Modelling the imposed magnetospheres of Mars-like exoplanets: star–planet interactions and atmospheric losses

2021 ◽  
Vol 502 (3) ◽  
pp. 3569-3581
Author(s):  
Arnab Basak ◽  
Dibyendu Nandy
Keyword(s):  
Magnetic Activity ◽  
Global Features ◽  
Mars Atmosphere ◽  
Strong Current ◽  
Pile Up ◽  
Magnetohydrodynamic Simulations ◽  
Stellar Magnetic Fields ◽  
The Impact ◽  
Atmospheric Mass ◽  
Planetary Habitability

ABSTRACT Based on 3D compressible magnetohydrodynamic simulations, we explore the interactions between the magnetized wind from a solar-like star and a Mars-like planet – with a gravitionally stratified atmosphere – that is either non-magnetized or hosts a weak intrinsic dipolar field. The primary mechanism for the induction of a magnetosphere around a non-magnetized conducting planet is the pile-up of stellar magnetic fields in the day-side region. The magnetopause stand-off distance decreases as the strength of the planetary dipole field is lowered and saturates to a minimum value for the case of a planet with no magnetic field. Global features such as bow shock, magnetosheath, magnetotail, and strong current sheets are observed in the imposed magnetosphere. We explore variations in atmospheric mass loss rates for different stellar wind strengths to understand the impact of stellar magnetic activity and plasma winds – and their evolution – on (exo)planetary habitability. In order to simulate a case analogous to the present-day Mars, a planet without atmosphere is considered. Our simulations are found to be in good agreement with observational data from Mars Global Surveyor and Mars Atmosphere and Volatile EvolutioN missions and is expected to complement observations from the Emirates (Hope) Mars Mission, China's Tianwen-1 and NASA's Mars 2020 Perseverance mission.

On Abnormally Strong Currents Observed on the Northern Coast of Peru during the 2015-2016 El Niño

2021 ◽  
Vol 8 (4) ◽  
pp. 205-210
Author(s):  
Chang-Woong Shin ◽  
Dimitri Gutiérrez
Keyword(s):  
Mixed Layer ◽  
El Niño ◽  
El Nino ◽  
Current Data ◽  
Kelvin Waves ◽  
Coastal Current ◽  
Northern Coast ◽  
El Niño Event ◽  
Strong Current ◽  
The Impact

The northern coast of Peru is a region that can rapidly detect the impact of an El Niño. To investigate the effects of the 2015-2016 El Niño on the oceanographic environment of the northern coast of Peru, the temperature and current data obtained from moored equipment at an oil platform were analyzed. Strong coastal along-shore currents of more than 0.60 m·s-1 were observed three times, although the mean current speed was 0.10 m·s-1 flowing toward the south-southwest. After the first strong current, the bottom temperature increased and the mixed layer deepened and remained there during the El Niño event. The temperature reached a maximum after the strong coastal current, then decreased gradually. An analysis of wind and sea surface height anomalies revealed that the coastal strong current was caused by Kelvin waves and the deepening of the mixed layer was not related to local winds, but to coastal Kelvin waves from the equator during the El Niño event.

Slurry Erosion Behaviors of Pseudoelastic TiNi Alloy

2007 ◽  
Author(s):  
Renbo Xu ◽  
Lishan Cui ◽  
Yanjun Zheng ◽  
Siwei Zhang
Keyword(s):  
Stainless Steel ◽  
Erosion Resistance ◽  
Deformation Mode ◽  
Experimental Results ◽  
Material Surface ◽  
Tini Alloy ◽  
Erosion Process ◽  
Slurry Erosion ◽  
Pile Up ◽  
The Impact

