Michel Menvielle

Network science landers for Mars

Abstract The NetLander Mission will deploy four landers to the Martian surface. Each lander includes a network science payload with instrumentation for studying the interior of Mars, the atmosphere and the subsurface, as well as the ionospheric structure and geodesy. The NetLander Mission is the first planetary mission focusing on investigations of the interior of the planet and the large-scale circulation of the atmosphere. A broad consortium of national space agencies and research laboratories will implement the mission. It is managed by CNES (the French Space Agency), with other major players being FMI (the Finnish Meteorological Institute), DLR (the German Space Agency), and other research institutes. According to current plans, the NetLander Mission will be launched in 2005 by means of an Ariane V launch, together with the Mars Sample Return mission. The landers will be separated from the spacecraft and targeted to their locations on the Martian surface several days prior to the spacecrafts arrival at Mars. The landing system employs parachutes and airbags. During the baseline mission of one Martian year, the network payloads will conduct simultaneous seismological, atmospheric, magnetic, ionospheric, geodetic measurements and ground penetrating radar mapping supported by panoramic images. The payloads also include entry phase measurements of the atmospheric vertical structure. The scientific data could be combined with simultaneous observations of the atmosphere and surface of Mars by the Mars Express Orbiter that is expected to be functional during the NetLander Missions operational phase. Communication between the landers and the Earth would take place via a data relay onboard the Mars Express Orbiter.

Constraints on thermal state and composition of the Earth's lower mantle from electromagnetic impedances and seismic data

Despite the tight constraints put by seismology on the elastic properties of the Earths lower mantle, its mineralogical composition and thermal state remain poorly known because the interpretation of seismic measurements suffers from the trade-off between temperature, iron content, and mineralogical composition. In order to overcome this difficulty, we complement seismic data with electromagnetic induction data. The latter data are mostly sensitive to temperature and iron content, while densities and acoustic speeds mostly constrain the mineralogy. A 0.5 log unit increase in electrical conductivity can be caused either by a 400 K increase of the temperature or by an increase of iron content from 10% to 12.5%. Acoustic velocity is only marginally sensitive to temperature but it increases by 0.8 km s−1 on average as the perovskite fraction increases from 50% to 100%. Olsens (1999) apparent resistivities in the period range [15 days, 11 years], and Preliminary reference Earth model (PREM) densities and acoustic speeds are jointly inverted in the depth range [800 km, 2600 km] by using a Monte Carlo Markov Chain method. Given the uncertainties on these data, estimates of perovskite fraction are well constrained over the whole depth range, but information on temperature and iron content is only obtained for depths less than 2000 km, corresponding to the penetration depth of the long-period electromagnetic field. All parameter values are determined with an uncertainty better than 15–20% at the 1σ confidence level. The temperature in the uppermost lower mantle (i.e., down to 1300 km depth) is close to a value of 2200 K and increases along a superadiabatic gradient of 0.4 K km−1 between 1300 and 2000 km depth. Extrapolation of this gradient at greater depth leads to a temperature close to 2800 K at 2600 km depth. The iron content of the lower mantle is found to be almost constant and equal to 10–11% whatever the depth, while a significant linear decrease of the perovskite content is observed throughout the whole depth range, from 80% at 800 km depth down to ∼65% at 2600 km depth.

