On the activity of comets: understanding the gas and dust emission from comet 67/Churyumov–Gerasimenko’s south-pole region during perihelion

2020 ◽  
Vol 493 (3) ◽  
pp. 3690-3715 ◽  
Author(s):  
B Gundlach ◽  
M Fulle ◽  
J Blum
Keyword(s):  
Dust Emission ◽  
Surface Region ◽  
The Sun ◽  
South Pole ◽  
Initial Water ◽  
Water Ice ◽  
Thermophysical Model ◽  
Dust Tail ◽  
Lift Off ◽  
Ice Content

ABSTRACT When comets approach the Sun, their surface is heated and the volatile species start to sublimate. Due to the increasing gas pressure, dust is ejected off the surface, which can be observed as cometary coma, dust tail, and trail. However, the underlying physical processes are not fully understood. Using state-of-the-art results for the transport of heat and gas as well as of the mechanical properties of cometary matter, we intend to describe the activity pattern of comets when they approach the Sun. We developed a novel thermophysical model to simulate the dust ejection from comet 67/Churyumov–Gerasimenko’s south-pole region at perihelion. Based on the input parameters, this model computes the sub-surface temperature profile, the pressure build-up, and the redistribution of volatiles inside the cometary sub-surface region and provides mass-loss rates of dust and gas as well as typical sizes and ice content of the ejected dust chunks. Our thermophysical model allows for continuous gas and dust ejection from the Southern hemisphere of comet 67/Churyumov–Gerasimenko at perihelion. We find that the model output is in general agreement with the observed Rosetta data. The sublimation of CO2 ice drives the ejection of very large ($\gtrsim 10\, \mathrm{cm}$) chunks, which contain $10\, {{\ \rm per\ cent}}$ to $90 \, {{\ \rm per\ cent}}$ of the initial water–ice content. In contrast, the outgassing of H2O ice causes the lift-off of small clusters of dust aggregates, which contain no ice.

scholarly journals Site-level model intercomparison of high latitude and high altitude soil thermal dynamics in tundra and barren landscapes

2014 ◽  
Vol 8 (5) ◽  
pp. 4959-5013 ◽  
Author(s):  
A. Ekici ◽  
S. Chadburn ◽  
N. Chaudhary ◽  
L. H. Hajdu ◽  
A. Marmy ◽  
...  
Keyword(s):  
High Arctic ◽  
Soil Freezing ◽  
Physical Processes ◽  
Thermal Dynamics ◽  
Water Ice ◽  
Temperature Regimes ◽  
Temperature Dynamics ◽  
Permafrost Soils ◽  
Level Model ◽  
Ice Content

Abstract. Modelling soil thermal dynamics at high latitudes and altitudes requires representations of specific physical processes such as snow insulation, soil freezing/thawing, as well as subsurface conditions like soil water/ice content and soil texture type. We have compared six different land models (JSBACH, ORCHIDEE, JULES, COUP, HYBRID8, LPJ-GUESS) at four different sites with distinct cold region landscape types (i.e. Schilthorn-Alpine, Bayelva-high Arctic, Samoylov-wet polygonal tundra, Nuuk-non permafrost Arctic) to quantify the importance of physical processes in capturing observed temperature dynamics in soils. This work shows how a range of models can represent distinct soil temperature regimes in permafrost and non-permafrost soils. Snow insulation is of major importance for estimating topsoil conditions and must be combined with accurate subsoil temperature dynamics to correctly estimate active layer thicknesses. Analyses show that land models need more realistic surface processes (such as detailed snow dynamics and moss cover with changing thickness/wetness) as well as better representations of subsoil thermal dynamics (i.e. soil heat transfer mechanism and correct parameterization of heat conductivity/capacities).

Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion

2021 ◽  
Author(s):  
Johanna Klahold ◽  
Christian Hauck ◽  
Florian Wagner
Keyword(s):  
Liquid Water ◽  
Joint Inversion ◽  
Time Lapse ◽  
Swiss Alps ◽  
Permafrost Degradation ◽  
Rock Matrix ◽  
Validation Data ◽  
Water Ice ◽  
Borehole Temperature ◽  
Ice Content

<p>Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without <em>a priori </em>constraints on the porosity model.</p>

Electrical Properties Probe Measures Water/Ice Content of Martian Soils Using Impedance Spectroscopy

2007 ◽  
Author(s):  
M. G. Buehler ◽  
K. B. Chin ◽  
S. Seshadri ◽  
D. Keymeulen ◽  
R. C. Anderson ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Impedance Spectroscopy ◽  
Water Ice ◽  
Ice Content

Thermal Physics of Cometary Nuclei

2020 ◽  
Author(s):  
Dina Prialnik
Keyword(s):  
Solar Energy ◽  
Thermal Emission ◽  
Thermal Evolution ◽  
Internal Heat ◽  
Thermal Inertia ◽  
Skin Depth ◽  
Physical Models ◽  
The Sun ◽  
Cometary Nuclei ◽  
Water Ice

