Mars on Earth: soil analogues for future Mars missions

Exploring Mars would be easier if researchers knew more about the properties and behaviour of martian soils. Jeffrey J Marlow, Zita Martins and Mark A Sephton explain how terrestrial analogues could help – especially if we had more of them.     

Mars: simply red?

Ernst Hauber and Gerhard Neukum present a new perspective on the martian surface on the basis of two years of observations by the High resolution Stereo Camera, part of ESA's Mars Express mission.
All HRSC images shown are copyright ESA/DLR/FU Berlin (G Neukum).     

Space debris and planet detection

Jane Greaves reviews the role of dusty debris in the detection and understanding of extrasolar planetary systems.     

Geomagnetic evolution: 400 years of change on planet Earth

Spherical harmonic coefficients of the geomagnetic field, calculated from historical observations of declination, inclination and intensity, and from archaeomagnetic inclination results, have been used to produce a film of geomagnetic change since 1600 A.D. The non-dipole geomagnetic field is found to be constantly changing: no fixed or standing non-dipole features are observed. Non-dipole foci are seen to have lifetimes of a few hundred years. The westward drift, which was an important feature of the 18th and early 19th century geomagnetic field, was less pronounced in the 17th century. The growth, evolution, decay and replacement of non-dipole foci, but not their movement are found to have been the major features producing century-long secular directional magnetic variation. Most of the low degree and order spherical harmonic coefficients have changed significantly over the last few hundred years. In particular the change in sign of the axisymmetric quadrupole around 1837 A.D. is noted. Sustained, century-long, intensity changes, however, appear to have been dominated by variations in the intensity of the centred dipole, rather than by non-dipole field fluctuations.     

Redefining active volcanoes: a discussion

The analysis of the current definitions of active volcanoes indicates that they are empirical, conventional, inaccurate, nongeological, and arbitrarily constraining. Redefinition is therefore needed. One possible approach is to refine the current empirical definitions. A statistically reasonable and practical redefinition using a geologically based time convention-Holocene or 10000 years-is suggested. A set of time conditions according to volcano typology-i.e. 1000; 10000 and 100000 years for high-frequency basaltic shields, andesitic-dacitic composite volcanoes and low-frequency large silicic calderas, respectively-as further refinement of the empirical definition is also envisaged. Devising a phenomenological definition as a theoretical approach is another possibility, but in practice extant diagnostic means are still unsatisfactory to discriminate accurately between dormant and extinct volcanoes. As a consequence of the redefinition, a classification of volcanoes according to their eruptive status is proposed. Redefinition of active volcanoes might increase accuracy in the usage of basic terms in volcanology and influence volcanic hazard assessment and risk mitigation projects.     

行星内部地震波及其对卫星轨道的影响

本文指出地震学在天文和行星学科里的重要作用.我们主要介绍最近提出的“潮汐—地震波共振”(tidal-seismic resonance)效应,并且讨论它对卫星轨道演化的作用.当在同步轨道以下周期运动的卫星引起的引潮力的频率和行星内部自由震荡频率吻合时,就会发生潮汐—地震波共振.此时,行星内部的地震波将被激发并引起行星表面的显著位移.升高和下降的地面会对卫星产生一个力矩从而使得卫星轨道下降.因为潮汐共振引起的动态地面位移可以比单纯引潮力引起的位移大两个数量级,所以潮汐共振会显著加速卫星下降速率.我们用我们开发的三维地震波场模拟程序AstroSeis数值计算了潮汐—地震波共振对轨道的影响,进而推测这一共振效应可能对行星早期吸积速度有显著影响.另外,因为行星内部的Q值和S波的波速对潮汐共振影响很大,未来研究微重力环境下的小行星或陨石内部地震波的速度和Q值对研究行星演化和太阳系的形成至关重要.     

Cracking up: faulting on Earth and Mars

Joyce Vetterlein and Gerald P Roberts describe research in progress on the structural evolution of Cerberus Fossae, Mars, with implications for cryosphere cracking in recent Mars history.     

Erosion of terrestrial planet atmosphere by surface motion after a large impact

The history of atmosphere accretion has a large significance in the evolution of the Earth and other planets. Here we present a quantitative analysis of the Earth's response to large impacts (in the 10³²–10³⁸ erg energy range), and the resulting atmosphere loss owing to the global radial surface motion. Our results show that it is possible to deplete the Earth's atmosphere via this mechanism in very large (lunar-sized, 10³⁸ erg) impacts.     

From Mars to M81

Martian dust, erosion on Callisto, interstellar gas and the solar wind all play their part in this issue's round-up of space science from Peter Bond .     

基于固体潮的地震模拟预警系统的初步设计

基于地震震中所受日月和行星引潮力及其参数的分布特征,提出一种行星地球地震模拟预警系统的模型及设计方案.该模型理论上可方便地提供任何地点的地震预警信息,并试图成为地震研究的辅助手段.采用NEIC提供的1973～2003年全球完整的4018次M≥6级地震数据,建成其测试版,并作初步检测,其中包括对1976年唐山地震和2004年印度洋地震的检验,以及模拟对美国旧金山地区所作10年(2006～2015年)6级以上的强震预测.     

Interaction of the solar wind with Mars from Mars Global Surveyor MAG/ER observations

The observations of the magnetometer/electron reflectometer (MAG/ER) investigation onboard the Mars Global Surveyor (MGS) have greatly contributed to improve our understanding of the interaction of the solar wind with Mars. These observations established conclusively that a global dynamo-generated magnetic field does not exist at Mars, and that the interaction with solar wind is of the atmospheric type. This article reviews the most important results obtained from MGS MAG/ER on the study of two major features in the Mars solar wind interaction. The first feature is the occurrence of large-amplitude, highly coherent waves at the proton cyclotron frequency in the region upstream from the Martian bow shock. The second feature is the magnetic pileup boundary (MPB), a well-defined plasma boundary inside of which the planetary exospheric ions outnumber the solar wind ions. The study of these two elements is crucial to characterize the properties of the Martian exosphere. In addition, the occurrence of an MPB at comets and Venus reveals common processes to all these unmagnetized atmospheric bodies in spite of their different physical nature and characteristic scales.     

Hydraulic modelling of Athabasca Vallis,Mars

Abstract

Palaeohydraulic modelling is presented for Athabasca Vallis, the youngest known catastrophic flood channel on Mars. This modelling incorporates three significant advantages over previous modelling of Martian channels: a step-backwater hydraulic model; more accurate topography; and improved flood height indicators. The maximum modelled palaeodischarge is between 1 × 10⁶ and 2 × 10⁶m³s^?1 depending on the friction coefficient selected. An anomalously high palaeostage indicator suggests a region of ponded backwater in the channel in which streamlined forms were created through deposition, with the additional possibility of post-flood subsidence/lowering of the channel slope due to magma extrusion.