arXiv subjects

Philippe Garnier

Publications and source records attributed to Philippe Garnier.

13 recordsLinked to original sources

arXiv2026

Ranking the drivers of the Venusian bow shock and ion composition boundary locations

The Venusian interaction with the solar wind leads to the formation of an induced magnetosphere structured by plasma boundaries. Their dynamics is complex, due to the combined influence of external (solar photons, solar wind plasma and interplanetary magnetic field (IMF)) and internal (ionized atmosphere) drivers. Studying these drivers helps understanding the transfer of energy and momentum throughout the Venusian system, and has thus implications for the erosion of the atmosphere through its coupling with the solar wind. We here analyze and rank the influence of the main drivers of the Venusian bow shock and ion composition boundary locations. We revisit the results by Signoles et al. (2023) based on Venus Express measurements by combining several methods such as the Akaike Information Criterion, Least Absolute Shrinkage Selection Operator regression, and partial correlations. These methods allow to investigate cross correlations that appear and can bias the interpretation, and allow to rank drivers with robust approaches. The bow shock appears primarily driven by the IMF intensity or Mach number, the IMF $\theta_{bn}$ angle separating quasi-perpendicular vs quasi-parallel shocks, and then the solar extreme ultraviolet fluxes and solar wind dynamic pressure (with little influence of the convective electric field induced asymmetries). The Ion Composition Boundary is primarily driven by extreme ultraviolet fluxes, with a more reduced influence of several solar wind parameters and IMF induced magnetic pileup asymmetries. We also compare the behaviors of both boundaries and then compare the bow shock driver rankings at Mars and Venus. Finally we propose an analysis of the drivers of the extreme bow shock and ion composition boundary excursions.

physics.space-ph↗

arXiv2024

Scenarios of future annual carbon footprints of astronomical research infrastructures

Research infrastructures have been identified as an important source of greenhouse gas emissions of astronomical research. Based on a comprehensive inventory of 1,211 ground-based observatories and space missions, we assessed the evolution of the number of astronomical facilities and their carbon footprint from 1945 to 2022. We found that space missions dominate greenhouse gas emissions in astronomy, showing an important peak at the end of the 1960ies, followed by a decrease that has turned again into a rise over the last decade. Extrapolating past trends, we predict that greenhouse gas emissions from astronomical facilities will experience no strong decline in the future, and may even rise substantially, unless research practices are changed. We demonstrate that a continuing growth in the number of operating astronomical facilities is not environmentally sustainable. These findings should motivate the astronomical community to reflect about the necessary evolutions that would put astronomical research on a sustainable path.

physics.soc-ph↗

arXiv2024

Assessment of the environmental impacts of the Cherenkov Telescope Array Mid-Sized Telescope

Astronomical observatories have been identified as substantial contributors to the carbon footprint of astrophysical research. Being part of the collaboration that currently develops the Medium-Sized Telescope (MST) of the Cherenkov Telescope Array, a ground-based observatory for very-high-energy gamma rays that will comprise 64 telescopes deployed on two sites, we assessed the environmental impacts of one MST on the Northern site by means of a Life Cycle Assessment. We identified resource use and climate change as the most significant impacts, being driven by telescope manufacturing and energy consumption during operations. We estimate life cycle greenhouse gas emissions of 2,660 +/- 274 tCO2 equivalent for the telescope, 44% of which arise from construction, 1% from on-site assembly and commissioning, and 55% from operations over 30 years. Environmental impacts can be reduced by using renewable energies during construction and operations, use of less electronic components and metal casting, and use of recycled materials. We propose complementing project requirements with environmental budgets as an effective measure for impact management and reductions.

astro-ph.IM↗

arXiv2023

Event Detection in Time Series: Universal Deep Learning Approach

Event detection in time series is a challenging task due to the prevalence of imbalanced datasets, rare events, and time interval-defined events. Traditional supervised deep learning methods primarily employ binary classification, where each time step is assigned a binary label indicating the presence or absence of an event. However, these methods struggle to handle these specific scenarios effectively. To address these limitations, we propose a novel supervised regression-based deep learning approach that offers several advantages over classification-based methods. Our approach, with a limited number of parameters, can effectively handle various types of events within a unified framework, including rare events and imbalanced datasets. We provide theoretical justifications for its universality and precision and demonstrate its superior performance across diverse domains, particularly for rare events and imbalanced datasets.

stat.ML↗

arXiv2023

A Comprehensive Python Library for Deep Learning-Based Event Detection in Multivariate Time Series Data and Information Retrieval in NLP

