Tianwen-1 MINPA observations in the solar wind

The Mars Ion and Neutral Particle Analyzer(MINPA)is one of the three scientific instruments onboard the Tianwen-1 orbiter to investigate the Martian space environment.During Tianwen-1’s transfer orbit to Mars,the MINPA was switched on to measure the solar wind ions.Here,we present the first results of the MINPA observations in the solar wind.During cruise,nearly half of the MINPA ion field-of-view(FOV)was blocked by the lander capsule;thus only the solar-wind ions with azimuthal speeds pointing towards the unblocked FOV sectors could be detected.We perform a detailed comparison of the MINPA’s solar wind observations with data from Earth-based missions when MINPA reached its count-rate peak,finding a general consistency of the ion moments between them.The blocking effect due to the lander is evaluated quantitatively under varying solar-wind velocity conditions.Despite the blocking effect,the MINPA’s solar wind measurements during the transfer orbit suggest a good performance.

A local Martian crustal field model: Targeting the candidate landing site of the 2020 Chinese Mars Rover

Unlike Earth,Mars lacks a global dipolar magnetic field but is dominated by patches of a remnant crustal magnetic field.In 2021,the Chinese Mars Rover will land on the surface of Mars and measure the surface magnetic field along a moving path within the possible landing region of 20°W-50°W,20°N-30°N.One scientific target of the Rover is to monitor the variation in surface remnant magnetic fields and reveal the source of the ionospheric current.An accurate local crustal field model is thus considered necessary as a field reference.Here we establish a local crust field model for the candidate landing site based on the joint magnetic field data set from Mars Global Explorer(MGS)and Mars Atmosphere and Volatile Evolution(MAVEN)data combined.The model is composed of 1,296 dipoles,which are set on three layers but at different buried depths.The application of the dipole model to the joint data set allowed us to calculate the optimal parameters of their dipoles.The calculated results demonstrate that our model has less fitting error than two other state-of-the art global crustal field models,which would indicate a more reasonable assessment of the surface crustal field from our model.

Upstream proton cyclotron waves: occurrence and amplitude dependence on IMF cone angle at Mars——from MAVEN observations

Proton cyclotron waves(PCWs)can be generated by ion pickup of Martian exospheric particles in the solar wind.The solar wind ion pickup process is highly dependent on the“IMF cone angle”—the angle between the solar wind velocity and the interplanetary magnetic field(IMF),which also plays an important role in the generation of PCWs.Using data from 2.15 Martian years of magnetic field measurements collected by the Mars Atmosphere and Volatile Evolution(MAVEN)mission,we have identified 3307 upstream PCW events.Their event number distribution decreases exponentially with their duration.A statistical investigation of the effects of IMF cone angle on the amplitudes and occurrence rates of PCWs reveals a slight tendency of PCWs’amplitudes to decrease with increasing IMF cone angle.The relationship between the amplitude and IMF cone angle is weak,with a correlation coefficient r=–0.3.We also investigated the influence of IMF cone angle on the occurrence rate of PCWs and found that their occurrence rate is particularly high for intermediate IMF cone angles(~18°–42°)even though highly oblique IMF orientation occurs most frequently in the upstream region of the Martian bow shock.We also conclude that these variabilities are not artefacts of temporal coverage biases in MAVEN sampling.Our results demonstrate that whereas IMF cone angle strongly influences the occurrence of PCWs,IMF cone angle may also weakly modulate their amplitudes in the upstream region of Mars.

EUV-dependence of Venusian dayside ionopause altitude:VEX and PVO observations

The Venusian dayside ionosphere, similar to other planetary ionospheres, is produced primarily by ionization of its neutral upper atmosphere due to solar extreme ultraviolet (EUV) radiation. It has become clear that the expansion of the ionosphere may be strongly controlled by the EUV level, as exhibited in data collected by the Pioneer Venus Orbiter (PVO) during one solar cycle (1978 1992). However, the EUV-dependence of the Venusian dayside ionopause altitude, which defines the outer boundary of the ionosphere, remains obscure because the PVO crossed the dayside ionopause only during the solar maximum;its periapsis lifted too high during the solar minimum. Recently, during the period 2006 2014, which included the longest and quietest solar minimum of the past several decades, Venus Express (VEX) provided measurements of the photoelectron boundary (PEB) over the northern high-latitude region. Since the photoelectron boundary is closely related to the ionopause, we have an opportunity to analyze the EUV effect on the dayside ionopause by combining PVO and VEX observations. We have evaluated and then reduced the orbit bias effect in data from both PVO and VEX, and then used the results to derive a relationship between solar EUV level and the dayside ionopause altitude. We find that the dayside ionopause altitude increases as the solar EUV level increases, which is consistent with theoretical expectations.

