Miniaturized laser-induced plasma spectrometry for planetary in situ analysis – The case for Jupiter’s moon Europa

Jupiter’s icy moon Europa is one of most promising places in our Solar System where possible extraterrestrial life forms could exist either in the past or even presently. The Europa Lander mission, an exciting part of the international Europa Jupiter System Mission (EJSM/Laplace), considers in situ planetary exploration of the moon. The distance of Europa from the Earth and the Sun asks for autonomous analytical tools that maximize the scientific return at minimal resources, demanding new experimental concepts. We propose a novel instrument, based on the atomic spectroscopy of laser generated plasmas for the elemental analysis of Europa’s surface materials as far as it is in reach of the lander for example by a robotic arm or a mole, or just onboard the lander. The technique of laser-induced plasma spectrometry provides quantitative elemental analysis of all major and many trace elements. It is a fast technique, i.e. an analysis can be performed in a few seconds, which can be applied to many different types of material such as ice, dust or rocks and it does not require any sample preparation. The sensitivity is in the range of tens of ppm and high lateral resolution, down to 50 μm, is feasible. In addition, it provides the potential of depth profiling, up to 2 mm in rock material and up to a few cm in more transparent icy matrices. Key components of the instrument are presently developed in Germany for planetary in situ missions. This development program is accompanied by an in-depth methodical investigation of this technique under planetary environmental conditions.     

In situ analysis of Europa ices by short-range melting probes

A key aspect for understanding the astrobiological potential of planets and moons in the Solar system is the analysis of material embedded in or underneath icy layers on the surface. In particular in case of the icy crust of Jupiters moon Europa such investigation would be of greatest interest. For a Europa lander to be launched in the 2020–2030 timeframe, we propose to use a simplified instrumented melting probe which is able to access and sample depths of a few meters without the necessity of heavy and complicated drilling equipment.     

Landforms of Europa and selection of landing sites

Three major features make Europa a unique scientific target for a lander-oriented interplanetary mission: (1) the knowledge of the composition of the surface of Europa is limited to interpretations of the spectral data, (2) a lander could provide unique new information about outer parts of the solar system, and (3) Europa may have a subsurface ocean that potentially may harbor life, the traces of which may occur on the surface and could be sampled directly by a lander. These characteristics of Europa bring the requirement of safe landing to the highest priority level because any successful landing on the surface of this moon will yield scientific results of fundamental importance. The safety requirements include four major components. (1) A landing site should preferentially be on the anti-Jovian hemisphere of Europa in order to facilitate the orbital maneuvers of the spacecraft. (2) A landing site should be on the leading hemisphere of Europa in order to extend the lifetime of a lander and sample pristine material of the planet. (3) Images with the highest possible resolution must be available for the selection of landing sites. (4) The terrain for landing must have morphology (relief) that minimizes the risk of landing and represents a target that is important from a scientific point of view. These components severely restrict the selection of regions for landing on the surface of Europa. After the photogeologic analysis of all Galileo images with a resolution of better than about 70 m/pixel taken for the leading hemisphere of Europa, we propose one primary and two secondary (backup) landing sites. The primary site (51.8°S, 177.2°W) is within a pull-apart zone affected by a small chaos. The first backup site (68.1°S, 196.7°W) is also inside of a pull-apart zone and is covered by images of the lower resolution (51.4 m/pixel). The second backup site (2.4°N, 181.1°W) is imaged by relatively low-resolution images (∼70 m/pixel) and corresponds to a cluster of small patches of dark and probably smooth plains that may represent landing targets of the highest scientific priority from the scientific point of view. The lack of the high-resolution images for this region prevents, however, its selection as the primary landing target.     

Stationkeeping of halo orbits in Jupiter-Europa-Io system

Europa is one of the most promising exploration targets in search for extraterrestrial life. In the observation of Europa, halo orbits are suitable locations, because they are periodic and three-dimensional, and stationary with respect to Europa. However, halo orbits are naturally unstable and thus need stationkeeping. This study addresses the stationkeeping problem of halo orbits in the Jupiter-Europa system perturbated by another Galilean moon Io, in which case Io’s mass and orbital rate are assumed to be unknown. A tight stationkeeping scheme is proposed while accounting for autonomous navigation. To deal with the unknown gravitational perturbation from Io, the mass and orbital rate of Io are estimated during the flight and are then used to enhance the control robustness and stability, and improve the navigation accuracy. The control saturation problem is addressed by introducing adjustable parameters into the control law. The accuracy and error distribution of estimation is evaluated through Monte Carlo simulation.     

