1- 1Swedish Institute of Space Physics - Uppsala, Sweden (ne@irfu.se)
- *A full list of authors appears at the end of the abstract
On 18 February 2025, Solar Orbiter conducted its fourth Venus gravity assist manoeuvre, reaching a closest approach altitude of 378 km. This was significantly deeper than during previous flybys and brought the spacecraft into the topside ionosphere for the first time. The magnetometer (MAG) and Radio and Plasma Wave (RPW) instruments operated in burst mode during most of the flyby, providing high time resolution measurements. Solar Orbiter approached Venus from the tail region and entered the plasma environment without detecting a clear inbound bow shock crossing. The upstream solar wind appeared steady and calm, as inferred from stable magnetosheath conditions. The ionosphere was encountered in an unmagnetized state, characterized by generally weak magnetic fields in the ionosphere. Two ionopause crossings were observed, one inbound and one outbound, clearly seen in magnetic field, electric field and plasma density data. High-time-resolution electron density measurements, derived from spacecraft potential sampled at 256 Hz and calibrated using the plasma frequency line, revealed fine structure at the ionopause boundary on spatial scales of ~10 km. This is comparable to the local O⁺ inertial length, suggesting the influence of kinetic processes such as ion-scale waves or current sheets. The peak electron density during the flyby reached approximately 2x104 cm⁻³, corresponding to a spacecraft potential of about –45 V. Assuming pressure balance between external magnetic pressure and internal thermal pressure at the ionopause, the electron temperature is estimated to be around 0.6 eV. Near closest approach, approximately 15 magnetic flux ropes were observed, identified by strong peaks in magnetic field magnitude and characteristic rotations in LMN coordinates. These structures were accompanied by simultaneous electron density depletions. Applying a pressure balance assumption across the flux ropes (noting that this may not always be valid) yields an upper limit on the electron temperature of 0.8–2.0 eV within these features. On the outbound leg, Solar Orbiter passed through a still stable dayside magnetosheath and eventually crossed a quasi-perpendicular bow shock.
Niklas J.T. Edberg(1), J. Jordi Boldú(1,2), David Andrews(1), Andrew Dimmock (1), Anders I. Eriksson (1), Yuri V. Khotyaintsev(1,2), Moa Persson(1), Thomas Chust (3), Lina Z. Hadid(3), David Pisa(4), Jan Soucek (4), Antonio Vecchio (5), Matthieu Kretzschmar (6), Milan Maksimovic (7), Stuart Bale(8) Tim Horbury (9), Lorenzo Matteini (9), Marina Galand (9), Ingo Mueller-Wodarg(9), Helen O'Brien(9), Alastair Crabtree(9), Jean Morris(9) (1) Swedish Institute of Space Physics, Uppsala, Sweden (2) Department of Physics and Astronomy, Uppsala University, Sweden, (3) LPP, CNRS, Observatoire de Paris, PSL Research University, Sorbonne Université, École Polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France (4) Dept. of Space Physics, Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czechia (5) Radboud Radio Lab, Department of Astrophysics, Radboud University, Nijmegen, The Netherlands (6) LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France (7) LPC2E, UMR7328 CNRS, University of Orléans, 3A avenue de la recherche scientifique, Orléans, France (8) Space Sciences Laboratory, University of California, Berkeley, CA, USA (9) Department of Physics, Imperial College, SW7 2AZ London, UK
How to cite: Edberg, N. and the Solar Orbiter RPW & MAG team: Solar Orbiter in Venus ionosphere: results from the 4th flyby, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-302, https://doi.org/10.5194/epsc-dps2025-302, 2025.
