Resumo:

This study explores mechanical properties of asteroids as granular systems at the laboratory scale, exploring their significance in space mission design, Earth collision hazard assessment, and the comprehension of collisional processes. We present a comprehensive laboratory-scale characterization of granular media, focusing on both quasi-static and dynamic regimes. The use of laboratory-scale experiments provides a cost-effective alternative to in-situ measurements. The self-gravity of asteroids induces a stress distribution that remains poorly understood, but evidence suggests a gradient with increasing values towards the asteroid’s interior. The micro-gravity conditions on asteroids introduce unique mechanical properties, which are challenging to replicate on Earth. Despite being non-realistic, our experiments can be regarded as an accelerated aging representation of asteroids subjected to external stresses from impacts and emperature changes. They are particularly relevant for comprehending the propagation of seismic waves within asteroids ranging from a few km to tens of km in radius. The experimental results demonstrate that granular media exhibit quasi-elastic behavior during each compression cycle, with increasing elasticity. The stress-strain curve exhibits irreversible compaction with significant hysteresis during relaxation. Another focus of this study is understanding the nature of active asteroids, which could be due to a shaken mechanism induced by the propagation of seismic waves into the interior. Seismic waves generated by impacts and vibrations in our experimental device show high attenuation. The wave speed follows a power-law relationship $v \propto p^{1/2}$, and the elasticity of granular media depends on the time and strain scales. Remarkably, our experiments indicate that the speed of impact-generated and shaker-born seismic body waves does not exhibit a strong dependence on the origin mechanism. This suggests that safer wave-generating methods, may be used in low-gravity laboratory experiments instead of risky impact devices. Our research serves as foundational work for enhancing our understanding of asteroid interiors and boulder distribution.

Resumo:

We shall summarize the main conclusions of the article on Surface Composition of the Trojan Asteroids, to be published in a future volume of the `Space Science Review (SSR)'' on the Lucy mission (Emery et al. 2023). The properties of this asteroidal population will be discussed in the context of posible analog populations of minor bodies of the Solar System and meteorites. We shall review their spectral reflectance in the UV, the visible and the near IR, as well as as the thermophysical models derived from the measurements in the IR and in particular the NEO-WISE results and their estimates of albedo and size. We will also make a brief reference to the scenarios of formation proposed so far but we will describe in greater detail composition and evolutionary models (`nature'' vs. `nurture'') carried out so far and their main conclusions. Finally, we shal discuss how the data obtained by the LUCY mission will hep to solve the main questions that remain at the present time regarding this peculiar population. Surface Compositions of Trojan Asteroids. 2023. J.P. Emery, .P. Binzel, D.T. Britt,.E. Brown,.J.A. Howett, A.C. Martin, M.D. Melita, .C. Souza-Feliciano, I. Wong. The Lucy mission. Space Science Review (SSR). Submitted.

Resumo:

We shall summarize the results of the photometric observations of Near Earth Objects made at the Jorge Sahade (2.15m) telescope, located at the Complejo Astronomico El Leoncito (San Juan, Argentina). At the moment we have observed 42 nights since October 2021. We have data from 29 different objects. Our data includes sparse Johnson-BVRI colors to determine phase curves and spectro-photometric properties in the visible and/or lightcurves in the Johnson-R filter to determine rotation periods and shape properties. We are presenting the detailed data per object and we shall discuss the scope of this campaign, based on our results so far. Our sample includes 2 binaries and a posible tumbler. This project is a contribution to the campaign of observations of Near Earth Objects carried out at the Observatorio Astronomico do Sertao de Itaparica.

Resumo:

The Near-Earth Objects (NEOs) population is quite interesting since the observation of its members allow us to investigate the physical properties of the smallest Solar System bodies and better understand their formation and evolution. We present results from a photometric survey of NEOs performed using the 1.0-meter telescope at the Observatório Astronômico do Sertão de Itaparica (Itacuruba, Brazil) within the IMPACTON project. Since February 2021, more than 80 observing nights have allowed obtaining the rotational light curves, solar phase curves and photometric spectra for nearly 15 NEOs. From the light curves, with magnitudes in the Johnson-Cousins R-filter, we derived the rotational period using a Fourier analysis. The phase curves, in the Johnson-Cousins R- and V-filter, allowed derive the absolute magnitude, H, as well the G1-G2 parameters. Finally, from the photometric spectra, using the SDSS g', r', i', z' filters, we were able to derive a taxonomic classification for the selected NEOs. We will discuss how the complete and simultaneous determination of the main physical properties of a NEO can help better understand its correlation with other populations of small bodies, in particular, those in the Main Belt. It is important to mention that these are the preliminary results of the observational campaign that will use complementary observations acquired with the Complejo Astronómico El Leoncito (San Juan, Argentina) within a collaborative project.

