Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos

An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred meters to a few kilometres in size have relatively high spin rates, from less than 4 h, down to $\sim$2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environment has been carried out -- in the frame of the Hera mission and the EC-H2020 NEO-MAPP project -- according to the available shape model, known physical parameters and orbital information available before the DART impact. The presence of orbiting particles in the system is likely for most of the estimated range of values for mass and volume. The spatial mass density of ejected material is calculated for different particle sizes and at different heliocentric orbit epochs, revealing that large particles dominate the density distribution and that small particle abundance depends on observation epoch. Estimates of take off and landing areas on Didymos are also reported. Available estimates of the system mass and primary extents, after the DART mission, confirm that the main conclusions of this study are valid in the context of current knowledge

Lofting of low speed ejecta produced in the DART experiment and production of a dust cloud

NASA sent the DART (Double Asteroid Redirection Test) mission to impact Dimorphos, the satellite of the asteroid binary system (65803) Didymos. DART will release LICIACube prior to impact to obtain high-resolution post-impact images. The impact will produce a crater and a large amount of material ejected at high speed (several tens of m/s), producing an ejecta cone that will quickly disperse. We analyzed an additional effect: the lofting of material at low velocity due to the generation of seismic waves that propagate inside Dimorphos, producing surface shaking far from the impact point. We divide the process into different stages: from the generation of impact-induced waves, the interaction of them with surface particles, the ejection of dust particles at velocities, and the prediction of the observability of the dust coma and trail. We anticipate the following observable effects: i) generation of a dust cloud that will produce a hazy appearance of Dimorphos' surface, detectable by LICIACube; ii) brightness increase of the binary system due to enhancement of the cross section produced by the dust cloud; iii) generation of a dust trail, similar to those observed in some Active Asteroids, which can last for several weeks after impact. Numerical prediction of the detectability of these effects depends on the amount and size distribution of ejected particles, which are largely unknown. In case these effects are observable, an inversion method can be applied to compute the amount of ejected material and its velocity distribution, and discuss the relevance of the shaking process.Comment: 12 pages, 13 figure

Ground-based observability of Dimorphos DART impact ejecta: Photometric predictions

The Double Asteroid Redirection Test (DART) is a NASA mission intended to crash a projectile on Dimorphos, the secondary component of the binary (65803) Didymos system, to study its orbit deflection. As a consequence of the impact, a dust cloud will be be ejected from the body, potentially forming a transient coma- or comet-like tail on the hours or days following the impact, which might be observed using ground-based instrumentation. Based on the mass and speed of the impactor, and using known scaling laws, the total mass ejected can be roughly estimated. Then, with the aim to provide approximate expected brightness levels of the coma and tail extent and morphology, we have propagated the orbits of the particles ejected by integrating their equation of motion, and have used a Monte Carlo approach to study the evolution of the coma and tail brightness. For typical power-law particle size distribution of index --3.5, with radii r$_{rmin}$=1 $\mu$m and r$_{max}$=1 cm, and ejection speeds near 10 times the escape velocity of Dimorphos, we predict an increase of brightness of $\sim$3 magnitudes right after the impact, and a decay to pre-impact levels some 10 days after. That would be the case if the prevailing ejection mechanism comes from the impact-induced seismic wave. However, if most of the ejecta is released at speeds of the order of $\gtrsim$100 $\mathrm{m\; s^{-1}}$, the observability of the event would reduce to a very short time span, of the order of one day or shorter.Comment: Accepted by MNRAS, June 30, 202

On the genesis of the Haumea system

The scenarios proposed in the literature for the genesis of the system formed by the dwarf planet 136108 Haumea, its two satellites and a group of some 10 bodies (the family) with semimajor axes, eccentricities and inclinations close to Haumea's values, are analysed against collisional, physical, dynamical and statistical arguments in order to assess their likelihood. All scenarios based on collisional events are reviewed under physical arguments and the corresponding formation probabilities in a collisional environment are evaluated according to the collisional evolution model alicandep. An alternative mechanism is proposed based on the potential possibility of (quasi-) independent origin of the family with respect to Haumea and its satellites. As a general conclusion the formation of the Haumea system is a low-probability event in the currently assumed frame for the evolution of the outer Solar system. However, it is possible that current knowledge is missing some key element in the whole story that may contribute to increase the odds for the formation of such a system.This research was partially supported by Spanish grants AYA2011-06202-C02-01 (JLO) and AYA2011-06202-C02-02 (ACB). RGH gratefully acknowledges financial support by CONICET through PIP 114-201101-00358 and Junta de Andalucia 2012-FQM1776

Ground-based obser v ability of Dimor phos DART impact ejecta: photometric predictions

