Pioneer 10 data analysis: Investigation on periodic anomalies

International audienceThe Pioneer Anomaly refers to the difference between the expected theoretical tra jectory of the Pioneer 10 and 11 spacecrafts and the observed tra jectory through Doppler measurements. It has been interpreted by the Jet Propulsion Laboratory (JPL) as a constant anomalous acceleration (Anderson et al. 2002). For this analysis, the Groupe Anomalie Pioneer (GAP) composed of several french laboratories has developped a specific tra jectography software, ODYSSEY, which enables to test different anomaly models. The paper will present, after a brief description of the software and the implemented models, the last results obtained: in addition to the constant anomaly, time dependent signatures of the anomaly have been noticed which can be described geometrically. The fit of the Pioneer 10 data with these new models yields a reduction of the standard deviation of the residual by a factor 2 with respect to the simple constant anomaly

Pioneer 10 Doppler data analysis: disentangling periodic and secular anomalies

This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data analysis as independent as possible from that of J. Anderson et al. \citep{anderson}, using the same data set. A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8 nms$^{-2}$ compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azimuthal angle $\varphi$ defined by the directions Sun-Earth Antenna and Sun-Pioneer. An improved fit is obtained with periodic variations written as the sum of a secular acceleration and two sinusoids of the angles $\varphi$ and $2\varphi$. The tests which have been performed for assessing the robustness of these results are presented.Comment: 13 pages, 6 figures, minor amendment

Effects of glucose and lactate on <em>Streptococcus </em><em>mutans </em>abundance in a novel multispecies oral biofilm model

The oral microbiome plays an important role in protecting oral health. Here, we established a controlled mixed-species in vitro biofilm model and used it to assess the impact of glucose and lactate on the ability of Streptococcus mutans, an acidogenic and aciduric species, to compete with commensal oral bacteria. A chemically defined medium was developed that supported the growth of S. mutans and four common early colonizers of dental plaque: Streptococcus gordonii, Actinomyces oris, Neisseria subflava, and Veillonella parvula. Biofilms containing the early colonizers were developed in a continuous flow bioreactor, exposed to S. mutans, and incubated for up to 7 days. The abundance of bacteria was estimated by quantitative polymerase chain reaction (qPCR). At high glucose and high lactate, the pH in bulk fluid rapidly decreased to approximately 5.2, and S. mutans outgrew other species in biofilms. In low glucose and high lactate, the pH remained above 5.5, and V. parvula was the most abundant species in biofilms. By contrast, in low glucose and low lactate, the pH remained above 6.0 throughout the experiment, and the microbial community in biofilms was relatively balanced. Fluorescence in situ hybridization confirmed that all species were present in the biofilm and the majority of cells were viable using live/dead staining. These data demonstrate that carbon source concentration is critical for microbial homeostasis in model oral biofilms. Furthermore, we established an experimental system that can support the development of computational models to predict transitions to microbial dysbiosis based on metabolic interactions. 38376204</strong

A resonant-term-based model including a nascent disk, precession, and oblateness: application to GJ 876

Investigations of two resonant planets orbiting a star or two resonant satellites orbiting a planet often rely on a few resonant and secular terms in order to obtain a representative quantitative description of the system's dynamical evolution. We present a semianalytic model which traces the orbital evolution of any two resonant bodies in a first- through fourth-order eccentricity or inclination-based resonance dominated by the resonant and secular arguments of the user's choosing. By considering the variation of libration width with different orbital parameters, we identify regions of phase space which give rise to different resonant ''depths,'' and propose methods to model libration profiles. We apply the model to the GJ 876 extrasolar planetary system, quantify the relative importance of the relevant resonant and secular contributions, and thereby assess the goodness of the common approximation of representing the system by just the presumably dominant terms. We highlight the danger in using ''order'' as the metric for accuracy in the orbital solution by revealing the unnatural libration centers produced by the second-order, but not first-order, solution, and by demonstrating that the true orbital solution lies somewhere ''in-between'' the third- and fourth-order solutions. We also present formulas used to incorporate perturbations from central-body oblateness and precession, and a protoplanetary or protosatellite thin disk with gaps, into a resonant system. We quantify these contributions to the GJ 876 system, and thereby highlight the conditions which must exist for multi-planet exosystems to be significantly influenced by such factors. We find that massive enough disks may convert resonant libration into circulation; such disk-induced signatures may provide constraints for future studies of exoplanet systems.Comment: 39 pages of body text, 21 figures, 5 tables, 1 appendix, accepted for publication in Celestial Mechanics and Dynamical Astronom

