also the Canary Islands. We are cooperating with FRIPON and the MOFID networks in the study of common events in France, and Morocco, respectively. In this paper we have presented the first fireball with atmospheric trajectory and heliocentric orbit reconstructed over the Canary Islands, analyzed entirely by a national team. The event SPMN30032021 comes from the asteroid belt and is not associated with any meteor shower, so it is of sporadic origin. With our activities we expect to continue increasing the number of meteorites recovered with reliable orbits and increase our understanding of the origin of meter-sized meteoroids disrupting into the Earth’s atmosphere [7]. By increasing the number of meteorite-dropping bolides we expect to gain insight on the physical processes that might produce the detachment of these rocks in near-Earth space [13]. Acknowledgements This research has been funded by the research project PGC2018-⁠097374-⁠B-⁠I00, (MCI-⁠AEI-⁠FEDER, UE). EPA and AR have received funding from the European Research Council (ERC) No. 865657. References [1] Murad, E., & Williams, I. P. (2002) CUP. UK, 234 pp [2] Ceplecha, Z., Borovička, J., Elford, W. G., ReVelle, D. O., Hawkes, R. L., Porubčan, V., & Šimek, M. (1998) 84(3), 327-471 [3] Trigo-Rodríguez J.M. (2019) Colonna G., Capitelli M. and Laricchiuta A. (eds.), IOP, pp. 4-1/4-23. [4] Jenniskens, P. (1998). Planets and Space, 50, pp. 555. [5] Moreno-Ibáñez, M., Gritsevich, M., Trigo-Rodríguez, J.M., and Silber, E.A. (2020) MNRAS 494, 316–324. [6] Trigo-Rodríguez J.M. et al. (2006) Astronomy & Geophysics 47, 6.26 [7] Peña-Asensio, E., Trigo-Rodríguez, J. M., Gritsevich, M., & Rimola, A. (2021) MNRAS 504(4), 4829-4840. [8] Bannister, S. M., Boucheron, L. E., & Voelz, D. G. (2013) ASP125(931), 1108. [9] Borovička, J. (1992) AICAS, 79. [10] Ceplecha, Z. (1987) BAIC, 38, 222-234. [11] Motzkin, T. S. (1956) In SAM, 6,109-125. [12] Powell, M. J. (1964) TCJ, 7(2), 155-162. [13] Trigo-Rodríguez J.M. et al. (2007) MNRAS 382, 1933-1939.

Understanding metal oxide MO2 (M = Ti, Ru, and Ir)-water interfaces is essential to assess the catalytic behavior of these materials. The present study analyzes the H2O-MO2 interactions at the most abundant (110) and (011) surfaces, at two different water coverages: isolated water molecules and full monolayer, by means of Perdew-Burke-Ernzerhof-D2 static calculations and ab initio molecular dynamics (AIMD) simulations. Results indicate that adsorption preferably occurs in its molecular form on (110)-TiO2 and in its dissociative form on (110)-RuO2 and (110)-IrO2. The opposite trend is observed at the (011) facet. This different behavior is related to the kind of octahedral distortion observed in the bulk of these materials (tetragonal elongation for TiO2 and tetragonal compression for RuO2 and IrO2) and to the different nature of the vacant sites created, axial on (110) and equatorial on (011). For the monolayer, additional effects such as cooperative H-bond interactions and cooperative adsorption come into play in determining the degree of deprotonation. For TiO2, AIMD indicates that the water monolayer is fully undissociated at both (110) and (011) surfaces, whereas for RuO2, water monolayer exhibits a 50% dissociation, the formation of H3O2 - motifs being essential. Finally, on (110)-IrO2, the main monolayer configuration is the fully dissociated one, whereas on (011)-IrO2, it exhibits a degree of dissociation that ranges between 50 and 75%. Overall, the present study shows that the degree of water dissociation results from a delicate balance between the H2O-MO2 intrinsic interaction and cooperative hydrogen bonding and adsorption effects.

Drolshagen, E., et al., [Context] In meteor physics, the luminous efficiency τ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, a lack of sufficiently accurate verification methods or adequate laboratory tests mean that discussions around this parameter are a subject of controversy. [Aims] In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein. [Methods] Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required. [Results] We find τ-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10-6-100 kg. The derived τ-values have a median of τmedian = 2.17%. Most of them are of the order of 0.1-10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of τ on the pre-atmospheric velocity of the meteor, ve, is noticeable with a relation of τ = 0.0023 ve2.3. Furthermore, a dependence of τ on the initial meteoroid mass, Me, is found with negative linear behaviour in log-log space: τ = 0.48 Me-0.47. [Conclusions] The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of τ on Me implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.