The Double Asteroid Redirection Test (DART) is a NASA mission intended to crash a projectile on Dimorphos, the secondary component of the binary (65803) Didymos system, to study its orbit deflection. As a consequence of the impact, a dust cloud will be be ejected from the body, potentially forming a transient coma- or comet-like tail on the hours or days following the impact, which might be observed using ground-based instrumentation. Based on the mass and speed of the impactor, and using known scaling laws, the total mass ejected can be roughly estimated. Then, with the aim to provide approximate expected brightness levels of the coma and tail extent and morphology, we have propagated the orbits of the particles ejected by integrating their equation of motion, and have used a Monte Carlo approach to study the evolution of the coma and tail brightness. For typical power-law particle size distribution of index –3.5, with radii r rmin = 1 μm and r max = 1 cm, and ejection speeds near 10 times the escape velocity of Dimorphos, we predict an increase of brightness of ∼3 magnitudes right after the impact, and a decay to pre-impact levels some 10 d after. That would be the case if the pre v ailing ejection mechanism comes from the impact-induced seismic wave. Ho we ver, if most of the ejecta is released at speeds of the order of 100 m s −1 , the observability of the event would reduce to a very short time span, of the order of 1 d or shorter.ANII: FCE_1_2019_1_15645

Early collisional evolution of TNOs

Any early or late dynamical instability in the outer Solar system should have left their footprint on the trans-Neptunian object (TNO) populations. Here, we study the collisional and dynamical evolution of such populations numerically by an updated version of ALICANDEP, which suitably takes into account the onset of an early dynamical instability. Key parameters for collisional and dynamical evolution are chosen to match results with current observables. The new model (ALICANDEP-22) considers an original region located between 22 and 30 au, containing 20–30 M_Earth from which bodies are either dynamically ejected from the region or implanted into the current plutinos and hot classical trans-Neptunian belt. An in situ population of objects is also present since the beginning, corresponding to the current cold-classical population. Collisional and dynamical evolution is allowed starting from initial conditions accounting for streaming instability models and observational constraints. ALICANDEP-22 successfully reproduces observational constraints as well as the shape of the size-frequency distribution expected for the Trojan population. The model concludes that Arrokoth is likely a primordial body but cannot be conclusive on the origin of comet 67P/Churyumov–Gerasimenko. The current presence of bodies larger than Pluto in the outer TNO population – waiting to be discovered – is compatible with the initial distributions that allow the model to match current constraints

Gravitational re-accumulation as the origin of most contact binaries and other small body shapes

Asteroids show a variety of shapes, ranging from roundish to elongated to binary systems and ‘contact binaries’ like (25143) Itokawa, the target of the Hayabusa mission (JAXA). These bodies spend most of their time within a collisional system, the asteroid belt, where impact processes are relatively frequent. Speculations on the origin of asteroid shapes invoke mechanisms such as collisions and spin-up effects. N-body numerical simulations of fragment evolution following catastrophic collisions have been recently carried out (Campo Bagatin et al., 2018). In this study the idea that the stochastic process of gravitational re-accumulation may be responsible for many observed asteroid shapes is introduced. Asteroid ‘contact binaries’ are shown to be regularly produced by the gravitational re-accumulation process following catastrophic impact. Similar processes may have occurred in the case of some comets and Trans-Neptunian Objects.ACB and PGB acknowledge funding from AYA2016-79500-R (2016–2018) grant by the Spanish Ministerio de Economía, Industria y Competitividad

Destrezas matemáticas previas de los estudiantes de grado en Ingenierías y Arquitectura

Muchos profesores de asignaturas de física y de matemáticas que imparten docencia en el primer curso de las titulaciones técnicas de Grado detectan un empeoramiento de las destrezas matemáticas básicas de los alumnos de nuevo ingreso. Esta situación dificulta el proceso de enseñanza-aprendizaje y lastra negativamente las posibilidades de éxito de muchos estudiantes de primer curso. Esta clara sensación, sin embargo necesita de una definición cuantitativa. En este proyecto, nos planteamos realizar un análisis cuantitativo de las destrezas en matemáticas básicas de los nuevos matriculados en las titulaciones de Grado de la Escuela Politécnica Superior (EPS), para impulsar un debate en la comunidad universitaria y pre-universitaria que lleve a proponer medidas concretas dirigidas a mejorar las habilidades en nuestros estudiantes

Internal structure of asteroid gravitational aggregates

The internal structure of small asteroids is fundamentally unknown due to lack of direct measurements. The only clues on this topic come from theoretical considerations and from the comparison between measured bulk densities of asteroids and their corresponding analogue meteorite densities. The mass distribution and the void space between components in a gravitational aggregate determine the structure of such objects. In this paper we study numerically the dynamical and collisional evolution of the reaccumulation process of the fragments created in catastrophic collisions of asteroids in the 500 m to 10 km size range. An effort to consider irregularly shaped fragments is made by taking advantage of the results of laboratory experiments that provide relative mass distributions and aspect ratios for fragment shapes. We find that the processes that govern the final properties of the resulting aggregates are mainly stochastic, however interesting patterns can be identified. This study matches estimated macro-porosities of S-type asteroids and finds a loose linear relationship between macro-prorosity of asteroid aggregates and the mass ratio of the largest component to the whole aggregate (for both S and C-types). As for observed C-type asteroids, we conclude that their interiors should be more fragmented than in the case of S-type asteroids, explaining the difference in the estimated macro-porosity of real C asteroids with respect to S-types. We also find that slow rotators may be interpreted as a natural result in the process of gravitational reaccumulation.This work has been possible thanks to the grants AYA2008- 06202C0303 and AYA2011-30106-C02-02 by the extinct Spanish Ministerio de Ciencia e Innovación