Autonomous robotic arm manipulators have the potential to make planetary exploration and in-situ resource utilization missions more time efficient and productive, as the manipulator can handle the objects itself and perform goal-specific actions. We train a manipulator to autonomously study objects of which it has no prior knowledge, such as planetary rocks. This is achieved using causal machine learning in a simulated planetary environment. Here, the manipulator interacts with objects, and classifies them based on differing causal factors. These are parameters, such as mass or friction coefficient, that causally determine the outcomes of its interactions. Through reinforcement learning, the manipulator learns to interact in ways that reveal the underlying causal factors. We show that this method works even without any prior knowledge of the objects, or any previously-collected training data. We carry out the training in planetary exploration conditions, with realistic manipulator models.
Daniel J. Bailey, Erik V. Johnstone, Martin C. Stennett
et al.
99Tc and 129I are two long-lived, highly soluble and mobile fission products that pose a long-term hazard. A proposed wasteform for the disposal of radio-iodine is iodovanadinite (Pb5(VO4)3I), an apatite-structured vanadate. In this investigation, a suite of potential iodovanadinite wasteforms designed for the co-disposal of Tc and I or the sole disposal of I were synthesised via hot isostatic pressing (with Mo as a surrogate for Tc). It was found that direct synthesis from oxide and iodide precursors was possible using hot isostatic pressing (HIPing). Increasing overpressure during HIPing was found to improve the density of the final product. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicated that the use of AgI as the source of iodine affected the formation of the target iodovanadinite phase and produced unfavourable phase assemblages. Here, we report the direct synthesis of Pb5(VO4)3I in a single step by hot isostatic pressing.
The electron density profile on a plasma surface has a decisive influence on the mechanism and characteristics of the plasma high-order harmonic generation. When the pre-pulse has a similar spatial and temporal distribution as the main laser pulse, the plasma surface on the target will expand to form a convex profile of the similar size as the focal spot of the main pulse. We experimentally observed that the divergence of the harmonics generated by the relativistic laser light incident on a silica target has a saddle-shaped structure. The two-dimensional particle-in-cell simulation with convex plasma surfaces explains the experimental results very well and infers a 0.12λL plasma scale length around the center of the convex profile. Further, we qualitatively explained that the asymmetry of the saddle-shaped harmonic divergence is caused by oblique incidence.
Mars is the next frontier for the space explorers to demonstrate the extent of human presence in space beyond low-earth orbit. Both government and private space industries have been fascinated by Mars quest to attempt a crewed expedition to the red planet. The journey to Mars is vastly challenging as it endowed with numerous challenges from the inception of the mission engage to the mission achievement. Therefore, it is substantial to overcome those challenges for a reliable mission. Hence we have studied and emphasized the comprehensive challenges under the categorization of terrestrial, Earth-bound, interplanetary, Mars-bound, and planetary surface challenges. These challenges are suspected to encounter by the astronauts and mission planners throughout the mission timeline. Our research is different from other studies as it reports complete challenges and their implications on the way to human exploration of Mars.
