Search

Neutral sodium (Na I) is an alkali metal with a favorable absorption cross section such that tenuous gases are easily illuminated at select transiting exoplanet systems. We examine both the time-averaged and time-series alkali spectral flux individually, over 4 nights at a hot Saturn system on a $\sim$ 2.8 day orbit about a Sun-like star WASP-49 A. Very Large Telescope/ESPRESSO observations are analyzed, providing new constraints. We recover the previously confirmed residual sodium flux uniquely when averaged, whereas night-to-night Na I varies by more than an order of magnitude. On HARPS/3.6-m Epoch II, we report a Doppler redshift at $v_{ \Gamma, \mathrm{NaD}} =$ +9.7 $\pm$ 1.6 km/s with respect to the planet's rest frame. Upon examining the lightcurves, we confirm night-to-night variability, on the order of $\sim$ 1-4 % in NaD rarely coinciding with exoplanet transit, not readily explained by stellar activity, starspots, tellurics, or the interstellar medium. Coincident with the $\sim$+10 km/s Doppler redshift, we detect a transient sodium absorption event dF$_{\mathrm{NaD}}$/F$_{\star}$ = 3.6 $\pm$ 1 % at a relative difference of $\Delta F_{\mathrm{NaD}} (t) \sim$ 4.4 $\pm$ 1 %, enduring $\Delta t_{\mathrm{NaD}} \gtrsim$ 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly $\sim$ -5.7 km/s, the radial velocity is rather at +15.4 km/s, far larger than any known exoplanet system. Given that the redshift magnitude v$_{\Gamma}$ is in between the Roche limit and dynamically stable satellite orbits, the transient sodium may be a putative indication of a natural satellite orbiting WASP-49 A b., Comment: Accepted to ApJ Letters (2024 August 2)

We present a plausible and coherent view of the evolution of the protosolar disk that is consistent with the cosmochemical constraints and compatible with observations of other protoplanetary disks and sophisticated numerical simulations. The evidence that high-temperature condensates, CAIs and AOAs, formed near the protosun before being transported to the outer disk can be explained by either an early phase of vigorous radial spreading of the disk, or fast transport of these condensates from the vicinity of the protosun towards large disk radii via the protostellar outflow. The assumption that the material accreted towards the end of the infall phase was isotopically distinct allows us to explain the observed dichotomy in nucleosynthetic isotopic anomalies of meteorites and leads to intriguing predictions on the isotopic composition of refractory elements in comets. When the infall of material waned, the disk started to evolve as an accretion disk. Initially, dust drifted inwards, shrinking the radius of the dust component to ~ 45 au, probably about 1/2 of the width of the gas component. Then structures must have emerged, producing a series of pressure maxima in the disk which trapped the dust on My timescales. This allowed planetesimals to form at radically distinct times without changing significantly of isotopic properties. There was no late accretion of material onto the disk via streamers. The disk disappeared in ~5 Myr, as indicated by paleomagnetic data in meteorites. In conclusion, the evolution of the protosolar disk seems to have been quite typical in terms of size, lifetime, and dust behavior, suggesting that the peculiarities of the Solar system with respect to extrasolar planetary system probably originate from the chaotic nature of planet formation and not at the level of the parental disk., Comment: In press in Astronomy and Astrophysics

Target of NASA's DART mission, the system of Didymos and Dimorphos will once again be visited by a space mission -- ESA's Hera mission, scheduled to be launch in 2024. Hera will arrive in the system approximately 4 years after the DART impact, a long period compared to Dimorphos' orbital period (about 12 hours). It is therefore imperative to understand the dynamics of material in this environment on a long timescale. Here, we explore the long-term dynamics of the binary system (65038) Didymos, in the context of the perturbed, planar, circular and restricted 3-body problem. We design an analytical description for a symmetrical top-shaped object, the shape assumed for the Didymos, while the Dimorphos is considered an ellipsoid. In the absence of external effects, we identify seven stable equatorial regions where particles persist for more than a decade. However, in the presence of the solar radiation effect, the lifetime of small particles (

We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K-M binary system. Analysis of the spectra and rotation period reveal it to be a young star with an age of $200^{+400}_{-200}$Myr. TOI-815b has a 11.2-day period and a radius of 2.94$\pm$0.05$\it{R_{\rm\mathrm{\oplus}}}$ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62$\pm$0.10$\it{R_{\rm\mathrm{\oplus}}}$, based on observations of three non-consecutive transits with TESS, while targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6$\pm$1.5 $\it{M_{\rm \mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=1.64$^{+0.33}_{-0.31}$gcm$^{-3}$) and 23.5$\pm$2.4$\it{M_{\rm\mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=7.2$^{+1.1}_{-1.0}$gcm$^{-3}$) respectively. Thus, the planets have very different masses, unlike the usual similarity of masses in compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those suffering strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere constituting a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3$\sigma$ level., Comment: 24 pages, 27 figures, 6 tables

Hot rocky super-Earths are thought to be sufficiently irradiated by their host star to melt their surface and thus allow for long-lasting magma oceans. Some processes have been proposed for such planets to have retained primordial hydrogen captured during their formation while moving inward in the planetary system. The new generation of space telescopes such as the JWST may provide observations precise enough to characterize the atmospheres and perhaps the interiors of such exoplanets. We use a vaporization model that calculates the gas-liquid equilibrium between the atmosphere (including hydrogen) and the magma ocean, to compute the elemental composition of a variety of atmospheres for different quantities of hydrogen. The elemental composition is then used in a steady-state atmospheric model to compute the atmospheric structure and generate synthetic emission spectra. With this method, we confirm previous results showing that silicate atmospheres exhibit a thermal inversion, with notably an emission peak of SiO at 9~$\mu m$. We compare our method to the literature on the inclusion of hydrogen in the atmosphere, and show hydrogen reduces the thermal inversion, because of the formation of H2O which has a strong greenhouse potential. However planets that are significantly irradiated by their host star are sufficiently hot to dissociate H2O and thus also maintain a thermal inversion. The observational implications are twofold: 1) H2O is more likely to be detected in colder atmospheres; 2) Detecting a thermal inversion in hotter atmospheres does not a priori exclude the presence of H (in its atomic form). Due to the impact of H on the overall chemistry and atmospheric structure, and therefore observations, we emphasize the importance of including volatiles in the calculation of the gas-liquid equilibrium. Finally, we provide a criterion to determine potential targets for observation., Comment: 22 pages, 17 figures + 12 figures in appendices. Accepted for publication in Astronomy & Astrophysics

Dimorphos' oblate shape challenges formation models. Landslides on Didymos, induced by YORP effect, probably created a debris ring from which Dimorphos would have formed. Nonetheless, ring-derived satellites typically form with a prolate lemon shape. In light of the newest Dimorphos shape model, we revisit our previous work, Madeira et al. (2023a), and conducted new 1D simulations with material deposition in an extended region from 1.0 to 1.5 Didymos radii. An instantaneous landslide leads to a fast formation of a prolate Dimorphos directly from the ring. Now, if Didymos progressively deposits mass, Dimorphos grows through low-velocity impacts with large impactor-to-target mass ratio (pyramidal regime growth). Even during rapid, day-scale depositions, Dimorphos experiences one of these impacts, while for slower depositions, the satellite formation is primarily via pyramidal impacts. This process might reshape the satellite into an oblate shape (Leleu et al., 2018) or even in a contact-binary shape, a scenario worthy of investigation that should be studied in the future with more suitable tools. Our conclusions can be applied to Dinkinesh's satellite, recently discovered by NASA's Lucy mission., Comment: Note accepted for publication in Icarus journal

