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PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

Asteroids have called the attention of researchers around the world. Its chemical and physical composition can give us important information about the formation of our Solar System. In addition, the hypothesis of mining some of these objects is considered, since they contain precious metals. However, some asteroids have their orbits close to the orbit of the Earth. These nearby objects can pose a danger to our life in the planet, since some of them are large enough to cause catastrophic damage to the Earth. We will pay attention to the theme of deflecting a potentially dangerous asteroid. There are currently two main forms of this deviation: i) the impact of an object at high velocity with the asteroid, which can be a space vehicle or a smaller asteroid; ii) the use of a gravitational "tractor", which consist in placing an object (another asteroid or part of an asteroid), close to the body that is approaching the Earth, such that this gravitational interference can deflect its trajectory. In this work, we will evaluate the influence of gravitational perturbations in the most commonly mentioned asteroid deflection model in the literature, the kinetic impact deflection technique. With the impact, it is intended to change the kinetic energy of the asteroid, changing its orbit enough so that it does not present risks of impacts with the Earth., Comment: 8 pages, 7 figures, ICSSA

The aim of this work is to verify the stability of the proposed orbital solutions for the third moonlet (Delta) taking into account a realistic gravitational potential for the central body of the quadruple system (Alpha). We also aim to estimate the location and size of a stability region inside the orbit of Gamma. First, we created a set of test particles with intervals of semi-major axis, eccentricities, and inclinations that covers the region interior to the orbit of Gamma, including the proposed orbit of Delta and a wide region around it. We considered three different models for the gravitational potential of Alpha: irregular polyhedron, ellipsoidal body and oblate body. For a second scenario, Delta was considered a massive spherical body and Alpha an irregular polyhedron. Beta and Gamma were assumed as spherical massive bodies in both scenarios. The simulations showed that a large region of space is almost fully stable only when Alpha was modeled as simply as an oblate body. For the scenario with Delta as a massive body, the results did not change from those as massless particles. Beta and Gamma do not play any relevant role in the dynamics of particles interior to the orbit of Gamma. Delta's predicted orbital elements are fully unstable and far from the nearest stable region. The primary instability source is Alpha's elongated shape. Therefore, in the determination of the orbital elements of Delta, it must be taken into account the gravitational potential of Alpha assuming, at least, an ellipsoidal shape.

The spin-orbit obliquity of a planetary system constraints its formation history. A large obliquity may either indicate a primordial misalignment between the star and its gaseous disk or reflect the effect of different mechanisms tilting planetary systems after formation. Observations and statistical analysis suggest that system of planets with sizes between 1 and 4 R$_{\oplus}$ have a wide range of obliquities ($\sim0-30^{\circ}$), and that single- and multi-planet transiting have statistically indistinguishable obliquity distributions. Here, we revisit the ``breaking the chains'' formation model with focus in understanding the origin of spin-orbit obliquities. This model suggests that super-Earths and mini-Neptunes migrate close to their host stars via planet-disk gravitational interactions, forming chain of planets locked in mean-motion resonances. After gas-disk dispersal, about 90-99\% of these planetary systems experience dynamical instabilities, which spread the systems out. Using synthetic transit observations, we show that if planets are born in disks where the disk angular momentum is virtually aligned with the star's rotation spin, their final obliquity distributions peak at about $\sim$5 degrees or less, and the obliquity distributions of single and multi-planet transiting systems are statistically distinct. By treating the star-disk alignment as a free-parameter, we show that the obliquity distributions of single and multi-planet transiting systems only become statistically indistinguishable if planets are assumed to form in primordially misaligned natal disks with a ``tilt'' distribution peaking at $\gtrsim$10-20 deg. We discuss the origin of these misalignments in the context of star formation and potential implications of this scenario for formation models., Comment: 11 pages, 9 figures, 2 tables. Accepted for publication in MNRAS