The slurry erosion behaviors of pseudoelastic TiNi alloy were studied using the liquid/solid impingement system and compared with SUS 630 and 2Cr12NiMo1W1V alloy. The influences of erosion time and angle on erosion resistance of three materials were surveyed. The experimental results show that TiNi alloy has the highest erosion resistance among the three materials and SUS 630 stainless steel is more resistant than 2Cr12NiMoW1V alloy. The KQL-300 indentation tester was used to simulate the impact of particle on material surface during erosion process. The results show that the deformation mode of indention can be pile-up or sink-in and there is a good correlation between erosion resistance of material and its indentation deformation mode. The sink-in deformation mode indicates the higher resistance to erosion, and the pile-up deformation mode implies the lower erosion resistance.

scholarly journals Stellar activity and coronal heating: an overview of recent results

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140259 ◽  
Author(s):  
Paola Testa ◽  
Steven H. Saar ◽  
Jeremy J. Drake
Keyword(s):  
Magnetic Activity ◽  
Coronal Heating ◽  
Complementary Information ◽  
Stellar Activity ◽  
X Ray ◽  
Solar Observations ◽  
Term Evolution ◽  
Wide Range ◽  
Stellar Magnetic Fields

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

Atmospheric escape from rocky M-dwarf planets orbiting within the habitable zone

2020 ◽  
Author(s):  
Chuanfei Dong
Keyword(s):  
Space Weather ◽  
Climate Science ◽  
Magnetic Activity ◽  
Habitable Zone ◽  
Atmospheric Escape ◽  
Dwarf Planets ◽  
James Webb Space Telescope ◽  
Wide Range ◽  
The Many ◽  
The Impact

<p>In the last two decades, the field of exoplanets has witnessed a tremendous creative surge. Research in exoplanets now encompasses a wide range of fields ranging from astrophysics to heliophysics and climate science. One of the primary objectives of studying exoplanets is to determine the criteria for habitability, and whether certain exoplanets meet these requirements. The classical definition of the Habitable Zone (HZ) is the region around a star where liquid water can exist on the planetary surface given sufficient atmospheric pressure. However, this definition largely ignores the impact of the stellar wind and stellar magnetic activity on the erosion of an exoplanet's atmosphere. Amongst the many factors that determine habitability, understanding the mechanisms of atmospheric loss is of paramount importance.</p><p>We will discuss the impact of exoplanetary space weather on the long-term climate evolution and habitability, which offers fresh insights concerning the habitability of exoplanets, especially those orbiting M-dwarfs, such as Proxima b and the TRAPPIST-1 planets. We will focus on a wide range of atmospheric compositions, ranging from exo-Venus candidates to Earth twins, as many factors remain unresolved at this stage. Future missions such as the James Webb Space Telescope (JWST) will play a crucial role in constraining the atmospheres of those exoplanets. For each of these cases, we will demonstrate the importance of the exoplanetary space weather on atmospheric ion loss and habitability.</p>

scholarly journals Stellar magnetic activity and their influence on the habitability of exoplanets

2014 ◽  
Vol 10 (S305) ◽  
pp. 333-339
Author(s):  
T. Lüftinger ◽  
M. Güdel ◽  
C. Johnstone
Keyword(s):  
Magnetic Fields ◽  
International Research ◽  
Planetary Systems ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Research Network ◽  
Stellar Rotation ◽  
Theoretical Understanding ◽  
Points Of View ◽  
Stellar Magnetic Fields

AbstractStellar magnetism, explorable via polarimetry, is a crucial driver of activity, ionization, photodissociation, chemistry and winds in stellar environments. Thus it has an important impact on the atmospheres and magnetospheres of surrounding planets. Modeling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only recent ground breaking advances in observational instrumentation - as were discussed during this Symposium - and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and winds and the resulting influence on surrounding planets in more and more detail. We have initiated a national and international research network (NFN): ‘Pathways to Habitability - From Disks to Active Stars, Planets to Life’, to address questions on the formation and habitability of environments in young, active stellar/planetary systems. In this contribution we discuss the work we are carrying out within this project and focus on how stellar magnetic fields, their winds and the relation to stellar rotation can be assessed observationally with relevant techniques such as Zeeman Doppler Imaging (ZDI), field extrapolation and wind simulations.

scholarly journals Shock heating in numerical simulations of kink-unstable coronal loops