Here we investigate how small amounts of hydrogen (much smaller than the mass of the exoplanet) above a magma ocean on a rocky exoplanet may modify the atmospheric chemistry and atmospheric escape.We use a chemical model of a magma ocean coupled to a gas equilibrium code. An energy-limited model is used to compute atmospheric escape. The composition of the vapor above a magma ocean is drastically modified by hydrogen, even for very modest amounts of H ($\ll 10^{-6}$ planetary mass). Hydrogen consumes much of the O$_2$(g), which, in turn, promotes the evaporation of metals and metal oxides (SiO, Mg, Na, K, Fe) from the magma ocean. Vast amounts of H$_2$O are produced by the same process. At high hydrogen pressures, new hydrogenated species such as SiH$_4$ form in the atmosphere. In all cases, H, H$_2$, and H$_2$O are the dominant nonmetal-bearing volatile species. Sodium is the dominant atmospheric metal-bearing species at T$<$ 2000K and low H content, whereas Fe is dominant at high H content and low temperature, while SiO predominates at T>3000 K. We find that the atmospheric Mg/Fe, Mg/Si, and Na/Si ratios deviate from those in the underlying planet and from the stellar composition. As such, their determination may constrain the planet's mantle composition and H content. As the presence of hydrogen promotes the evaporation of silicate mantles, it is conceivable that some high-density, irradiated exoplanets may have started life as hydrogen-bearing planets and that part of their silicate mantle evaporated (up to a few $10 \%$ of Si, O, and Fe) and was subsequently lost owing to the reducing role of H. Even very small amounts of H can alter the atmospheric composition and promote the evaporation to space of heavy species derived from the molten silicate mantle of rocky planets., Comment: Accepted for publication in A&A

We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by $\sim$ 734 days, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 $\pm$ 0.08 R$_\oplus$ and a period of 10.924709 $\pm$ 0.000032 days, whilst HD 15906 c has a radius of 2.93$^{+0.07}_{-0.06}$ R$_\oplus$ and a period of 21.583298$^{+0.000052}_{-0.000055}$ days. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 $\pm$ 13 K and 532 $\pm$ 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm ($\lesssim$ 700 K) sub-Neptune sized planets transiting a bright star (G $\leq$ 10 mag). It is an excellent target for detailed characterisation studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution., Comment: 30 pages, 20 figures, 11 tables (including appendix). Published in MNRAS

HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright ($G=9.0$ mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of $3.9 \pm 0.044$ $R_\oplus$ (HIP 9618 b) and $3.343 \pm 0.039$ $R_\oplus$ (HIP 9618 c). While the 20.77291 day period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-day gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE and CAFE revealed a mass of $10.0 \pm 3.1 M_\oplus$ for HIP 9618 b, which, according to our interior structure models, corresponds to a $6.8\pm1.4\%$ gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of $< 18M_\oplus$. Follow-up and archival RV measurements also reveal a clear long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion ($0.08^{+0.12}_{-0.05} M_\odot$) orbiting at $26^{+19}_{-11}$ au. This detection makes HIP 9618 one of only five bright ($K<8$ mag) transiting multi-planet systems known to host a planet with $P>50$ d, opening the door for the atmospheric characterisation of warm ($T_{\rm eq}<750$ K) sub-Neptunes., Comment: 19 pages, 16 figures, 9 tables. Accepted at MNRAS. CHEOPS, RV and ground-based photometric data is available on CDS at https://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/523/3069

Phobos is the target of the return sample mission Martian Moons eXploration by JAXA that will analyze in great details the physical and compositional properties of the satellite from orbit, from the surface and in terrestrial laboratories, giving clues about its formation. Some models propose that Phobos and Deimos were formed after a giant impact giving rise to an extended debris disk. Assuming that Phobos formed from a cascade of disruptions and re-accretions of several parent bodies in this disk, and that they are all characterized by a low material cohesion, Hesselbrock & Milton (2017) have showed that a recycling process may happen during the assembling of Phobos, by which Phobos' parents are destroyed into a Roche-interior ring and reaccreted several times. In the current paper we explore in details the recycling model, and pay particular attention to the characteristics of the disk using 1D models of disk/satellite interactions. In agreement with previous studies we confirm that, if Phobos' parents bodies are gravitational aggregates (rubble piles), then the recycling process does occur. However, Phobos should be accompanied today by a Roche-interior ring. Furthermore, the characteristics of the ring are not reconcilable with today`s observations of Mars' environment, which put stringent constraints on the existence of a ring around Mars. The recycling mechanism may or may not have occurred at the Roche limit for an old moon population, depending on their internal cohesion. However, the Phobos we see today cannot be the outcome of such a recycling process., Comment: Accept in The Astronomical Journal

Didymos is a binary near-Earth asteroid. It is the target of the DART and HERA space missions. The primary body, Didymos, rotates close to the spin at which it is expected to shed mass. The secondary body, Dimorphos, is a 140 meters moon that orbits the primary body in about 12 hours. Here we investigate the possible origin of Dimorphos. Using 1D models of ring/satellite interactions, we study the evolution of material lost from Didymos' surface and deposited as a ring at its equator. We find that due to viscous spreading, the ring spreads outside the Didymos' Roche limit forming moonlets. A fraction of the mass will form Dimorphos and a set of objects near the Roche limit, while most of the ring's mass falls back on Didymos. To match the properties of today's Dimorphos, the total mass that must be deposited in the ring is about 25% of Didymos' mass. It is possible that a fraction of the material travelled several times between the ring and the surface of Didymos. The models produce an orbit similar to that observed for a Didymos tidal parameter k2/Q<1e-5. If the ring deposition timescale is long (>100 yr) (so the material flux is small) Dimorphos could be irregularly shaped as it forms from the collision of similar-sized satellitesimals. However, the top-shape of Didymos is expected to be achieved due to a fast spin-up of the asteroid, which would result in a short deposition timescale (

This chapter of the Planetary Exploration Horizon 2061 Report reviews the way the six key questions about planetary systems, from their origins to the way they work and their habitability, identified in chapter 1, can be addressed by means of solar system exploration, and how one can find partial answers to these six questions by flying to the different provinces to the solar system: terrestrial planets, giant planets, small bodies, and up to its interface with the local interstellar medium. It derives from this analysis a synthetic description of the most important space observations to be performed at the different solar system objects by future planetary exploration missions. These observation requirements illustrate the diversity of measurement techniques to be used as well as the diversity of destinations where these observations must be made. They constitute the base for the identification of the future planetary missions we need to fly by 2061, which are described in chapter 4. Q1- How well do we understand the diversity of planetary systems objects? Q2- How well do we understand the diversity of planetary system architectures? Q3- What are the origins and formation scenarios for planetary systems? Q4- How do planetary systems work? Q5- Do planetary systems host potential habitats? Q6- Where and how to search for life?, Comment: 107 pages, 37 figures, Horizon 2061 is a science-driven, foresight exercise, for future scientific investigations

