Search Publications
Solar Wind Protons Forming Partial Ring Distributions at Comet 67P
Gunell, H.; Nilsson, H.; Richter, I. +5 more
We present partial ring distributions of solar wind protons observed by the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. The formation of ring distributions is usually associated with high activity comets, where the spatial scales are larger than multiple ion gyroradii. Our observations are made at a low-activity comet at a heliocentric …
Indirect Observations of Electric Fields at Comet 67P
Gunell, H.; Nilsson, H.; Goetz, C. +2 more
No spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At thi…
Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov-Gerasimenko
Nilsson, Hans; Goetz, Charlotte; Volwerk, Martin +5 more
The plasma environment at a comet can be divided into different regions with distinct plasma characteristics. Two such regions are the solar wind ion cavity, which refers to the part of the outer coma that does not contain any solar wind ions anymore; and the diamagnetic cavity, which is the region of unmagnetized plasma in the innermost coma. Fro…
Ion-Ion Cross-Field Instability of Lower Hybrid Waves in the Inner Coma of Comet 67P
Karlsson, Tomas; Stenberg Wieser, Gabriella; Odelstad, Elias +2 more
We show that an ion-ion cross-field streaming instability between cold newborn cometary ions and heated heavy ions that were picked up upstream is likely a contributing source of observed lower hybrid (LH) waves in the inner coma of comet 67P/Churyumov-Gerasimenko. Electric field oscillations in the LH frequency range are common here, and have pre…
Observations of a Solar Energetic Particle Event From Inside and Outside the Coma of Comet 67P
Coates, A. J.; Palmerio, E.; Jones, G. H. +12 more
We analyze observations of a solar energetic particle (SEP) event at Rosetta's target comet 67P/Churyumov-Gerasimenko during 6-10 March 2015. The comet was 2.15 AU from the Sun, with the Rosetta spacecraft approximately 70 km from the nucleus placing it deep inside the comet's coma and allowing us to study its response. The Eastern flank of an int…
The Influence of Spacecraft Charging on Low-Energy Ion Measurements Made by RPC-ICA on Rosetta
Stenberg Wieser, Gabriella; Wieser, Martin; Eriksson, Anders +2 more
Spacecraft charging is problematic for low-energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC-ICA) on board the Rosetta spacecraft is suffering from this effect. RPC-ICA was measuring positi…
The Influence of Varying Spacecraft Potentials and Debye Lengths on In Situ Low-Energy Ion Measurements
Stenberg Wieser, Gabriella; Wieser, Martin; Eriksson, Anders +2 more
Low-energy ions are difficult to measure, mainly due to spacecraft charging. The ions are attracted to or repelled from the charged surface prior to detection, which changes both the energy and travel direction of the ions. This results in distortions of the data, and the changed travel directions distort the effective field of view (FOV) of the i…
Plasma Density and Magnetic Field Fluctuations in the Ion Gyro-Frequency Range Near the Diamagnetic Cavity of Comet 67P
Nilsson, H.; André, M.; Vaivads, A. +8 more
We report the detection of large-amplitude, quasi-harmonic density fluctuations with associated magnetic field oscillations in the region surrounding the diamagnetic cavity of comet 67P. Typical frequencies are ∼0.1 Hz, corresponding to ∼10 times the water and ≲ 0.5 times the proton gyro-frequencies, respectively. Magnetic field oscillations are n…
Plasma Turbulence at Comet 67P/Churyumov-Gerasimenko: Rosetta Observations
Halekas, J. S.; Howes, G. G.; Ruhunusiri, S.
We perform a power spectral analysis of magnetic field fluctuations measured by the Rosetta spacecraft's magnetometer at comet 67P/Churyumov-Gerasimenko. We interpret the power spectral signatures in terms of plasma turbulent processes and discover that different turbulent processes are prominent during different active phases of the comet. During…
Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P
André, M.; Henri, P.; Rubin, M. +7 more
A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find io…