Contribution of magnetic measurements onboard NetLander to Mars exploration

Abstract In the frame of the international cooperation for Mars exploration, a set of 4 NetLanders developed by an European consortium is expected to land on the planet during the forthcoming years. Among other instruments, the geophysical package of each lander will include a magnetometer. The different possible contributions of magnetic measurements onboard the NetLander stations are presented. Intrinsic planetary field and remanent magnetisation investigations by means of magnetometers onboard a network of landers are first considered, and the information that can be thus derived on the Martian core dynamo and surface rocks, soil, and dust is discussed. The contribution of permanent recording of the magnetic transient variations at a network of surface stations is then discussed. The transient variations of the magnetic field at the surface of a planet has a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic field at the surface of Mars by means of three component magnetometers installed onboard NetLander stations will therefore allow study of both the internal structure of Mars and dynamics of its ionised environment. The expected characteristics of transient magnetic variations, and their relation with plasma flow and current in the Mars ionised environment are discussed. The use of the network magnetic data to probe the internal structure of Mars is also considered. The used techniques are presented, and the information that can be thus obtained on the Mars permafrost, lithosphere and mantle structure illustrated by numerical simulations. Finally, the specifications of the instrument allowing to achieve these objectives are discussed, and the instrument described.

A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes

[1] From one year (2004) of thermosphere total density data inferred from CHAMP/ STAR accelerometer measurements, we calculate the global thermosphere response to auroral magnetic activity forcing at middle and low latitudes using a method based on a singular value decomposition of the satellite data. This method allows separating the large-scale spatial variations in the density, mostly related to altitude/latitude variations and captured by the first singular component, from the time variations, down to timescales on the order of the orbital period, which are captured by the associated projection coefficient. This projection coefficient is used to define a disturbance coefficient that characterizes the global thermospheric density response to auroral forcing. For quiet to moderate magnetic activity levels (Kp < 6), we show that the disturbance coefficient is better correlated with the magnetic am indices than with the magnetic ap indices. The latter index is used in all empirical thermosphere models to quantify the auroral forcing. It is found that the NRLMSISE-00 model correctly estimates the main features of the thermosphere density response to geomagnetic activity, i.e., the morphology of Universal Time variations and the larger relative increase during nighttime than during daytime. However, it statistically underestimates the amplitude of the thermosphere density response by about 50%. This underestimation reaches 200% for specific disturbed periods. It is also found that the difference between daytime and nighttime responses to auroral forcing can statistically be explained by local differences in magnetic activity as described by the longitude sector magnetic indices. Citation: Lathuillere, C., M. Menvielle, A. Marchaudon, and S. Bruinsma (2008), A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes,

Solar flare effects at Ebre: Regular and reversed solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents

This paperp resentsth e resultso f the analysiso f geomagnetice ffectso f solarf lares (sfe) recordeda t Ebre observatory(4 0.8o l atitudeN , 0.5o l ongitudeE ) during3 3 years( 1953- 1985). At Ebre, locatedn eart he focusl atitude,t wo typeso f sfe can be observedr:e gulara nd reverseds fe.R egulars fea ret hosew hichh avep hased ifferencelse sst han9 0o w ith the regular diurnal magnetic variation of the day, Sn. Reversed sfe are those which have phase differences greatert han 90o with Sn.F rom these3 3 years,1 40 sfe eventsw ere selecteda nd a statistical studyw as performed.W e founda local time dependencoef the phased ifferencesb etweent he sfe and S n vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90 o, concentrate between1 0 and 12 hours.R everseds fe showa dominante quinoctiacl haracterA. lso, a weaker correlationw as foundb etweens olara ctivityw ith reverseds fe (r=-0.47)t han with regulars fe (r=-0.68).U sing data from 67 observatoriesw, e performeda globals tudyo f a sfe case,s een at Ebre as reverseds fe. In this case,i n the northernh emispheret,h e sfe systemw as about 1 hour of local time eastward of the S n system and formed 4 o higher in latitude. Finally, we presenta model of two elliptical ionospherice quivalentc urrent systemsw ith focus offset about1 hour in local time to explaint he phased ifferenceb etweent he sfe and Sq magnetic vectorso bserveda t Ebre. The parameterso f this model have been fitted from the resultso f a previouss tatisticaal nalysisf rom Ebre data. Spatiala nd temporald istributiono f the sfe and

A sophisticated lander for scientific exploration of Mars: scientific objectives and implementation of the Mars-96 Small Station

q vector phasesa re calculatedw ith this model, and conditionsf or reverseds fe occurrence are predicted.

