hermean environment

SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

Hermean environment(from Milillo et al., SSR, 2005)SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008


NASA-MESSENGERSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The environment is one of the high-priority scientific target of the mission:What is the nature of Mercury's magnetic field?What are the unusual materials at Mercury's poles?What volatiles are important at Mercury?MESSENGERs instruments devoted to the environment are:Magnetometer (MAG)Energetic Particle and Plasma Spectrometer (EPPS)Mercury Atmospheric and Surface Composition Spectrometer (MASCS)X-Ray Spectrometer (XRS)


ESA-JAXA BepiColomboThe mission has among its major scientific objectives Determination of the composition, origin and dynamics of Mercury's exosphere and polar deposits and Investigation of the structure and dynamics of Mercury's magnetosphere. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008BepiColombo is composed by two spacecraft: the MMO is completely devoted to environment, while MPO has different instruments devoted to the environment.



InstrumentTarget MERMAGMPO/MAGVector magnetic field (accuracy 10 pT and time res. up to 128 Hz)MMO/MGFMMO/PWIEWO(OFA/WFC/EFD) SORBET AM2P WPT MEFISTO LF-SC DB-SCdc electric field, plasma waves, radio waves *electric field (DC~10MHz)*magnetic field (0.1Hz~640kHz)*electron density and temperature MMO/MPPEMEA, HEP-ele, MIA, MSA, HEP-ion, and ENAelectrons (3eV-30keV, 30-700keV), ions (5eV/q-30keV/q, 5eV/q-40keV/q, 30keV-1.5MeV), and energetic neutral atoms (

HEWG - Padova, 29 September, 2006EXOSPHEREINTERPLANETARY SPACEMAGNETOSPHERE

HEWG - Padova, 29 September, 2006

A two spacecraft missionSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The inter-instrument collaborations planned onboard each spacecraft and the opportunities afforded to perform two-point simultaneous measurements at Mercury constitute exciting features of the mission.A 1:4 resonant orbit configuration for the two spacecraft is currently considered so that the closest approach between the two satellites will be a few 1000 km. Before that during the first two weeks in orbit, the two spacecraft will have a few close encounters


The Solar wind and IMF at MercurySERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The Parker spiral forms an angle of about 20 with the solar wind radial direction, less than half of the value at the Earths orbit (~45); this implies a change of the relative ratio of the Interplanetary Magnetic Field (IMF) components with respect to the near-Earth conditions, and an increase of the weight of the IMF Bx component.The average solar wind density is about ten times higher than that at the Earth, but this value varies considerably due to the high eccentricity of the orbit of the planet (from 32 cm-3 to 73 cm-3). BThe IMF intensity changes by a similar factor.Which are the effects of these different conditions?Bvv


Mercury has an internal magnetic fieldSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The Mariner 10 observations seem to proove the existence of an internal dipolar-like magnetic field (Ness et al, 1975).The estimated dipole moment ranges between 284 and 358 nT RM3, Nothward oriented, (confirmed by recent MESSENGER results).Hermean magnetosphere is only 5% of that of the Earth. In a zero order analysis, the spatial dimensions must be scaled by a factor of ~7.(Milillo et al, 2005)


Typical scale magnitudes.SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008k map at the magnetopause(Massetti et al., 2006)The time scale variations of the magnetospheric processes are few minutes at Mercury (compared with 1 hour at the Earth)The field variation length scale of the Hermean magnetosphere is comparable to the gyroradii of the heaviest ions.Adiabaticity parameter < 3 in the cusp regions where the B field is lower; thus, the SW can enter in a non-adiabatic manner inside the magnetosphere (Massetti et al., 2006)

Effects of the ExB drift paths curvature are no more negligible (Delcourt et al., 2002)


Direct entry through the cuspsSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The IMF orientation and intensity and the weak internal magnetic field of Mercury likely produce a direct entry through the cusps inside the Hermean dayside magnetosphere. Solar wind plasma circulates inside the magnetosphere and eventually may hit the surface. (Mura et al, 2005)(Kallio et al, 2008)(Kallio et al, 2003)


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008SW precipitation: high SW pressure(Kabin et al., 2000)(Kallio and Janhunen, 2003)(Vsw= 860 km/s) (Vsw= 1100 km/s) The observations of SEPs from the Sun by MPO/SIXS could provide a useful index for a kind of near-real-time forecast of solar activity that could be used to alert other MPO instruments, such as SERENA, MIXS and PHEBUS (which aim to evaluate the planets response to solar disturbances)


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Dayside coordinated measurements 1Joint measurements of MPPE-MEA and MIA, MGF and PWI, on the MMO spacecraft and SIXS, SERENA-MIPA and PICAM and MAG on the MPO spacecraft, will confirm plasma penetration inside the magnetosphere.