Cometary nuclei, as small, spinning, ice-rich objects revolving around the sun in eccentric orbits, are powered and activated by solar radiation. Far from the sun, most of the solar energy is reradiated as thermal emission, whereas close to the sun, it is absorbed by sublimation of ice. Only a small fraction of the solar energy is conducted into the nucleus interior. The rate of heat conduction determines how deep and how fast this energy is dissipated. The conductivity of cometary nuclei, which depends on their composition and porosity, is estimated based on vastly different models ranging from very simple to extremely complex. The characteristic response to heating is determined by the skin depth, the thermal inertia, and the thermal diffusion timescale, which depend on the comet’s structure and dynamics. Internal heat sources include the temperature-dependent crystallization of amorphous water ice, which becomes important at temperatures above about 130 K; occurs in spurts; and releases volatiles trapped in the ice. These, in turn, contribute to heat transfer by advection and by phase transitions. Radiogenic heating resulting from the decay of short-lived unstable nuclei such as 26Al heats the nucleus shortly after formation and may lead to compositional alterations. The thermal evolution of the nucleus is described by thermo-physical models that solve mass and energy conservation equations in various geometries, sometimes very complicated, taking into account self-heating. Solutions are compared with actual measurements from spacecraft, mainly during the Rosetta mission, to deduce the thermal properties of the nucleus and decipher its activity pattern.

scholarly journals Seasonal variations in the incidence of auroral radio absorption events at very high latitude, and the influence of the magnetotail

2007 ◽  
Vol 25 (3) ◽  
pp. 711-720 ◽  
Author(s):  
J. K. Hargreaves
Keyword(s):  
Statistical Analysis ◽  
Seasonal Variations ◽  
Polar Region ◽  
Winter Season ◽  
Magnetic Activity ◽  
Time Of Day ◽  
Activity Level ◽  
The Sun ◽  
South Pole ◽  
Very High

Abstract. A statistical analysis has been made of the incidence of auroral radio absorption events at South Pole, and of its dependence on basic geophysical parameters such as season, time of day, and magnetic activity level. It is found that at low and moderate levels of activity the incidence of events in the winter season is at least twice that in the summer. However, at high activity no events at all occurred during the local summer night, which appears to be explicable as the effect of the magnetotail and the consequent distortion of the magnetosphere when the southern polar region is tilted strongly towards the Sun. Previous results from even higher latitudes show the effect in an even more exaggerated form, in that both the day and night periods of absorption activity exhibit strong seasonal variations.

Determination of Mars Solar-Belt by Modeling of Solar Radiation Using Artificial Neural Networks

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Tamer Khatib ◽  
Irjuwan Abunajeeb ◽  
Zainab Heneni
Keyword(s):  
Solar Radiation ◽  
Back Propagation ◽  
Photovoltaic System ◽  
Photovoltaic Systems ◽  
The Sun ◽  
Water Ice ◽  
Available Energy ◽  
Feed Forward Back Propagation ◽  
Solar Radiation Intensity ◽  
Artificial Neural

Missions to Mars need a power source, while, one of the most compatible sources for such a purpose is the photovoltaic system. Photovoltaic systems generate power based on the available energy from the Sun, and thus, solar radiation intensity at Mars should be known for design purposes. In this research, the feed-forward back-propagation artificial neural network is developed to predict solar radiation in terms of longitude, latitude, time of the day, temperature, altitude, pressure, amount of dust, and volume mixing ratio of water ice clouds. Data which are used to develop this model are obtained from the Mars Climate Database. The results of the developed method are accurate as compared with other methods whereas the correlation (R2) coefficient for the developed model is 0.97. The developed model then is used to predict mean solar radiation and mean temperature for every location on Mars and then the data are presented on Mars maps in order to determine the best location for harvesting energy from the Sun by photovoltaic systems. According to results, the solar radiation-temperature belt on Mars is found to be between latitudes 20 deg south and 15 deg north.

scholarly journals On the variable intensity of ter­restrial magnetism, and the influence of the aurora borealis upon it

1837 ◽  
Vol 3 ◽  
pp. 37-38
Keyword(s):  
Magnetic Force ◽  
The Sun ◽  
South Pole ◽  
Variable Intensity ◽  
Aurora Borealis ◽  
The North ◽  
The Earth ◽  
Northern Latitudes ◽  
Snow Storms ◽  
Magnetic Needle

