Six transiting planets and a chain of Laplace resonances in TOI-178

<p class="p1">Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. As unveiled by TESS, CHEOPS, ESPRESSO, NGTS and SPECULOOS, TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, all planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet. TOI-178 have hence several characteristics that were not previously observed in a single system, making it a key system for the study of processes of formation and evolution of planetary systems. We will review what we know of TOI-178, and what we expect from futur observations.</p>

Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

<p>Compared to preindustrial, the mid-Holocene (6 ka) had significantly greater Northern Hemisphere summer insolation, slightly warmer global surface temperature, and slightly lower CO<sub>2</sub> concentration. Vegetation was also different during the mid-Holocene. Possibly most prominent was the growth of temperate vegetation in the now barren Sahara. This Saharan vegetation response was related to intensification of the African Monsoon associated with the mid-Holocene orbital configuration. Hydroclimate of the Asian Monsoon and South American Monsoon also responded to mid-Holocene forcings, with general wetting and drying, respectively.</p><p>The mid-Holocene is frequently used for model-proxy comparison studies. However, climate models often struggle to replicate the proxy signals of this period. Here, we attempt to reduce these model-proxy discrepancies by exploring the significance of a vegetated Sahara during the mid-Holocene. Using the water isotopologue tracer enabled version of the Community Earth System Model (iCESM1), we perform mid-Holocene simulations that include and exclude temperate vegetation in the Sahara. We compare our model results with δ<sup>18</sup>O values from mid-Holocene speleothem records in the Asian and South American Monsoon regions.</p><p>We find that inclusion of vegetated Sahara during the mid-Holocene leads to global warming, alters the hemispheric distribution of energy, and generally amplifies the δ<sup>18</sup>O of precipitation responses in the South American and Asian Monsoon regions; these feedbacks improve the δ<sup>18</sup>O agreement between model outputs and speleothem records of the mid-Holocene. Our results highlight the importance of regional vegetation alteration for accurate simulation of past climate, even when the region of study is far from the source of vegetation change.</p>

Ionospheric Plasma Transported into the Martian Magnetosheath

<p>How the heavy ionospheric ions escape the Martian atmosphere is still not solved. Missions such as the Mars Express (MEX) satellite have observed significant heavy ions (O<sub>2<sup>+</sup></sub> and Co<sub>2<sup>+</sup></sub>) on the night side of the terminator. The hot oxygen corona when ionized gives rise to the pickup ions but they are of lighter mass.  With the more comprehensive instrumentation on the MAVEN mission, it is clear that cold heavy ions are transported down the tail of the planet. However, there has not yet been a good explanation of how heavy ions can reach into the Martian sheath in high density concentrations. In December 2020 the MAVEN satellite was observing on the dusk side tailward of the terminator with an orbital configuration allowing the density changes and the ion compositions to be followed. In this presentation the focus is on three subsequent orbits where a channel of heavy ions with high densities reaches out into the sheath. In this presentation we will argue for different possible processes that could explain the observations.</p>

An early dynamical instability among the Solar System’s giant planets triggered by the gas disk’s dispersal

The Solar System’s orbital structure is thought to have been sculpted by a dynamical instability among the giant planets[1–4]. Yet the instability trigger and exact timing have proved hard to pin down[5–9]. The giant planets formed within a gas-dominated disk around the young Sun. Motivated by giant exoplanet systems found in mean motion resonance[10], hydrodynamical modeling has shown that while the disk was present the giant planets migrated into a compact orbital configuration, in a chain of resonances[2,11]. Here we use a suite of dynamical simulations to show that the giant planets’ instability was likely triggered by the dispersal of the Sun’s gaseous disk. As the disk evaporated from the inside-out, its inner edge swept successively across and dynamically perturbed each planet’s orbit in turn. Saturn and each ice giants’ orbits were torqued strongly enough to migrate outward. As a given planet migrated outward with the disk’s inner edge the orbital configuration of the exterior system was compressed, triggering dynamical instability. The final orbits of our simulated systems match those of the Solar System for a viable range of astrophysical parameters. Our results demonstrate that the giant planet instability happened as the gaseous disk dissipated, constrained by astronomical observations to be a few to ten million years after the birth of the Solar System [12]. Late-stage terrestrial planet formation would occur mostly after such an early giant planet instability [13,14], thereby avoiding the possibility of de-stabilizing the terrestrial planets [15] and naturally accounting for the small mass of Mars relative to Earth and the mass depletion of the main asteroid belt [16].

