We perform a statistical analysis of data from the Mars Atmosphere and Volatile Evolution (MAVEN) project on the global distribution of protons in the Martian magnetosheath. Our results show that the proton number den...We perform a statistical analysis of data from the Mars Atmosphere and Volatile Evolution (MAVEN) project on the global distribution of protons in the Martian magnetosheath. Our results show that the proton number density distribution has a south-north asymmetry. This south-north asymmetry is most likely caused by the south-north asymmetric distributions of the crustal magnetic fields at Mars. The strong crustal magnetic fields push the inner boundary of magnetosheath to a higher altitude in the southern hemisphere. Due to the outward movement of the inner boundary of the magnetosheath, a compressed magnetosheath forms, causing subsequent increases in proton number density, thermal pressure, and total pressure. Eventually, a balance is reached between the increased total pressure inside the magnetosheath and the increased magnetic pressure inside the induced magnetosphere. Our statistical study suggests that the Martian crustal magnetic fields can strongly affect the proton number density distribution in the Martian magnetosheath.展开更多
The Martian hydrogen exosphere extends out of the bow shock, forming a "hydrogen corona". The solar wind interacts directly with the hydrogen corona. During an ICME event on 7 March 2015, the SWIA instrument...The Martian hydrogen exosphere extends out of the bow shock, forming a "hydrogen corona". The solar wind interacts directly with the hydrogen corona. During an ICME event on 7 March 2015, the SWIA instrument onboard Mars Atmosphere and Volatile Evolution mission (MAVEN) observed that the pick-up H+ fluxes in upstream solar wind were enhanced. Also increased were the penetrating H+ fluxes in the Martian atmosphere. Quantitatively, these penetrating H+ fluxes cannot increase by a factor of 5 simply due to a factor of 3 increase in the solar wind density, suggesting that the increased abundance of exospheric hydrogen upstream of the bow shock was a consequence of the passage of the ICME. A denser outer hydrogen corona at high altitudes suggests that the expansion of the neutral atmosphere was caused by the ICME. The excited and heated hydrogen exosphere probably indicates an elevated hydrogen escape rate during an ICME.展开更多
A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was lo...A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was located in the dayside magnetosheath at an altitude of about 70o km above the northern hemisphere.Collisions between the hot solar wind protons and the cold heavy ions/neutrals in the subsolar region can cool the protons and heat the heavy ions.As a result,the magnetosheath protons are siphoned into the ionosphere due to the thermal pressure gradient of protons and the heated heavy ions escape along the open magnetic field lines.Although direct collisions in the lower-altitude region were not detected,this physical process is demonstrated by MAVEN measurements of enhanced proton density,decreased proton temperature and oppositely directed motions of hot and cool protons within the flux rope,which are very different from the observational features of the flux transfer events near the Earth's magnetopause.This mechanism could universally exist in many contexts where a collisionless plasma region is connected to a collisional plasma region.By reconstructing the magnetic geometry and the cross-section of the flux rope using the Grad-Shafranov technique,the ion loss rates are quantitatively estimated to be on the order of 1023 s-l,which is much higher than previously estimated.展开更多
基金funded by the Science and Technology Development Fund, Macao SAR (File no.0035/2018/AFJ)the National Natural Science Foundation of China (NSFC) under grants 41564007 and 41731067
文摘We perform a statistical analysis of data from the Mars Atmosphere and Volatile Evolution (MAVEN) project on the global distribution of protons in the Martian magnetosheath. Our results show that the proton number density distribution has a south-north asymmetry. This south-north asymmetry is most likely caused by the south-north asymmetric distributions of the crustal magnetic fields at Mars. The strong crustal magnetic fields push the inner boundary of magnetosheath to a higher altitude in the southern hemisphere. Due to the outward movement of the inner boundary of the magnetosheath, a compressed magnetosheath forms, causing subsequent increases in proton number density, thermal pressure, and total pressure. Eventually, a balance is reached between the increased total pressure inside the magnetosheath and the increased magnetic pressure inside the induced magnetosphere. Our statistical study suggests that the Martian crustal magnetic fields can strongly affect the proton number density distribution in the Martian magnetosheath.
基金funded by the Science and Technology Development Fund, Macao SAR (File no.0002/2019/A1)National Natural Science Foundation of China (NSFC) under grant 41731067supported by CNRS, CNES, Observatoire de Paris and Université Paul Sabatier, Toulouse
文摘The Martian hydrogen exosphere extends out of the bow shock, forming a "hydrogen corona". The solar wind interacts directly with the hydrogen corona. During an ICME event on 7 March 2015, the SWIA instrument onboard Mars Atmosphere and Volatile Evolution mission (MAVEN) observed that the pick-up H+ fluxes in upstream solar wind were enhanced. Also increased were the penetrating H+ fluxes in the Martian atmosphere. Quantitatively, these penetrating H+ fluxes cannot increase by a factor of 5 simply due to a factor of 3 increase in the solar wind density, suggesting that the increased abundance of exospheric hydrogen upstream of the bow shock was a consequence of the passage of the ICME. A denser outer hydrogen corona at high altitudes suggests that the expansion of the neutral atmosphere was caused by the ICME. The excited and heated hydrogen exosphere probably indicates an elevated hydrogen escape rate during an ICME.
基金National Natural Science Foundation of China(42122061)the Science and Technology Development Fund of Macao SAR(0002/2019/A1)Macao Foundation,and the pre-research project on Civil Aerospace Technologies No.D020308 and D020104 funded by China National Space Administration.C.M.thanks the Austrian Science Fund(FWF):P31521-N27.C.J.F.thanks NASA grant:80NSSC19K1293.A basic version of the Grad-Shafranov reconstruction method in Matlab is available at https://github.com/cmoestl/interplanetarygrad-shafranov.We acknowledge the MAVEN contract for support.All MAVEN data are available on the Planetary Data System(https://pds.nasa.gov).
文摘A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was located in the dayside magnetosheath at an altitude of about 70o km above the northern hemisphere.Collisions between the hot solar wind protons and the cold heavy ions/neutrals in the subsolar region can cool the protons and heat the heavy ions.As a result,the magnetosheath protons are siphoned into the ionosphere due to the thermal pressure gradient of protons and the heated heavy ions escape along the open magnetic field lines.Although direct collisions in the lower-altitude region were not detected,this physical process is demonstrated by MAVEN measurements of enhanced proton density,decreased proton temperature and oppositely directed motions of hot and cool protons within the flux rope,which are very different from the observational features of the flux transfer events near the Earth's magnetopause.This mechanism could universally exist in many contexts where a collisionless plasma region is connected to a collisional plasma region.By reconstructing the magnetic geometry and the cross-section of the flux rope using the Grad-Shafranov technique,the ion loss rates are quantitatively estimated to be on the order of 1023 s-l,which is much higher than previously estimated.