Exomoons are a missing piece of exoplanetary science. Recently, two promising candidates were proposed, Kepler-1625 b-I and Kepler-1708 b-I. While the latter still lacks a dynamical analysis of its stability, Kepler-1625 b-I has already been the subject of several studies regarding its stability and origin. Moreover, previous works have shown that this satellite system could harbour at least two stable massive moons. Motivated by these results, we explored the stability of co-orbital exomoons using the candidates Kepler-1625 b-I and Kepler-1708 b-I as case studies. To do so, we performed numerical simulations of systems composed of the star, planet, and the co-orbital pair formed by the proposed candidates and another massive body. For the additional satellite, we varied its mass and size from a Mars-like to the case where both satellites have the same physical characteristics. We investigated the co-orbital region around the Lagrangian equilibrium point $L_4$ of the system, setting the orbital separation between the satellites from $\theta_{min} = 30^{\circ}$ to $\theta_{max} = 90^{\circ}$. Our results show that stability islands are possible in the co-orbital region of Kepler-1708 b-I as a function of the co-orbital companion's mass and angular separation. Also, we identified that resonances of librational frequencies, especially the 2:1 resonance, can constrain the mass of the co-orbital companion. On the other hand, we found that the proximity between the host planet and the star makes the co-orbital region around Kepler-1625 b-I unstable for a massive companion. Finally, we provide TTV profiles for a planet orbited by co-orbital exomoons., Comment: 15 pages, 11 figures, accepted for publication on MNRAS

The first proposed Brazilian mission to deep space, the ASTER mission, has the triple asteroid system (153591) 2001 SN263 as a target. One of the mission's main goals is to analyze the physical and dynamical structures of the system to understand its origin and evolution. The present work aims to analyze how the asteroid's irregular shape interferes with the stability around the system. The results show that the irregular shape of the bodies plays an important role in the dynamics nearby the system. For instance, the perturbation due to the (153591) 2001 SN263 Alpha's shape affects the stability in the (153591) 2001 SN263 Gamma's vicinity. Similarly, the (153591) 2001 SN263 Beta's irregularity causes a significant instability in its nearby environment. As expected, the prograde case is the most unstable, while the retrograde scenario presents more stability. Additionally, we investigate how the solar radiation pressure perturbs particles of different sizes orbiting the triple system. We found that particles with a 10-50 cm radius could survive the radiation pressure for the retrograde case. Meanwhile, to resist solar radiation, the particles in prograde orbit must be larger than the particles in retrograde orbits, at least one order of magnitude., Comment: 12 pages, 13 figures

The contact binary Kuiper Belt object (486958) Arrokoth, targeted by New Horizons mission, has a unique slope pattern, which is a result of its irregular bilobate surface shape and high spin period. Thus, some peculiar topographic regions on its surface are predisposed to lose or accumulate material, as a long circular depression feature, an impact crater called Maryland, on its small lobe. The equilibrium points of Arrokoth are also directly related to the structure of the environment near these surface features. In this work, we performed numerical simulations around Arrokoth to explore the fate of particles close to equilibrium points and their dynamical connection with its surface features. Our results suggest that most of these particles in a ring inside the Arrokoth's rotational Roche lobe fall near the equatorial region of the Maryland impact crater or close to the Bright spots area on the large lobe. Also, particles in a spherical cloud orbiting Arrokoth accumulate preferentially near low-mid-latitudes regions close to the longitudes of Maryland crater and Bright spots area. In contrast, a few particles will fall in regions diametrically opposite to them, as in the LL_Term boundary on the large lobe. High-latitudes are those more empty of impacts, as in polar sites. In addition, particles larger than a couple of microns are not significantly perturbed by solar radiation pressure in the environment around Arrokoth., Comment: 26 pages, 14 figures and 5 tables. Accepted for publication by the Astrophysics and Space Science. Simulation codes available on this https://github.com/a-amarante. Animated movies of simulation results available from this https://youtube.com/playlist?list=PLepZc10dZiUqwQ-psqfAKD1lZ2XdhnzGY

Since it was proposed the exomoon candidate Kepler-1625 b-I changed the way we see satellite systems. Because of its unusual physical characteristics, many questions about the stability and origin of this candidate were raised. Currently, we have enough theoretical studies to assure that if Kepler-1625 b-I is indeed confirmed, it will be stable. The origin of this candidate was also explored. Previous works indicated that the most likely scenario is capture, even though conditions for in situ formation were also investigated. In this work, we assume that Kepler-1625 b-I is an exomoon and studied the possibility of an additional, massive exomoon being stable in the same system. To model this scenario we perform N-body simulations of a system including the planet, Kepler-1625 b-I and one extra Earth-like satellite. Based on previous results, the satellites in our system will be exposed to tidal interactions with the planet and gravitation effects due to the rotation of the planet. We found that the satellite system around Kepler-1625 b is capable of harbouring two massive satellites. The extra Earth-like satellite would be stable in different locations between the planet and Kepler-1625 b-I, with a preference for regions inside $25$ $R_p$. Our results suggest that the strong tidal interactions between the planet and the satellites is an important mechanism to assure the stability of satellites in circular orbits closer to the planet, while the 2:1 mean motion resonance between the Earth-like satellite and Kepler-1625 b-I would provide stability for satellites in wider orbits., Comment: 15 pages, 10 figures, accepted for publication on MNRAS