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140266 ◽  
Author(s):  
M. R. Bareford ◽  
A. W. Hood
Keyword(s):  
Magnetic Reconnection ◽  
Large Scale ◽  
Magnetic Energy ◽  
Coronal Loops ◽  
Current Sheets ◽  
Shock Heating ◽  
Strong Current ◽  
Coronal Magnetic Fields ◽  
Magnetohydrodynamic Simulations ◽  
The Magnetic Field

An analysis of the importance of shock heating within coronal magnetic fields has hitherto been a neglected area of study. We present new results obtained from nonlinear magnetohydrodynamic simulations of straight coronal loops. This work shows how the energy released from the magnetic field, following an ideal instability, can be converted into thermal energy, thereby heating the solar corona. Fast dissipation of magnetic energy is necessary for coronal heating and this requirement is compatible with the time scales associated with ideal instabilities. Therefore, we choose an initial loop configuration that is susceptible to the fast-growing kink, an instability that is likely to be created by convectively driven vortices, occurring where the loop field intersects the photosphere (i.e. the loop footpoints). The large-scale deformation of the field caused by the kinking creates the conditions for the formation of strong current sheets and magnetic reconnection, which have previously been considered as sites of heating, under the assumption of an enhanced resistivity. However, our simulations indicate that slow mode shocks are the primary heating mechanism, since, as well as creating current sheets, magnetic reconnection also generates plasma flows that are faster than the slow magnetoacoustic wave speed.

scholarly journals Impact of magnetic activity on inferred stellar properties of main-sequence Sun-like stars

2021 ◽  
Vol 502 (4) ◽  
pp. 5808-5820
Author(s):  
Alexandra E L Thomas ◽  
William J Chaplin ◽  
Sarbani Basu ◽  
Ben Rendle ◽  
Guy Davies ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Frequency Separation ◽  
Near Surface ◽  
Global Properties ◽  
Modelling Analysis ◽  
Inclination Angles ◽  
Stellar Properties ◽  
Oscillation Frequencies ◽  
Frequency Ratios ◽  
The Impact

ABSTRACT The oscillation frequencies observed in Sun-like stars are susceptible to being shifted by magnetic activity effects. The measured shifts depend on a complex relationship involving the mode type, the field strength, and spatial distribution of activity, as well as the inclination angle of the star. Evidence of these shifts is also present in frequency separation ratios that are often used when inferring global properties of stars in order to avoid surface effects. However, one assumption when using frequency ratios for this purpose is that there are no near-surface perturbations that are non-spherically symmetric. In this work, we studied the impact on inferred stellar properties when using frequency ratios that are influenced by non-homogeneous activity distributions. We generate several sets of artificial oscillation frequencies with various amounts of shift and determine stellar properties using two separate pipelines. We find that for asteroseismic observations of Sun-like targets we can expect magnetic activity to affect mode frequencies that will bias the results from stellar modelling analysis. Although for most stellar properties this offset should be small, typically less than 0.5 per cent in mass, estimates of age and central hydrogen content can have an error of up to 5 per cent and 3 per cent, respectively. We expect a larger frequency shift and therefore larger bias for more active stars. We also warn that for stars with very high or low inclination angles, the response of modes to activity is more easily observable in the separation ratios and hence will incur a larger bias.

Solar Rotation, Irradiance Changes and Climate

1994 ◽  
Vol 143 ◽  
pp. 244-251
Author(s):  
Elizabeth Nesme-Ribes ◽  
Dmitry Sokoloff ◽  
Robert Sadourny
Keyword(s):  
Magnetic Fields ◽  
Internal Rotation ◽  
Solar Rotation ◽  
Total Solar Irradiance ◽  
Magnetic Activity ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Solar Type ◽  
Activity Cycles ◽  
The Impact