Resumo:

It has been demonstrated that asteroids are composed of granular media. Tancredi et al. (2012) predicted, through numerical simulations, the formation of dust clouds at low escaping velocities after an impact. Specifically, they concluded that a layer of particles shocked from below could lead to particles rising to the surface, with some even reaching escape velocities in environments with very low gravity. This concept, known as the "cocoa effect," was further supported by Tancredi et al. (2023) while analyzing the potential lofting of surface material on Dimorphos caused by shaking far from the actual impact point. Currently, our research focuses on studying the velocities of ejected particles in soft granular media, specifically rubber sieved in various sizes. The objective is to understand how the cocoa effect behaves at a laboratory scale by measuring the height to which particles are lofted and their velocity. We have opted to work with a soft granular medium because the velocity of waves within it is significantly slower than that in harder media, allowing us to capture the movement using high-speed cameras. The experimental setup consists of an acrylic prism filled with rubber, placed atop a shaker. An accelerometer measures the applied acceleration. We have varied the volume occupied by the granular material, as well as the amplitude and frequency of the acceleration. The movement of the particles is recorded using a high-speed camera and analyzed with Particle Image Velocimetry (PIV) software. Preliminary results indicate the height at which lofting begins and how the velocity changes throughout the column of material. Despite the significant modification of ejection conditions by Earth's gravity, we remain convinced that the experimental data gathered from our research are invaluable for enhancing the comprehension of ejection processes in asteroids.

Resumo:

The most widely accepted meteorite database worldwide is the Meteoritical Society, which maintains the Meteoritical Bulletin Database (hereafter MBD), which compiles information on meteorites recovered worldwide. As of 30/07/2023 there are 72182 meteorites registered with their respective taxonomic classification. Meteorites recovered after observations of their passage through the atmosphere are called falls; whereas, those that are found by chance, or that definitely cannot be associated with passage are called finds. In the MBD, there are 1214 recorded falls with official names. The aim of this work was to combine information from the database (and others) to analyze the temporal distribution of meteorite falls. The database includes information on falls spread over several centuries, but with a uniform coverage over the last century, with a considerable increase since the XXI century. The frequency of the falls was calculated as a function of the day of the year and the longitude of the Sun; and was compared with a Poisson process, in order to look for dates with higher frequency than expected, which could signal a meteor stream. A subset of the falls that are of great concern are those meteors that directly affect humans or their belongings (damaging falls). From an analysis of recorded meteorite falls and the damaging subset over the past and present century, an average rate of 7.45 falls and 1.63 damaging falls on urban Earth per year was calculated from the database. Subsequently, ~57 falls per year over the entire Earth’s surface, and ~17 falls per year over Earth’s landmass were estimated.

Resumo:

Transitional objects are bodies that share some characteristics with asteroids and others with comets. Asteroids in Cometary Orbits (ACOs) behave dynamically like comets but have not shown cometary activity and Activated Asteroids (AAs) have a typical asteroidal orbit and have shown dust ejections at some point. We present the monitoring of a set of these objects using archival images as well as new observations. Two techniques were used to search for signs of activity: i) the surface brightness profile of the objects was obtained and compared with the profile of stars in the field, in search of a widening that indicates the presence of activity; ii) data on the reported magnitudes of these objects were obtained from the Minor Planet Center database, to which were added those obtained in the observations, for studying the reduced magnitude as a function of the heliocentric distance, in search of increases in brightness that could be due to activity. We analyze the surface brightness profiles of 133 ACOs and seven AAs. For the study of the reduced magnitude, we obtained data of all the existing ACOs at the time of the analysis (705). Ten ACOs presented some deviation in the surface brightness profile or in the reduced magnitude and one in both. We found a very small percentage of objects with signs of activity, which would rule out a slow transition from active to inert. Four AAs were active in the images, three were coincident with the activity periods reported by other observers, while in the case of P/2015 X$_6$, the data analyzed was obtained 19 days before the first activity report. We could observe that the episodes of activity of these objects are very restricted in time and do not always occur in the same region of the orbit.