Methods and measurements to assess physical and geochemical conditions at the surface of Europa

An international effort dedicated to the science exploration of Jupiter system planned by ESA and NASA in the beginning of the next decade includes in-depth science investigation of Europa. In parallel to EJSM (Europa-Jupiter System Mission) Russia plans a Laplace-Europa Lander mission, which will include another orbiter and the surface element: Europa Lander. In-situ methods on the lander provide the only direct way to assess environmental conditions, and to perform the search for signatures of life. A critical advantage of such in situ analysis is the possibility to enhance concentration and detection limits and to provide ground truth for orbital measurements. The science mission of the lander is biological, geophysical, chemical, and environmental characterizations of the Europa surface. This review is dedicated to methods and strategies of geophysical and environmental measurements to be performed at the surface of Europa, and their significance for the biological assessment, basing on the concept of a relatively large softly landed module, allowing to probe a shallow subsurface. Many of the discussed methods were presented on the workshop “Europa Lander: Science Goals and Experiments” held in Moscow in February 2009. Methods and instruments are grouped into geophysical package, means of access to the subsurface, methods of chemical and structural characterization, and methods to assess physical conditions on the surface.     

Low-altitude,near-polar and near-circular orbits around Europa

The dynamics of orbits around planetary satellites, taking into account the gravitational attraction of a third-body and the non-uniform distribution of mass of the planetary satellite, is studied. The Hamiltonian considered is explicitly time-dependent. Conditions for frozen orbits are presented. Low-altitude, near-polar orbits, very desirable for scientific missions to study planetary satellites such as the Jupiter’s moon Europa, are analyzed. Lifetimes for these orbits are computed through the single and double averaged method. Comparison between the results obtained by the single and double averaged method is presented. The single-averaged model is more realistic, since it does not eliminate the term due to the equatorial ellipticity of the planetary satellite as done by the double-averaged problem. Considering the single-averaged method, we found unstable frozen orbits where the satellite does not impact with the surface of Europa for at least 200 days. We present an approach using the unaveraged disturbing potential to analyze the effects of these terms in the amplitude of the eccentricity.     

Measuring tidal deformations at Europa’s surface

Key information on Europa’s interior can be gained by monitoring tidally-induced surface deformations from orbiting and landed spacecraft. Such observations would provide constraints on the thickness and rheology of Europa’s ice and liquid water layer, being thus an important tool to characterize basic physical properties of the satellite’s putative subsurface water ocean. Focusing on the outer ice-I layer we will present relations between the interior of Europa and key tidal parameters that can be retrieved from an instrument suite monitoring tidally-induced changes of local gravity, tilt, latitude and strain at the surface. A most promising approach would involve laser altimetry and gravitational field observations from an orbiting spacecraft combined with monitoring of tidally-induced gravity and tilt changes at the surface. However, tidal measurements at the surface may be significantly impeded by instrumental drift, instrument coupling to the surface, local sources of noise and the presumably short life-time of the instruments due to the harsh radiation environment.     

Europa planetary protection for Juno Jupiter Orbiter

NASA’s Juno mission launched in 2011 and will explore Jupiter and its near environment starting in 2016. Planetary protection requirements for avoiding the contamination of Europa have been taken into account in the Juno mission design. In particular Juno’s polar orbit, which enables scientific investigations of parts of Jupiter’s environment never before visited, also greatly assist avoiding close flybys of Europa and the other Galilean satellites.     

Lunar laser altimetry in the SELENE project

Lunar laser altimeter (LALT) has been developed for the Japanese lunar exploration SELENE (SELenological and ENgineering Explorer) in 2003. Lunar laser altimetry and two other selenodetic missions are put together and called RISE (Researches In SElenodesy) project that has been developed mainly by National Astronomical Observatory of Japan. Main objective of this measurements is to construct a more global and accurate topographic model of the moon than Clementine's GLTM-2. The newly developed topography of the moon will make a great contribution to many problems of lunar geology, geophysics, and the reduction of lunar occultation data. In order to expand the coverage in latitude, LALT has a function of slant ranging in the direction about 40 degrees aside from nadir. LALT is designed to have a capability of detecting most of returned pulses from the lunar surface even for the slant ranging with proper threshold level.     

Return to Europa: Overview of the Jupiter Europa orbiter mission

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander.     