Magnetic activity cycles for solar-type stars are believed to originate from non-uniform internal rotation. To determine this depthwise angular velocity distribution, helioseismology is a valuable source of information. Surface rotation, as traced by sunspot motion, is a well-observed parameter with data going back to the beginning of the telescopic era. This long sunspot series can be used in understanding the behaviour of the Sun’s surface rotation, the connection with its internal rotation, and thereby its magnetic activity. Apparent solar diameter is another important parameter. This is related to the structure of the convective envelope and how it reacts to the presence of magnetic fields. Both these parameters are related to the solar output, and can provide a surrogate for total solar irradiance, by way of a theoretical modeling of the response of the convective zone to the emergence of periodic magnetic fields. The impact of solar variability on the terrestrial climate is also addressed.

scholarly journals The impact on global magnetohydrodynamic simulations from varying initialisation methods: results from GUMICS-4

2017 ◽  
Vol 35 (4) ◽  
pp. 907-922 ◽  
Author(s):  
Antti Lakka ◽  
Tuija I. Pulkkinen ◽  
Andrew P. Dimmock ◽  
Adnane Osmane ◽  
Ilja Honkonen ◽  
...  
Keyword(s):  
High Speed ◽  
Synthetic Data ◽  
Constant Density ◽  
Satellite Measurements ◽  
Wind Measurements ◽  
Sinusoidal Functions ◽  
Magnetohydrodynamic Simulations ◽  
The Impact ◽  
Different Parts ◽  
Good Agreement

Abstract. We investigate the effects of different initialisation methods of the GUMICS-4 global magnetohydrodynamic (MHD) simulation to the dynamics in different parts of the Earth's magnetosphere and hence compare five 12 h simulation runs that were initiated by 3 h of synthetic data and followed by 9 h of solar wind measurements using the OMNI data as input. As a reference, we use a simulation run that includes nearly 60 h of OMNI data as input prior to the 9 h interval examined with different initialisations. The selected interval is a high-speed stream event during a 10-day interval (12–22 June 2007). The synthetic initialisations include stepwise, linear and sinusoidal functions of the interplanetary magnetic field with constant density and velocity values. The results show that the solutions converge within 1 h to give a good agreement in both the bow shock and the magnetopause position. However, the different initialisation methods lead to local differences which should be taken into consideration when comparing model results to satellite measurements.

scholarly journals Atmospheric mass-loss from high-velocity giant impacts

2019 ◽  
Vol 486 (2) ◽  
pp. 2780-2789 ◽  
Author(s):  
Almog Yalinewich ◽  
Hilke Schlichting
Keyword(s):  
Mass Loss ◽  
High Velocity ◽  
Surface Velocity ◽  
Shock Propagation ◽  
Hydrodynamic Simulations ◽  
Giant Impacts ◽  
Self Similar ◽  
The Impact ◽  
Atmospheric Mass ◽  
Impact Shock Wave

ABSTRACT Using moving mesh hydrodynamic simulations, we determine the shock propagation and resulting ground velocities for a planet hit by a high-velocity impactor. We use our results to determine the atmospheric mass-loss caused by the resulting ground motion due to the impact shock wave. We find that there are two distinct shock propagation regimes. In the limit in which the impactor is significantly smaller than the target (Ri << Rt), the solutions are self-similar and the shock velocity at a fixed point on the target scale as $m_{\rm i}^{2/3}$, where mi is the mass of the impactor. In addition, the ground velocities follow a universal profile given by vg/vi = (14.2x2 − 25.3x + 11.3)/(x2 − 2.5x + 1.9) + 2ln Ri/Rt, where x = sin (θ/2), θ is the latitude on the target measured from the impact site, and vg and vi are the ground velocity and impact velocity, respectively. In contrast, in the limit in which the impactor is comparable to the size of the target (Ri ∼ Rt), we find that shock velocities decline with the mass of the impactor significantly more weakly than $m_{\rm i}^{2/3}$. We use the resulting surface velocity profiles to calculate the atmospheric mass-loss for a large range of impactor masses and impact velocities and apply them to the Kepler-36 system and the Moon forming impact. Finally, we present and generalize our results in terms of the vg/vi and the impactor to target size ratio (Ri/Rt) such that they can easily be applied to other collision scenarios.

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