The Sun-Earth relations chainhas its root in the sun and influence the Earth's environment, it can be schematized following the two main regions of the heliosphere.

The Sun

In 1962, the Mariner 2 probe confirmed the suspicions of the astronomers of the XIXth century: a "solar wind" permanently blows from the Sun to the confines of the solar system and delimits its "area of influence", the heliosphere. It consists of a plasma (ionized gas) which mainly contains protons and electrons. Although corresponding to a loss of mass of a million tons a second, this plasma is far from dense. It nevertheless conveys the magnetic field of the Sun, which thus arrives to the Earth. ULYSSES probe revealed that in fact there are two kinds of wind: a "fast" wind (700 km/s) which especially escapes from the poles through coronal holes, areas where the magnetic field of the Sun is less intense, and a "slow" wind (400 km/s), mainly in the low heliographic latitudes, where the constraint of the magnetic field is stronger.

Our star has another characteristic: has it is not a rigid body, its different regions do not rotate at the same speed at the poles and the equator. This differential rotation makes the lines of magnetic field twist, break and reconnect, forming loops. Sometimes, these ones, filled with plasma, break in a brutal release of energy in the form of radiation (, X, UV) and of particles. The hot gas is expelled in the heliosphere. Then it is a flare. If it occurs on the side of the Sun facing the Earth, the flood of very fast particles (faster than 30.000 km/s) hardly takes 30 to 60 minutes to travel the 150 million kilometers which separate us from the Sun.

Higher, in the corona - a very wide area constituting the external atmosphere of the Sun (it is the very thin silver plated veil which can be seen durint solar eclipses) -, similar phenomena can occur: coronal matter ejections, commonly called CME (Coronal Mass Ejections). These disturbances of solar wind (probably due to magnetic phenomena) producing an expulsion of plasma and a shock wave which propagates in the heliosphere. Ejected particles, although slower than the ones from the flares, arrive to the Earth within two or three days.

To monitor the solar activity, the scientists use a fundamental indicator: sunspots. Noticed by the Chinese more than 2.000 years ago, particularly observed by Galileo around 1610, these black spots lying between 10° and 40° latitude. Their diameter varies between 50 and 50.000 km for largest ones. They result from the confinement of solar plasma by magnetic field lines. Thus insulated, it cools and appears as a darker area. The first to have noticed a periodicity in the appearance of the spots is a German amatteur astronomer, a pharmacist, Samuel Heinrich Schwabe, in 1843. He observed the Sun during 17 years. He observede that the spots follow a 11 years cycle with an increase phase (about 4 years), during which their number grows, while they migrate towards the equatorial areas, then a maximum and a decrease phase, generally longer (about 7 years). The peaks of the cycle of the spots correspond to an increase in the magnetic energy of the Sun. The cause is still poorly understood. But it can be noted that the more spots, the more frequently the Sun's violent phenomena - flares and CME - do occure.

We are currently, for the astronomers, the minimum of the 23rd cycle took place in 2008-2009. The beginning of the 24th cycle is planned for 2010 with a maximum in 2012-2013.

Against the sudden changes of the Sun, our planet has two natural protections: the magnetosphere, a screen brought by internal magnetism, and the ionosphere, the upper layer of the atmosphere.

The magnetosphere

Fortunately, our planet has a protection against the particles coming from the Sun: its natural magnetic field. If it did not exist, the amount of radiation would make the planet totally uninhabitable. The Earth is lying in a cavity, the magnetosphere, which deflects the flows of particles coming from the solar wind and the flares. In addition, the Earth's atmosphere absorbs more than half of the solar radiation, ultraviolet and X-ray included.

The protection of the Earth against the Sun activities, ensured by its natural magnetic field, is not a 100% effective. At the time of the flares and CMEs, the charged particles which arrive in the vicinity of the Earth are deflected by the magnetosphere. But the magnetosphere has a weak point: the high latitudes, particularly the poles. The lines of the magnetic field converge there and form a kind of funnel. The protons can be engulfed there.

The CMEs, when they reach the Earth, are accompanied by a shock wave which compresses the magnetosphere. It can be lower to only 20.000 km of the surface of the Earth. In addition, the magnetic field of the Sun, that they transport, disturbs the terrestrial magnetosphere.

The terrestrial magnetosphere is a region easily reachable to satellites, which can measure in situ the characteristics of the plasma: density, ionization level, composition, particles energy distribution, waves, etc...