We have observed the very low-mass Class 0 protostar IRAS 15398−3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and C18O line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398−3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s−1 over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398−3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution. The authors thank the anonymous reviewer for invaluable comments. They are also grateful to Hauyu Baobab Liu for useful discussions. This paper makes use of the following ALMA data set: ADS/JAO.ALMA#2018.1.01205.L (PI: Satoshi Yamamoto). ALMA is a partnership of the ESO (representing its member states), the NSF (USA) and NINS (Japan), together with the NRC (Canada) and the NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, the AUI/NRAO, and the NAOJ. The authors thank to the ALMA staff for their excellent support. This work is supported by the projects PRIN-INAF-MAIN-STREAM 2017 Protoplanetary disks seen through the eyes of new-generation instruments, ARIEL and the astrochemical link between circumstellar disks and planets, and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programmes: The Dawn of Organic Chemistry (DOC), grant agreement No. 741002, and Astro-Chemistry Origins (ACO), grant No. 811312. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. I.J.-S. has received partial support from the Spanish FEDER (project number ESP2017-86582-C4-1-R) and the State Research Agency (AEI; project number PID2019-105552RB-C41). D.J. is supported by NRC Canada and by an NSERC Discovery Grant. This project is also supported by a Grant-in-Aid from Japan Society for the Promotion of Science (KAKENHI: Nos. 18H05222, 19H05069, 19K14753). Yuki Okoda thanks the Advanced Leading Graduate Course for Photon Science (ALPS) and Japan Society for the Promotion of Science (JSPS) for financial support. Peerreview

Interstellar grains are known to be important actors in the formation of interstellar molecules such as H$_2$, water, ammonia, and methanol. It has been suggested that the so-called interstellar complex organic molecules (iCOMs) are also formed on the interstellar grain icy surfaces by the combination of radicals via reactions assumed to have an efficiency equal to unity. In this work, we aim to investigate the robustness or weakness of this assumption by considering the case of acetaldehyde (CH$_3$CHO) as a starting study case. In the literature, it has been postulated that acetaldehyde is formed on the icy surfaces via the combination of HCO and CH$_3$. Here we report new theoretical computations on the efficiency of its formation. To this end, we coupled quantum chemical calculations of the energetics and kinetics of the reaction CH$_3$ + HCO, which can lead to the formation of CH$_3$CHO or CO + CH$_4$. Specifically, we combined reaction kinetics computed with the Rice-Ramsperger-Kassel-Marcus (RRKM) theory (tunneling included) method with diffusion and desorption competitive channels. We provide the results of our computations in the format used by astrochemical models to facilitate their exploitation. Our new computations indicate that the efficiency of acetaldehyde formation on the icy surfaces is a complex function of the temperature and, more importantly, of the assumed diffusion over binding energy ratio $f$ of the CH$_3$ radical. If the ratio $f$ is $\geq$0.4, the efficiency is equal to unity in the range where the reaction can occur, namely between 12 and 30 K. However, if $f$ is smaller, the efficiency dramatically crashes: with $f$=0.3, it is at most 0.01. In addition, the formation of acetaldehyde is always in competition with that of CO + CH$_4$., Comment: 14 pages, 12 figures, 11 tables, accepted in A&A

The disruption of asteroids and comets produces cm-sized meteoroids that end up impacting the Earth's atmosphere and producing bright fireballs that might have associated shock waves or, in geometrically-favorable occasions excavate craters that put them into unexpected hazardous scenarios. The astrometric reduction of meteors and fireballs to infer their atmospheric trajectories and heliocentric orbits involves a complex and tedious process that generally requires many manual tasks. To streamline the process, we present a software package called SPMN 3D Fireball Trajectory and Orbit Calculator (3D-FireTOC), an automatic Python code for detection, trajectory reconstruction of meteors, and heliocentric orbit computation from video recordings. The automatic 3D-FireTOC package comprises of a user interface and a graphic engine that generates a realistic 3D representation model, which allows users to easily check the geometric consistency of the results and facilitates scientific content production for dissemination. The software automatically detects meteors from digital systems, completes the astrometric measurements, performs photometry, computes the meteor atmospheric trajectory, calculates the velocity curve, and obtains the radiant and the heliocentric orbit, all in all quantifying the error measurements in each step. The software applies corrections such as light aberration, refraction, zenith attraction, diurnal aberration and atmospheric extinction. It also characterizes the atmospheric flight and consequently determines fireball fates by using the $\alpha - \beta$ criterion that analyses the ability of a fireball to penetrate deep into the atmosphere and produce meteorites. We demonstrate the performance of the software by analyzing two bright fireballs recorded by the Spanish Fireball and Meteorite Network (SPMN)., Comment: Published on 10 April 2021