MICROSCOPE mission: first results of a space test of the equivalence principle

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10−15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[−1±9(stat)±9(syst)]×10−15 (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations

Pioneer doppler data analysis

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Use of Optical Density Detection Times To Assess the Effect of Acetic Acid on Single-Cell Kinetics

The growth of Listeria innocua at different acetic acid concentrations (0 to 2,000 ppm) was monitored by optical density measurements in a Bioscreen (Labsystems, Vantaa, Finland). The generated populations came from low inocula that were obtained by serial dilution. A new method to estimate both the growth rate and the lag time of single cells from the detection times (time to reach an optical density of 0.11) was developed. It assumes that the single-cell lag times follow a gamma distribution and takes into account the randomness of the inoculation level. (The initial cell number per well was assumed to follow a Poisson distribution.) In this way, relatively small numbers of replicates are sufficient to obtain a robust estimation of the distribution of single-cell lag times. The results were validated with plate count experiments. It was found that logarithms of both the growth rates and of population lag times increased linearly with the acetic acid concentration. The logarithm of the scale parameter of the gamma distribution of the single-cell lag times also increased linearly with the acetic acid concentration irrespective of the phase of the inoculum

Validation of the in-flight calibration procedures for the MICROSCOPE space mission,

International audienceThe MICROSCOPE space mission aims to test the Equivalence Principle with an accuracy of 10-15. The drag-free micro-satellite will orbit around the Earth and embark a differential electrostatic accelerometer including two cylindrical test masses submitted to the same gravitational field and made of different materials. The experience consists in testing the equality of the electrostatic acceleration applied to the masses to maintain them relatively motionless. The accuracy of the measurements exploited for the test of the Equivalence Principle is limited by our a priori knowledge of several physical parameters of the instrument. These parameters are partially estimated on-ground, but with an insufficient accuracy, and an in-orbit calibration is therefore required to correct the measurements. The calibration procedures have been defined and their analytical performances have been evaluated. In addition, a simulator software including the dynamics model of the instrument, the satellite drag-free system and the perturbing environment has been developed to numerically validate the analytical results. After an overall presentation of the MICROSCOPE mission, this paper will describe the calibration procedures and focus on the simulator. Such an in-flight calibration is mandatory for similar space missions taking advantage of a drag-free system

Semi-analytical investigations of the long term evolution of the eccentricity of Galileo and GPS-like orbits

International audienceThis paper aims at investigating the stability over 150 years of a very large number of trajectories in the Medium Earth Orbit (MEO) region, near the orbits devoted to radionavigation such as the Global Navigation Satellite Systems (GNSS like GPS, Glonass, Galileo, COMPASS). The stability is characterized by the long term evolution of the eccentricity, and a stable orbit will be defined by initial conditions not inducing through gravitational perturbations a high difference between the perigee and apogee altitudes over a 150 years (for keeping as low as possible the collision risk with operational orbits). The initial conditions of motion used for our tests cover a wide range of semi-major axes and inclinations, regularly sampled, so as to describe as exhaustively as possible the gravitational perturbations acting on the space debris population in these regions. In this study, we pay particular attention to the dynamical properties which can make the orbits eccentricity becoming very large, due to effects induced by the non-spherical shape of the Earth, and the luni-solar attraction, with an amplitude governed by the satellite inclination, as well. We show that even if apogee and perigee variations must be limited to less than 300 km (corresponding to a maximum allowed eccentricity growth of 0.01), there are some cases where the eccentricity growth can rise up to the order of 0.7 over a few decades. The paper is organized such as follows. We begin with the general and historical background of the study. We then give some detail about the semi-analytical modelling than we will propagate with about 36,000 various initial conditions over 150 years. These simulations are based on a parallelized code which works on a "Grid" with about 60,000 CPUs available, ensuring reasonable integration times. First interpretations are then addressed, from an analytical point of view, searching for combinations of angles and initial conditions inducing very long periodic terms in the temporal variations of the eccentricity