The plasma in the solar system is characterized by a cellular structure with fixed frontier zones separating areas of varied characteristics. Mass and energy transfers can be observed between these areas.

Three areas are particularly interesting to study :

The interface areas with the hot solar wind (bow shock, magnetosheath, magnetopause) where it is suddenly slowed down, heated and deflected from its trajectory by the Earth magnetic field,
The cold plasma "tanks" which are the ionosphere and the inner magnetosphere (plasmaphere),
The particles acceleration areas, ie the magnetospheric tail and above all the auroral areas.

The auroral areas located in the two hemispheres play a particular part in the operation of the magnetospheric machine, i.e. in the formation and the dissipation of the currents which connect the various areas of the magnetosphere.

It thus could be checked that the most important currents were on the ionosphere level, i.e. where the charged particles are swept by the neutral atmosphere. However there also are currents in the external magnetosphere and between it and the ionosphere. Their knowledge is essential to understand the particles dynamics in these areas.

Moreover the magnetosphere is characterized by the presence of static and dynamic electric and magnetic fields. The electromagnetic waves can be extremely intense as for example, the auroral kilometric radiation (AKR): its power is maximum towards 300 Khz and it constitutes the most intense natural radio source emitted by the Earth.

All these fields interact between themselves as well as with the ambient environment. They thus play a key part in the plasma transport and heating.

Ultimately, the ionized environment of the Earth is extremely complex and its understanding requires various space programs implementing several measurement techniques and at various scales.

Solar physics: interior and lower corona

The SOHO satellite strongly contributed to the knowledge of the structure of the Sun and the acknowledgement of the physics of the Sun - Earth relations.

The rigid rotation of the internal Sun appears slower than that of the external areas at certain latitudes. The role of the tachocline is recognized in the dynamo processes and the regulation of the cycles. Meridian convective circulation is shown. The image of an extremely structured solar interior, where the dynamics of fine layers proves to be fundamental, is essential today (Figure below). By combining solar physics and the physics of the particles, the validation of the model of the internal solar machinery is reached and neutrino oscillations can be highlighted and, therefore, its possible mass estimated.

Three-dimensional view of the variations speed in the internal Sun layers and on its surface. Jets in the polar areas, the presence of a strong shearing layer (tachocline, towards 0,7 Rs) and the latitude structuring of the rotation are quite apparent. These measurements are obtained by the heliosismology techniques and the Soho instruments.

The different modes of solar wind (fast and slow) and their bond with the solar activity and particular photospheric structures is described. The importance of the reconnection on the various scales in the coronal heating is stressed. The Moreton waves, precursor of the CMEs, are described. The magnetic structuring of the photosphere, the chromosphere and the low corona is nowaday recognized as crucial in the loss of mass phenomena. Moreover, the very small scales processes prove to be fundamental for the heating.

STEREO mission enabled for the first time to build not only the third dimension, but also the dynamics of the observed structures in the solar corona (see above). The observation of the polar regions of our star obtained by these probes unveilled strange objects called "polar plumes" whose structure is still poorly known, but which could play an important role in the solar wind acceleration. Until now, a controversy existed about the nature of these objects: are the plumes magnetic field tubes or alignment effects along the lign of sight? In fact, the results show that in fact the two kinds of structures can coexist.

Tri-dimentional reconstructions obtained thanks to STEREO mission

Solar physics (external area) and heliosphere

Differences between the corona and the traditional magnetohydrodynamic model were highlighted. The anisotropic temperatures and depending on the particles species, indicate a role of the cyclotronic waves in the corona heating. Systematic flows to the top were identified from the lower part of the corona in the coronal holes, suggesting that the wind is accelerated from the lower part of the corona. The detailed parameters measurements of the coronal plasma show the importance of the kinetic processes in the heating and the fundamental role of the very low corona for the wind acceleration.

The systematic observation of the CMEs and of the phenomena associated in the low corona made significant progress, in particular with regard to the disturbances on a large scale (EIT waves) emanating from the active areas. The couplings between instability on a large scale and magnetic structuring on a small scale are for the first time accessible to the observations.

The systematic presence of nonthermal populations of particles in solar wind and explosive processes of particles acceleration in the corona was observed, sometimes with relativistic energies (reached of GeV in a few seconds at the maximum!). The concept of "quiet" solar atmosphere lost its significance to the profit of a dynamic vision at all the observable scales.

The acceleration mechanisms of the eruptive Sun are varied and extraordinarily effective. However this effectiveness is not understood (Figure below). The in situ study of the interstellar medium/ heliosphere/ galaxy interaction begins.