Three frontside full halo coronal mass ejections with a nontypical geomagnetic response

A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars.

CONTRIBUTION OF SURFACE MAGNETIC RECORDINGS TO PLANETARY EXPLORATION

After analyzing the source regions of these halo CMEs, it was found that the halo associated with the strongest geomagnetic disturbance was the one that initiated farther away from disk center (source region at W66); while the other two CMEs originated closer to the central meridian but had weaker geomagnetic responses. Therefore, these three events do not fit into the general statistical trends that relate the location of the solar source and the corresponding geoeffectivity. We investigate possible causes of such a behavior. Nonradial direction of eruption, passage of the Earth through a leg of an interplanetary flux rope, and strong compression at the eastern flank of a propagating interplanetary CME during its interaction with the ambient solar wind are found to be important factors that have a direct influence on the resulting north-south interplanetary magnetic field (IMF) component and thus on the CME geoeffectiveness. We also find indications that interaction of two CMEs could help in producing a long-lasting southward IMF component. Finally, we are able to explain successfully the geomagnetic response using plasma and magnetic field in situ measurements at the L1 point. We discuss the implications of our results for operational space weather forecasting and stress the difficulties of making accurate predictions with the current knowledge and tools at hand.

Solar flare effects at Ebre: Unidimensional physical, integrated model

Abstract The transient variations of the magnetic field at the surface of a planet have a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic fields at the surface of Mars by means of three-component magnetometers installed on board landers would therefore allow study of both the internal structure of Mars and the dynamic of its ionized environment. The depth of penetration of an electromagnetic wave in a conductive medium depends on both the period of the wave and the electrical resistivity of the medium. The larger the period and the resistivity, the greater the depth of penetration (skin effect). The high frequency spectrum will therefore enable one to estimate the resistivity in the uppermost kilomettes of the planet, and to give information about the presence (or absence) of liquid water under the permafrost. The low frequency spectrum of the transient variations will give information on the presence (or absence) of sharp variations in the resistivity in the uppermost hundreds of kilometres of Mars, and thus on the thermodynamic conditions within the upper mantle of this planet. Averages of the measurements made during “quiet time measurements” would provide a very good estimate of the field of internal origin at the locations of the surface stations. If in addition a total duration of one year or more for the mission can be expected, and a drift on the order of 1 nT per year for the ground-based magnetometer, it might even be possible to detect some dynamo-related secular variation. In addition to the map of the Martian magnetic field which will be produced by the Mars Surveyor 1 orbiter, these ground-based local main field measurements will provide original information on the present and past magnetic field of Mars, and then on its present and past core dynamics. As is the case for the Earth, different possible controlling plasma processes will lead to different convection patterns inside the magnetosphere and therefore different magnetic signatures at the planetary surface. Continuous recordings of the transient variations of the magnetic field on board landers will then provide constraints on the convection within the Martian magnetosphere, that is a small magnetosphere where the ionosphere lies at great heights relative to the dimensions of the magnetospheric cavity.

The OPTIMISM/MAG Mars-96 experiment: magnetic measurements onboard landers and related magnetic cleanliness program

A great increase of the ionizing radiation during solar flares results in an immediate increase of the ionization production rate, electron densities and electric currents in the ionosphere, followed simultaneously by disturbances of the magnetic elements at ground level (solar flare effects (sfe)). In this paper an attempt is made to model sfe phenomena combining several semiempirical models derived from satellite and radar data obtained during the last two decades. The model allows us to quantify model values of the phase difference between the sfe and Sq vectors, for comparison to the measurable quantity. It explains the cause of the change in magnetic perturbation during a flare at Ebre Observatory (40.8° latitude N, 0.5° longitude E). Large phase shift of the magnetic vector observed before noon, result from a descent of the “center of gravity” of the conducting mass that, combined with a very different regime of neutral winds in the lower and in the middle parts of the dynamo region, produce a change in the direction of the integrated currents.