The magnetized wind from stars that impact exoplanets should lead to radio emissions. According to the scaling laws derived in the solar system, the radio emission should depend on the stellar wind, interplanetary magnetic field, and topology of the exoplanet magnetosphere. The aim of this study is to calculate the dissipated power and subsequent radio emission from exoplanet magnetospheres with different topologies perturbed by the interplanetary magnetic field and stellar wind, to refine the predictions from scaling laws, and to prepare the interpretation of future radio detections. We use the magnetohydrodynamic (MHD) code PLUTO in spherical coordinates to analyze the total radio emission level resulting from the dissipation of the kinetic and magnetic (Poynting flux) energies inside the exoplanet's magnetospheres. We apply a formalism to infer the detailed contribution in the exoplanet radio emission on the exoplanet's day side and magnetotail. The model is based on Mercury-like conditions, although the study results are extrapolated to exoplanets with stronger magnetic fields, providing the lower bound of the radio emission. The predicted dissipated powers and resulting radio emissions depends critically on the exoplanet magnetosphere topology and interplanetary magnetic field (IMF) orientation. The radio emission on the exoplanet's night and day sides should thus contain information on the exoplanet magnetic field topology. In addition, if the topology of an exoplanet magnetosphere is known, the radio emission measurements can be used as a proxy of the instantaneous dynamic pressure of the stellar wind, IMF orientation, and intensity.
Context: The first tentative detection of a magnetic field on the Hot Jupiter type exoplanet $τ$ Boötis b was recently reported by Turner et al. (2021). The magnetic field was inferred from observations of circularly-polarized radio emission obtained with the LOFAR telescopes. The radio emission is possibly a consequence of the interaction of the surrounding stellar wind with the planet's magnetic field. Methods: We perform magnetohydrodynamic simulations of the space environment around $τ$ Boötis b and its interaction with the stellar wind using the PLUTO code. We study the magnetospheric ene…
We present calculations of the auroral radio powers expected from exoplanets with magnetospheres driven by an Earth-like magnetospheric interaction with the solar wind. Specifically, we compute the twin cell-vortical ionospheric flows, currents, and resulting radio powers resulting from a Dungey cycle process driven by dayside and nightside magnetic reconnection, as a function of planetary orbital distance and magnetic field strength. We include saturation of the magnetospheric convection, as observed at the terrestrial magnetosphere, and we present power law approximations for the convection …
Jupiter's bright persistent polar aurora and Earth's dark polar region indicate that the planets' magnetospheric topologies are very different. High-resolution global simulations show that the reconnection rate at the interface between the interplanetary and jovian magnetic fields is too slow to generate a magnetically open, Earth-like polar cap on the timescale of planetary rotation, resulting in only a small crescent-shaped region of magnetic flux interconnected with the interplanetary magnetic field. Most of the jovian polar cap is threaded by helical magnetic flux that closes within the pl…
The outflowing magnetized wind from a host star shapes planetary and exoplanetary magnetospheres dictating the extent of its impact. We carry out three-dimensional (3D) compressible magnetohydrodynamic (MHD) simulations of the interactions between magnetized stellar winds and planetary magnetospheres corresponding to a far-out star-planet system, with and without planetary dipole obliquity. We identify the pathways that lead to the formation of a dynamical steady-state magnetosphere and find that magnetic reconnection plays a fundamental role in the process. The magnetic energy density is foun…
Context: The stellar wind and the interplanetary magnetic field modify the topology of planetary magnetospheres. Consequently, the hazardous effect of the direct exposition to the stellar wind, for example regarding the integrity of satellites orbiting the Earth or the habitability of exoplanets, depend upon the space weather conditions. Aims: The aim of the study is to analyze the response of an Earth-like magnetosphere for various space weather conditions and interplanetary coronal mass ejections. The magnetopause stand off distance, open-close field line boundary and plasma flows towards th…
Characterizing habitable exoplanets and/or their moons is of paramount importance. Here we show the results of our magnetic field topological modeling which demonstrate that terrestrial exoplanet-exomoon coupled magnetospheres work together to protect the early atmospheres of both the exoplanet and the exomoon. When exomoon magnetospheres are within the exoplanet's magnetospheric cavity, the exomoon magnetosphere acts like a protective magnetic bubble providing an additional magnetopause confronting the stellar winds when the moon is on the dayside. In addition, magnetic reconnection would cre…