Images obtained by the Soho instruments showing the topological complexity of the coronal magnetic fields as well as an example of coronal mass ejection. In this last case, the helicoidal organization of the field is clearly visible.

Terrestrial and planetary magnetospheres

The CLUSTER and DOUBLE STAR missions are a major contribution to the study of the terrestrial magnetosphere.

The physical scales of the shocks in the plasmas without collision were identified.

3D systematic structuring of the magnetospheric layers of currents and 3D characteristics of the reconnexion.
Physics of acceleration: relative role of the Alfven waves, the large scales electrostatic fields, the microscopic structures.
Characterization of turbulence and nonlinéaire evolution of the Alfven waves; with CLUSTER: measure currents (curlometer) and spectral decomposition (k-filtering).

The last generation of magnetospheric satellites opens indeed entirely new prospects for analyzes of the dynamics of space plasmas. 3D topology and microscopic structuring are fundamental elements (Figure below).

Micro example of "micro/macro" physics relation studied thanks to Cluster. Only the simultaneous presence of the four Cluster satellites makes it possible to rebuild the "interlaced" magnetic configuration, probably resulting from a reconnexion, shown in the center of the figure. In same time, the distribution functions of the particles are measured (here ions) and make it possible to identify at the microscopic level the finest modifications of the local state of plasma. Here, an evident heating (distribution 3) and a direct input of solar plasma in the terrestrial environment (distribution 4).

The first applications of the neutral imagery were born. GALILEO enables to discover new activity cycles related to Jupiter, dependant on fast relievings of rotation energy in the magnetosphere.

Interactions between magnetosphere/satellites.
First clean magnetosphere from a satellite. Ganymede was discovered. The planetary environments are privileged grounds of studies of new phenomena and processes.

DEMETER microsatellite launched in June 2004 is still operational with a nominal functioning of the instruments. Data collected around the Earth enabled to show effects of the human activity on the magnetosphere: influence of the TBF emitters used for communications on the particles of radiation belts, and influence of the radiations emitted by the harmonics of the 50 or 60 Hz. The figure below shows the geographical distribution of the 200 keV electron flux nearly trapped.

Geographical distribution of the 200 keV electron flux nearly trapped. A large increase of the flux above the South Atlantic anomaly can be observed with a decrease in its northern counterpart, a structure associated to the NWC emitter in Australia. This one is only detected from the west coast and follows the line L = 1.7 (dashes), as foretold for the electrons drift.

The intense solar flares of November 2003 were favourable to remarkable observations: formation of "bubbles" of plasma at low altitudes (60 km), generation of NOx molecules, strong decrease of ozone (70%) during the proton events. That such phenomena can still be discovered in our close environment, that processes as intense as the sprites are just described, are remarkable examples of vitality and potential of these domains (Figure below).

Recomposed view of the phenomena developing at the atmosphere/thermosphere/ionosphere interfaces, above the stormy systems (sprites, elves).

The decade was also that of the development of global couplings models (atmosphere/thermosphere/ionosphere/magnetosphere) and of the beginning of their experimental tests. These domains also cover the "space weather" themes.

In the planetary chapter, after GALILEO, first MARS EXPRESS and CASSINI results, new chapters have been opened about aeronomy, exospheric physico-chemistry and sputtering processes that are taking place on Mercury and will be studied by the BEPICOLOMBO mission. For example, with MARS EXPRESS and VENUS EXPRESS measurements, it was possible to clarify the general configuration of the magnetic obstacle induced by the interaction of the solar wind with Mars and Venus ionosphere. The first measurements of the escape rate of some ions have been made, proving the reality of the atmospheric erosion phenomenon.

From the analysis of these results three major axes can be identified:

Axis 1 : "inter-scales" interactions, turbulence and non-linearities

This axis concerns general issues of physics. Let us recall however that plasmas cannot be compared to the conventional fluids, liquids and gases. An essential difficulty comes from the absence of reasonably general and adequate "constitutive" equations to connect the physics of the small scales to the macroscopic evolutions. These mediums are often without collision and concepts related for example of diffusivity, compressibility, viscosity, adiabaticity do not have a raison d'être. Nowaday, some general statements are evident concerning the physics of the mediums of the solar system representative of the ionized and/or not very dense environments existing everywhere in the Universe :