The 99942 Apophis close encounter with Earth in 2029 may provide information about asteroid's physical characteristics and measurements of Earth's effects on the asteroid surface. In this work, we analysed the surface and the nearby dynamics of Apophis. The possible effects of its 2029 encounter on the surface and environment vicinity are also analysed. We consider a 340 metres polyhedron with a uniform density (1.29 g$\cdot$cm$^{-3}$, 2.2 g$\cdot$cm$^{-3}$ and 3.5 g$\cdot$cm$^{-3}$). The slope angles are computed, as well their variation that arises during the close approach. Such variation reaches 4$^{\circ}$ when low densities are used in our simulations and reaches 2$^{\circ}$ when the density is high. The zero-velocity curves, the equilibrium points, and their topological classification are obtained. We found four external equilibrium points and two of them are linearly stable. We also perform numerical simulations of bodies orbiting the asteroid, taking into account the irregular gravitational field of Apophis and two extra scenarios of perturbations: the solar radiation pressure and the Earth's perturbation during the close approach. The radiation pressure plays an important role in the vicinity of the asteroid, only cm-sized particles survived for the time of integration. For densities of 2.2 g$\cdot$cm$^{-3}$ and 3.5 g$\cdot$cm$^{-3}$, a region of 5 cm radius particles survived for 30 years of the simulation, and for 1.29 g$\cdot$cm$^{-3}$, only particles with 15 cm of radius survived. The ejections and collisions are about 30-50 times larger when the close encounter effect is added, but around 56-59% of particles still survive the encounter., Comment: 17 pages, 15 figures

Planets between 1-4 Earth radii with orbital periods <100 days are strikingly common. The migration model proposes that super-Earths migrate inwards and pile up at the disk inner edge in chains of mean motion resonances. After gas disk dispersal, simulations show that super-Earth's gravitational interactions can naturally break their resonant configuration leading to a late phase of giant impacts. The instability phase is key to matching the orbital spacing of observed systems. Yet, most previous simulations have modelled collisions as perfect accretion events, ignoring fragmentation. In this work, we investigate the impact of imperfect accretion on the breaking the chains scenario. We performed N-body simulations starting from distributions of planetary embryos and modelling the effects of pebble accretion and migration in the gas disk. Our simulations also follow the long-term dynamical evolution of super-Earths after the gas disk dissipation. We compared the results of simulations where collisions are treated as perfect merging events with those where imperfect accretion and fragmentation are allowed. We concluded that the perfect accretion is a suitable approximation in this regime, from a dynamical point of view. Although fragmentation events are common, only ~10% of the system mass is fragmented during a typical "late instability phase", with fragments being mostly reacreted by surviving planets. This limited total mass in fragments proved to be insufficient to alter qualitatively the final system dynamical configuration -- e.g. promote strong dynamical friction or residual migration -- compared to simulations where fragmentation is neglected., Comment: 13 pages, 8 figures and 1 table. Accepted for publication in MNRAS

PDS 110 is a young disk-hosting star in the Orion OB1A association. Two dimming events of similar depth and duration were seen in 2008 (WASP) and 2011 (KELT), consistent with an object in a closed periodic orbit. In this paper we present data from a ground-based observing campaign designed to measure the star both photometrically and spectroscopically during the time of predicted eclipse in September 2017. Despite high-quality photometry, the predicted eclipse did not occur, although coherent structure is present suggesting variable amounts of stellar flux or dust obscuration. We also searched for RV oscillations caused by any hypothetical companion and can rule out close binaries to 0.1 $M_\odot$. A search of Sonneberg plate archive data also enabled us to extend the photometric baseline of this star back more than 50 years, and similarly does not re-detect any deep eclipses. Taken together, they suggest that the eclipses seen in WASP and KELT photometry were due to aperiodic events. It would seem that PDS 110 undergoes stochastic dimmings that are shallower and shorter-duration than those of UX Ori variables, but may have a similar mechanism., Comment: Accepted to MNRAS; 12 pages, 7 figures; Supplementary photometric data in zipped latex source as all_photometry.csv

The large increase in exoplanet discoveries in the last two decades showed a variety of systems whose stability is not clear. In this work we chose the $\upsilon$ Andromedae system as the basis of our studies in dynamical stability. This system has a range of possible masses, as a result of detection by radial velocity method, so we adopted a range of masses for the planets $c$ and $d$ and applied the secular theory. We also performed a numerical integration of the 3-body problem for the system over a time span of 30 thousand years. The results exposed similarities between the secular perturbation theory and the numerical integration, as well as the limits where the secular theory did not present good results. The analysis of the results provided hints for the maximum values of masses and eccentricities for stable planetary systems similar to $\upsilon$ Andromedae.

