Continuation The Electric Comet Theory Boogaloo (Part 2)

looks like you're getting painted into a corner! How does a cliff collapse collimate the jets??? as observed in the images?

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How does a cliff collapse collimate the jets??? as observed in the images?

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Some did however saturate the NavCam CCD when the nucleus did
not (i.e. outburst #15, on 21/08/2016), so one can expect that after calibration they will appear at least as strong as the outbursts typically detected by OSIRIS.

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Cometary outbursts are one of the most spectacular aspects of comet behavior. They are characterized by an abrupt increase in cometary brightness followed by a gradual fall off to the pre-event brightness. Although there are several studies on outburst events, to our knowledge, no detailed analysis on the variation of the cometary plasma environment during an outburst has ever been reported. On 19 February 2016, when comet 67P/Churyumov-Gerasimenko was at a heliocentric distance of 2.4 AU, an outburst event, characterized by two orders of magnitude increase in coma surface brightness, took place. Rosetta was at a distance of 30 km from the comet nucleus, orbiting with a relative speed of 0.17 m/s. The Rosetta Plasma Consortium (RPC) provided in-situ measurements of the cometary plasma, embedded in the solar wind, and the associated magnetic field during this outburst, as the dust and gas expelled from the comet were passing by the spacecraft. While the neutral density (ROSINA/COPS) at the spacecraft position increased by a factor of 1.5, the local plasma density (RPC/MIP) was found to increase by a factor of 3 during the outburst event, driving the spacecraft potential more negative (RPC/LAP). The event was characterized by the energy degradation of energetic (10s of eV) electrons (RPC/IES). In response to the outburst, the local magnetic field exhibited a slight increase in amplitude and a slow rotation (RPC/MAG). A weakening of 10-100 mHz magnetic field fluctuations was also observed during the outburst. The RPC instruments show that the effects of the outburst on the plasma lasted for about 4 hours, from ~1000 UT to 1400 UT. Detailed analyses of the observations made by RPC along with ROSINA/COPS will be presented in the paper.

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And, do tell us Sol; how 'bright' were those OSIRIS images? Want me to go through it again with you? 6% of the incident sunlight. Now, how bright is this electric woo that you need? Please remind us.

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We present preliminary results of the first 3-D fully kinetic and electromagnetic simulations of the solar wind interaction with 67P/Churyumov–Gerasimenko at ~3 AU, before the comet transitions into its high-activity phase.

We focus on the global cometary environment and the electron-kinetic activity of the interaction. In addition to the background solar wind plasma flow, our model includes also plasma-driven ionization of cometary neutrals and collisional effects. We approximate mass loading of cold cometary oxygen and hydrogen using a hyperbolic relation with distance to the comet. We consider two primary cases: a weak outgassing comet (with the peak ion density ~10x the solar wind density) and a moderately outgassing comet (with the peak ion density ~50x the solar wind density).

The weak comet is characterized by the formation of a narrow region containing a compressed solar wind (the density of the solar wind ion population is ~3x the value far upstream of the comet) and a magnetic barrier (~2x to 4x the interplanetary magnetic field). Blobs of plasma are detached continuously from this sheath region. Standing electromagnetic waves are excited in the cometary wake due to a strong anisotropy in the plasma pressure, as the density and the magnetic field magnitude are anti-correlated.
The moderate mass-loading case shows more dynamics at the dayside region. The stagnation of the solar wind flow is accompanied by the formation of elongated density stripes, indicating the presence of a Rayleigh-Taylor instability. These density cavities are elongated in the direction of the magnetic field and encompass the dayside ionopause.

To conclude, we believe that our results provide vital information to disentangle the observations made by the Rosetta spacecraft and compose a global solar wind - comet interaction model.