The space structuring of the ionized and magnetized mediums is the primordial element of their dynamics and their activity. This structuring, 3D in the majority of the cases, governs for example the processes of creation and annihilation of the magnetic fields. This structuring is evolutionary, with temporal scales being spread out over many orders of magnitude, from "electronic" times to "MHD" emergence times. With the "shocks" propagation, the annihilation processes appear increasingly central in all the acceleration and heating mechanisms of the particles.
The activity of these mediums systematically implements microscopic modifications of the plasma's state. That the space structuring does not give an account alone of the phenomena observed is one of the recent lessons of in situ exploration. The bases of these microscopic modifications can be: the generation of coherent spacio-temporal structures, the development of a more or less coherent turbulence and/or waves/ particles interactions. These microscopic modifications probably control the development of the activity and fix the relative share of the heating, acceleration and the radiation resulting from the energy transfer.
The dynamics of these mediums cannot be understood by isolating structures (coronal arch, magnetic tail, disc in rotation, jet, etc) from their context and by neglecting the conditions of their formation. The role of the boundary conditions and the interactions between the various areas of an environment appears now fundamental. The examination of instabilities proper to isolated and idealized structures cannot give the key of the comprehension of the dynamics of these mediums.

Axis 1: Conceptualization of the "multi-scales" interactions and the bonds between "micro" and "macrophysics", formation and annihilation of the 3D structures, turbulence and dynamics of the complex systems are major scientific topics of the SHM disciplines which all belong to fundamental physics.

Any progress in these domains will have a direct impact on the resolution of conventional SHM problems: solar dynamo, structuring of the solar interior, heating of the corona, generation of the various winds, acceleration and heating of the ions and the electrons, magnetic balances and reconnection (THEMIS), under-storms and explosive dissipations of energies, shocks, interactions with the neutral populations. The applications to other astrophysical domains are obvious. It must also be noted that the problems treated under this angle are often connected to those of the laboratory and fusion plasma physics.

The difficulty of these themes justifies an ambitious experimental approach which combines (1) the 3D multi-scales analysis and (2) the high temporal resolution. This approach relates as much to the in situ analysis of the space medium than the "remote" observation of the environment and solar surface.

Axis 2: Exploration and knowledge of the environments

The study and the analysis of the environments of the solar system objects remain topical. The existence of a potential of discoveries, asking real questions related to the comprehension of the subjacent physico/chemical processes, is shown with each new exploration. This also relates to a medium however well studied: terrestrial environment. The main reason is the complexity of the inter-regional or interlayers relations of these environments and their primordial role in dynamics.

Axis 2: The analysis and the comprehension of the interlayers interactions of the environments of the solar system, in first chief of the Earth and the Sun but also of planets, are a fundamental axis of SHM futurology. This axis joined the concerns of "space weather".

The exploration of the objects and the environments of the solar system is an essential element of the experimental strategy of "SHM". Nowaday, this axis concerns in first chief the missions as MARS EXPRESS, Cassini and STEREO. In each case, the experimental effort goes with a development of specific digital and simulations models.

Axis 3: History of the relations Sun/planets, climatology and long solar cycles

For obvious reasons, this domain is currently in full explosion. The existence of variations of solar radiance during long cycles and their possible climatic effects is the core of a debate with strong society impact. These subjects offer an "historical" kind problems to SHM domain. They are related to some domains of the planets aeronomy, such as for example the slow transformation, over cosmogonic times, of planetary atmospheres because of their interactions with solar wind and the energetic solar populations. These questions join also fundamental interrogations about the life in the Universe. From a certain point of view, the appearance, the development and the sustaining of the life can be perceived as the results of a privileged relation between a source of energy (a star) and a substrate (a planet and its intrinsic chemistry). The study of these relations has a link with SHM themes, even if obviously the solar effects are only one of the many factors affecting the environments.

The PICARD mission should enable to establish the relation between the diameter of the Sun and the flux received by the Earth and also to ensure the continuity of measurements of irradiation with the SOHO mission.

Axis 3: The long-term evolutions of the environments have a dimension about the Sun/Earth and Sun/planet interactions. The study and the comprehension of the regulating processes of these interactions, allowing the development and the sustaining of the life, are strong prospective axes for SHM disciplines.

SHM experimental strategy must take into account the long-term dimension of the Sun/Earth and Sun/planets interactions. It justifies a "monitoring" aspect of the experiments.

CNES contributions to the Sun - Heliosphere - Magnetosphere (SHM) topic lie primarily in the technical and financial support of the French scientific teams selected on the European or international missions, except for the PICARD mission.