It is undeniable that life as we know it depends on liquid water. It is difficult to imagine any biochemical machinery that does not require water. On Earth, life adapts to the most diverse environments and, once established, it is very resilient. Considering that water is a common compound in the Universe, it seems possible (maybe even likely) that one day we will find life elsewhere in the universe. In this study, we review the main aspects of water as an essential compound for life: when it appeared since the Big Bang, and where it spread throughout the diverse cosmic sites. Then, we describe the strong relation between water and life, as we know it., Comment: 32 pages, 7 figures, chapter 3 of the book "Habitability of the Universe before Earth"

The Cassini spacecraft found a new and unique ring that shares the trajectory of Janus and Epimetheus, co-orbital satellites of Saturn. Performing image analysis, we found this to be a continuous ring. Its width is between 30% and 50% larger than previously announced. We also verified that the ring behaves like a firefly. It can only be seen from time to time, when Cassini, the ring and the Sun are arranged in a particular geometric configuration, in very high phase angles. Otherwise, it remains "in the dark", not visible to Cassini's cameras. Through numerical simulations, we found a very short lifetime for the ring particles, less than a couple of decades. Consequently, the ring needs to be constantly replenished. Using a model of particles production due to micrometeorites impacts on the surfaces of Janus and Epimetheus, we reproduce the ring, explaining its existence and the "firefly" behavior.

In general, small bodies of the solar system, e.g., asteroids and comets, have a very irregular shape. This feature affects significantly the gravitational potential around these irregular bodies, which hinders dynamical studies. The Poincar\'e surface of sec- tion technique is often used to look for stable and chaotic regions in two-dimensional dynamic cases. In this work, we show that this tool can be useful for exploring the surroundings of irregular bodies such as the asteroid 4179 Toutatis. Considering a rotating system with a particle, under the effect of the gravitational field computed three-dimensionally, we define a plane in the phase space to build the Poincar\'e surface of sections. Despite the extra dimension, the sections created allow us to find trajec- tories and classify their stabilities. Thus, we have also been able to map stable and chaotic regions, as well as to find correlations between those regions and the contri- bution of the third dimension of the system to the trajectory dynamics as well. As examples, we show details of periodic(resonant or not) and quasi-periodic trajectories.

The orbital structure of the asteroid belt holds a record of the Solar System's dynamical history. The current belt only contains ${\rm \sim 10^{-3}}$ Earth masses yet the asteroids' orbits are dynamically excited, with a large spread in eccentricity and inclination. In the context of models of terrestrial planet formation, the belt may have been excited by Jupiter's orbital migration. The terrestrial planets can also be reproduced without invoking a migrating Jupiter; however, as it requires a severe mass deficit beyond Earth's orbit, this model systematically under-excites the asteroid belt. Here we show that the orbits of the asteroids may have been excited to their current state if Jupiter and Saturn's early orbits were chaotic. Stochastic variations in the gas giants' orbits cause resonances to continually jump across the main belt and excite the asteroids' orbits on a timescale of tens of millions of years. While hydrodynamical simulations show that the gas giants were likely in mean motion resonance at the end of the gaseous disk phase, small perturbations could have driven them into a chaotic but stable state. The gas giants' current orbits were achieved later, during an instability in the outer Solar System. Although it is well known that the present-day Solar System exhibits chaotic behavior, our results suggest that the early Solar System may also have been chaotic., Comment: Accepted for publication in ApJ

