Ronco, P.
-
A fading radius valley towards M-dwarfs, a persistent density valley across stellar types
The radius valley separating super-Earths from mini-Neptunes is a fundamental benchmark for theories of planet formation and evolution. Observations show that the location of the radius valley decreases with decreasing stellar mass and with increasing orbital period. Here, we build from our previous pebble-based formation model, which unveiled the radius valley as a separator between rocky- and water-worlds. We here expand our models for stellar masses ranging from 0.1 to 1.5 Msun . We find that the location of the radius valley is in excellent agreement with observations. We also find very good agreement with the dependence of the radius valley on orbital period, both for FGK- and M-dwarfs. Additionally, we note that the radius valley gets filled towards low stellar masses (0.1-0.4 Msun). This is the result of orbital migration occurring at lower planet mass for less massive stars, which allows for low-mass water-worlds to reach the inner regions of the system, blurring the separation in mass (and size) between rocky- and water-worlds.
As with Sun-like stars, pebble accretion leaves its imprint on the overall exoplanet population as a depletion of planets with intermediate compositions (0 − 20% water mass fraction), carving a planet-depleted diagonal band in the mass-radius diagram. This band is better visualised when plotting the planet mean density in terms of Earth-like composition, making the valley emerge for all stellar masses.
Guilera, O.
-
Planetesimal and planet formation in transient pressure bumps
The ring-like structures in protoplanetary discs that are observed in the cold dust emission by ALMA, might be explained by dust aggregates trapped aerodynamically in pressure maxima. The effect of a transient pressure maximum is investigated that develops between two regimes with different turbulent levels. We study how such a pressure maximum collects dust aggregates and transforms them into large planetesimals and Moon-mass cores that can further grow to a few Earth-mass planets by pebble accretion, and eventually to giant planets, by considering the accretion of a gaseous envelope. We will show that such transient pressure maximum efficiently accumulates dust particles that can grow larger than mm-size. If this happens, dust aggregates can be transformed by the streaming instability process into such large planetesimals, which can grow further by pebble accretion, according to our assumptions. As the gas evolves to its steady state, the pressure maximum vanishes, and the concentrated pebbles that are not transformed to planetesimals and accreted by the growing planet, drift inward. During this inward drift, if the conditions of the streaming instability are met, planetesimals are formed in a wide radial range of the disc.
Saker, L.
-
Searching for signals of transiting planets in the TESS light curves of white dwarfs with dust discs
Approximately 97% of stars will end their lives as white dwarfs. These stars are, therefore, the most common stellar remnants in our Galaxy. 1-3% of white dwarfs show an IR excess produced by a circumstellar dust disc, which is being accreted by the star. Such debris disc result of tidal disruption by rocky planetesimals that originally formed a planetary system. In this contribution, we present a photometric analysis with data from the TESS space mission of a sample of white dwarfs with dust discs, with the purpose of detecting possible events of transits of rocky bodies that have survived the evolution of the star.
Hobson, M.
-
Exoplanets with Radial Velocities and Transits: an Overview
In this contribution, I will present the rapidly-growing population of exoplanets detected via radial velocities and transits. These complementary techniques allow us to obtain both radii and true masses, enabling in turn a study of the likely compositions of these planets. I will focus on some of the emerging sub-groups and what they can tell us, such as: warm giant planets and how they inform our understanding of giant planet formation; super-Earths and mini-Neptunes straddling the radius gap; and the push towards the detection of true Earth-twins.
Trógolo, N.
-
Didymos Primary’s Close-to-Critical Fast Spin: Effects on Mass Transfer and External Morphology of binary component
The primary of the NEA binary system (65603) Didymos is supposed to be a rubble pile asteroid, with a fast rotational period (2.2600 ± 0.0001 h) [Pravec et al., 2005], placing it near the critical stability limit. Trógolo, et al. (2023) have demonstrated that this asteroid may experience regolith loss from its equatorial region, as the centripetal force can potentially overcome the local surface gravity. In this study, we aim to refine our previous research by using the latest orbital and physical parameters of the binary, which have been provided by NASA’s DART investigation team [Naidu et al., in press]. We analyze the implication of Didymos’ actual spin state on its recent history and we compared the obtained results with the images taken by DART spacecraft and LICIACube to provide a possible explanation for their external stony configuration seen before the impact test.
Zoppetti, F.