Atmospheric dynamics on terrestrial planets with eccentric orbits

<p>The insolation a planet receives from its parent star is the main engine of the climate and depends on the planet's orbital configuration. Planets with non-zero obliquity and eccentricity experience seasonal insolation variations. As a result, the climate exhibits a seasonal cycle, with its strength depending on the orbital configuration and atmospheric characteristics. In this study, using an idealized general circulation model, we examine the climate response to changes in eccentricity for both zero and non-zero obliquity planets. In the zero obliquity case, a comparison between the seasonal response to changes in eccentricity and perpetual changes in the solar constant shows that the seasonal response strongly depends on the orbital period and radiative timescale. More specifically, using a simple energy balance model, we show the importance of the latitudinal structure of the radiative timescale in the climate response. We also show that the response strongly depends on the atmospheric moisture content. The combination of an eccentric orbit with non-zero obliquity is complex, as the insolation also depends on the perihelion position. Although the detailed response of the climate to variations in eccentricity, obliquity, and perihelion is involved, the circulation is constrained mainly by the thermal Rossby number and the maximum temperature latitude. Finally, we discuss the importance of different planetary parameters that affect the climate response to orbital configuration variations.</p>

CMIP6/PMIP4 simulations of the mid-Holocene and Last Interglacial using HadGEM3: comparison to the pre-industrial era, previous model versions and proxy data

Palaeoclimate model simulations are an important tool to improve our understanding of the mechanisms of climate change. These simulations also provide tests of the ability of models to simulate climates very different to today. Here we present the results from two brand-new simulations using the latest version of the UK's physical climate model, HadGEM3-GC3.1; they are the mid-Holocene (∼6 ka) and Last Interglacial (∼127 ka) simulations, both conducted under the auspices of CMIP6/PMIP4. This is the first time this version of the UK model has been used to conduct palaeoclimate simulations. These periods are of particular interest to PMIP4 because they represent the two most recent warm periods in Earth history, where atmospheric concentration of greenhouse gases and continental configuration are similar to the pre-industrial period but where there were significant changes to the Earth's orbital configuration, resulting in a very different seasonal cycle of radiative forcing. Results for these simulations are assessed firstly against the same model's pre-industrial control simulation (a simulation comparison, to describe and understand the differences between the pre-industrial – PI – and the two palaeo simulations) and secondly against previous versions of the same model relative to newly available proxy data (a model–data comparison, to compare all available simulations from the same model with proxy data to assess any improvements due to model advances). The introduction of this newly available proxy data adds further novelty to this study. Globally, for metrics such as 1.5 m temperature and surface rainfall, whilst both the recent palaeoclimate simulations are mostly capturing the expected sign and, in some places, magnitude of change relative to the pre-industrial, this is geographically and seasonally dependent. Compared to newly available proxy data (including sea surface temperature – SST – and rainfall) and also incorporating data from previous versions of the model shows that the relative accuracy of the simulations appears to vary according to metric, proxy reconstruction used for comparison and geographical location. In some instances, such as mean rainfall in the mid-Holocene, there is a clear and linear improvement, relative to proxy data, from the oldest to the newest generation of the model. When zooming into northern Africa, a region known to be problematic for models in terms of rainfall enhancement, the behaviour of the West African monsoon in both recent palaeoclimate simulations is consistent with current understanding, suggesting a wetter monsoon during the mid-Holocene and (more so) the Last Interglacial, relative to the pre-industrial era. However, regarding the well-documented “Saharan greening” during the mid-Holocene, results here suggest that the most recent version of the UK's physical model is still unable to reproduce the increases suggested by proxy data, consistent with all other previous models to date.