The origin and evolution of Martian moons have been intensively debated in recent years. It is proposed that Phobos and Deimos may originate directly from a splitting of an ancestral moon orbiting at around the Martian synchronous orbit. At this hypothetical splitting, the apocenter of the inner moon (presumed as Phobos) and the pericenter of the outer moon (presumed as Deimos) are reported to coincide, in that, their semi-major axes reside inside and outside the Martian synchronous orbit with non-zero eccentricities, respectively. However, the successive orbital evolution of the two moons is not studied. Here, we perform direct $N$-body orbital integrations of the moons, including the Martian oblateness of the $J_2$ and $J_4$ terms. We show that the two moons, while they precess, likely collide within $\sim 10^4$ years with an impact velocity of $v_{\rm imp} \sim 100-300$ m s$^{-1}$ ($\sim 10-30$ times moons' escape velocity) and with an isotropic impact direction. The impact occurs around the apocenter and the pericenter of the inner and outer moons, respectively, where the timescale of this periodic orbital alignment is regulated by the precession. By performing additional impact simulations, we show that such a high-velocity impact likely results in a disruptive outcome, forming a debris ring at around the Martian synchronous orbit, from which several small moons would accrete. Such an evolutionary path would eventually form a different Martian moons system from the one we see today. Therefore, it seems unlikely that Phobos and Deimos are split directly from a single ancestral moon., Comment: 11 pages, 5 Figures, accepted for publication in Planetary Science Journal (PSJ)

Context: TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young ($340\pm80$ Myr) K-type star. Although a validated planetary system, the orbits of the two outer planets were unconstrained as only two non-consecutive transits were seen in TESS photometry. This left 11 and 7 possible period aliases for each. Aims: To reveal the true orbits of these two long-period planets, precise photometry targeted on the highest-probability period aliases is required. Long-term monitoring of transits in multi-planet systems can also help constrain planetary masses through TTV measurements. Methods: We used the MonoTools package to determine which aliases to follow, and then performed space-based and ground-based photometric follow-up of TOI-2076 c and d with CHEOPS, SAINT-EX, and LCO telescopes. Results: CHEOPS observations revealed a clear detection for TOI-2076 c at $P=21.01538^{+0.00084}_{-0.00074}$ d, and allowed us to rule out three of the most likely period aliases for TOI-2076 d. Ground-based photometry further enabled us to rule out remaining aliases and confirm the $P=35.12537\pm0.00067$ d alias. These observations also improved the radius precision of all three sub-Neptunes to $2.518\pm0.036$, $3.497\pm0.043$, and $3.232\pm0.063$ $R_\oplus$. Our observations also revealed a clear anti-correlated TTV signal between planets b and c likely caused by their proximity to the 2:1 resonance, while planets c and d appear close to a 5:3 period commensurability, although model degeneracy meant we were unable to retrieve robust TTV masses. Their inflated radii, likely due to extended H-He atmospheres, combined with low insolation makes all three planets excellent candidates for future comparative transmission spectroscopy with JWST., Comment: 18 pages, 7 figure, 8 tables. Accepted for publication in Astronomy & Astrophysics. Photometry available on CDS/Vizier. Python package presented for modelling duotransiting planet candidates available at https://github.com/hposborn/MonoTools. Modelling & figure-creation code available at https://github.com/hposborn/TOI2076

We report the discovery and characterisation of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in TESS photometry. To characterise the system, we performed and retrieved CHEOPS, TESS, and ground-based photometry, HARPS high-resolution spectroscopy, and Gemini speckle imaging. We characterise the host star and determine $T_{\rm eff, \star}=4734\pm67$ K, $R_{\star}=0.726\pm0.007$ $R_{\odot}$, and $M_{\star}=0.748\pm0.032$ $M_{\odot}$. We present a novel detrending method based on PSF shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of $P_{\rm b}=6.44387\pm0.00003$ d, a radius of $R_{\rm b}=2.59\pm0.04$ $R_{\oplus}$, and a mass of $M_{\rm b}=13.5_{-1.8}^{+1.7}$ $M_{\oplus}$, whilst TOI-1064 c has an orbital period of $P_{\rm c}=12.22657^{+0.00005}_{-0.00004}$ d, a radius of $R_{\rm c}=2.65\pm0.04$ $R_{\oplus}$, and a 3$\sigma$ upper mass limit of 8.5 ${\rm M_{\oplus}}$. From the high-precision photometry we obtain radius uncertainties of $\sim$1.6%, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterised sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further RVs are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass-radius space, and it allows us to identify a trend in bulk density-stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets., Comment: 30 pages, 24 figures, 6 tables including the Appendix; accepted for publication in MNRAS

The formation of planetesimals is expected to occur via particle-gas instabilities that concentrate dust into self-gravitating clumps. Triggering these instabilities requires the prior pileup of dust in the protoplanetary disk. Until now, this has been successfully modeled exclusively at the disk's snowline, whereas rocky planetesimals in the inner disk were obtained only by assuming either unrealistically large particle sizes or an enhanced global disk metallicity. However, planetesimal formation solely at the snowline is difficult to reconcile with the early and contemporaneous formation of iron meteorite parent bodies with distinct oxidation states and isotopic compositions, indicating formation at different radial locations in the disk. Here, by modeling the evolution of a disk with ongoing accretion of material from the collapsing molecular cloud, we show that planetesimal formation may have been triggered within the first 0.5 million years by dust pileup at both the snowline (at approximately 5 au) and the silicate sublimation line (at approximately 1 au), provided turbulent diffusion was low. Particle concentration at approximately 1 au is due to the early outward radial motion of gas and is assisted by the sublimation and recondensation of silicates. Our results indicate that, although the planetesimals at the two locations formed about contemporaneously, those at the snowline accreted a large fraction of their mass (approximately 60 percent) from materials delivered to the disk in the first few 10,000 yr, whereas this fraction is only 30 percent for the planetesimals formed at the silicate line. Thus, provided that the isotopic composition of the delivered material changed with time, these two planetesimal populations should have distinct isotopic compositions, consistent with observations., Comment: Published online in Nature Astronomy on Dec. 22, 2021

The formation of planetesimals was a key step in the assemblage of planetary bodies, yet many aspects of their formation remain poorly constrained. Notably, the mechanism by which chondrules -- sub-millimetric spheroids that dominate primitive meteorites -- were incorporated into planetesimals remains poorly understood. Here we classify and analyze particle-size distributions in various CO carbonaceous chondrites found in the Atacama Desert. Our results show that the average circle-equivalent diameters of chondrules define a positive trend with the petrographic grade, which reflects the progressive role of thermal metamorphism within the CO parent body. We show that this relationship could not have been established by thermal metamorphism alone but rather by aerodynamic sorting during accretion. By modeling the self-gravitational contraction of clumps of chondrules, we show that (i) the accretion of the CO parent body(ies) would have generated a gradual change of chondrule size with depth in the parent body, with larger chondrules being more centrally concentrated than smaller ones, and (ii) any subsequent growth by pebble accretion would have been insignificant. These findings give substantial support to the view that planetesimals formed via gravitational collapse., Comment: Accepted in ApJL. 24 pages, 3 figures, 2 tables, 1 appendix

Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior, and orbital properties of the planetary companions. $\nu^2$ Lupi (HD 136352) is a naked-eye ($V = 5.78$) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity monitoring (Udry et al. 2019). The two inner planets (b and c) were recently found to transit (Kane et al. 2020), prompting a photometric follow-up by the brand-new $CHaracterising\:ExOPlanets\:Satellite\:(CHEOPS)$. Here, we report that the outer planet d is also transiting, and measure its radius and mass to be $2.56\pm0.09$ $R_{\oplus}$ and $8.82\pm0.94$ $M_{\oplus}$, respectively. With its bright Sun-like star, long period, and mild irradiation ($\sim$5.7 times the irradiation of Earth), $\nu^2$ Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b likely has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the $\nu^2$ Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets., Comment: Published in Nature Astronomy. 60 pages, 18 Figures, 6 Tables. This is the authors' version of the manuscript. The final authenticated version is available online at https://www.nature.com/articles/s41550-021-01381-5

Pressure maxima are regions in protoplanetary disks where pebbles can be trapped because of the local absence of pressure gradient. These regions could be ideal places to form planetesimals or to isolate isotopic reservoirs. Observations of protoplanetary disks show that dusty rings structures are common, and pressure maxima are sometime invoked as a possible explanation. In our Solar System, pressure bumps have been suggested as a possible mechanism for separating reservoirs with different nucleosynthetic compositions. In this letter we detail a mechanism by which pressure maxima form just inward the snow-line in stratified disks. This mechanism does not need the presence of a planet. Using a combination of analytical and numerical investigation we explore the range of conditions for a pressure maximum to form inside the dead-zone and just inward the snow-line. When the vertically averaged $\alpha$ is a decreasing function of surface density then the release of water vapor at the snow-line lowers the sound velocity, and in turn, a pressure bump appears. This requires a constant inflow of icy pebbles with pebbles influx to gas influx $>0.6$ for a power law disk with $1\%$ ice/gas ratio, and $>1.8$ for a disk with ice/gas ratio $\sim 0.3\%$. If these conditions are met, then a Pressure-maximum appears just inward the snow-line due to a process coupling the dead and active layers at the evaporation front. The pressure bump survives as long as the icy pebble flux is high enough. The formation of the pressure bump is triggered by the drop of sound velocity inward the snow-line, due to the release of water vapor. This mechanism is promising for isolating early reservoirs carrying different isotopic signatures in the Solar System and for promoting dry planetesimal formation inward the snow-line, provided the vertically averaged description of a dead-zone is valid., Comment: 12 pages, 6 Figures, 1 Figures in Appendix, accepted for publication in Astronomy & Astrophysics (A&A)

Dynamical scenarios of terrestrial planets formation involve strong perturbations of the inner part of the solar system by the giant-planets, leading to enhanced impact velocities and subsequent collisional erosion. We quantitatively estimate the effect of collisional erosion on the resulting composition of Earth, and estimate how it may provide information on the dynamical context of its formation. We simulate and quantify the erosion of Earth's crust in the context of Solar System formation scenarios, including the classical model and Grand Tack scenario that invokes orbital migration of Jupiter during the gaseous disk phase (Walsh et al., 2011; Raymond et al., 2018). We find that collisional erosion of the early crust is unlikely to produce an excess of about 6% of the Sm/Nd ratio in terrestrial rock samples compared to chondrites for most simulations. Only Grand Tack simulations in which the last giant impact on Earth occurred later than 50 million years after the start of Solar System formation can account for such an offset. However, this time frame is consistent with current cosmochemical and dynamical estimates of the Moon forming impact (Chyba, 1991; Walker, 2009; Touboul et al.,2007, 2009, 2015; Pepin and Porcelli, 2006; Norman et al., 2003; Nyquist et al., 2006; Boyet et al.,2015). Such a late fractionation in the Sm/Nd ratio is unlikely to be responsible for a 20-ppm $^{142}$Nd excess in terrestrial rocks due to the half life of the radiogenic system. Additionally, such a large and late fractionation in the Sm/Nd ratio would accordingly induce non-observed anomalies in the $^{143}$Nd/$^{144}$Nd ratio. Considering our results, the Grand Tack model with a late Moon-forming impact cannot be easily reconciled with the Nd isotopic Earth contents., Comment: 22 pages, 3 figures, supplementary, to be published

While it is generally accepted that the magnetic field and its non-ideal effects play important roles during the stellar formation, simple models of pure hydrodynamics and angular momentum conservation are still widely employed in the studies of disk assemblage in the framework of the so-called "alpha-disk" model due to their simplicity. There has only been a few efforts trying to bridge the gap between a collapsing prestellar core and a developed disk. The goal of the present work is to revisit the assemblage of the protoplanetary disk (PPD), by performing 3D MHD simulations with ambipolar diffusion and full radiative transfer. We follow the global evolution of the PPD from the prestellar core collapse for 100 kyr, with resolution of one AU. The formed disk is more realistic and is in agreement with recent observations of disks around class-0 young stellar objects. The mass flux arriving onto the disk and the radial mass accretion rate within the disk are measured and compared to analytical self-similar models. The surface mass flux is very centrally peaked, implying that most of the mass falling onto the star does not transit through the mid-plane of the disk. The disk mid-plane is almost dead to turbulence, whereas upper layers and the disk outer edge are very turbulent. The snow-line is significantly further away than in a passive disk. We developed a zoomed rerun technique to quickly obtain a reasonable disk that is highly stratified, weakly magnetized inside, and strongly magnetized outside. During the class-0 phase of PPD formation, the interaction between the disk and the infalling envelope is important and ought not be neglected. Accretion onto the star is found to mostly depend on dynamics of the collapsing envelope, rather than the detailed disk structure., Comment: Accepted for publication in A\&A on Feb. 14th 2021

The CHaracterising ExOPlanet Satellite (CHEOPS) was selected in 2012, as the first small mission in the ESA Science Programme and successfully launched in December 2019. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys and to following phase curves. CHEOPS will provide prime targets for future spectroscopic atmospheric characterisation. Requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars in the magnitude range between 6 and 9 by achieving a photometric precision of 20 ppm in 6 hours of integration. For K stars in the magnitude range between 9 and 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration. This is achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter telescope. The 280 kg spacecraft has a pointing accuracy of about 1 arcsec rms and orbits on a sun-synchronous dusk-dawn orbit at 700 km altitude. The nominal mission lifetime is 3.5 years. During this period, 20% of the observing time is available to the community through a yearly call and a discretionary time programme managed by ESA., Comment: Submitted to Experimental Astronomy