Judy J. Chebly, Julián D. Alvarado-Gómez, Katja Poppenhaeger
The cumulative effect of the magnetized stellar winds on exoplanets dominates over other forms of star-planet interactions. When combined with photoevaporation, these winds will lead to atmospheric erosion. This is directly connected with the concept of Habitable Zone (HZ) planets around late-type stars. Our knowledge of these magnetized winds is limited, making numerical models useful tools to explore them. In this preliminary study, we focus on solar-like stars exploring how different stellar wind properties scale with one another. We used one of the most detailed physics-based models, the 3D Alfvén Wave Solar Model part of the Space Weather ModelingFramework, and applied it to the stellar winds domain. Our simulations showed that the magnetic field topology on the star surface plays a fundamental role in shaping the different stellar wind properties (wind speed, mass loss rate, angular momentum loss rate). We conclude that a characterization of the Alfvén surface is crucial when studying star-planet interaction as it can serve as an inner-boundary of the HZ
We announce the second data release (DR2) of the NOIRLab Source Catalog (NSC), using 412,116 public images from CTIO-4 m+DECam, the KPNO-4 m+Mosaic3, and the Bok-2.3 m+90Prime. NSC DR2 contains over 3.9 billion unique objects, 68 billion individual source measurements, covers ≈35,000 square degrees of the sky, has depths of ≈23 mag in most broadband filters with ≈1%–2% photometric precision, and astrometric accuracy of ≈7 mas. Approximately 1.9 billion objects within ≈30,000 square degrees of sky have photometry in three or more bands. There are several improvements over NSC DR1. DR2 includes 156,662 (61%) more exposures extending over 2 more years than in DR1. The southern photometric zero-points in griz are more accurate by using the Skymapper DR1 and ATLAS-Ref2 catalogs, and improved extinction corrections were used for high-extinction regions. In addition, the astrometric accuracy is improved by taking advantage of Gaia DR2 proper motions when calibrating the astrometry of individual images. This improves the NSC proper motions to ∼2.5 mas yr−1 (precision) and ∼0.2 mas yr−1 (accuracy). The combination of sources into unique objects is performed using a DBSCAN algorithm and mean parameters per object (such as mean magnitudes, proper motion, etc.) are calculated more robustly with outlier rejection. Finally, eight multi-band photometric variability indices are calculated for each object and variable objects are flagged (23 million objects). NSC DR2 will be useful for exploring solar system objects, stellar streams, dwarf satellite galaxies, quasi-stellar objects, variable stars, high proper-motion stars, and transients. Several examples of these science use cases are presented. The NSC DR2 catalog is publicly available via the NOIRLab’s Astro Data Lab science platform.
Igor Aleinov, Michael J. Way, Christopher W. Hamilton
et al.
The origin, distribution, depth and volume of lunar volatiles remain open questions. One of the possible sources of Moon's volatiles is their volcanic outgassing during the peak of lunar volcanic activity ~3.5 Ga. This same outgassing would also produce a tenuous transient atmosphere which would promote the delivery of volatiles from the volcanic sources to the polar cold traps. Though such an atmosphere could have played an important role in the evolution of the Moon, little is known about it due to high uncertainty level in the mechanisms involved. The only reliable proxy for the ancient lunar atmosphere are the primordial volatiles deposited by it, which are expected to be preserved in the polar cold traps, and could be studied through sample return. In this white paper we therefore advocate that a volatile sample return from the Moon's polar cold traps should be a fundamental part of the Artemis program.
The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, in Lunar orbit, and in the vicinity of the Lunar Gateway) require new solutions for positioning, navigation and timing (PNT). Here, I describe COMPASS (Combined Observational Methods for Positional Awareness in the Solar System), a spacecraft navigation system to provide cost-effective techniques for the positioning of large numbers of spacecraft in cislunar space. COMPASS will use beacons that emit coherent ultra-wideband signals designed to be interoperable with existing and future Very Long Baseline Interferometry (VLBI) networks. Using differential VLBI, COMPASS will provide rapid determination of the interferometric phase delay with picosecond level accuracy during routine VLBI observing sessions. Multi-baseline phase-referenced COMPASS-VLBI observations with simultaneous calibrator observations should thus enable sub-meter accuracy transverse positioning and meter level lunar orbit determination using with small femtospacecraft beacons and a few seconds of observation per position determination.
We propose a densification algorithm to improve the Line Of Variations (LOV) method for impact monitoring, which can fail when the information is too little, as it may happen in difficult cases. The LOV method uses a 1-dimensional sampling to explore the uncertainty region of an asteroid. The close approaches of the sample orbits are grouped by time and LOV index, to form the so-called returns, and each return is analysed to search for local minima of the distance from the Earth along the LOV. The strong non-linearity of the problem causes the occurrence of returns with so few points that a successful analysis can be prevented. Our densification algorithm tries to convert returns with length at most 3 in returns with 5 points, properly adding new points to the original return. Due to the complex evolution of the LOV, this operation is not necessarily achieved all at once: in this case the information about the LOV geometry derived from the first attempt is exploited for a further attempt. Finally, we present some examples showing that the application of our method can have remarkable consequences on impact monitoring results, in particular about the completeness of the virtual impactors search.
