Romanelli N.,Astrophysical Plasmas |
Bertucci C.,Astrophysical Plasmas |
Gomez D.,Astrophysical Plasmas |
Mazelle C.,Geophysique Planetaire et Plasmas Spatiaux GPPS |
Delva M.,Space Research Institute
Planetary and Space Science | Year: 2013
We present a study on the properties of electromagnetic plasma waves in the region upstream of the Martian bow shock, detected by the magnetometer and electron reflectometer (MAG / ER) onboard the Mars Global Surveyor (MGS) spacecraft during the period known as Science Phasing Orbits (SPO). The frequency of these waves, measured in the MGS reference frame (SC), is close to the local proton cyclotron frequency. Minimum variance analysis (MVA) shows that these 'proton cyclotron frequency' waves (PCWs) are characterized - in the SC frame - by a left-hand, elliptical polarization and propagate almost parallel to the background magnetic field. They also have a small degree of compressibility and an amplitude that decreases with the increase of the interplanetary magnetic field (IMF) cone angle and radial distance from the planet. The latter result supports the idea that the source of these waves is Mars. In addition, we find that these waves are not associated with the foreshock and their properties (ellipticity, degree of polarization, direction of propagation) do not depend on the IMF cone angle. Empirical evidence and theoretical approaches suggest that most of these observations correspond to the ion-ion right hand (RH) mode originating from the pick-up of ionized exospheric hydrogen. The left-hand (LH) mode might be present in cases where the IMF is almost perpendicular to the Solar Wind direction. PCWs occur in 62% of the time during SPO1 subphase, whereas occurrence drops to 8% during SPO2. Also, SPO1 PCWs preserve their characteristics for longer time periods and have greater degree of polarization and coherence than those in SPO2. We discuss these results in the context of possible changes in the pick-up conditions from SPO1 to SPO2, or steady, spatial inhomogeneities in the wave distribution. The lack of influence from the Solar Wind's convective electric field upon the location of PCWs indicates that, as suggested by recent theoretical results, there is no clear relation between the spatial distribution of PCWs and that of pick-up ions. © 2012 Elsevier Ltd. All rights reserved.
Delva M.,Austrian Academy of Sciences |
Bertucci C.,Astrophysical Plasmas |
Schwingenschuh K.,Austrian Academy of Sciences |
Volwerk M.,Austrian Academy of Sciences |
Romanelli N.,Astrophysical Plasmas
Planetary and Space Science | Year: 2014
The approach of the Rosetta S/C to Comet Churyumov-Gerasimenko in 2014 reactivates the interest in the plasma interaction of the solar wind with the cometary coma. In preparation for the upcoming S/C observations and the start of outgassing of the cometary nucleus, we reinvestigate the magnetic field data from the Vega-1 S/C at the flyby of Comet Halley (1986), in search of the magnetic pileup boundary and increase of field line draping. The magnetic pileup boundary has been identified as a common feature for unmagnetized bodies with an induced magnetosphere. This boundary marks the outer edge of the magnetic pileup region, also known as the magnetic barrier region, in which the magnetic field is strong and highly draped. Initially, the magnetic field draping around Comet Halley was clearly identified from the Vega-1 magnetometer data through reversal of the field component in direction to the Sun at closest approach. Here, a detailed analysis is performed in regions further upstream in the magnetosheath. The Vega-1 high resolution magnetometer data on the in- and outbound leg but inside the bow wave are reinvestigated in search for the magnetic pileup boundary as an indicator for the outer edge of the magnetic barrier. The magnetic field pileup region is studied using the correlation between the field component towards the Sun and the radial component in an aberrated cometocentric frame; this technique proved very successful for Mars and also for comets Giacobini-Zinner and Halley in the case of Giotto observations. We can clearly identify the different regimes in the magnetic field data, on the in- and outbound leg of the orbit. Waves just within the newly determined magnetic pileup region have properties different from mirror mode waves, whereas waves observed out of the magnetic pileup boundary are confirmed as mirror mode. The boundaries found at Comet Halley prove that also the detailed structure of the interaction of unmagnetized bodies with an atmosphere with the solar wind is valid for active comets, but with larger space scale. © 2014 Elsevier Ltd. All rights reserved.