Resumo:

Dwarf planets are objects in the Solar System orbiting the Sun, which are massive enough to be on hydrostatic equilibrium, but do not dynamically dominate the environments to which they belong. So far, there are five confirmed dwarf planets, where four of them are located in the transneptunian region, namely: Pluto, Eris, Haumea and Makemake. All four have natural satellites. Pluto is accompanied by its main satellite, Charon in addition to other satellites with a few tens of kilometers: Styx, Nyx, Kerberos and Hydra. Eris is accompanied by Dysnomia, Haumea by Hi'iaka and Namaka, and Makemake by MK2. It is well know tha the Pluto-Charon have the rotations synchronized with the orbital motions. This synchronous state is a natural consequence of the tidal interaction between the dwarf planet and its principal satellite. In this work, we propose to investigate the tidal orbital evolution of Pluto and Charon using the creep model, where the main parameter is the viscosity attributed to the deformed body. Regarding the tidal action on both bodies, we integrated the average equations over about $10^9$ years, in order to conclude when and how the system could have entered into synchronism. Furthermore, we extend this analysis to other dwarf planets and their respective satellites.

Resumo:

Several objects in asteroidal orbits have presented comaes and tails like the ones presented by comets for short period of times. There are at present ~46 objects that has presented, at least for a brief period, this cometary-like appearance. These objects are generally coined “Active Asteroids”, implicitly implying that some kind of on-going endogenous or exogenous active process is the mechanism that produce the long-lasting tails. Nevertheless, what we observe is that those asteroids are temporally dressed as comets. Several hypotheses have been proposed to explain the “activity” of these object. {\bf Lessons from DART}: The NASA-DART experiment give us an opportunity to review our knowledge of this population. Following the impact of the space probe against asteroid Dimorphos on September 26, 2022, several thousand tons of material were ejected at a wide range of velocities. Tancredi et al. (2023) dubbed the DART experiment as the creation of the first artificial “Active Asteroid”. They proposed that the production of a large amount of low-speed ejected material could be described by the “cocoa effect”: the lofting of small particles from the top of a dust layer when shaking the ground. The combination of the impact induced seismic shaking plus the “cocoa effect” can produce the ejection of particles from a large fraction of the impacted hemisphere. They predicted a brightness increase due to a slowly moving dust cloud, the obscuration of Dimorphos’ surface by this cloud, and the generation of a long-lasting tail, which were confirmed by the close-by observations of LICIACube, as well as long-range tracking from HST and the ground. By July 2023, over 250 days after impact, the tail is still visible. Based on these results, we review the relevance of the different mechanism proposed to explain the appearance of the population of asteroids temporally dressed as comets.

Resumo:

Polarimetry is one of the observational techniques that allows us to obtain information on the physical properties of asteroidal surfaces, but it has the important limitation of the difficulty and slowness with which polarimetric observations are obtained. As a consequence, the asteroid polarimetric database was very small until the 1990s and very few objects had their polarimetric parameters well determined at that time. The improvement in the instrumentation from the last 20 years allowed the development of several observation campaigns in order to increase the observation database and achieve the determination of polarimetric parameters for a greater number of objects. This poster presents the latest version of the Catalogue of Asteroid Polarization Curves (July 2023), which concentrates some 6300 observations for almost 800 objects and lists the polarimetric parameters for more than 200 asteroids. Additionally, some of the results obtained from the available data are shown.

Resumo:

In the Hilda region there is an unstable zone inhabited by asteroids and comets, this zone is called the quasi-Hilda Region. While comets are bodies with a core of mixed ice and dust, asteroids are bodies composed mainly of dust. However, from a physical point of view it is difficult to distinguish between the two populations, so the only way to do so is through dynamical analysis. In recent years we have initiated a campaign to identify comets that have recently arrived to the quasi-Hilda region from beyond Jupiter's orbit, resulting in 11 quasi-Hilda comets (QHCs) candidates, of which one has been observed and confirmed to be a comet. In this talk we present an update on the QHCs candidate. Our results show that the population has increased by 500% in the last few years.