Solar-like oscillations are excited in cool stars with convective envelopes and provide a powerful tool to constrain fundamental stellar properties and interior physics. We provide a brief history of the detection of solar-like oscillations, focusing in particular on the space-based photometry revolution started by the CoRoT and Kepler Missions. We then discuss some of the lessons learned from these missions, and highlight the continued importance of smaller space telescopes such as BRITE constellation to characterize very bright stars with independent observational constraints. As an example, we use BRITE observations to measure a tentative surface rotation period of 28.3+/-0.5 days for alpha Cen A, which has so far been poorly constrained. We also discuss the expected yields of solar-like oscillators from the TESS Mission, demonstrating that TESS will complement Kepler by discovering oscillations in a large number of nearby subgiants, and present first detections of oscillations in TESS exoplanet host stars.
Instrumental data are affected by systematic effects that dominate the errors and can be relevant when searching for small signals. This is the case of the K2 mission, a follow up of the Kepler mission, that, after a failure on two reaction wheels, has lost its stability properties rising strongly the systematics in the light curves and reducing its photometric precision. In this work, we have developed a general method to remove time related systematics from a set of light curves, that has been applied to K2 data. The method uses the Principal Component Analysis to retrieve the correlation between the light curves due to the systematics and to remove its effect without knowing any information other than the data itself. We have applied the method to all the K2 campaigns available at the Mikulski Archive for Space Telescopes, and we have tested the effectiveness of the procedure and its capability in preserving the astrophysical signal on a few transits and on eclipsing binaries. One product of this work is the identification of stable sources along the ecliptic plane that can be used as photometric calibrators for the upcoming Atmospheric Remote-sensing Exoplanet Large-survey mission.
AIMS To report the long-term outcome of a single institution series of pure ductal carcinoma in situ (DCIS) treated with accelerated partial irradiation using intraoperative electrons (IOERT). METHODS From 2000 to 2010, 180 DCIS patients, treated with quadrantectomy and 21 Gy IOERT, were analyzed in terms of ipsilateral breast recurrences (IBRs) and survival outcomes by stratification in two subgroups. The low-risk group included patients who fulfilled the suitable definition according to American Society of Radiation Oncology (ASTRO) Guidelines (size ≤2.5 cm, grade 1-2 and surgical margins ≥3 mm) (Suitable), while the remaining ones formed the high-risk group (Non-Suitable). RESULTS Eighty-four and 96 patients formed the Suitable and Non-Suitable groups, respectively. In the whole population, the cumulative incidence of IBR at 5, 7 and 10 years was 19%, 21%, and 25%, respectively. In the Suitable group, the cumulative incidence of IBR remained constant at 11% throughout the years, while in the Non-Suitable group increased from 26% at 5 years to 36% at 10 years (p < 0.0001). When hormonal positivity and HER2 absence of expression were added to the selection of the Suitable group, the cumulative incidence of IBR dropped and stabilized at 4% at 10 years. None died of breast cancer. In the whole population, 5-year and 10-year overall survival rate was 98% and 96.5%, respectively, without any difference between the two groups. CONCLUSIONS The overall and by group IBR rates were high and stricter criteria are required for acceptable local control for Suitable DCIS. Because of the concerns raised, IOERT should not be used in clinical practice.
The numerical modeling of co-existing circumplanetary disks/rings and satellites is particularly challenging because each part of the system requires a very different approach. Disks are generally well represented by a fluid-like dense medium, whose evolution can be calculated by a hydrocode. On the other hand, the orbital evolution of satellites is generally performed using N-body integrators. We have developed a new numerical model that combines a 1-dimensional hydrocode with the N-body integrator SyMBA. The disk evolves due to its viscosity, and resonant torques from satellites. The latter is applied to the satellites as an additional "kick" to their accelerations. The integrator also includes the ability to spawn new moonlets at the disk's outer edge if the latter expands beyond a material-dependent Roche limit, as well as the effects of tidal dissipation in the planet and/or the satellite on the satellite orbits. The resulting integrator allows one to accurately model the evolution of an inner circumplanetary disk, and the formation of satellites by accumulation of disk material, all within a single self-consistent framework. Potential applications include the formation of Earth's Moon, the evolution of the inner Saturn system, the martian and uranian moons, and compact exoplanetary systems.