Exoplanet accretion monitoring spectroscopic survey (ENTROPY) I. Evidence for magnetospheric accretion in the young isolated planetary-mass object 2MASS J11151597+1937266
ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) - II. Time series of Balmer line profiles of Delorme 1(AB)b
Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；CNRS（法国国家科学研究中心）；IPAG（天体物理学与行星学研究所）；Institutionen för astronomi, Stockholms universitet（斯德哥尔摩大学天文系）；AlbaNova universitetscentrum（阿尔巴诺瓦大学中心）；Institute for Advanced Study, Tsinghua University（清华大学高等研究院）；Department of Astronomy, Tsinghua University（清华大学天文系）；Department of Earth and Planetary Science, The University of Tokyo（东京大学地球行星科学系）；Department of Physics, Faculty of Science, Chulalongkorn University（朱拉隆功大学理学院物理系）；Institute for Astrophysical Research and Department of Astronomy, Boston University（波士顿大学天体物理研究所及天文系）
On June 7th, 2021 the Juno spacecraft visited Ganymede and provided the first in situ observations since Galileo's last flyby in 2000. The measurements obtained along a one-dimensional trajectory can be brought into global context with the help of three-dimensional magnetospheric models. Here we apply the magnetohydrodynamic model of Duling et al. (2014) to conditions during the Juno flyby. In addition to the global distribution of plasma variables we provide mapping of Juno's position along magnetic field lines, Juno's distance from closed field lines and detailed information about the magnet…
Revealing a Systematic High-latitude Current Sheet at Jupiter
Southern University of Science and Technology (SUSTech)（南方科技大学）；the University of Hong Kong（香港大学）；Southwest Research Institute（西南研究院）；University of Texas at San Antonio（德克萨斯大学圣安东尼奥分校）；Beihang University（北京航空航天大学）；Peking University（北京大学）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）
Nearly everything we know about extrasolar planets to date comes from optical astronomy. While exoplanetary aurorae are predicted to be bright at low radio frequencies (< 1 GHz), we consider the effect of an exoplanet transit on radio emission from the host star. As radio emission from solar-like stars is concentrated in active regions, a planet occulting a starspot can cause a disproportionately deep transit which should be detectable with major radio arrays currently under development, such as the Square Kilometre Array (SKA). We calculate the radiometric sensitivity of the SKA stages and co…
Exoplanets in extremely close-in orbits are immersed in a local interplanetary medium (i.e., the stellar wind) much denser than the local conditions encountered around the solar system planets. The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (likely higher for host stars more active than the Sun). Here, we quantitatively investigate the nature of the interplanetary media surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensi…
We simulate the space environment around AU Microscopii b and the interaction between the magnetized stellar wind with a planetary atmospheric outflow for ambient stellar wind conditions and Coronal Mass Ejection (CME) conditions. We also calculate synthetic Ly$α$ absorption due to neutral hydrogen in the ambient and the escaping planetary atmosphere affected by this interaction. We find that the Ly$α$ absorption is highly variable due to the highly-varying stellar wind conditions. A strong Doppler blue-shift component is observed in the Ly$α$ profile, in contradiction to the actual escape vel…
The nearby M dwarf WX UMa has recently been detected at radio wavelengths with LOFAR. The combination of its observed brightness temperature and circular polarisation fraction suggests that the emission is generated via the electron-cyclotron maser instability. Two distinct mechanisms have been proposed to power such emission from low-mass stars: either a sub-Alfvénic interaction between the stellar magnetic field and an orbiting planet, or reconnection at the edge of the stellar magnetosphere. In this paper, we investigate the feasibility of both mechanisms, utilising the information about th…
The great majority of exoplanets discovered so far are orbiting cool, low-mass stars whose properties are relatively similar to the Sun. However, the stellar magnetism of these stars can be significantly different from the solar one, both in topology and intensity. In addition, due to the present-day technology used in exoplanetary searches, most of the currently known exoplanets are found orbiting at extremely close distances to their host stars ($< 0.1$ au). The dramatic differences in stellar magnetism and orbital radius can make the interplanetary medium of exoplanetary systems remarkably …
The circumstellar environment of the young, low-mass dipper star JH 223. Accretion and large-scale magnetic field topology
Universidade Federal de Minas Gerais（米纳斯吉拉斯联邦大学）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；California Institute of Technology（加州理工学院）；European Southern Observatory（欧洲南方天文台）；INAF - Osservatorio Astrofisico di Catania（意大利国家天体物理研究所卡塔尼亚天文台）；Crimean Astrophysical Observatory（克里米亚天体物理观测站）；Seoul National University（首尔国立大学）；SETI Institute（搜寻地外文明研究所）；Univ. de Toulouse（图卢兹大学）
This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJ's upp…
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 3…
Stellar Wind Driven Alfvén Wing Dynamics in Planetary and Exoplanetary Magnetospheres