Planets form in protoplanetary discs. Their masses, distribution, and orbits sensitively depend on the structure of the protoplanetary discs. However, what sets the initial structure of the discs in terms of mass, radius and accretion rate is still unknown. We perform non-ideal MHD numerical simulations using the adaptive mesh refinement code Ramses, of a collapsing, one solar mass, molecular core to study the disc formation and early, up to 100 kyr, evolution, paying great attention to the impact of numerical resolution and accretion scheme. We found that while the mass of the central object is almost independent of the numerical parameters such as the resolution and the accretion scheme onto the sink particle, the disc mass, and to a lower extent its size, heavily depend on the accretion scheme, which we found, is itself resolution dependent. This implies that the accretion onto the star and through the disc are largely decoupled. For a relatively large domain of initial conditions (except at low magnetisation), we found that the properties of the disc do not change too significantly. In particular both the level of initial rotation and turbulence do not influence the disc properties provide the core is sufficiently magnetized. After a short relaxation phase, the disc settles in a stationary state. It then slowly grows in size but not in mass. The disc itself is weakly magnetized but its immediate surrounding is on the contrary highly magnetized. Our results show that the disc properties directly depend on the inner boundary condition, i.e. the accretion scheme onto the central object, suggesting that the disc mass is eventually controlled by the small scale accretion process, possibly the star-disc interaction. Because of ambipolar diffusion and its significant resistivity, the disc diversity remains limited and except for low magnetisation, their properties are (abridged)., Comment: accepted for publication in A&A

The isotopic heterogeneity of the Solar System shown by meteorite analyses is more pronounced for its earliest objects, the Calcium-Aluminum-rich Inclusions (CAIs). This suggests that it was inherited from spatial variations in different stardust populations in the protosolar cloud. We model the formation of the solar protoplanetary disk following its collapse and find that the solid-weighted standard deviation of different nucleosynthetic contributions in the disk is reduced by one order of magnitude compared to the protosolar cloud, whose successive isotopic signatures are fossilized by CAIs. The enrichment of carbonaceous chondrites in r-process components, whose proportions are inferred to have diminished near the end of infall, is consistent with their formation at large heliocentric distances, where the early signatures would have been preferentially preserved after outward advection. We also argue that thermal processing had little effect on the (mass-independent) isotopic composition of bulk meteorites for refractory elements., Comment: 20 pages, 10 figures

The short-lived radionuclide $^{26}$Al is widely used to determine the relative ages of chondrite components and timescales of physical and thermal events that attended the formation of the Solar System. However, an important assumption for using $^{26}$Al as a chronometer is its homogeneous distribution in the disk. Yet, the oldest components in chondrites, the Ca-Al-rich inclusions (CAIs), which are usually considered as time anchors for this chronometer, show evidence of $^{26}$Al/$^{27}$Al variations independent of radioactive decay. Since their formation epoch may have been contemporaneous with the collapse of the parent cloud that formed the disk, this suggests that $^{26}$Al was heteregeneously distributed in the cloud. We model the collapse of such an heterogeneous cloud, using two different $^{26}$Al distributions (monotonic and non-monotonic), and follow its re-distribution in the first condensates and bulk dust that populate the forming disk. We find that CAIs inherit the $^{26}$Al/$^{27}$Al ratio of the matter infalling at the time of their formation, so that variations of $^{26}$Al/$^{27}$Al among primordial CAIs can be accounted for, independently of radioactive decay. The prevalence of a canonical ratio among them and its necessity for the differentiation of the first planetesimals suggest a (monotonic) scenario where $^{26}$Al sharply rose relatively close to the center of the protosolar cloud and essentially remained at a high level outward (rather than decreased since). As the $ ^{26}$Al abundance would be relatively homogeneous after cessation of infall, this would warrant the use of the Al-Mg chronometer from the formation of "regular" CAIs onward, to chondrules and chondrite accretion., Comment: ArXiv version

Almost all the planets of our solar system have moons. Each planetary system has however unique characteristics. The Martian system has not one single big moon like the Earth, not tens of moons of various sizes like for the giant planets, but two small moons: Phobos and Deimos. How did form such a system? This question is still being investigated on the basis of the Earth-based and space-borne observations of the Martian moons and of the more modern theories proposed to account for the formation of other moon systems. The most recent scenario of formation of the Martian moons relies on a giant impact occurring at early Mars history and having also formed the so-called hemispheric crustal dichotomy. This scenario accounts for the current orbits of both moons unlike the scenario of capture of small size asteroids. It also predicts a composition of disk material as a mixture of Mars and impactor materials that is in agreement with remote sensing observations of both moon surfaces, which suggests a composition different from Mars. The composition of the Martian moons is however unclear, given the ambiguity on the interpretation of the remote sensing observations. The study of the formation of the Martian moon system has improved our understanding of moon formation of terrestrial planets: The giant collision scenario can have various outcomes and not only a big moon as for the Earth. This scenario finds a natural place in our current vision of the early solar system when conditions were favorable for giant collisions to occur. The next step in exploration of Martian moon is a sample return mission to test the giant collision scenario for their origin, and to provide tests of models of early solar system dynamics since Mars may retain material exchanged between the inner and outer solar system., Comment: 30 pages, 8 figures, 2 tables. Accepted for publication in the Oxford Research Encyclopedia of Planetary Science

It is important to clarify where and when rocky and icy planetesimals are formed in a viscously evolving disk. We wish to understand how local runaway pile-up of solids occurs inside or outside the snow line. We assume an icy pebble contains micron-sized silicate grains that are uniformly mixed with ice and are released during the ice sublimation. Using a local one-dimensional code, we solve the radial drift and the turbulent diffusion of solids and the water vapor, taking account of their sublimation/condensation around the snow line. We systematically investigate effects of back-reactions of the solids to gas on the radial drift and diffusion of solids, scale height evolution of the released silicate particles, and possible difference in effective viscous parameters between that for turbulent diffusion ($\alpha_{\rm tur}$) and that for the gas accretion rate onto the central star ($\alpha_{\rm acc}$). We study the dependence on the ratio of the solid mass flux to the gas ($F_{\rm p/g}$). We show that the favorable locations for the pile-up of silicate grains and icy pebbles are the regions in the proximity of the water snow line inside and outside it, respectively. We found that runaway pile-ups occur when both the back-reactions for radial drift and diffusion are included. In the case with only the back-reaction for the radial drift, no runaway pile-up is found except for extremely high pebble flux, while the condition of streaming instability can be satisfied for relatively large $F_{\rm p/g}$ as found in the past literatures. If the back-reactions for radial diffusion is considered, the runaway pile-up occurs for reasonable value of pebble flux. The runaway pile-up of silicate grains that would lead to formation of rocky planetesimals occurs for $\alpha_{\rm tur} \ll \alpha_{\rm acc}$, while the runaway pile-up of icy pebbles is favored for $\alpha_{\rm tur} \sim \alpha_{\rm acc}$., Comment: Accepted for publication in Astronomy & Astrophysics (A&A); 13pages, 8 figures