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008(Mura et al, PSS, 2005)SW Plasma circulation inside the magnetosphere(Mura et al., 2005)


Energetic electrons flow inside the magnetosphereSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Energetic electron fluxes are registered by Mariner 10.Are they magnetic fluxes as observed during substorms at the Earth or direct solar wind coupling?

Are there also solar wind protons and heavy ions of planetary origin circulating inside the Hermean magnetosphere? Is any ionosphere present there?Dipolarization event ?(Christon et al, 1986)


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008First the magnetic field measurements of MMO/MGF and MPO/MAG will register signatures of stretching and dipolarization of the magnetic field lines as well as disturbances related to magnetotail reconnection plasmoids, and field-aligned currents. Also, the ion and electron sensors of MMO/MPPE will provide important information about the time-scale of substorms, carriers of field-aligned currents and the effects of heavy ions. Plasma injections will be monitored at two points, MMO/MPPE and MPO/SERENA, during its evolution.To catch a substorm event by two spacecraft in the night-side magnetosphere


OxygenH, He, and O were detected in the atmosphere by the onboard UV spectrometer (Broadfoot et al., 1974). Later, Na, K, and Ca were detected through ground-based observations (Potter and Morgan, 1985, 1986; Bida et al., 2000). SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The small amount of observed atmospheric oxygen relative (

Sodium and Potassium observationsSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008(Killen et al. SSR, 2007)The mid latitudes intensification of exospheric Na and K seems to be related to solar wind precipitation through the cusp.Another possible explanation is the association of Na and K with radar and visible bright spots on Mercury's surface (Sprague et al. 1998; Sprague and Massey 2007). However, the images of Na emission obtained from 1997 to 2003 by Potter et al. (2006) showed no evidence of a topographic effect.


CalciumThe neutral Calcium was observed by Bida et al. (2000).It is likely that Ca is released in the molecular form, possibly as CaO. If so, CaO could be dissociated in the atmosphere, for instance by Ly photons, giving the Ca atom excess energy as observed (Killen et al., 2005). SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008


Sodium observationsvariabilitytailDawn-duskasymmetriesSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008(Schleicher et al. A&A, 2004)(Potter et al., 1999)(Potter et al., 2002)


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Exospheric coordinated measurementsThe exospheric configuration and composition will be measured by MPO/PHEBUS, and MMO/MSASI and MPO/SERENA-STROFIO in terms of column density, composition and profile variations. STROFIO, in particular, will be the only instrument able to determine the night side exospheric composition.


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Dayside coordinated measurements 2Together with plasma penetration measurements described above, other dedicated instruments will observe the response of the planet in term of radiation and particles release. MIXS will observe the X-Ray emission of planetary aurorae while SERENA-ELENA will monitor the emission of neutral atoms. SERENA-STROFIO and PHEBUS and MSASI will observe the exospheric response of Mercury in terms of column density, composition and profile variations.


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Due to the strong link between the exosphere and the surface it is possible by measuring neutrals and ions at relatively low altitudes to obtain information regarding the composition of the upper surface of the regolith. However, some release processes are non-stoichiometric and involve only selected species.Eventually, to be able to successfully infer a source composition from exospheric measurements, it is really important to know the mechanism of ejection and the properties of the particular surface.


Particle release processes invesigationSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008TDPSDISMIV(Environment Simulation Tool (EST) at IFSI)


Ion sputtering analysisSERENA-ELENA will produce a kind of mapping of ion sputtering action on the surface of the planet (Orsini et al. 2008).SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008This measurement correlated with the observation of ion flux to the surface seen by MPO/SERENA-MIPA will provide the surface efficiency in particle releasing via IS


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Impulsive event (meteoroid 0.1 m)Frequency ~ 2 events/day (Marchi et al., 2005)

Duration ~ 10-30 minAmplitude ~ 2000 km

(Mangano et al., 2007)


SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008EXOSPHEREMPO/MERTISThe surface elemental abundances mapped by MIXS, the surface mineralogy mapped by MERTIS and the surface cratering mapped by SIMBIO-SYS will allow released exospheric atoms to be related to the constitution of the surface.


