Comet 67P/Churyumov-Gerasimenko at a large heliocentric distance

Context. The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko from 2014 to September 2016. The mission provided in situ observations of the cometary plasma during different phases of the cometary activity, which enabled us to better understand its evolution as a function of heliocentric distance. Aims. In this study, different electron populations, called warm and hot, observed by the Ion and Electron Sensor (IES) of the Rosetta Plasma Consortium (RPC) are investigated near the comet during the escorting phase of the Rosetta mission. Methods. The estimates for the suprathermal electron densities and temperatures were extracted using IES electron data by fitting a double-kappa function to the measured velocity distributions. The fitting results were validated using observations from other RPC instruments. We give upgraded estimates for the warm and hot population densities compared to values previously shown in literature. Results. The fitted density and temperature estimates for both electron populations seen by IES are expressed as a function of heliocentric distance to study their evolution with the cometary activity. In addition, we studied the dependence between the electron properties and cometocentric distance. Conclusions. We observed that when the neutral outgassing rate of the nucleus is high (i.e., near perihelion) the suprathermal electrons are well characterized by a double-kappa distribution. In addition, warm and hot populations show a significant dependence with the heliocentric distance. The populations become clearly denser near perihelion while their temperatures are observed to remain almost constant. Moreover, the warm electron population density is shown to be strongly dependent on the radial distance from the comet. Finally, based on our results we reject the hypothesis that hot electron population seen by IES consists of solely suprathermal (halo) solar wind electrons, while we suggest that the hot electron population mainly consists of solar wind thermal electrons that have undergone acceleration near the comet.

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Near-perihelion activity of comet 67P/Churyumov–Gerasimenko. A first attempt of non-static analysis

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa865 ◽

2020 ◽

Vol 494 (3) ◽

pp. 3310-3316 ◽

Cited By ~ 1

Author(s):

Yu Skorov ◽

H U Keller ◽

S Mottola ◽

P Hartogh

Keyword(s):

Heliocentric Distance ◽

Active Area ◽

Water Production ◽

South Pole ◽

Free Layer ◽

Dust Layer ◽

Polar Day ◽

Inert Dust ◽

Transient Thermal ◽

Comet 67P

ABSTRACT The observed rate of water production of comet 67P/Churyumov–Gerasimenko near its perihelion can be approximated by a very steep power function of the heliocentric distance. Widely used thermophysical models based on a static dust layer on top of the icy/refractory matrix are poorly consistent with these observations. We analyse published model results and demonstrate that thermophysical models with a uniform and static ice free layer do not reproduce the observed steep water production rates of 67P near perihelion. Based on transient thermal modeling we conclude that the accelerated gas activity can be explained assuming that the active area fraction near the south pole is increased. The deeper penetration of the heat wave during polar day (no sunset) can activate sublimation through thicker inert dust layers. This can also lead to removal of thicker dust layers and consequently to an expansion of the active area.

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The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound

Astronomy and Astrophysics ◽

10.1051/0004-6361/201527564 ◽

2016 ◽

Vol 587 ◽

pp. A155 ◽

Cited By ~ 27

Author(s):

F. Moreno ◽

C. Snodgrass ◽

O. Hainaut ◽

C. Tubiana ◽

H. Sierks ◽

...

Keyword(s):

Heliocentric Distance ◽

Distance Range ◽

Comet 67P

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Comparison of neutral outgassing of comet 67P/Churyumov-Gerasimenko inbound and outbound beyond 3 AU from ROSINA/DFMS

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833536 ◽

2019 ◽

Vol 630 ◽

pp. A30 ◽

Cited By ~ 1

Author(s):

A. Luspay-Kuti ◽

K. Altwegg ◽

J. J. Berthelier ◽

A. Beth ◽

F. Dhooghe ◽

...

Keyword(s):

Southern Hemisphere ◽

Heliocentric Distance ◽

Seasonal Effects ◽

Time Variability ◽

Volatile Species ◽

Neutral Species ◽

Nadir Point ◽

Chemical Variability ◽

Comet 67P ◽

Strong Erosion

Context. Pre-equinox measurements of comet 67P/Churyumov-Gerasimenko with the mass spectrometer ROSINA/DFMS on board the Rosetta spacecraft revealed a strongly heterogeneous coma. The abundances of major and various minor volatile species were found to depend on the latitude and longitude of the nadir point of the spacecraft. The observed time variability of coma species remained consistent for about three months up to equinox. The chemical variability could be generally interpreted in terms of surface temperature and seasonal effects superposed on some kind of chemical heterogeneity of the nucleus. Aims. We compare here pre-equinox (inbound) ROSINA/DFMS measurements from 2014 to measurements taken after the outbound equinox in 2016, both at heliocentric distances larger than 3 AU. For a direct comparison we limit our observations to the southern hemisphere. Methods. We report the similarities and differences in the concentrations and time variability of neutral species under similar insolation conditions (heliocentric distance and season) pre- and post-equinox, and interpret them in light of the previously published observations. In addition, we extend both the pre- and post-equinox analysis by comparing species concentrations with a mixture of CO2 and H2O. Results. Our results show significant changes in the abundances of neutral species in the coma from pre- to post-equinox that are indicative of seasonally driven nucleus heterogeneity. Conclusions. The observed pre- and post-equinox patterns can generally be explained by the strong erosion in the southern hemisphere that moves volatile-rich layers near the surface.