Dynamics in the Phobos environment

The dynamical environment on and about the Martian moon Phobos is explored. This planetary moon provides a unique dynamical environment in the solar system, being subject to extreme tidal forces and having a characteristically non-spherical shape. Further, it is not in a fully circular orbit, meaning that it has librations that arise from its eccentricity, contributing to a periodic forcing environment. Thus, to plan and implement missions in the vicinity of and on Phobos will require these considerations be taken into account. In this paper the latest published models of the Phobos shape and dynamics are used to characterize its dynamical environment in close proximity orbit about the body, for motion across its surface and for controlled hovering motion in its vicinity. It is found that surface motion is subject to a number of “speed limits” that can cause a moving vehicle to leave the surface and to possibly escape the moon and enter orbit about Mars. In terms of orbital stability, the existence of libration orbit families are characterized down to the surface using an exact potential, and the known stable QSO orbits are shown to be associated with families of stable quasi-periodic orbits.     

Cosmic dust measurements in lunar orbit

On 15th February 1992, ISAS space engineering satellite HITEN was successfully inserted into an elliptical orbit around the moon with perilune between some 100 km and 8000 km and apolune of about 50.000 km. On board was a small scientific experiment designed to detect cosmic dust particles, MDC - Munich Dust Counter. During a period of more than one year, until Hiten's hard landing on the moon surface at 10th of April 1993 (UTC), measurements of impact velocity, mass and crude flight direction of micrometeoroid particles have been performed. In total 150 cosmic dust impacts were detected and evaluated. From these measurements, the impact rate versus time and the dust flux versus distance from the moon are derived. The evidence of moon ejecta and some indications of particles which are orbiting the moon will be discussed. The spatial distribution of the measured particles is shown in lunarcentric as well as in heliocentric coordinate systems. The directional distribution is also given, showing the different populations of cosmic dust particles. Finally, the gathered data will be compared with previous results from measurements in the vicinity of the Earth and in the geomagnetic tail region.     

新型月地空间运输平台概念设计

随着宇航技术的不断发展,月球探索将成为人类的重要活动,地月之间的旅行将变得越来越频繁.但是,目前探索月球的太空旅行费用相当高昂.提出了一种旨在降低地月往返运输成本的新型空间投射-拦截平台概念.它是空间绳系系统、储能系统和空间站系统概念的有机结合.利用该系统有望将现有空间探索能耗水平降低至少一个数量级.阐述了这种新系统的优势及可能遇到的关键技术问题,并初步分析了新系统的可行性.     

Model of energetic populations at Ganymede,implications for an orbiter

A model is developed to study the energetic particle populations in Ganymede’s magnetosphere. The main objective is to estimate to what extent the moon could protect an orbiter from radiations. Using Liouville’s theorem, the phase space density of particles coming from Jupiter’s magnetosphere is calculated at any point of Ganymede’s environment. Up to energies of ∼50–100 keV for ions and ∼10–20 MeV for electrons, Ganymede’s magnetic field appears to be able to form distinctive populations as loss-cones over the polar caps and radiation belts. At larger energies, these features are blurred by Larmor radius effects; the moon absorption simply creates a quasi-isotropic layer of ∼500 km thickness where the flux is reduced by ∼40–50%. The predictions are compared to Galileo measurements. In particular, we demonstrate the importance of the moon sweeping in reducing the flux over the polar caps. Interestingly, this can be accounted for by assuming that the particles bouncing between Jupiter and Ganymede are ideally scattered in pitch angle and permanently re-fill the loss-cone, which increases the precipitation on Ganymede’s polar cap. In overall, it is estimated that the radiation dose received by an orbiter of Ganymede will be reduced by more than 50–60% compared to the expected dose at Jupiter/Ganymede distance. This should have a positive impact on the design of a future orbiter of Ganymede.     

月表磁异常影响的太阳风电子反射运动

模拟太阳风电子向月表运动的轨迹, 研究由于月表磁异常的存在造成的电子反射运动. 首先设定行星际磁场Bsw 指向月球并与月表垂直, 将月表的磁异常区看成是一个磁偶极子, 偶极矩大小为Mcb; 然后分别考察该偶极矩与行星际磁场方向平行, 反平行以及±90° 的情形, 通过计算发现, 被反射的电子数目会随着磁偶极矩和行星际磁场的方向改变而改变. 在偶极矩与行星际磁场平行的情况下, 反射率最大; 随着夹角的增大, 反射率减小. 这些结果为利用电子反射法高精度遥测月表磁场提供了很重要的信息.      

Implementing planetary protection requirements for sample return missions.