-
Resonant transport of Pluto’s minor moons enabled by a post-impact water-vapor disk
The formation of Pluto’s satellite system was probably the result of a Giant Impact on a primordial body [Canup2005]. Impact simulations are capable of simultaneously forming an intact Charon and a compact ice-rich debris disk [Canup2011]. However, four minor moons were recently observed in the system in much wider orbits and remarkably close to N:1 mean-motion-resonances with Charon (with N=3,4,5 and 6) [Weaver+2016]. The hypothesis of resonant transport of debris as Charon’s orbit tidally expands is a natural explanation for the small moon’s orbits [Canup+2021] but transporting four bodies at once has proven to be a highly unstable process [Cheng+2014]. Here we show that a post-impact water-vapor disk, similar to the one that has recently been proposed for the formation of the moons of Uranus [Ida+2020], greatly stabilizes the resonant transport of debris through aerodynamical drag. Despite the extreme complexity of each particular resonance, we can transport the four moons to orbits very similar to the observed ones, using standard hydrodynamical parameters of the disk and tidal factors of the binary components.
Planes, B.
-
Dust-dust collisions in cometary comas and their effect on size distributions
The mission of the European Space Agency, Rosetta, at comet 67P/Churyumov-Gerasimenko was the first space mission to measure a reliable dust size distribution in a comet and it was equipped with the instruments COSIMA, GIADA and MIDAS designed to study cometary dust. The radius of the aggregates collected by COSIMA was in the range between 7 and 150 microns with a differential size distribution which may be approximated by a power-law relationship. Assuming that the particles collected by COSIMA are pristine and neglecting fragmentation during collection, a power-law index characteristic of dust in protoplanetary disks would be expected. However, the differential size distribution of the dust particle flux suggests an index shallower than expected for large aggregates and a steeper one for small particles.
We apply our recently published Collision of Porous Aggregates (CPA) software in the COSIMA to study dust-dust collisional processes as the aggregates leave the nucleus and pass through the coma, and show that it influences the size distribution of ejected particles. We present the final distributions of mass, size and porosity of the dust population after a given number of random collisions between the aggregates and find good agreement between our results and the dust particle flux measured by COSIMA. Our results could be generalizable to other comets exhibiting comparable dust production patterns.
Lunch
-
Cerioni, M.
-
A Six-Planet Resonant Chain in K2-138?
The K2-138 system hosts six planets and presents an interesting case study due to its distinctive dynamical structure. Its five inner planets are near a chain of 3/2 two-body mean-motion resonances, while the outermost body (planet g) is significantly detached, having a mean-motion ratio of n_f /n_g ∼ 3.3 with its closest neighbor. We show that the orbit of m_g is actually consistent with the first-order three-planet resonance (3P-MMR) characterized by the relation 2 n_e − 4 n_f + 3 n_g = 0 and is the first time a pure first-order 3P-MMR is found in a multi-planet system and tied to its current dynamical structure. Adequate values for the masses allow to trace the dynamical history of the system from an initial capture in a 6-planet chain (with n_f /n_g in a 3/1 resonance), up to its current configuration due to tidal interactions over the age of the star. The increase in resonance offset with semi-major axis, as well as its large value for n_f /n_g can be explained by the slopes of the pure three-planet resonances in the mean-motion ratio plane. The triplets slide outward over these curves when the innermost pair is pulled apart by tidal effects, in a pantograph-like manner. The capture into the 3P-MMR is found to be surprisingly robust given similar masses for m_g and m_f, and it is possible that the same effect may also be found in other compact planetary systems.
Araujo Furlán, S.
-
A study of the radio activity of magnetar XTE J1810-197 four years after its outburst
Magnetars are a particular class of young neutron stars. They are characterised by their long rotational periods and gigantic surface magnetic fields (10**13-10**15 G). They exhibit a rich transient phenomenology observed mainly in X-Ray, including events such as giant flares, short bursts and outburst. Of the total 30 known magnetars, only 6 had emission detected in radio frequencies. Five of them had radio emission associated with X-ray outbursts, the six of them had Fast Radio Burst /FRB)-like emission. Magnetar XTE J1810-197 had an outburst in late 2018, observed in X-ray and radio. We started a high cadence monitoring campaing of this source in September 2022 with the radiotelescopes of the Instituto Argentino de Radioastronomía (IAR). We performed the observations with a highest freequency of 1456 MHz and a time resolution of 146 us. Here we present an study of the transient radio emission detected from the magnetar 4 years from it outburst.