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Interpretation through experimental simulations of phase functions revealed by Rosetta in 67P/Churyumov-Gerasimenko dust coma

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834894 ◽

2019 ◽

Vol 630 ◽

pp. A20 ◽

Cited By ~ 5

Author(s):

A. C. Levasseur-Regourd ◽

J.-B. Renard ◽

E. Hadamcik ◽

J. Lasue ◽

I. Bertini ◽

...

Keyword(s):

Heliocentric Distance ◽

Size Range ◽

Interplanetary Dust ◽

Dust Particles ◽

Zodiacal Cloud ◽

Cometary Dust ◽

Microgravity Conditions ◽

Dust Coma ◽

Phase Functions ◽

Comet 67P

Context. The dust-brightness phase curves that have been measured by the OSIRIS cameras on board the Rosetta spacecraft within the coma of comet 67P/Churyumov-Gerasimenko (67P) present a remarkable flattened u-shape. Aims. Our goal is to compare these phase curves with those of tentatively analog dust samples to assess the key dust properties that might induce this shape. Methods. Light-scattering measurements have been made with the PROGRA2 instrument in the laboratory and in microgravity conditions on samples of different physical properties and compositions that are likely to be representative of cometary dust particles. Results. We find that the brightness phase curves of a series of interplanetary dust analogs that have been recently developed (to fit the polarimetric properties of the inner zodiacal cloud and their changes with heliocentric distance) are quite comparable to those of 67P. Key dust properties seem to be related to the composition and the porosity. Conclusions. We conclude that the shape of the brightness phase curves of 67P has to be related to the presence of a significant amount of organic compounds (at least 50% in mass) and of fluffy aggregates (of a size range of 10–200 μm). We also confirm similarities between the dust particles of this Jupiter-family comet and the particles within the inner zodiacal cloud.

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Energy conversion in cometary atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732353 ◽

2018 ◽

Vol 616 ◽

pp. A81 ◽

Cited By ~ 7

Author(s):

J. Lindkvist ◽

M. Hamrin ◽

H. Gunell ◽

H. Nilsson ◽

C. S. Wedlund ◽

...

Keyword(s):

Solar Wind ◽

Energy Conversion ◽

Heliocentric Distance ◽

Extreme Ultraviolet ◽

Poynting Flux ◽

High Ionization ◽

Electromagnetic Generators ◽

Hybrid Plasma ◽

Electromagnetic Generator ◽

Comet 67P

Aims. We wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets. Methods. We used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. Other parameters corresponded to the conditions of comet 67P/Churyumov–Gerasimenko at a heliocentric distance of 1.5 AU. Results. We find that a shock-like structure is formed upstream of the comet and acts as an electromagnetic generator, similar to the bow shock at Earth that slows down the solar wind. The Poynting flux transports electromagnetic energy toward the inner coma, where newly born cometary ions are accelerated. Upstream of the shock-like structure, we find local energy transfer from solar wind ions to cometary ions. We show that mass loading can be a local process with a direct transfer of energy, but also part of a dynamo system with electromagnetic generators and loads. Conclusions. The energization of cometary ions is governed by a dynamo system for weak ionization, but changes into a large conversion region with local transfer of energy directly from solar wind protons for high ionization.

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Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937022 ◽

2020 ◽

Vol 635 ◽

pp. A51

Author(s):

Rajkumar Hajra ◽

Pierre Henri ◽

Xavier Vallières ◽

Marina Galand ◽

Martin Rubin ◽

...

Keyword(s):