NASA is committed to exploring space while avoiding the biological contamination of other solar system bodies and protecting the Earth against potential harm from materials returned from space. NASA's planetary protection program evaluates missions (with external advice from the US National Research Council and others) and imposes particular constraints on individual missions to achieve these objectives. In 1997 the National Research Council's Space Studies Board published the report, Mars Sample Return: Issues and Recommendations, which reported advice to NASA on Mars sample return missions, complementing their 1992 report, The Biological Contamination of Mars Issues and Recommendations. Meanwhile, NASA has requested a new Space Studies Board study to address sample returns from bodies other than Mars. This study recognizes the variety of worlds that have been opened up to NASA and its partners by small, relatively inexpensive, missions of the Discovery class, as well as the reshaping of our ideas about life in the solar system that have been occasioned by the Galileo spacecraft's discovery that an ocean under the ice on Jupiter's moon Europa might, indeed, exist. This paper will report on NASA's planned implementation of planetary protection provisions based on these recent National Research Council recommendations, and will suggest measures for incorporation in the planetary protection policy of COSPAR.     

Interactions of solar wind plasma with dust grains: Effects of strong plasma anisotropy

In this paper we re-examined the fundamental physics of charging of a dust particle in the moon environment by tenuous anisotropic solar wind plasma. The majority of work on dusty (complex) plasmas is largely concerns with laboratory plasmas, in which charging process of dust grains is very fast, thus making practical the working concept of dynamically equilibrium floating potential and grain charge. However, solar wind plasma parameters are considerably different at the moon orbit, and we found the characteristic charging time of lunar dust grains to be considerably longer, ranging from 3 to 4.6 min for micron size particles, and up to 7.6 h for 10-nm grains, depending on the value of plasma streaming velocity. These findings make it clear that the transient stage of charging process is important in the moon environment, and equilibrium floating potential and grain charge could be considered as long time asymptotic values. For this reason we re-formulated the moon dust charging process as an inherently time-dependent problem and derived the time-dependent charging equation for the grain potential for general case of anisotropic solar wind plasma. Using the results of our kinetics analysis we found that the distribution of charge density over grain surface submerged into solar wind plasma is highly anisotropic, thus making the OML model, which is based on the assumption of isotropic distribution of surface charge density, not applicable to the grain charging problem by the solar wind plasma.     

“嫦娥4号”中继星使命轨道段定轨计算与分析

"嫦娥4号"中继星是"嫦娥4号"探测器实现月球背面着陆与巡视的关键,目前正稳定运行在地-月L2点使命轨道上,该使命轨道为平均周期约14天的南族Halo轨道。因任务的需要,中继星本体系+Z轴需调整指向,处于正对太阳和非正对太阳两种状态。太阳光压在中继星+Z轴对日的情况下会加速卫星的角动量累积,增加卫星卸载喷气频次。基于中继星使命轨道段测控支持条件,采用重叠弧段法对两种状态下的中继星定轨精度进行分析与评估。结果表明,在中继星+Z轴非对日运行状态下,重叠弧段位置误差为1.6 km,速度误差为8 mm/s;在中继星+Z轴对日运行状态下,重叠弧段位置误差为0.6 km,速度误差为3 mm/s,这对中继星的长期运行具有重要参考价值。     

Charged particles on the Earth–Jupiter–Europa spacecraft trajectory

Charged particle fluxes on the trajectory of future Russian space research mission to Jupiter and its satellite Europa are investigated. The existing experimental data and models of Jupiter’s main magnetic field and radiation belts are summarized. Preliminary results of computations of energetic particle fluxes and radiation doses for each stage of the flight are given. Special attention is paid to estimation of radiation conditions in Europa’s orbit and on its surface; influence of the satellite on spatial distribution of the fluxes of charged particles of various energies is studied.     

Simulation of the land surface temperature from moon-based Earth observations

The land surface temperature (LST) is a key parameter for the Earth’s energy balance. As a natural satellite of the Earth, the orbital of the moon differs from that of current Earth observation satellites. It is a new way to measure the land surface temperature from the moon and has many advantages compared with artificial satellites. In this paper, we present a new method for simulating the LST measured by moon-based Earth observations. Firstly, a modified land-surface diurnal temperature cycle (DTC) method is applied to obtain the global LST at the same coordinated universal time (UTC) using the Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. The lunar elevation angles calculated using the ephemeris data (DE405) from the Jet Propulsion Laboratory (JPL) were then applied to simulate the Earth coverage observed from the moon. At the same time, the modified DTC model was validated using in situ data, MODIS LST products, and the FengYun-2F (FY-2F) LST, respectively. The results show that the fitting accuracy (root-mean-square error, RMSE) of the modified DTC model is not greater than 0.72?°C for eight in situ stations with different land cover types, and the maximum fitting RMSE of the modified model is smaller than that of current DTC models. By the comparison of the simulated LST with MODIS and FY-2F LST products, the errors of the results were feasible and accredited, and the simulated global LST has a reasonable spatiotemporal distribution and change trend. The simulated LST data can therefore be used as base datasets to simulate the thermal infrared imagery from moon-based Earth observations in future research.