Uranus and Neptune, and their diverse satellite and ring systems, represent the least explored environments of our Solar System, and yet may provide the archetype for the most common outcome of planetary formation throughout our galaxy. Ice Giants will be the last remaining class of Solar System planet to have a dedicated orbital explorer, and international efforts are under way to realise such an ambitious mission in the coming decades. In 2019, the European Space Agency released a call for scientific themes for its strategic science planning process for the 2030s and 2040s, known as Voyage 2050. We used this opportunity to review our present-day knowledge of the Uranus and Neptune systems, producing a revised and updated set of scientific questions and motivations for their exploration. This review article describes how such a mission could explore their origins, ice-rich interiors, dynamic atmospheres, unique magnetospheres, and myriad icy satellites, to address questions at the heart of modern planetary science. These two worlds are superb examples of how planets with shared origins can exhibit remarkably different evolutionary paths: Neptune as the archetype for Ice Giants, whereas Uranus may be atypical. Exploring Uranus' natural satellites and Neptune's captured moon Triton could reveal how Ocean Worlds form and remain active, redefining the extent of the habitable zone in our Solar System. For these reasons and more, we advocate that an Ice Giant System explorer should become a strategic cornerstone mission within ESA's Voyage 2050 programme, in partnership with international collaborators, and targeting launch opportunities in the early 2030s., Comment: 34 pages, 9 figures, accepted to Planetary and Space Science

Chondritic meteorites, the building blocks of terrestrial planets, are made of an out-of-equilibrium assemblage of solids formed at high and low temperatures, either in our Solar system or previous generations of stars. This was considered for decades to result from large scale transport processes in the Sun's isolated accretion disk. However, mounting evidences suggest that refractory inclusions in chondrites formed contemporaneously with the disk building. Here we numerically investigate, using a 1D model and several physical and chemical processes, the formation and transport of rocky materials during the collapse of the Sun's parent cloud and the consequent Solar Nebula assembling. The interplay between the cloud collapse, the dynamics of gas and dust, vaporization, recondensation and thermal processing of different species in the disk, results in a local mixing of solids with different thermal histories. Moreover, our results also explains the overabundance of refractory materials far from the Sun and their short formation timescales, during the first tens of kyr of the Sun, corresponding to class 0-I, opening new windows into the origin of the compositional diversity of chondrites., Comment: Received on 13/08/2018, accepted 24/10/2018. Astrophysical Journal Letters

Rings are ubiquitous around giant planets in our Solar System. They evolve jointly with the nearby satellite system. They could form either during the giant planet formation process or much later, as a result of large scale dynamical instabilities either in the local satellite system, or at the planetary scale. We review here the main characteristics of rings in our solar system, and discuss their main evolution processes and possible origin. We also discuss the recent discovery of rings around small bodies., Comment: Accepted for the Handbook of Exoplanets

Several tens of white dwarfs are known to host circumstellar discs of dusty debris, thought to arise from the tidal disruption of rocky bodies originating in the star's remnant planetary system. This paper investigates the evolution of such discs if they are very massive, as may be the case if their progenitor was a terrestrial planet, moon, or dwarf planet. Assuming the discs are physically thin and flat, like Saturn's rings, their evolution is governed by Poynting-Robertson drag or viscous spreading, where the disc's effective viscosity is due to self-gravity wakes. For discs with masses >10^26 g, located in the outer parts of the tidal disruption zone, viscous spreading dominates the evolution, and mass is transported both in- and outwards. When outwards-spreading material flows beyond the Roche limit, it coagulates into new (minor) planets in a process analogous to the ongoing formation of moonlets at the outer edge of Saturn's rings. The newly formed bodies migrate outwards by exchanging angular momentum with the disc and coalesce into larger objects through mutual collisions. Eventually, the disc's Roche-limit overflow recycles tens of percent of the original disc mass; most ends up in a single large body near 2:1 mean-motion resonance with the disc's outer edge. Hence, the recycling of a tidally disrupted super-Earth, for example, could yield an Earth-mass planet on a ~10-h orbit, located in the habitable zone for 2-to-10-Gyr-old white dwarfs. The recycling process also creates a population of smaller bodies just outside the Roche limit, which may explain the minor planets recently postulated to orbit WD 1145+017., Comment: 28 pages, 11 figures, accepted for publication in MNRAS

Recent works have shown that Martian moons Phobos and Deimos may have accreted within a giant impact-generated disk whose composition is about an equal mixture of Martian material and impactor material. Just after the giant impact, the Martian surface is heated up to $\sim3000-6000$ K and the building blocks of moons, including volatile-rich vapor, are heated up to $\sim2000$ K. In this paper, we investigate the volatile loss from the building blocks of Phobos and Deimos by hydrodynamic escape of vapor and radiation pressure on condensed particles. We show that a non-negligible amount of volatiles ($> 10\%$ of the vapor with temperature $> 1000$ K via hydrodynamic escape, and moderately volatile dusts that condense at $\sim700-2000$ K via radiation pressure) could be removed just after the impact during their first signle orbit from their pericenters to apocenters. Our results indicate that bulk Phobos and Deimos are depleted in volatile elements. Together with future explorations such as JAXA's MMX (Martian Moons eXploration) mission, our results would be used to constrain the origin of Phobos and Deimos., Comment: 15 pages, 8 figures. Accepted for publication in ApJ

The origin of Phobos and Deimos in a giant impact generated disk is gaining larger attention. Although this scenario has been the subject of many studies, an evaluation of the chemical composition of the Mars' moons in this framework is missing. The chemical composition of Phobos and Deimos is unconstrained. The large uncertainty about the origin of the mid-infrared features, the lack of absorption bands in the visible and near-infrared spectra, and the effects of secondary processes on the moons' surface make the determination of their composition very difficult from remote sensing data. Simulations suggest a formation of a disk made of gas and melt with their composition linked to the nature of the impactor and Mars. Using thermodynamic equilibrium we investigate the composition of dust (condensates from gas) and solids (from a cooling melt) that result from different types of Mars impactors (Mars-, CI-, CV-, EH-, comet-like). Our calculations show a wide range of possible chemical compositions and noticeable differences between dust and solids depending on the considered impactors. Assuming Phobos and Deimos as result of the accretion and mixing of dust and solids, we find that the derived assemblage (dust rich in metallic-iron, sulphides and/or carbon, and quenched solids rich in silicates) can be compatible with the observations. The JAXA's MMX (Martian Moons eXploration) mission will investigate the physical and chemical properties of the Maroons, especially sampling from Phobos, before returning to Earth. Our results could be then used to disentangle the origin and chemical composition of the pristine body that hit Mars and suggest guidelines for helping in the analysis of the returned samples., Comment: Accepted for publication in ApJ (13/12/2017)

