Articles | Volume 39, issue 1
https://doi.org/10.5194/angeo-39-53-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-39-53-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Ion acoustic waves near a comet nucleus: Rosetta observations at comet 67P/Churyumov–Gerasimenko
Herbert Gunell
CORRESPONDING AUTHOR
Department of Physics, Umeå University, 90187 Umeå, Sweden
Charlotte Goetz
Space Research and Technology Centre, European Space Agency,
Keplerlaan 1, 2201AZ Noordwijk, the Netherlands
Elias Odelstad
Department of Space and Plasma Physics, Royal Institute of
Technology, 10044 Stockholm, Sweden
Arnaud Beth
Department of Physics, Umeå University, 90187 Umeå, Sweden
Maria Hamrin
Department of Physics, Umeå University, 90187 Umeå, Sweden
Pierre Henri
LPC2E, CNRS, 45071 Orléans, France
Lagrange, OCA, CNRS, UCA, Nice, France
Fredrik L. Johansson
Swedish Institute of Space Physics, Box 537, 75121 Uppsala, Sweden
Hans Nilsson
Swedish Institute of Space Physics, Box 812, 98128 Kiruna, Sweden
Gabriella Stenberg Wieser
Swedish Institute of Space Physics, Box 812, 98128 Kiruna, Sweden
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Boundaries in the plasma around comet 67P separate regions with different properties. Many have been identified, including a new boundary called an infant bow shock. Here, we investigate how the plasma and fields behave at this boundary and where it can be found. The main result is that the infant bow shock occurs at intermediate activity and intermediate distances to the comet. Most plasma parameters behave as expected; however, some inconsistencies indicate that the boundary is non-stationary.
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The plasma environment of comet 67P provides a unique laboratory to study plasma phenomena in the solar system. Previous studies have reported the existence of mirror modes at 67P but no further systematic investigation has so far been done. This study aims to learn more about these waves. We investigate the magnetic field measured by Rosetta and find 565 mirror mode signatures. The detected mirror modes are likely generated upstream of the observation and have been modified by the plasma.
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Freshly created ions in solar wind start gyrating around the interplanetary magnetic field. When they cross the bow shock, they get an extra kick, and this increases the plasma pressure against the magnetic pressure. This leads to the creation of so-called mirror modes, regions where the magnetic field decreases in strength and the plasma density increases. These structures help in exploring how energy is transferred from the ions to the magnetic field and where around Venus this is happening.
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Ann. Geophys., 41, 225–251, https://doi.org/10.5194/angeo-41-225-2023, https://doi.org/10.5194/angeo-41-225-2023, 2023
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Mirror modes are magnetic bottles found in the space plasma environment of planets contributing to the energy exchange with the solar wind. We use magnetic field measurements from the NASA Mars Atmosphere and Volatile EvolutioN mission to detect them around Mars and show how they evolve in time and space. The structures concentrate in two regions: one behind the bow shock and the other closer to the planet. They compete with other wave modes depending on the solar flux and heliocentric distance.
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Magnetic holes are curious localized dropouts of magnetic field strength in the solar wind (the flow of ionized gas continuously streaming out from the sun). In this paper we show that these magnetic holes can cross the bow shock (where the solar wind brake down to subsonic velocity) and enter the region close to Earth’s magnetosphere. These structures may therefore represent a new type of non-uniform solar wind–magnetosphere interaction.
Katharina Ostaszewski, Karl-Heinz Glassmeier, Charlotte Goetz, Philip Heinisch, Pierre Henri, Sang A. Park, Hendrik Ranocha, Ingo Richter, Martin Rubin, and Bruce Tsurutani
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Plasma waves are an integral part of cometary physics, as they facilitate the transfer of energy and momentum. From intermediate to strong activity, nonlinear asymmetric plasma and magnetic field enhancements dominate the inner coma of 67P/CG. We present a statistical survey of these structures from December 2014 to June 2016, facilitated by Rosetta's unprecedented long mission duration. Using a 1D MHD model, we show they can be described as a combination of nonlinear and dissipative effects.
Charlotte Goetz, Herbert Gunell, Fredrik Johansson, Kristie LLera, Hans Nilsson, Karl-Heinz Glassmeier, and Matthew G. G. T. Taylor
Ann. Geophys., 39, 379–396, https://doi.org/10.5194/angeo-39-379-2021, https://doi.org/10.5194/angeo-39-379-2021, 2021
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Boundaries in the plasma around comet 67P separate regions with different properties. Many have been identified, including a new boundary called an infant bow shock. Here, we investigate how the plasma and fields behave at this boundary and where it can be found. The main result is that the infant bow shock occurs at intermediate activity and intermediate distances to the comet. Most plasma parameters behave as expected; however, some inconsistencies indicate that the boundary is non-stationary.
Martin Volwerk, David Mautner, Cyril Simon Wedlund, Charlotte Goetz, Ferdinand Plaschke, Tomas Karlsson, Daniel Schmid, Diana Rojas-Castillo, Owen W. Roberts, and Ali Varsani
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The magnetic field in the solar wind is not constant but varies in direction and strength. One of these variations shows a strong local reduction of the magnetic field strength and is called a magnetic hole. These holes are usually an indication that there is, or has been, a temperature difference in the plasma of the solar wind, with the temperature along the magnetic field lower than perpendicular. The MMS spacecraft data have been used to study the characteristics of these holes near Earth.
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Short summary
When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is enhanced in front of the comet, and the field lines are draped around it. This happens because electric currents are induced in the plasma. When these currents flow through the plasma, they can generate waves. In this article we present observations of ion acoustic waves, which is a kind of sound wave in the plasma, detected by instruments on the Rosetta spacecraft near comet 67P/Churyumov–Gerasimenko.
When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is...