Orbital evolution of Saturn’s satellites due to the interaction between the moons and the massive rings

Context. Saturn’s mid-sized moons (satellites) have a puzzling orbital configuration with trapping in mean-motion resonances with every-other pairs (Mimas-Tethys 4:2 and Enceladus-Dione 2:1). To reproduce their current orbital configuration on the basis of a recent model of satellite formation from a hypothetical ancient massive ring, adjacent pairs must pass first-order mean-motion resonances without being trapped. Aims. The trapping could be avoided by fast orbital migration and/or excitation of the satellite’s eccentricity caused by gravitational interactions between the satellites and the rings (the disk), which are still unknown. In our research we investigate the satellite orbital evolution due to interactions with the disk through full N-body simulations. Methods. We performed global high-resolution N-body simulations of a self-gravitating particle disk interacting with a single satellite. We used N ∼ 105 particles for the disk. Gravitational forces of all the particles and their inelastic collisions are taken into account. Results. Dense short-wavelength wake structure is created by the disk self-gravity and a few global spiral arms are induced by the satellite. The self-gravity wakes regulate the orbital evolution of the satellite, which has been considered as a disk spreading mechanism, but not as a driver for the orbital evolution. Conclusions. The self-gravity wake torque to the satellite is so effective that the satellite migration is much faster than was predicted with the spiral arm torque. It provides a possible model to avoid the resonance capture of adjacent satellite pairs and establish the current orbital configuration of Saturn’s mid-sized satellites.

Effect of Lanthanum Substituted CoFe2-xLaxO4 on Change of Structure Parameter and Phase Formation

In this research, CoFe2-xLaxO4-based smart magnetic material has been developed which will be applied as a microwave absorbing material. This smart magnetic material is an artificial advanced material which has properties such as electromagnetic waves so that it is able to respond to the presence of microwaves through the mechanism of spin electron resonance and wall resonance domain. This smart magnetic material consists of a combination of rare earth metal elements (spin magnetic in the f orbital configuration) and transition metal elements (spin magnetic in the d orbital configuration) with a semi-hard magnetic structure. This semi-hard is a characteristic of magnetic properties which is between hard magnetic and soft magnetic properties. This characteristic of the semi-hard magnetic properties is needed so that this material has the ability to absorb microwaves. Substitution of lanthanum into cobalt ferrite CoFe2-xLaxO4 for La3+ (x = 0 - 0.8) has been synthesized using the solid reaction method through mechanical deformation techniques. The refinement result of X-ray diffraction shows that the sample contains 2 phases with increasing of x compositions. Particle morphology and elementary analysis were observed respectively by using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). It was concluded that the effect of La substitution on CoFe2-xLaxO4 resulted in changes in the crystal structure parameters and phase transformation as a function of composition.

Is There Still Something Left That Gravity Probe B Can Measure?

We perform a full analytical and numerical treatment, to the first post-Newtonian (1pN) order, of the general relativistic long-term spin precession of an orbiting gyroscope due to the mass quadrupole moment J 2 of its primary without any restriction on either the gyro’s orbital configuration and the orientation in space of the symmetry axis k ^ of the central body. We apply our results to the past spaceborne Gravity Probe B (GP-B) mission by finding a secular rate of its spin’s declination δ which may be as large as ≲30–40 milliarcseconds per year mas yr − 1 , depending on the initial orbital phase f 0 . Both our analytical calculation and our simultaneous integration of the equations for the parallel transport of the spin 4-vector S and of the geodesic equations of motion of the gyroscope confirm such a finding. For GP-B, the reported mean error in measuring the spin’s declination rate amounts to σ δ ˙ GP − B = 18.3 mas yr − 1 . We also calculate the general analytical expressions of the gravitomagnetic spin precession induced by the primary’s angular momentum J . In view of their generality, our results can be extended also to other astronomical and astrophysical scenarios of interest like, e.g., stars orbiting galactic supermassive black holes, exoplanets close to their parent stars, tight binaries hosting compact stellar corpses.