Center of Excellence in Space Sciences India, Indian Institute of Science Education and Research Kolkata（印度空间科学卓越中心，印度科学教育研究所加尔各答分校）；Department of Physical Sciences, Indian Institute of Science Education and Research Kolkata（印度科学教育研究所加尔各答分校物理科学系）；Center for High Energy Systems and Sciences, Defence Research and Development Organization（国防研究与发展组织高能系统与科学中心）；Department of Physics, Fakir Chand College（法基尔昌德学院物理系）
(abridged abstract) Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the planetary atmosphere. We wish to quantify the flux of Galactic cosmic rays to an exoplanetary atmosphere as a function of the particle energy and of the planetary m…
We present calculations of auroral radio powers of magnetised hot Jupiters orbiting Sun-like stars, computed using global magnetohydrodynamic (MHD) modelling of the magnetospheric and ionospheric convection arising from the interaction between the magnetosphere and the stellar wind. Exoplanetary auroral radio powers are traditionally estimated using empirical or analytically-derived relations, such as the Radiometric Bode's Law (RBL), which relates radio power to the magnetic or kinetic energy dissipated in the stellar wind-planet interaction. Such methods risk an oversimplification of the mag…
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Physikalisches Institut, University of Bern（伯尔尼大学物理研究所）；Janusz Gil Institute of Astronomy, University of Zielona Góra（热舒夫-西德纳戈拉大学扬努什·吉尔天文学研究所）；Nicolaus Copernicus Superior School, College of Astronomy and Natural Sciences（尼古拉·哥白尼高等学院天文与自然科学学院）；Research Centre for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava（奥帕瓦西里西亚大学物理学院计算物理与数据处理研究中心）；Department of Earth, Planetary, and Space Sciences, University of California–Los Angeles（加州大学洛杉矶分校地球、行星与空间科学系）；Institute for Fusion Studies, Department of Physics, University of Texas at Austin（德克萨斯大学奥斯汀分校物理学院聚变研究所）；International Space Science Institute (ISSI)（国际空间科学研究所）
The Decline and Fall of ROME. V. A Preliminary Search for Star-Disrupted Planet Interactions and Coronal Activity at 5 GHz Among White Dwarfs within 25 pc
Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；University of Groningen（格罗宁根大学）；Université Paris-Saclay（巴黎萨克雷大学）；Sorbonne Université（索邦大学）；Université Paris Cité（巴黎西岱大学）；University of Amsterdam（阿姆斯特丹大学）；Leiden University（莱顿大学）；Rhodes University（罗德兹大学）
(Abridged) The upper atmospheres of close-in gas giant exoplanets are subjected to intense heating/tidal forces from their parent stars. Atomic/ionized hydrogen (H) layers are sufficiently rarefied that magnetic pressure may dominate gas pressure for expected planetary magnetic field strength. We examine the magnetospheric structure using a 3D isothermal magnetohydrodynamic model that includes: a static "dead zone" near the magnetic equator containing magnetically confined gas; a "wind zone" outside the magnetic equator in which thermal pressure gradients and the magneto-centrifugal-tidal effe…
Intense but Harmless: Exo-Space Weather Around an M Dwarf with a Single-Hemisphere Dynamo
Peking University（北京大学）；National Space Science Center, Chinese Academy of Sciences（中国科学院国家空间科学中心）；Leibniz Institute for Astrophysics Potsdam（波茨坦阿斯特拉诺伊莱布尼茨研究所）；University of Massachusetts Lowell（马萨诸塞大学洛厄尔分校）；Lockheed Martin Solar and Astrophysics Laboratory（洛克希德·马丁太阳与天体物理实验室）；University of Potsdam（波茨坦大学）；Nanjing University（南京大学）
Spectropolarimetric characterisation of exoplanet host stars in preparation of the $Ariel$ mission II. The magnetised wind environment of TOI-1860, DS Tuc A, and HD 63433
Solar Magnetic Configuration Control over Radiation Belt Electrons
Northumbria University（诺森比亚大学）；University College London, Mullard Space Science Laboratory（伦敦大学学院穆拉德空间科学实验室）；Donostia International Physics Center (DIPC)（圣塞巴斯蒂安国际物理中心）；Johns Hopkins University, Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）
A Jupiter-like radio aurora in the L3.5 dwarf LSPM J0036+1821
Universitat de València（瓦伦西亚大学）；Centro de Astrobiología, CSIC-INTA（西班牙国家研究委员会-国家航空航天技术研究所天体生物学中心）；Lowell Observatory（洛厄尔天文台）；Trinity College Dublin, The University of Dublin（都柏林大学圣三一学院）；University of Colorado Boulder（科罗拉多大学博尔德分校）；American Museum of Natural History（美国自然历史博物馆）
We present a follow up study of the sensitivity of the Earth's magnetosphere to solar wind activity using a particles-in-cell model [Baraka and Ben Jaffel, 2007], but here during northward IMF. The formation of the magnetospheric cavity and its elongation is obtained with the classical structure of a magnetosphere with parallel lobes. An impulsive disturbance is then applied to the system by changing the bulk velocity of the solar wind to simulate a decrease in the solar wind dynamic pressure followed by its recovery. In response to the imposed disturbance, a gap [abrupt depression] in the inc…
Magnetic reconnection plays an important role in converting energy while modifying field topology. This process takes place in varied plasma environments in which the transport of magnetic flux is intrinsic. Identifying active magnetic reconnection sites in in-situ observations is challenging. A new technique, Magnetic Flux Transport (MFT) analysis, has been developed recently and proven in numerical simulation for identifying active reconnection efficiently and accurately. In this study, we examine the MFT process in 37 previously reported electron diffusion region (EDR)/reconnection-line cro…