We present the results of an extensive study of the final stage of terrestrial planet formation in disks with different surface density profiles and for different orbits of Jupiter and Saturn. We carried out simulations for disk densities proportional to r^-0.5, r^-1, and r^-1.5, and also for partially depleted disks as in the recent model of Mars formation by Izidoro et al (2014). The purpose of our study is to determine how the final assembly of planets and their physical properties are affected by the total mass of the disk and its radial profile. Because of the important roles of secular resonances in orbits and properties of the final planets, we studied the effects of these resonances as well. We have divided this study into two parts. In Part 1, we are interested in examining the effects of secular resonances on the formation of Mars and orbital stability of terrestrial planets. In Part 2, our goal is to determine trends that may exist between the disk surface density profile and the final properties of terrestrial planets. In the context of the depleted disk model, results show that the nu_5 resonance does not have a significant effect on the final orbits of terrestrial planets. However, nu_6 and nu_16 resonances play important roles in clearing their affected areas ensuring that no additional mass will be scattered into the accretion zone of Mars so that it can maintain its mass and orbital stability. In Part 2, our results indicate that despite some small correlations, in general, no trend seems to exist between the disk surface density profile and the mean number of the final planets, their masses, time of formation, and distances to the central star. We present the results of our simulations and discuss their implications for the formation of Mars and other terrestrial planets, as well as the physical properties of these objects such as their masses and water contents., Comment: 36 pages, 14 figures. Part 1 presents a complete study of the effects of secular resonances in the classical and depleted-disk models for different disk surface density profiles. Part 2 (page 25) presents a detailed analysis of the orbital and physical properties of the final planets for different disk surface densities. Accepted for publication in Celestial Mechanics and Dynamical Astronomy

The Erigone family is a C-type group in the inner main belt. Its age has been estimated by several researchers to be less then 300 My, so it is a relatively young cluster. Yarko-YORP Monte Carlo methods to study the chronology of the Erigone family confirm results obtained by other groups. The Erigone family, however, is also characterized by its interaction with the $z_2$ secular resonance. While less than 15% of its members are currently in librating states of this resonance, the number of objects, members of the dynamical group, in resonant states is high enough to allow to use the study of dynamics inside the $z_2$ resonance to set constraints on the family age. Like the ${\nu}_{6}$ and $z_1$ secular resonances, the $z_2$ resonance is characterized by one stable equilibrium point at $\sigma = 180^{\circ}$ in the $z_2$ resonance plane $(\sigma, \frac{d\sigma}{dt})$, where $\sigma$ is the resonant angle of the $z_2$ resonance. Diffusion in this plane occurs on timescales of $\simeq 12$ My, which sets a lower limit on the Erigone family age. Finally, the minimum time needed to reach a steady-state population of $z_2$ librators is about 90 My, which allows to impose another, independent constraint on the group age., Comment: This paper has 11 pages, 12 figures, and 1 table. Accepted for publication in MNRAS

Context: Co-orbital systems are bodies that share the same mean orbit. They can be divided into different families according to the relative mass of the co-orbital partners and the particularities of their movement. Janus and Epimetheus are unique in that they are the only known co-orbital pair of comparable masses and thus the only known system in mutual horseshoe orbit. Aims: We aim to establish whether the Janus-Epimetheus system might have formed by disruption of an object in the current orbit of Epimetheus. Methods: We assumed that four large main fragments were formed and neglected smaller fragments. We used numerical integration of the full N-body problem to study the evolution of different fragment arrangements. Collisions were assumed to result in perfectly inelastic merging of bodies. We statistically analysed the outcome of these simulations to infer whether co-orbital systems might have formed from the chosen initial conditions. Results: Depending on the range of initial conditions, up to 9% of the simulations evolve into co-orbital systems. Initial velocities around the escape velocity of Janus yield the highest formation probability. Analysis of the evolution shows that all co-orbital systems are produced via secondary collisions. The velocity of these collisions needs to be low enough that the fragments can merge and not be destroyed. Generally, collisions are found to be faster than an approximate cut-off velocity threshold. However, given a sufficiently low initial velocity, up to 15% of collisions is expected to result in merging. Hence, the results of this study show that the considered formation scenario is viable., Comment: 9 Pages, 8 Figures

Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoplanetary disk between 1 and 3 AU. The Grand Tack model invokes a specific migration history of the giant planets to remove most of the mass initially beyond 1 AU and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas-drag, as has been proposed to explain the formation of close-in super Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar System. We performed a series of simulations of terrestrial planet formation and asteroid belt evolution starting from disks of planetesimals and planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Disks with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogs significantly more massive than the real planet. In contrast, a disk with a surface density gradient proportional to $r^{-5.5}$ reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disk profile can simultaneously explain the structure of the terrestrial planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario., Comment: Accepted for publication in MNRAS