Southern Hemisphere ◽

Total Electron Content ◽

Northern Hemisphere ◽

Hemispheric Asymmetry ◽

Heliocentric Distance ◽

Electron Content ◽

Total Electron ◽

Ionospheric Total Electron Content ◽

Tec Variability ◽

Comet 67P

We study the evolution of a cometary ionosphere, using approximately two years of plasma measurements by the Mutual Impedance Probe on board the Rosetta spacecraft monitoring comet 67P/Churyumov-Gerasimenko (67P) during August 2014–September 2016. The in situ plasma density measurements are utilized to estimate the altitude-integrated electron number density or cometary ionospheric total electron content (TEC) of 67P based on the assumption of radially expanding plasma. The TEC is shown to increase with decreasing heliocentric distance (rh) of the comet, reaching a peak value of ~(133 ± 84) × 109 cm−2 averaged around perihelion (rh < 1.5 au). At large heliocentric distances (rh > 2.5 au), the TEC decreases by ~2 orders of magnitude. For the same heliocentric distance, TEC values are found to be significantly larger during the post-perihelion periods compared to the pre-perihelion TEC values. This “ionospheric hysteresis effect” is more prominent in the southern hemisphere of the comet and at large heliocentric distances. A significant hemispheric asymmetry is observed during perihelion with approximately two times larger TEC values in the northern hemisphere compared to the southern hemisphere. The asymmetry is reversed and stronger during post-perihelion (rh > 1.5 au) periods with approximately three times larger TEC values in the southern hemisphere compared to the northern hemisphere. Hemispheric asymmetry was less prominent during the pre-perihelion intervals. The correlation of the cometary TEC with the incident solar ionizing fluxes is maximum around and slightly after perihelion (1.5 au < rh < 2 au), while it significantly decreases at larger heliocentric distances (rh > 2.5 au) where the photo-ionization contribution to the TEC variability decreases. The results are discussed based on cometary ionospheric production and loss processes.

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Blocks Size Frequency Distribution in the Enceladus Tiger Stripes Area: Implications on Their Formative Processes

Universe ◽

10.3390/universe7040082 ◽

2021 ◽

Vol 7 (4) ◽

pp. 82

Author(s):

Maurizio Pajola ◽

Alice Lucchetti ◽

Lara Senter ◽

Gabriele Cremonese

Keyword(s):

Frequency Distribution ◽

Power Law ◽

Size Frequency Distribution ◽

Surface Stresses ◽

Size Frequency ◽

The One ◽

Power Law Index ◽

Comet 67P ◽

South Polar ◽

Degree Of Fragmentation

We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.

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Author Correction: Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko

Nature Astronomy ◽

10.1038/s41550-021-01373-5 ◽

2021 ◽

Author(s):

M. Galand ◽

P. D. Feldman ◽

D. Bockelée-Morvan ◽

N. Biver ◽

Y.-C. Cheng ◽

...

Keyword(s):

Far Ultraviolet ◽

Comet 67P

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The Balloon-Borne Investigation of Temperature and Speed of Electrons in the Corona (BITSE): Mission Description and Preliminary Results

Solar Physics ◽

10.1007/s11207-020-01751-8 ◽

2021 ◽

Vol 296 (1) ◽

Author(s):

N. Gopalswamy ◽

J. Newmark ◽

S. Yashiro ◽

P. Mäkelä ◽

N. Reginald ◽

...

Keyword(s):

Heliocentric Distance ◽

Signal To Noise Ratio ◽

Flow Speed ◽

Science Data ◽

Uncertainty Interval ◽

Heliospheric Observatory ◽

Flash Storage ◽

Goddard Space Flight Center ◽

Good Agreement ◽

Polarization Camera

AbstractWe report on the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission launched recently to observe the solar corona from $\approx 3$ ≈ 3 Rs to 15 Rs at four wavelengths (393.5, 405.0, 398.7, and 423.4 nm). The BITSE instrument is an externally occulted single stage coronagraph developed at NASA’s Goddard Space Flight Center in collaboration with the Korea Astronomy and Space Science Institute (KASI). BITSE used a polarization camera that provided polarization and total brightness images of size $1024 \times 1024$ 1024 × 1024 pixels. The Wallops Arc Second Pointer (WASP) system developed at NASA’s Wallops Flight Facility (WFF) was used for Sun pointing. The coronagraph and WASP were mounted on a gondola provided by WFF and launched from the Fort Sumner, New Mexico station of Columbia Scientific Balloon Facility (CSBF) on September 18, 2019. BITSE obtained 17,060 coronal images at a float altitude of $\approx \mbox{128,000}$ ≈ 128,000 feet ($\approx 39$ ≈ 39 km) over a period of $\approx 4$ ≈ 4 hrs. BITSE flight software was based on NASA’s core Flight System, which was designed to help develop flight quality software. We used EVTM (Ethernet Via Telemetry) to download science data during operations; all images were stored on board using flash storage. At the end of the mission, all data were recovered and analyzed. Preliminary analysis shows that BITSE imaged the solar minimum corona with the equatorial streamers on the east and west limbs. The narrow streamers observed by BITSE are in good agreement with the geometric properties obtained by the Solar and Heliospheric Observatory (SOHO) coronagraphs in the overlapping physical domain. In spite of the small signal-to-noise ratio ($\approx 14$ ≈ 14 ) we were able to obtain the temperature and flow speed of the western steamer. In the heliocentric distance range 4 – 7 Rs on the western streamer, we obtained a temperature of $\approx 1.0\pm 0.3$ ≈ 1.0 ± 0.3 MK and a flow speed of $\approx 260$ ≈ 260 km s−1 with a large uncertainty interval.

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