Event detection in time series data is crucial in various domains, including finance, healthcare, cybersecurity, and science. Accurately identifying events in time series data is vital for making informed decisions, detecting anomalies, and predicting future trends. Despite extensive research exploring diverse methods for event detection in time series, with deep learning approaches being among the most advanced, there is still room for improvement and innovation in this field. In this paper, we present a new deep learning supervised method for detecting events in multivariate time series data. Our method combines four distinct novelties compared to existing deep-learning supervised methods. Firstly, it is based on regression instead of binary classification. Secondly, it does not require labeled datasets where each point is labeled; instead, it only requires reference events defined as time points or intervals of time. Thirdly, it is designed to be robust by using a stacked ensemble learning meta-model that combines deep learning models, ranging from classic feed-forward neural networks (FFNs) to state-of-the-art architectures like transformers. This ensemble approach can mitigate individual model weaknesses and biases, resulting in more robust predictions. Finally, to facilitate practical implementation, we have developed a Python package to accompany our proposed method. The package, called eventdetector-ts, can be installed through the Python Package Index (PyPI). In this paper, we present our method and provide a comprehensive guide on the usage of the package. We showcase its versatility and effectiveness through different real-world use cases from natural language processing (NLP) to financial security domains.

cs.LG↗

arXiv2022

Space Plasma Physics Science Opportunities for the Lunar Orbital Platform -Gateway

The Lunar Orbital Platform-Gateway (LOP-Gateway, or simply Gateway) is a crewed platform that will be assembled and operated in the vicinity of the Moon by NASA and international partner organizations, including ESA, starting from the mid-2020s. It will offer new opportunities for fundamental and applied scientific research. The Moon is a unique location to study the deep space plasma environment. Moreover, the lunar surface and the surface-bounded exosphere are interacting with this environment, constituting a complex multi-scale interacting system. This paper examines the opportunities provided by externally mounted payloads on the Gateway in the field of space plasma physics, heliophysics and space weather, but also examines the impact of the space environment on an inhabited platform in the vicinity of the Moon. It then presents the conceptual design of a model payload, required to perform these space plasma measurements and observations. It results that the Gateway is very well-suited for space plasma physics research. It allows a series of scientific objectives with a multidisciplinary dimension to be addressed.

physics.space-ph↗

arXiv2022

The carbon footprint of IRAP

We present an assessment of the greenhouse gases emissions of the Institute for Research in Astrophysics and Planetology (IRAP), located in Toulouse (France). It was performed following the established "Bilan Carbone" methodology, over a large scope compared to similar previous studies, including in particular the contribution from the purchase of goods and services as well as IRAP's use of external research infrastructures, such as ground-based observatories and space-borne facilities. The carbon footprint of the institute for the reference year 2019 is 7400 +/- 900 tCO2e. If we exclude the contribution from external research infrastructures to focus on a restricted perimeter over which the institute has some operational control, IRAP's emissions in 2019 amounted to 3300 +/- 400 tCO2e. Over the restricted perimeter, the contribution from purchasing goods and services is dominant, about 40% of the total, slightly exceeding the contribution from professional travel including hotel stays, which accounts for 38%. Local infrastructures make a smaller contribution to IRAP's carbon footprint, about 25% over the restricted perimeter. We note that this repartition may be specific to IRAP, since the energy used to produce the electricity and heating has a relatively low carbon footprint. Over the full perimeter, the large share from the use of ground-based observatories and space-borne facilities and the fact that the majority of IRAP purchases are related to instrument development indicate that research infrastructures represent the most significant challenge for reducing the carbon footprint of research at our institute. With ~260 staff members employed, our results imply that performing research in astronomy and astrophysics at IRAP according to the standards of 2019 produces average GHG emissions of 28 tCO2e/yr per person involved in that activity (Abridged).

astro-ph.IM↗

arXiv2022

Estimate of the carbon footprint of astronomical research infrastructures

The carbon footprint of astronomical research is an increasingly topical issue with first estimates of research institute and national community footprints having recently been published. As these assessments have typically excluded the contribution of astronomical research infrastructures, we complement these studies by providing an estimate of the contribution of astronomical space missions and ground-based observatories using greenhouse gas emission factors that relates cost and payload mass to carbon footprint. We find that worldwide active astronomical research infrastructures currently have a carbon footprint of 20.3$\pm$3.3 MtCO$_2$ equivalent (CO$_2$e) and an annual emission of 1,169$\pm$249 ktCO$_2$e yr$^{-1}$ corresponding to a footprint of 36.6$\pm$14.0 tCO$_2$e per year per astronomer. Compared with contributions from other aspects of astronomy research activity, our results suggest that research infrastructures make the single largest contribution to the carbon footprint of an astronomer. We discuss the limitations and uncertainties of our method and explore measures that can bring greenhouse gas emissions from astronomical research infrastructures towards a sustainable level.

astro-ph.IM↗

arXiv2019

Flattened loose particles from numerical simulations compared to Rosetta collected particles