Phobos and Deimos are the two small Martian moons, orbiting almost on the equatorial plane of Mars. Recent works have shown that they can accrete within an impact-generated inner dense and outer light disk, and that the same impact potentially forms the Borealis basin, a large northern hemisphere basin on the current Mars. However, there is no a priori reason for the impact to take place close to the north pole (Borealis present location) nor to generate a debris disk in the equatorial plane of Mars (in which Phobos and Deimos orbit). In this paper, we investigate these remaining issues on the giant impact origin of the Martian moons. First, we show that the mass deficit created by the Borealis impact basin induces a global reorientation of the planet to realign its main moment of inertia with the rotation pole (True Polar Wander). This moves the location of the Borealis basin toward its current location. Next, using analytical arguments, we investigate the detailed dynamical evolution of the eccentric inclined disk from the equatorial plane of Mars that is formed by the Martian-moon-forming impact. We find that, as a result of precession of disk particles due to the Martian dynamical flattening $J_{2}$ term of its gravity field and particle-particle inelastic collisions, eccentricity and inclination are damped and an inner dense and outer light equatorial circular disk is eventually formed. Our results strengthen the giant impact origin of Phobos and Deimos that can finally be tested by a future sample return mission such as JAXA's Martian Moons eXploration (MMX) mission., Comment: 13 pages, 5 figures. Accepted for publication in ApJ

Phobos and Deimos are the two small moons of Mars. Recent works have shown that they can accrete within an impact-generated disk. However, the detailed structure and initial thermodynamic properties of the disk are poorly understood. In this paper, we perform high-resolution SPH simulations of the Martian moon-forming giant impact that can also form the Borealis basin. This giant impact heats up the disk material (around $\sim 2000$ K in temperature) with an entropy increase of $\sim 1500$ J K$^{-1}$ kg$^{-1}$. Thus, the disk material should be mostly molten, though a tiny fraction of disk material ($< 5\%$) would even experience vaporization. Typically, a piece of molten disk material is estimated to be meter sized due to the fragmentation regulated by their shear velocity and surface tension during the impact process. The disk materials initially have highly eccentric orbits ($e \sim 0.6-0.9$) and successive collisions between meter-sized fragments at high impact velocity ($\sim 3-5$ km s$^{-1}$) can grind them down to $\sim100 \mu$m-sized particles. On the other hand, a tiny amount of vaporized disk material condenses into $\sim 0.1 \mu$m-sized grains. Thus, the building blocks of the Martian moons are expected to be a mixture of these different sized particles from meter-sized down to $\sim 100 \mu$m-sized particles and $\sim 0.1 \mu$m-sized grains. Our simulations also suggest that the building blocks of Phobos and Deimos contain both impactor and Martian materials (at least 35%), most of which come from the Martian mantle (50-150 km in depth; at least 50%). Our results will give useful information for planning a future sample return mission to Martian moons, such as JAXA's MMX (Martian Moons eXploration) mission., Comment: 11 pages, 6 figures. Accepted for publication in ApJ

The hypothesis of a recent origin of Saturn's rings and its mid-sized moons is actively debated. It was suggested that a proto-Rhea and a proto-Dione might have collided recently, giving birth to the modern system of mid-sized moons. It is also suggested that the rapid viscous spreading of the debris may have implanted mass inside Saturn's Roche limit, giving birth to the modern Saturn's ring system. However, this scenario has been only investigated in very simplified way for the moment. This paper investigates it in detail to assess its plausibility by using $N$-body simulations and analytical arguments. When the debris disk is dominated by its largest remnant, $N$-body simulations show that the system quickly re-accrete into a single satellite without significant spreading. On the other hand, if the disk is composed of small particles, analytical arguments suggest that the disk experiences dynamical evolutions in three steps. The disk starts significantly excited after the impact and collisional damping dominates over the viscous spreading. After the system flattens, the system can become gravitationally unstable when particles are smaller than $\sim$ 100 m. However, the particles grow faster than spreading. Then, the system becomes gravitationally stable again and accretion continues at a slower pace, but spreading is inhibited. Therefore, the debris is expected to re-accrete into several large bodies. In conclusion, our results show that such a scenario may not form the today's ring system. In contrast, our results suggest that today's mid-sized moons are likely re-accreted from such a catastrophic event., Comment: 12 pages, 8 figures, accepted for publication in AJ

The origin of rings around giant planets remains elusive. Saturn's rings are massive and made of 90-95% of water ice. In contrast, the much less massive rings of Uranus and Neptune are dark and likely to have higher rock fraction. Here we investigate, for the first time, the tidal disruption of a passing object, including the subsequent formation of planetary rings. First, we perform SPH simulations of the tidal destruction of big differentiated objects ($M_{\rm body}=10^{21-23}$) that experience close encounters with Saturn or Uranus. We find that about $0.1-10$% of the mass of the passing body is gravitationally captured around the planet. However, these fragments are initially big chunks and have highly eccentric orbits around the planet. Then, we perform N-body simulations including the planet's oblateness, starting with data obtained from the SPH simulations. Our N-body simulations show that the chunks are tidally destroyed during their next several orbits. Their individual orbits then start to precess incoherently around the planet's equator, which enhances their encounter velocities on longer-term evolution, resulting in more destructive impacts. These collisions would damp their eccentricities resulting in a progressive collapse of the debris cloud into a thin equatorial and low-eccentricity ring. These high energy impacts are expected to be catastrophic enough to produce small particles. Our numerical results also show that the mass of formed rings is large enough to explain current rings including inner regular satellites around Saturn and Uranus. In the case of Uranus, a body can go deeper inside the planet's Roche limit resulting in a more efficient capture of rocky material compared to Saturn's case in which mostly ice is captured. Thus, our results can naturally explain the compositional difference between the rings of Saturn, Uranus and Neptune., Comment: 33 pages, 21 figures; accepted in Icarus

Centaurs are minor planets orbiting between Jupiter and Neptune that have or had crossing orbits with one or more giant planets. Recent observations and reinterpretation of previous observations have revealed the existence of ring systems around 10199 Chariklo and 2060 Chiron. However, the origin of the ring systems around such a minor planet is still an open question. Here, we propose that the tidal disruption of a differentiated object that experiences a close encounter with a giant planet could naturally form diverse ring-satellite systems around the Centaurs. During the close encounter, the icy mantle of the passing object is preferentially ripped off by the planet's tidal force and the debris is distributed mostly within the Roche limit of the largest remnant body. Assuming the existence of $20-50$wt% silicate core below the icy mantle, a disk of particles is formed when the objects pass within $0.4-0.8$ of the planet's Roche limit with the relative velocity at infinity $3-6$km s$^{-1}$ and 8h initial spin period of the body. The resultant ring mass is $0.1-10$% of the central object's mass. Such particle disks are expected to spread radially, and materials spreading beyond the Roche limit would accrete into satellite(s). Our numerical results suggest that ring formation would be a natural outcome of such extreme close encounters and Centaurs can naturally have such ring systems because they cross the orbits of the giant planets., Comment: 8 pages, 3 figures, published in ApJL

