Abstract:Abstract. Multiple plasma boundaries have been observed at comet 67P/Churyumov-Gerasimenko. Among them was an infant bow shock, an asymmetric structure in the plasma environment that separates the less disturbed solar wind from a plasma with warmer, slower protons. Rosetta crossings of the infant bow shock have so far only been reported for two days. Here, we aim to investigate this phenomenon further by focusing on the proton behaviour and surveying all of the Rosetta comet phase data. We find over 300 events… Show more
“…It was found by Goetz et al. ( 2020a ) that the infant bow shock is seen more often at intermediate outgassing rates. Fig.…”
Section: Large Scale Structuresmentioning
confidence: 93%
“…Goetz et al. ( 2020a ) performed a statistical study of the complete data set for the whole mission, and found that this shocked solar wind plasma had been observed on 152 days.…”
Section: Large Scale Structuresmentioning
confidence: 99%
“…In the left-hand panel the red circles mark the position of comet 67P on each of the 152 days on which shocked solar wind plasma was observed (Goetz et al. 2020a ). The second panel shows the magnetic flux density magnitude in a hybrid simulation of the infant bow shock.…”
Section: Large Scale Structuresmentioning
confidence: 99%
“…It is possible that these signatures also indicate the crossing of a plasma boundary, which builds up as the solar wind dynamic pressure increases.” This can now be identified as one of the first encounters of the infant bow shock and it is part of the infant bow shock database used in the statistical study by Goetz et al. ( 2020a ).…”
The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency’s Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet’s orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.
“…It was found by Goetz et al. ( 2020a ) that the infant bow shock is seen more often at intermediate outgassing rates. Fig.…”
Section: Large Scale Structuresmentioning
confidence: 93%
“…Goetz et al. ( 2020a ) performed a statistical study of the complete data set for the whole mission, and found that this shocked solar wind plasma had been observed on 152 days.…”
Section: Large Scale Structuresmentioning
confidence: 99%
“…In the left-hand panel the red circles mark the position of comet 67P on each of the 152 days on which shocked solar wind plasma was observed (Goetz et al. 2020a ). The second panel shows the magnetic flux density magnitude in a hybrid simulation of the infant bow shock.…”
Section: Large Scale Structuresmentioning
confidence: 99%
“…It is possible that these signatures also indicate the crossing of a plasma boundary, which builds up as the solar wind dynamic pressure increases.” This can now be identified as one of the first encounters of the infant bow shock and it is part of the infant bow shock database used in the statistical study by Goetz et al. ( 2020a ).…”
The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency’s Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet’s orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.
“…This allowed detection of the bow shock as it began to form, or an infant bow shock (Gunell et al 2018). Statistical analyses of the full Rosetta dataset showed that the spacecraft encountered the infant bow shock multiple times between 3.0 and 1.7 AU inbound to the Sun and then again outbound starting at around 1.8 AU (Goetz et al 2021b). Additionally, a method for detecting the existence of a bow shock from inside the shock was discovered.…”
Once a cometary plasma cloud has been created through ionisation of the cometary neutrals, it presents an obstacle to the solar wind and the magnetic field within it. The acceleration and incorporation of the cometary plasma by the solar wind is a complex process that shapes the cometary plasma environment and is responsible for the creation of boundaries such as a bow shock and diamagnetic cavity boundary. It also gives rise to waves and electric fields which in turn contribute to the acceleration of the plasma. This chapter aims to provide an overview of how the solar wind is modified by the presence of the cometary plasma, and how the cometary plasma is incorporated into the solar wind. We will also discuss models and techniques widely used in the investigation of the plasma environment in the context of recent findings by Rosetta. In particular, this chapter highlights the richness of the processes and regions within this environment and how processes on small scales can shape boundaries on large scales. It has been fifteen years since the last book on Comets was published and since then we have made great advances in the field of cometary research. But many open questions remain which are listed and discussed with particular emphasis on how to advance the field of cometary plasma science through future space missions.
We analyze observations of an SEP event at Rosetta's target comet 67P/Churyumov-Gerasimenko during March 6th-10th 2015. The comet was 2.15AU from the Sun, with the Rosetta spacecraft approximately 70km from the nucleus placing it deep inside the comet's coma and allowing us to study its response. The Eastern flank of an ICME also encountered Rosetta on March 6th and 7th. Rosetta's RPC data indicate increases in ionization rates, and cometary water group pickup ions exceeding 1keV. Increased charge exchange reactions between solar wind ions and cometary neutrals also indicate increased upstream neutral populations consistent with enhanced SEP induced surface activity.In addition, the most intense parts of the event coincide with observations interpreted as an infant cometary bow shock, indicating that the SEPs may have enhanced the formation and/or intensified the observations. These solar transient events may also have pushed the cometopause closer to the nucleus.We track and discuss characteristics of the SEP event using remote observations by SOHO, WIND and GOES at the Sun, in-situ measurements at STEREO A, Mars and Rosetta, and ENLIL modeling. Based on its relatively prolonged duration, gradual and anisotropic nature and broad angular spread in the heliosphere, we determine the main particle acceleration source to be a distant ICME which emerged from the Sun on March 6th 2015 and was detected locally in the Martian ionosphere but was never encountered by 67P directly. The ICME's shock produced SEPs for several days which traveled to the in-situ observation sites via magnetic field line connections.
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