Cometary dust particles are remnants of the primordial accretion of refractory material that occurred during the initial stages of the Solar System formation. Understanding their physical structure can help constrain their accretion process. We have developed a simple numerical simulation of aggregate impact flattening to interpret the properties of particles collected by COSIMA. The aspect ratios of flattened particles from both simulations and observations are compared to differentiate between initial families of aggregates characterized by different fractal dimensions $D_f$. This dimension can differentiate between certain growth modes. The diversity of aspect ratios measured by COSIMA is consistent with either two families of aggregates with different initial $D_f$ (a family of compact aggregates with fractal dimensions close to 2.5-3 and some fluffier aggregates with fractal dimensions around 2). Alternatively, the distribution of morphologies seen by COSIMA could originate from a single type of aggregation process, such as DLPA, but to explain the range of aspect ratios observed by COSIMA a large range of dust particle cohesive strength is necessary. Furthermore, variations in cohesive strength and velocity may play a role in the higher aspect ratio range detected (>0.3). Our work allows us to explain the particle morphologies observed by COSIMA and those generated by laboratory experiments in a consistent framework. Taking into account all observations from the three dust instruments on-board Rosetta, we favor an interpretation of our simulations based on two different families of dust particles with significantly distinct fractal dimensions ejected from the cometary nucleus.

astro-ph.EP↗

arXiv2015

Theory for planetary exospheres: III. Radiation pressure effect on the Circular Restricted Three Body Problem and its implication on planetary atmospheres

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the stellar radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this third paper, we investigate the effect of the stellar radiation pressure on the Circular Restricted Three Body Problem (CR3BP), called also the photogravitational CR3BP, and its implication on the escape and the stability of planetary exospheres, especially for Hot Jupiters. In particular, we describe the transformation of the equipotentials and the location of the Lagrange points, and we provide a modified equation for the Hill sphere radius that includes the influence of the radiation pressure. Finally, an application to the hot Jupiter HD 209458b reveals the existence of a blow-off escape regime induced by the stellar radiation pressure.

astro-ph.EP↗

arXiv2015

Theory for planetary exospheres: II. Radiation pressure effect on exospheric density profiles

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this second part of our work, we present here the density profiles of atomic Hydrogen in planetary exospheres subject to the radiation pressure. We first provide the altitude profiles of ballistic particles (the dominant exospheric population in most cases), which exhibit strong asymmetries that explain the known geotail phenomenon at Earth. The radiation pressure strongly enhances the densities compared with the pure gravity case (i.e. the Chamberlain profiles), in particular at noon and midnight. We finally show the existence of an exopause that appears naturally as the external limit for bounded particles, above which all particles are escaping.

astro-ph.EP↗

arXiv2015

Theory for planetary exospheres: I. Radiation pressure effect on dynamical trajectories

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this first paper, we present the complete exact solutions of particles trajectories, which are not conics, under the influence of the solar radiation pressure. This problem was recently partly solved by Lantoine and Russell (2011) and completely by Biscani and Izzo (2014). We give here the full set of solutions, including solutions not previously derived, as well as simpler formulations for previously known cases and comparisons with recent works. The solutions given may also be applied to the classical Stark problem (Stark,1914): we thus provide here for the first time the complete set of solutions for this well-known effect in term of Jacobi elliptic functions.

astro-ph.EP↗

arXiv2012

The Planeterrella experiment: from individual initiative to networking

Space weather is a relatively new discipline which is generally unknown to the wider public, despite its increasing importance to all of our daily lives. Outreach activities can help in promoting the concept of space weather. In particular the visual beauty and excitement of the aurora make these lights a wonderful inspirational hook. A century ago Norwegian experimental physicist Kristian Birkeland, one of the founding fathers of modern space science, demonstrated with his Terrella experiment the formation of the aurora. Recently a modernised version of the Terrella has been designed. This Planeterrella experiment is very flexible, allowing the visualization of many phenomena occurring in our space environment. Although the Planeterrella was originally designed to be small to be demonstrated locally by a scientist, the Planeterrella has proved to be a very successful public outreach experiment. We believe that its success is due to two main factors (i) the Planeterrella is not patented and the plans are given freely to any public institution and (ii) the advertisement does not rely on press release, books or web sites but mainly on National and European scientific networks such as COST ES 0803. Today, nine Planeterrellas are operating or under construction in four different countries, and more are in the pipleline. In five years, about 50,000 people in Europe have been able to see live demonstrations of the formation of auroral lights, picture the space environment and get an introduction to space weather with this experiment. Many more have seen the Planeterrella demonstrated on TV shows. This paper presents the process that led to the making of the Planeterrella and proposes some lessons learned from it.

physics.ed-ph↗