Computational modeling of protein/surface systems is challenging since the conformational variations of the protein and its interactions with the surface need to be considered at once. Adoption of first-principles methods to this purpose is overwhelming and computationally extremely expensive so that, in many cases, dramatically simplified systems (e.g., small peptides or amino acids) are used at the expenses of modeling nonrealistic systems. In this work, we propose a cost-effective strategy for the modeling of peptide/surface interactions at a full quantum mechanical level, taking the adsorption of polyglycine on the TiO2 (101) anatase surface as a test case. Our approach is based on applying the periodic boundary conditions for both the surface model and the polyglycine peptide, giving rise to full periodic polyglycine/TiO2 surface systems. By proceeding this way, the considered complexes are modeled with a drastically reduced number of atoms compared with the finite-analogous systems, modeling the polypeptide structures at the same time in a realistic way. Within our modeling approach, full periodic density functional theory calculations (including implicit solvation effects) and ab initio molecular dynamics (AIMD) simulations at the PBE-D2* theory level have been carried out to investigate the adsorption and relative stability of the different polyglycine structures (i.e., extended primary, β-sheet, and α-helix) on the TiO2 surface. It has been found that, upon adsorption, secondary structures become partially denatured because the peptide C═O groups form Ti-O═C dative bonds. AIMD simulations have been fundamental to identify these phenomena because thermal and entropic effects are of paramount importance. Irrespective of the simulated environments (gas phase and implicit solvent), adsorption of the α-helix is more favorable than that of the β-sheet because in the former, more Ti-O═C bonds are formed and the adsorbed secondary structure results less distorted with respect to the isolated state. Under the implicit water solvent, additionally, adsorbed β-sheet structures weaken with respect to their isolated states as the H-bonds between the strands are longer due to solvation effects. Accordingly, the results indicate that the preferred conformation upon adsorption is the α-helix over the β-sheet.

There are different environments in the interstellar medium (ISM), depending on the density, temperature and chemical composition. Among them, molecular clouds, often referred to as the cradle of stars, are paradigmatic environments relative to the chemical diversity and complexity in space. Indeed, there, radio to far-infrared observations revealed the presence of several molecules in the gas phase, while near-infrared spectroscopy detected the existence of submicron sized dust grains covered by H2O -dominated ice mantles. The interaction between gas-phase species and the surfaces of water ices is measured by the binding energy (BE), a crucial parameter in astrochemical modelling. In this work, the BEs of a set of sulphur-containing species on water ice mantles have been computed by adopting a periodic ab initio approach using a crystalline surface model. The Density Functional Theory (DFT)-based B3LYP-D3(BJ) functional was used for the prediction of the structures and energetics. DFT BEs were refined by adopting an ONIOM-like procedure to estimate them at CCSD(T) level toward complete basis set extrapolation, in which a very good correlation between values has been found. Moreover, we show that geometry optimization with the computationally cheaper HF-3c method followed by single point energy calculations at DFT to compute the BEs is a suitable cost-effective recipe to arrive at BE values of the same quality as those computed at full DFT level. Finally, computed data were compared with the available literature data., Proceedings of the 21st International Conference on Computational Science and Its Applications, ICCSA 2021

The issue of formation of dust grains in the interstellar medium is still a matter of debate. One of the most developed proposals suggests that atomic and heteromolecular seeds bind together to initiate a nucleation process leading to the formation of nanostructures resembling very small grain components. In the case of silicates, nucleated systems can result in molecular nanoclusters with diameters ≤ 2 nm. A reasonable path to further increase the size of these proto-silicate nanoclusters is by mutual aggregation. The present work deals with modeling this proto-silicate nanocluster aggregation process by means of quantum chemical density functional theory calculations. We simulate nanocluster aggregation by progressively reducing the size of a periodic array of initially well-separated nanoclusters. The resulting aggregation leads to a set of silicate bulk structures with gradually increasing density which we analyze with respect to structure, energetics and spectroscopic properties. Our results indicate that aggregation is a highly energetically favorable process, in which the infrared spectra of the finally formed amorphous silicates match well with astronomical observations.

International audience; The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.