A planetary perspective on Earth's space environment evolution

The planet Earth is an integrated system, in which its multi-spheres are coupled, from the space to the inner core. Whether the space environment in short to long terms has been controlled by the earth's interior process is contentious. In the past several decades,space weather and space climate have been extensively studied based on either observation data measured directly by man-made instruments or ancient data inferred indirectly from some historical medium of past thousands of years. The acquired knowledge greatly helps us to understand the dynamic processes in the space environment of modern Earth, which has a strong magnetic dipole and an oxygen-rich atmosphere. However, no data is available for ancient space weather and climate(>5 ka). Here, we propose to take the advantage of " space-diversity" to build a " generalized planetary space family", to reconcile the ancient space environment evolution of planet Earth from modern observations of other planets in our solar system. Such a method could also in turn give us a valuable insight into other planets' evolution.

A new inclination-based method to evaluate the global geomagnetic configuration and axial dipole moment

The strength and configuration of the geomagnetic field control the average shape of the magnetosphere.The pure dipole assumption and the virtual dipole moment(VDM),determined by individual records,have been widely adopted to evaluate the strength of the geomagnetic field in geological time.However,such an assumption might not be valid during geomagnetic transitions,such as reversals and excursions.The traditional spherical harmonic modeling of the geomagnetic field could be difficult to implement because accurate global records are lacking.Here,we report that an empirical relationship exists between the ratio of the VDM to the true axial dipole moment(VDM/ADM)and the ratio of the power of the axial dipole to that of the non-axial dipole(AD/NAD)based on a new method utilizing globally distributed inclination records.The root mean square global deviation of inclination(RMSΔI)to the standard inclination distribution of the AD was fitted to the AD/NAD with a cubic polynomial by utilizing a large number of geodynamo simulations.Tests with geomagnetic field models showed that the AD/NAD derived from the RMSΔI agreed well with that calculated by using the Gauss coefficients,and the estimated ADM was consistent with the true value.Finally,the application of volcanic records during the Laschamp excursion showed the VDM might overestimate the ADM by a factor of 3.Our new method will be useful in future studies that characterize the configuration of the geomagnetic field and the strength of the axial dipole.

Recent investigations of the near-Mars space environment by the planetary aeronomy and space physics community in China

The present issue of Earth and Planetary Physics is dedicated to the near-space neutral and plasma environments of Mars.The issue includes nine papers that present new results on the properties of the Martian exosphere,ionosphere,and magnetosphere,from both observational and modeling points of view.Due to the similarity between the two objects,the issue also includes two additional papers on the near-Venus plasma environment.

火星全大气模式与沙尘活动模拟研究:回顾与展望

基于火星全大气模式的数值模拟研究有助于深入理解火星陆面-大气-空间环境多圈层相互耦合过程,是当今国际研究热点.模式对整个火星大气区域气象要素的描述亦可作为保障火星探测活动顺利开展的重要参考依据.沙尘活动显著影响着火星气候与天气变化,也对火星表面探测器可造成巨大安全威胁.对沙尘活动及其影响完善的模拟是目前全大气模式开发与研究工作中的重点之一.本文回顾了火星全大气模式的发展历程,概述了其构建方法,总结了相关科研成果,多角度论述了自主发展火星全大气模式的重要科研与工程价值,建议以火星沙尘活动为重点研究方向,牵引我国火星全大气模式的自主研发.模式的开发与应用涉及行星科学、空间科学、大气科学、计算机科学多领域协同合作.其开发过程势必带动我国行星科学全面发展,为相关研究领域积累经验、储备人才.

我国未来在轨监测火星沙尘暴的设想和方案

火星是地球的近邻,它的自转周期(约为24.6 h)及自转倾角(约为25°)都与地球的接近.火星公转周期为687 d,有稀薄的大气(主要成分为CO_(2)),有四季交替的气候变化,表面温度(夏天)最高时可达20°C.火星两极被冰(干冰和水冰的混合物)所覆盖,并有着消融和冰冻的季节周期变化.火星表面布满河道、峡谷、沟壑、冲积平原等地貌特征.在太阳系行星系统中,火星的气候环境最为接近地球.

沙尘暴对火星表面探测器的影响:回顾与展望

沙尘暴会对火星表面探测器带来发电量减少、环境温度降低、通信不稳定和仪器污染等方面的影响.为保障我国祝融号火星车的安全运行及未来火星表面探测任务的顺利开展,亟须评估沙尘暴对火星表面探测器的影响.通过系统性地回顾1997~2018年间火星表面探测器(包括着陆器与火星车)对沙尘的响应,初步认清了沙尘对火星表面探测器的影响规律——探测器太阳能电池阵列表面的尘埃以比较稳定的速率积累,而尘埃的沉积速率在沙尘暴期间,尤其是全球性沙尘暴期间会大大加快;同时,受多方面影响,电池阵列表面也会发生具有季节性模式的除尘事件.为规避沙尘暴带来的风险,在美国洞察号着陆器(InSight)的设计阶段就全面评估了沙尘暴对其着陆硬件系统及太阳能电池阵列的影响,并采取了一系列应对措施.洞察号应对沙尘暴的举措为我国未来的火星采样返回任务提供了重要启迪——前瞻性的科学指导是保障工程任务成功实施的关键.通过分析我国火星采样返回任务的初步轨道设计方案,建议未来火星探测器发射的最优窗口为2028年1月左右,以合理规避沙尘暴带来的风险.