Resumo:

Asteroids and comets are the remnants of the accretion process that formed the planets about 4.6 billion years ago. Their physical nature, chemical composition, and orbital characteristics depend on the region of the solar system where they originally formed. Traditionally, asteroids are considered rocky, inert objects, while comets are icy, active bodies. Also, in general, asteroids have more stable orbits and longer dynamic lifetimes than comets, due to much less close encounters with the planets (especially Jupiter). However, this boundary has become more blurred, especially among near-Earth objects (defined as those reaching perihelion distances $q$ < 1.3 au). For instance, near-Earth asteroid 3552 Don Quixote shows cometary activity (Mommert et al. 2014, The Astrophysical Journal 781), and in the other hand some near-Earth comets were found to have stable orbits like asteroids (Fernández and Sosa 2015, Planetary and Space Science 118).\\ Following Fernández et al. 2014 (Icarus 238), we analyze a sample of 327 near-Earth asteroids (NEAs) that approach or cross Jupiter’s orbit (aphelion distances $Q$ > 4.8 au), with Tisserand parameters 2 < $T$ < 3 and orbital periods $P$ < 20 yr, i.e. resembling the orbital characteristics of the Jupiter family comets. We also constrain the sample to those objects with better quality orbits (i.e. condition codes < 6). We use the NASA JPL Small-Body Database. We integrated the orbits of the selected objects plus 50 clones of each one, for 10.000 yr in the past and in the future, to study their dynamic evolution. We also analyze the conditions for photometric observations of selected objects which could improve our physical knowledge of this population. We present the preliminary results, based in an updated and larger (by a factor of 2) orbital database of NEAs, and numerical integrations with ten times more clones than the previous work.

Resumo:

Comet C/2021 A1 (Leonard) was discovered on January 2021 with a magnitude of $V \approx 19$ at a heliocentric distance $r_H= 5\, au$ . Leonard is an hyperbolic comet reaching perihelion in January 2022 which achieved visibility with the naked eye in late 2021 and then showed spectacular gas and dust tails. However, Leonard became photometrically unstable in December 2021 and January 2022 when its morphology has changed, getting diffuse and with the tail becoming more relevant on January 22, 2022 at $r_H \approx 0.74\, au$. In a previous paper images of the Leonard disruption were presented estimating that the complete disintegration of the nucleus was near mid-December, 2021 explaining that the rotational instability driven by out-gassing torques offers the most plausible mechanism for the disruption. In this poster we present images of this comet on the broadband B, V, and R filters taken with the 0.6 m HSH telescope in CASLEO, Argentina on December 21 and 22, 2021; close to the estimated date of the disruption event. Our goal is to study the comet dust behavior in the previous moments to the disintegration event.

Resumo:

\noindent In this work, we present the results of the photometric analysis of just over a dozen asteroids whose rotational period has not been estimated, and which we consider fortuitous since they were not the primary target of the photometric observations. However, they were present in the same field of view as the main asteroid and exhibited sufficient brightness for photometric analysis.\\ \noindent The analyzed images correspond to 23 nights during the year 2022, and were obtained from the National Astronomical Observatory of San Pedro Mártir, using the 84 cm telescope. Image processing, aperture photometry, and differential photometry were performed to calculate light curves. Subsequently, a search for the corresponding rotational period value was carried out using Fourier series analysis.

Resumo:

Since 2019 we have deployed a network of stations with allsky cameras for the detection of bright meteors (fireballs). By October 2021, 6 stations were installed in the south of Uruguay, in what made up the first stage of the {\it Red de Detección de Bólidos del Cono Sur (BOCOSUR)}. These first stations were built using a Watec 902H2 CCTV camera with an Arecont vision fisheye lens (f/2.0, 1.55mm). The stations run an application developed by our group (see Caldas et al. in this conference), which detects any change in brightness in consecutive frames. While the variations persist, a short video of less than 10 seconds is recorded. In these videos you can detect animals, planes, rain, clouds, lightning or other phenomena, in addition to the fireballs that are of interest to us. Therefore, a classification should be made between videos with and without fireball. Initially a manual classification was made. In 2022, a group of Electrical Engineering students (Ballestrino et al. 2022) developed an algorithm based on machine learning for the automatic classification of the videos, using the classification we had done as a training base. The algorithm called {\it Autobol} was developed in python, and is available at https://github.com/jpballestrino/AutoBol github. To train the {\it Autobol} package, we used the manual classification of at $\sim 8000$ videos, where 363 of them have fireballs. The classification was made by team members, as well as high-school students and teachers that participate in the project (see Velasco et al. in this conference for a description of the training workshops). In this poster we will present the results of applying these predictive classification models to a database of over 250,000 videos. We will present statistics on the performance of the network and the classification algorithm. References: Ballestrino, J. et al., https://hdl.handle.net/20.500.12008/32619