M. D. Sizova, E. S. Postnikova, A. P. Demidov
et al.
We examined the influence of the Hyades star cluster on the possibility of the appearance of long-period comets in the Solar system. It is known that the Hyades cluster is extended along the spatial orbit on tens of parsecs. To our estimations, 0.85 million years ago, there was a close approach of the cluster to the Sun of 24.8 pc. The approach of one of the cluster stars to the Sun at the minimally known distance of about 6.9 pc was 1.6 million years ago. The main part of the cluster was close to the Sun from 1 to 2 million years ago. Such proximity is not essential for the impact on the dynamics of small bodies in the external part of the Oort cloud, although the view may change after additional study of the cluster structure. Possible orbits perihelion displacements of the small bodies of the outer part of the Oort cloud make some of them in observable comets region.
Lewis J. Whitehouse, J. Farihi, P. J. Green
et al.
Dwarf carbon stars make up the largest fraction of carbon stars in the Galaxy with around 1200 candidates known to date primarily from the Sloan Digital Sky Survey. They either possess primordial carbon-enhancements, or are polluted by mass transfer from an evolved companion such that C/O is enhanced beyond unity. To directly test the binary hypothesis, a radial velocity monitoring survey has been carried out on 28 dwarf carbon stars, resulting in the detection of variations in 21 targets. Using Monte Carlo simulations, this detection fraction is found to be consistent with a 100% binary population and orbital periods on the order of hundreds of days. This result supports the post-mass transfer nature of dwarf carbon stars, and implies they are not likely hosts to carbon planets.
We show that the ideal hydrodynamics of an eccentric astrophysical disc can be derived from a variational principle. The nonlinear secular theory describes the slow evolution of a continuous set of nested elliptical orbits as a result of the pressure in a thin disc. In the artificial but widely considered case of a 2D disc, the hydrodynamic Hamiltonian is just the orbit-averaged internal energy of the disc, which can be determined from its eccentricity distribution using the geometry of the elliptical orbits. In the realistic case of a 3D disc, the Hamiltonian needs to be modified to take into account the dynamical vertical structure of the disc. The simplest solutions of the theory are uniformly precessing nonlinear eccentric modes, which make the energy stationary subject to the angular momentum being fixed. We present numerical examples of nonlinear eccentric modes up to their limiting amplitudes. Although it lacks dissipation, which is important in many astrophysical contexts, this formalism allows a simpler theoretical approach to the nonlinear dynamics of eccentric discs than that derived from stress integrals, and also connects better with established methods of celestial mechanics for cases in which the disc interacts gravitationally with one or more orbital companion.
Liprin-α1 and ERC1 are interacting scaffold proteins regulating the motility of normal and tumor cells. They act as part of plasma membrane-associated platforms at the edge of motile cells to promote protrusion by largely unknown mechanisms. Here we identify an amino-terminal region of the liprin-α1 protein (liprin-N) that is sufficient and necessary for the interaction with other liprin-α1 molecules. Similar to liprin-α1 or ERC1 silencing, expression of the liprin-N negatively affects tumor cell motility and extracellular matrix invasion, acting as a dominant negative by interacting with endogenous liprin-α1 and causing the displacement of the endogenous ERC1 protein from the cell edge. Interfering with the localization of ERC1 at the cell edge inhibits the disassembly of focal adhesions, impairing protrusion. Liprin-α1 and ERC1 proteins colocalize with active integrin β1 clusters distinct from those colocalizing with cytoplasmic focal adhesion proteins and influence the localization of peripheral Rab7-positive endosomes. We propose that liprin-α1 and ERC1 promote protrusion by displacing cytoplasmic adhesion components to favour active integrin internalization into Rab7-positive endosomes.