火星沙尘暴监测方法

沙尘暴是火星表面-大气-空间构成的圈层耦合系统中一种重要的天气现象.火星沙尘暴具有显著的季节性,但对不同时空尺度和等级的沙尘暴的发生规律至今仍认识不清.沙尘暴会对火星表面探测器带来诸多影响,如降低太阳能电池板发电量、降低环境温度、扰动大气密度和风场、阻碍通信、污染仪器等,是火星表面探测任务面临的最大安全威胁之一.本文系统性地回顾了人类历史上对火星沙尘暴的监测方法及其数据反演方法,以期为我国构建完善的火星沙尘暴监测体系提供基本的方法支撑.为了更好地保障和服务我国未来火星采样返回任务和后续火星探测任务,我国应考虑尽早建立完善的火星沙尘暴监测体系,这一体系应包含的探测方法包括着陆器可见光相机监测、环绕器可见-红外多光谱相机监测和地基光学望远镜监测.通过这些不同平台、不同时空尺度的监测手段相互配合,既能有效保障我国的火星探测任务安全实施,也将极大促进我国的火星系统科学研究.

Exploring the universe and protecting the Earth:Young Chinese scientists in action

The 5th Youth Scientist Forum of Planetary Science(YSFPS)took place from March 25 to 29,2023,in Sanya,a picturesque coastal city in the Hainan Province of southern China.This forum,one of China’s largest gatherings of its kind,experienced over 1,000 participants from domestic universities and research institutes discussing advancements in a variety of topics,including the surface,atmosphere,interior,core of planets,exoplanet exploration,asteroids,and comets(as shown in Figure 1A).One of the international hot topics in this meeting was lunar science research.With the return of lunar samples from the Chang’e-5 mission,scientists have immediately carried out various studies,forming new understandings about the moon’s evolution and raising new questions.

祝融号火星车巡视区2022年沙尘暴活动趋势初步分析

作为我国首次火星探测任务天问一号的重要部分,祝融号火星车于2021年5月15日着陆在乌托邦平原南部,22日成功驶离着陆平台,开展科学探测工作.目前,火星已经进入沙尘暴多发季节,而祝融号所处区域——乌托邦平原南部则是火星季节性沙尘暴的高发区.利用火星全球沙尘光学厚度的历史数据,本文分析了第24~35火星年(1998~2021年)的全球沙尘暴发生特征,对当前和未来一段时间内祝融号巡视区沙尘暴的活动趋势进行了预测.分析结果表明,祝融号巡视区在2022年3~12月可能出现强沙尘暴,对祝融号的探测工作可能造成显著影响.火星的探测研究是国家战略和科学前沿,火星沙尘暴的分析和预测是行星科学界与探测工程界共同关注的重大问题,需要更多学者尽快对此开展更广泛、更深入的研究.

The solar wind plasma upstream of Mars observed by Tianwen-1:Comparison with Mars Express and MAVEN

On the great journey to Mars,China’s first planetary exploration mission,the Tianwen-1 came within 26 million kilometers of Mars from 31 October 2020 to 25 January 2021 and was getting closer to its destination,the red planet,in search of answers to the cataclysmic climate change that occurred in Martian history.Both the escape of the Martian atmosphere and the loss of surface water were firmly influenced by solar activities.Tianwen-1 provided a unique chance to depict the solar wind streams between Earth and Mars during the minimum of Solar Cycle 25.During the three-month cruise phase of Tianwen-1,the solar wind flows were successively observed at Earth,Tianwen-1,and Mars.After the field of view correction and noise reduction,the solar wind velocity and density measured by Tianwen-1 show good agreement with those at Earth and Mars.The results indicate that the performance of the ion analyzer onboard the Tianwen-1 orbiter is reliable and stable.It is worth looking forward to the joint observations of ion escape with other Mars probes in the following Martian years.

Ablation of Venusian oxygen ions by unshocked solar wind

As an Earth-like planet Venus probably had a primordial dipole field for several million years after formation of the planet.Since this dipole field eventually vanished the ionosphere of Venus has been exposed to the solar wind.The solar wind is shocked near Venus,and then scavenges the ionospheric particles through the magnetosheath and the magnetotail.The escape rate of oxygen ions(O^+)estimated from spacecraft observations over the past several decades has manifested its importance for the evolution of planetary habitability,considering the accumulated effect over the history of Venus.However,all the previous observations were made in the shocked solar wind and/or inside the wake,though some simulations showed that unshocked solar wind can also ablate O^+ions.Here we report Venus Express observations of O^+ions in the unshocked solar wind during the solar minimum.The observations suggest that these O^+ions are accelerated by the unshocked solar wind through pickup processes.The estimated O^+escape rate,2.1×10^(24) ions/s,is comparable to those measured in the shocked solar wind and the wake.This escape rate could result in about 2 cm global water loss over 4.5 billion years.Our results suggest that the atmospheric loss at unmagnetized planets is significantly underestimated by previous observations,and thus we can emphasize the importance of an Earth-like dipole for planetary habitability.