Planet traps are necessary to prevent forming planets from falling onto their host star by type I migration. Surface mass density and temperature gradient irregularities favor the apparition of traps and deserts. Such features are found at the dust sublimation lines and heat transition barriers. We study how planets may remain trapped or escape as they grow and as the disk evolves. We model the temporal viscous evolution of a protoplanetary disk by coupling its dynamics, thermodynamics, geometry and composition. The resulting mid-plane density and temperature profiles allow the modeling of the interactions of such an evolving disk with potential planets, even before the steady state is reached. We follow the viscous evolution of a MMSN and compute the Lindblad and corotation torques that such a disk would exert on potential planets of various masses located within the planetary formation region. We determine the position of planet traps and deserts in relationship with the sublimation lines, shadowed regions and heat transition barriers. Planets that are a few tens of Earth masses can be trapped at the sublimation lines until they reach a certain mass while planets more massive than 100ME can only be trapped permanently at the heat transition barriers. Coupling a bimodal planetary migration model with a self-consistent evolved disk, we were able to distinguish several potential planet populations after 5 million years of evolution: two populations of giant planets that could stay trapped around 5.5 and 9 au and possibly open gaps, some super-Earths trapped around 5 and 7.5 au and a population of close-in super-Earths trapped inside 1 au. The traps corresponding to the last group could help validating the in-situ formation scenarios of the observed close-in super-Earths., Comment: 12 pages, 7 figures, accepted in A&A

Aims. We track the time evolution of planet traps and snowlines in a viscously evolving protoplanetary disk using an opacity table that accounts for the composition of the dust material. Methods. We coupled a dynamical and thermodynamical disk model with a temperature-dependent opacity table (that accounts for the sublimation of the main dust components) to investigate the formation and evolution of snowlines and planet traps during the first million years of disk evolution. Results. Starting from a minimum mass solar nebula (MMSN), we find that the disk mid-plane temperature profile shows several plateaux (0.1-1 AU wide) at the different sublimation temperatures of the species that make up the dust. For water ice, the correspond- ing plateau can be larger than 1 AU, which means that this is a snow "region" rather than a snow "line". As a consequence, the surface density of solids in the snow region may increase gradually, not abruptly. Several planet traps and desert regions appear naturally as a result of abrupt local changes in the temperature and density profiles over the disk lifetime. These structures are mostly located at the edges of the temperature plateaux (surrounding the dust sublimation lines) and at the heat-transition barrier where the disk stellar heating and viscous heating are of the same magnitude (around 10 AU after 1 Myr). Conclusions. Several traps are identified: although a few appear to be transient, most of them slowly migrate along with the heat- transition barrier or the dust sublimation lines. These planet traps may temporarily favor the growth of planetary cores., Comment: 13pages, 16 figures, accepted in A&A

Violent stochastic collisional events have been invoked as a possible explanation for some debris discs displaying pronounced asymmetries or having a great luminosity excess. So far, no thorough modelling of the consequences of such events has been carried out, mainly because of the extreme numerical challenge of coupling the dynamical and collisional evolution of dust. We perform the first fully self-consistent modelling of the aftermath of massive breakups in debris discs. We follow the collisional and dynamical evolution of dust released after the breakup of a Ceres-sized body at 6 AU from its central star. We investigate the duration, magnitude and spatial structure of the signature left by such a violent event, as well as its observational detectability. We use the recently developed LIDT-DD code (Kral et al., 2013), which handles the coupled collisional and dynamical evolution of debris discs. The main focus is placed on the complex interplay between destructive collisions, Keplerian dynamics and radiation pressure forces. We use the GRaTer package to estimate the system's luminosity at different wavelengths. The breakup of a Ceres-sized body at 6 AU creates an asymmetric dust disc that is homogenized, by the coupled action of collisions and dynamics, on a timescale of a few $10^5$ years. The luminosity excess in the breakup's aftermath should be detectable by mid-IR photometry, from a 30 pc distance, over a period of $\sim 10^6$ years that exceeds the duration of the asymmetric phase of the disc (a few $10^5$ years). As for the asymmetric structures, we derive synthetic images for the SPHERE/VLT and MIRI/JWST instruments, showing that they should be clearly visible and resolved from a 10 pc distance. Images at 1.6$\mu$m (marginally), 11.4 and 15.5$\mu$m would show the inner disc structures while 23$\mu$m images would display the outer disc asymmetries., Comment: 16 pages, 14 figures, abstract shortened, accepted for publication in A&A

Observations of protoplanetary disks show that some characteristics seem recurrent, even in star formation regions that are physically distant such as surface mass density profiles varying as $r^{-1}$, or aspect ratios about 0.03 to 0.23. Accretion rates are also recurrently found around $10^{-8} - 10^{-6}~\mathrm{M_{\odot}~yr^{-1}}$ for disks already evolved (Isella et al., 2009, Andrews et al., 2009, 2010). Several models have been developed in order to recover these properties. However, most of them usually simplify the disk geometry if not its mid-plane temperature. This has major consequences for modeling the disk evolution over million years and consequently planet migration. In the present paper, we develop a viscous evolution hydrodynamical numerical code that determines simultaneously the disk photosphere geometry and the mid-plane temperature. We then compare our results of long-term simulations with similar simulations of disks with a constrained geometry along the Chiang & Goldreich (1997) prescription (dlnH/dlnr = 9/7). We find that the constrained geometry models provide a good approximation of the disk surface density evolution. However, they differ significantly regarding the temperature time evolution. In addition, we find that shadowed regions naturally appear at the transition between viscously dominated and radiation dominated regions that falls in the region of planetary formation. We show that $\chi$ (photosphere height to pressure scale height ratio) cannot be considered as a constant, consistently with Watanabe et al. (2008). Comparisons with observations show that all disk naturally evolve toward a shallow surface density disk ($\Sigma \propto r^{-1}$). The mass flux across the disk stabilizes in about 1 million year typically., Comment: 43 pages, 16 figures Accepted in Astrophysical Journal

In most current debris disc models, the dynamical and the collisional evolutions are studied separately, with N-body and statistical codes, respectively, because of stringent computational constraints. We present here LIDT-DD, the first code able to mix both approaches in a fully self-consistent way. Our aim is for it to be generic enough so as to be applied to any astrophysical cases where we expect dynamics and collisions to be deeply interlocked with one another: planets in discs, violent massive breakups, destabilized planetesimal belts, exozodiacal discs, etc. The code takes its basic architecture from the LIDT3D algorithm developed by Charnoz et al.(2012) for protoplanetary discs, but has been strongly modified and updated in order to handle the very constraining specificities of debris discs physics: high-velocity fragmenting collisions, radiation-pressure affected orbits, absence of gas, etc. In LIDT-DD, grains of a given size at a given location in a disc are grouped into "super-particles", whose orbits are evolved with an N-body code and whose mutual collisions are individually tracked and treated using a particle-in-a-box prescription. To cope with the wide range of possible dynamics, tracers are sorted and regrouped into dynamical families depending on their orbits. The code retrieves the classical features known for debris discs, such as the particle size distributions in unperturbed discs, the outer radial density profiles (slope in -1.5) outside narrow collisionally active rings, and the depletion of small grains in "dynamically cold" discs. The potential of the new code is illustrated with the test case of the violent breakup of a massive planetesimal within a debris disc. The main potential future applications of the code are planet/disc interactions, and more generally any configurations where dynamics and collisions are expected to be intricately connected., Comment: Accepted for publication in A&A. 20 pages, 17 figures. Abstract shortened for astro-ph