Exo-ionosphereThe photo-ionisation of exospheric atoms creates an ionised thermal plasma population, especially on the dayside. Confirmed by MESSENGER observation. (Leblanc et al., 2004)SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008The ions produced at thermal energies are energised and become part of the magnetospheric ion populations. Part of this plasma is eventually lost to the SW.


The close-to-planet observations of SERENA-PICAM will provide the composition and velocity distribution of planetary ions. Electron and ion phase space densities by MPPE-HEP-e and MEA can be obtained at different distances from the planet. Magnetic fields observations at two vantage points by MAG and MGF and of the electric fields (PWI) will complement the measurements of particle dynamics and currents (Delcourt et al., 2003)Planetary ions circulationSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008


BepiColombo: an outstanding tool for Hermean environment investigstionSERENA-HEWG meeting, Santa Fe, 12-14 May, 2008Co-ordinated measurements made by different onboard instruments will answer important key questions regarding the planets environment. The opportunity offered by the BC mission to perform two-point simultaneous measurements provides a powerful and unique investigative tool at a location other than the Earth. The interaction processes acting at Mercury are present also in other interplanetary environments. For example, the plasma-surface interaction is present wherever a body in the Solar System lacks an atmosphere (Moon, asteroids, Jupiters satellites and many other satellites of the giant planets).




*Hermean environment-> complex system : many internal processes between surface exosphere and magnetosphere, many interactions with the external agents, like Solar wind or Interplanetary medium (dust, meteoroids,)For this reason, in the BC mission the joint studies of different instruments looking at different targets are very important. **Paris, April 21-22, 2005Hence, the scientific collaboration with other teams of instruments involved in the characterization of the exosphere, magnetosphere, surface could be a mutual benefit. ***SW entering into the Hermean magnetosphere can eventually impact the surface.The SW impacting region is in first approximation the footprint of open field linesOpen field lines mapped on the Hermean surface depend on solar wind conditionsParis, April 21-22, 2005First example of MMO-MPO configuration : SW plasma detection inside the magnetosphere

Paris, April 21-22, 2005Protons are circulating from the cusp inside the magnetosphere, trough the action of B and E fields in different configurations (South cusp entrance is not simulated, here). Low energy (upper panels), E>1 keV (lower panels)protons flowing over the north pole ExB driven and those drifting in the dawn side grad B drivenParis, April 21-22, 2005third example of MMO-MPO configuration : planetary ions detection inside the magnetosphere

*Paris, April 21-22, 2005First example of MMO-MPO configuration : SW plasma detection inside the magnetosphere

Paris, April 21-22, 2005First example of MMO-MPO configuration : SW plasma detection inside the magnetosphere

The exosphere is the combination of different release processes acting in the same time, especially in the dayside.In the dayside, the TD produces a dense exosphere but at very low altitudes. It follows that its effect is to deplete the surface of volatile atoms thus producing a reduction of effectiveness of other release processes. PSD is the main source at altitudes of MPO orbit. While PSD and TD are release processes mainly active at low latitudes close to the subsolar point or at dawn, and produce only thermal neutrals, the ion-sputtering is mainly active at intermediate latitudes (45 deg) and maintain a tail at higher energies. Particle precipitation could cause increase in PSD efficiency, too (Killen)In the night side probably the two main active processes are the micrometeoroid impact and the planetary ion sputtering. Hence, if observable, they could be better discriminated from the others.

Paris, April 21-22, 2005The impact of a meteoroid produces a strong increase of the exospheric density of many refractory species.This signal could be the most useful information of surface composition detectable on the exosphere,since this process is non-stoichiometric, differently from other processes like PSD. Paris, April 21-22, 2005Observable by SERENA , PHEBUS and MMO/MSASITo be related to surface composition maps obtained by MIXSIMBIO-SYS would be able to register the generation of a new crater.

**

hermean environment

Documents

santa fe

mercuryserenahewg meeting

electric field dc

mercurys poles

dynamics of mercurys

average solar wind density

plasma waves

solar wind radial direction