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The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has observed signatures of magnetic field dropouts in the inner coma region of comet 67P/Churyumov-Gerasimenko at distances from 30km to 400km, which is larger than what has been predicted by numerical simulations of the cometary plasma environment. It is still unclear how these magnetic field dropouts form in the inner coma region. In the present work, we use our newly developed multi-fluid plasma-neutral interaction model (Huang et al. 2016) to investigate this problem. The model solves the governing multi-ion MHD equations for the cometary and solar wind ions and electrons, and the Euler equations for the neutral gas fluid. We show that a strong local increase of electron pressure is capable to generate the features of the magnetic field dropouts observed by RPC-MAG: the simulation results show that a low magnetic field region is formed and the recovery phase of the magnetic field magnitude is faster than the declining phase, which suggests that the mechanism proposed here based on localized enhancement of electron pressure may provide a possible explanation for the unusually large distance of the observed magnetic field dropouts.

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At distances close enough to the Sun, when comets are characterised by a significant outgassing, the cometary neutral density may become large enough for both the cometary plasma and the cometary gas to be coupled, through ion-neutral and electron-neutral collisions. This coupling enables the formation of an unmagnetised expanding cometary ionosphere around the comet nucleus, also called diamagnetic cavity, within which the solar wind magnetic field cannot penetrate.
The instruments of the Rosetta Plasma Consortium (RPC), onboard the Rosetta Orbiter, enable us to better constrain the structure, dynamics and stability of the plasma around comet 67P/CG. Recently, magnetic field measurements (RPC-MAG) have shown the existence of such a diamagnetic region around comet 67P/CG [Götz et al., 2016]. Contrary to a single, large scale, diamagnetic cavity such as what was observed around comet Halley, Rosetta have crossed several diamagnetic structures along its trajectory around comet 67P/CG.
Using electron density measurements from the Mutual Impedance Probe (RPC-MIP) during the different diamagnetic cavity crossings, identified by the flux gate magnetometer (RPC-MAG), we map the unmagnetised plasma density around comet 67P/CG. Our aims is to better constrain the structure, dynamics and stability of this inner cometary plasma layer characterised by cold electrons (as witnessed by the Langmuir Probes RPC-LAP).
The ionisation ratio in these unmagnetised region(s) is computed from the measured electron (RPC-MIP) and neutral gas (ROSINA/COPS) densities. In order to assess the importance of solar EUV radiation as a source of ionisation, the observed electron density will be compared to a the density expected from an ionospheric model taking into account solar radiation absorption.
The crossings of diamagnetic region(s) by Rosetta show that the unmagnetised cometary plasma is particularly homogeneous, compared to the highly dynamical magnetised plasma observed in adjacent magnetised regions. Moreover, during the crossings of multiple, successive diamagnetic region(s) over time scales of tens of minutes or hours, the plasma density is almost identical in the different unmagnetised regions, suggesting that these unmagnetised regions may be a single diamagnetic structure crossed several times by Rosetta.

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Because of the inclination of the rotational axis to the orbital plane and the orbital motion around the Sun, the sunlit regions on the nucleus surface of comet 67P/Churyumov-Gerasimenko moved from the northern hemisphere to the sourthern hemisphere between August, 2014 and August, 2015. From the comparison of the dust jet features in images taken at successive time series, the footpoints of these jets can be identified by a projection method. The distributiosn of the corresponding source regions can be compared with the geomorphology of the nucleus surface from inbound to outbound. The correlation of the dust jet activity with the volatile outgassing phenomenon as monitored by different scientific instruments onboard Rosetta will provide important information on the sublimation process.

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Sol88 said:

AGU Fallmeeting more nails in the coffin for the dirtysnowball!

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• Plasma response to a cometary outburst: Rosetta Plasma Consortium observations during comet 67P/Churyumov-Gerasimenko outburst event on 19 February 2016
• P43A-2098: The singing comet 67P: utilizing fully kinetic simulations to study its interaction with the solar wind plasma
• P43A-2091: Increased electron pressure as possible origin of magnetic field dropouts observed by RPC-MAG of comet 67P/Churyumov-Gerasimenko
• P43A-2095: Structure and dynamics of the umagnetized plasma around comet 67P/CG
• P43A-2087: Mapping of the source regions of the dust jets on comet 67P/Churyumov-Gerasimenko

Sol88 said:

They are characterized by an abrupt increase in cometary brightness followed by a gradual fall off to the pre-event brightness. bit like an electric discharge!!

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.....dust jet activity with the volatile outgassing phenomenon as monitored by different scientific instruments onboard Rosetta will provide important information on the sublimation process.

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Looks like we wait for the paper to be accepted, eh!! They are characterized by an abrupt increase in cometary brightness followed by a gradual fall off to the pre-event brightness. bit like an electric discharge!!

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The in situ images of the 67P/Churyumov-Gerasimenko nucleus acquired by the CIVA cameras on-board PHILAE revealed a rough, irregular and inhomogeneous terrains dominated by fractures and agglomerates of consolidated materials. While the composition of these materials is unknown, they provide unique structures to constrain the conditions prevailing at the surface of a comet and also possibly to the nucleus formation. A quantitative analysis of some microscopic structures (namely fractures and grains that look like pebbles) will be presented using a manual extraction from the CIVA data set with the software ArcGIS. Fractures/cracks are rather ubiquitous at various spatial scales with network and size (from sub-cm to 10 cm) well correlated to the texture of the landscape. The pebble size distribution are reasonably well fitted by power-laws having different cumulative indexes. The nature of the landscape of the landing site will be then discussed in relation to both endogenic and exogenic processes that could have sculpted it. The block seen in CIVA#1 is interpreted to be a close-up of fractured boulders/cliff belonging to the boulder field identified from the orbit near Abydos, this boulder field being itself the result of gravitational regressive erosion due to sublimation (Lucchetti et al. 2016). The observed fractures are best explained by thermal insolation leading to thermal fatigue and/or to loss of volatile materials (e.g., desiccation). This surficial fragmentation (up to >10 cm length) could generate macroscopic erosion that is also visible at larger scale from the orbit. While the pebbles are difficult to be formed by any current physical processes, there is at least an intriguing possibility that they are remnants of primordial accretion processes, as there are several lines of evidence that the nucleus could be primordial (Davidsson et al., 2016), and not a collisional rubble piles of a large body (Morbidelli and Rickman A&A, 2015). We thus speculate that the Abydos landscape could be in favour of pebble accretion model instead of runaway coagulation model with a formation location in the outer region of the Solar System.

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A pebble is a clast of rock with a particle size of 2 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter). A rock made predominantly of pebbles is termed a conglomerate.

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During the more than 3 hours of the MUPUS PEN insertion phase at Abydos, the Comet Acoustic Surface Sounding Experiment (CASSE), part of SESAME, recorded hammer strokes of MUPUS with all three accelerometers, which are housed in Philae’s feet. Stroke times recorded in the MUPUS housekeeping data, the identification of two adjacent strokes in a single recording, and laboratory experiments concerning the properties of sound transmission through Philae’s legs and feet foster the identification of the recorded signals as hammer strokes, and as elastic waves transmitted through the comet. A hammer stroke exerted on a surface dominantly excites surface waves of the Rayleigh type. By comparison of arrival times at the individual feet, we estimate the propagation velocity of these Rayleigh waves to be at least 80 m/s. With the bulk density of 533 ± 6 kg/m3 as derived from tracking Rosetta (Pätzold et al., Nature, vol. 530, 2016), this velocity translates into a shear modulus of the comet material of at least 3.2 MPa. Shear modulus scales with velocity squared, so when taking into account the formal uncertainties arising from the arrival time inversion, the shear modulus may easily be as large as 10 MPa. This is still low compared to solid rock or monocrystalline ice, but is compatible with highly porous materials. The recorded signals are only weakly dispersive: Energy at frequencies below approx. 200 Hz arrives slightly later than at higher frequencies. This indicates the presence of a surface layer, to which the above propagation velocity and shear modulus apply, on top of a material with an even lower propagation velocity and shear modulus. The boundary between the two materials is likely more than 20 cm below the surface. We conclude that the results of CASSE listening to MUPUS support the hypothesis of surficial sintering at least for the Abydos site on 67P/Churyumov-Gerasimenko.

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Rayleigh waves are a type of surface acoustic wave that travel on solids. They can be produced in materials in many ways, such as by a localized impact or by piezo-electric transduction, and are frequently used in non-destructive testing for detecting defects. They are part of the seismic waves that are produced on the Earth by earthquakes. When guided in layers they are referred to as Lamb waves, Rayleigh–Lamb waves, or generalized Rayleigh waves.

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jonesdave116 said:

Err, no. The nucleus is reflecting ~6% of the incident light. It is dark as hell. There were no outbursts that were self-illuminated. End of story.
They don't look like 'electric discharges', they don't behave like 'electric discharges', and they sure as hell haven't shown up on instruments that would detect them, as 'electric discharges'.
They are NOT electric discharges. Finish. Only an idiot would believe that.

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Analysis of the propagation of the CONSERT signal throughout the small lobe of 67P/CG nucleus permitted to deduce the real part of the permittivity, at a value of 1.27± 0.05 [1]. The first interpretation of this value using the dielectric properties of mixtures of ices (H2O, CO2), dusts and porosity, led to the conclusion that the comet porosity ranges between 75 – 85%. In addition, the dust to ice ratio was found to range between 0.4-2.6 and the permittivity of dust (including 30% of porosity) was determined to be lower than 2.9. This last value corresponds to a permittivity lower than 4 for a material without any porosity.

This paper is intended to refine the dust permittivity estimate by taking into account the updated values of nucleus densities and dust/ice ratio, and to provide further insights into the nature of the constituents of comet 67P/CG. We adopted a systematic approach: determination of the dust permittivity as a function of the Ice / Dust and Vacuum (i.e. porosity) volume fraction and comparison with the permittivity of meteoritic, mineral and organic material from literature and laboratory measurements. Then different composition models of the nuclei corresponding to cosmochemical endmembers of 67P/CG dust are tested. For each of these models the location in the I/D/V diagram is calculated based on available dielectric measurements, and confronted to the locus of 67P/CG. The number of compliant models is small and the cosmochemical implications of each are discussed to conclude on a preferred model [2]. An important fraction of carbonaceous material is required in the dust in order to match CONSERT permittivity observations, establishing that comets represent a massive carbon reservoir.

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Rosetta’s observations of 67P/Churyumov-Gerasimenko have highlighted the dynamic nature of a comet’s plasma environment. In this work, we study the suprathermal electrons excited in the coma using observations from the Ion and Electron Sensor (IES) and other instruments onboard the Rosetta spacecraft. We fit the IES electron observations with the summation of 2 kappa distributions, which are characterized as a dense, warm population and a rarefied, hot population. The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. It was previously determined that the hot population is likely solar wind halo electrons, but the warm population remains a mystery. Consequently, we focus our analysis on the warm population to determine its origin by comparing the density and temperature to the neutral density and magnetic field strength. We find that the warm electron temperature above 100,000 K is strongly correlated with the neutral density, which is in contrast to previous results that found cometary electron temperature to be anti-correlated with neutral density. Additionally, we found that the warm electron temperature is closely related to the electrostatic wave power near the lower hybrid frequency. We conclude that the warm electron population is being heated by lower hybrid waves driven by the two-stream instability of solar wind protons and newly-formed, cometary ions created in localized, dense neutral streams.

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Sol88 said:

P43A-2093: Cometary Electron Heating Driven by Solar Wind Interaction with the Coma



Really excited now!

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jonesdave116 said:

Err, no. The nucleus is reflecting ~6% of the incident light. It is dark as hell. There were no outbursts that were self-illuminated. End of story.
They don't look like 'electric discharges', they don't behave like 'electric discharges', and they sure as hell haven't shown up on instruments that would detect them, as 'electric discharges'.
They are NOT electric discharges. Finish. Only an idiot would believe that.

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Sol88 said:

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Sol88 said:

Carbonaceous chondrite

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