The author gives the results of a series of observations on the vibrations of the magnetic needle, which he undertook last summer, for the purpose of ascertaining whether the intensity of its directive force is affected by the changes in the earth’s distance from the sun, or by its declination with respect to the plane of its equator. He observed that the magnetic intensity is subject to frequent variations, which are sometimes sudden, and of short duration. These anomalies he has been unable to refer to any obvious cause, except when they were accompanied by the appearance of the aurora borealis, which evidently affected the needle on many occasions. He also thinks that the vibrations of the needle became less rapid with a moist atmosphere, and more so when it was very dry. Changes of the wind and snow storms appeared also to be attended with fluc­tuations in the intensity of the magnetism. He endeavoured to ascertain whether there existed any decided and constant difference in the directive force of each pole; conceiving that, on the hypothesis of a central magnetic force, the north pole of the magnet would, in these northern latitudes, be acted upon with much greater energy than the south pole. From his observing that the relative intensity of the two poles is not always the same, he infers the probability of the earth’s magnetism being derived from the agency of electric currents existing under its surface as well as above it, and that the rapid fluctuations in its intensity are owing to meteorological changes. The author is led to conclude that the aurora borealis is an elec­trical phenomenon, and that it usually moves during the night nearly from north to south, and in an opposite direction during the day ; that it is of the nature of positive electricity; and that its elevation above the earth is much greater than a thousand, and perhaps thou­sands of miles.

scholarly journals Modeling hole size, lifetime and fuel consumption in hot-water ice drilling

2014 ◽  
Vol 55 (68) ◽  
pp. 115-123 ◽  
Author(s):  
L. Greenler ◽  
T. Benson ◽  
J. Cherwinka ◽  
A. Elcheikh ◽  
F. Feyzi ◽  
...  
Keyword(s):  
Water Flow Rate ◽  
Hot Water ◽  
Hole Size ◽  
South Pole ◽  
Neutrino Detector ◽  
Water Ice ◽  
Fuel Savings ◽  
Highly Sensitive ◽  
The Antarctic ◽  
Drill System

AbstractIceCube, a cubic-kilometer neutrino detector, was built at the South Pole using a hot-water drill system. Deep holes were drilled into the Antarctic ice sheet and filled with highly sensitive optical instrumentation. For the hot-water drilling, a computer model was developed to predict the hole sizes and hole lifetimes during construction. The goal was to predict ultimate size and freezeback rates based on water flow rate and temperature, drill speed, ice temperature and ream parameters (for a secondary operation where hot water continues to flow as the drill is withdrawn). This model proved to be very successful. It increased confidence that the holes would remain open long enough after drilling to allow the deployment of the necessary instrumentation. It also allowed for a decrease, over the course of the project, in the amount of overdrilling that was used as a margin against a too-rapid freeze-in. This resulted in significant fuel savings.

scholarly journals Thermophysical model for icy cometary dust particles

2020 ◽  
Vol 643 ◽  
pp. A16
Author(s):  
J. Markkanen ◽  
J. Agarwal
Keyword(s):  
Energy Balance ◽  
Balance Equation ◽  
Volume Fraction ◽  
Computational Cost ◽  
Direct Simulation Monte Carlo ◽  
Energy Balance Equation ◽  
Dust Particles ◽  
Cometary Dust ◽  
Thermophysical Model ◽  
Ice Content

Context. Cometary dust particles are subjected to various forces after being lifted off the nucleus. These forces define the dynamics of dust, trajectories, alignment, and fragmentation, which, in turn, have a significant effect on the particle distribution in the coma. Aims. We develop a numerical thermophysical model that is applicable to icy cometary dust to study the forces attributed to the sublimation of ice. Methods. We extended the recently introduced synoptic model for ice-free dust particles to ice-containing dust. We introduced an additional source term to the energy balance equation accounting for the heat of sublimation and condensation. We use the direct simulation Monte Carlo approach with the dusty gas model to solve the mass balance equation and the energy balance equation simultaneously. Results. The numerical tests show that the proposed method can be applied for dust particles covering the size range from tens of microns to centimetres with a moderate computational cost. We predict that for an assumed ice volume fraction of 0.05, particles with a radius, r ≫ 1 mm, at 1.35 AU, may disintegrate into mm-sized fragments due to internal pressure build-up. Particles with r < 1 cm lose their ice content within minutes. Hence, we expect that only particles with r > 1 cm may demonstrate sustained sublimation and the resulting outgassing forces.

The 3.1 μm absorption feature on asteroids (24) Themis and (65) Cybele is not due to surface water ice

2021 ◽  
Author(s):  
Laurence O'Rourke ◽  
Thomas G. Müller ◽  
Nicolas Biver ◽  
Dominique Bockelée-Morvan ◽  
Sunao Hasegawa ◽  
...  
Keyword(s):  
Surface Water ◽  
Line Emission ◽  
Thermal Inertia ◽  
Infrared Camera ◽  
Far Infrared ◽  
Subsurface Water ◽  
Absorption Feature ◽  
Water Ice ◽  
V Band ◽  
Thermophysical Model

&lt;p&gt;Previous research on Asteroids (24) Themis and (65) Cybele have shown the presence of an absorption feature at 3.1 &amp;#956;m reported to be directly linked to surface water ice. We searched for water vapor escaping from these asteroids with the Herschel Space Observatory HIFI (Heterodyne Instrument for the Far Infrared) Instrument. While no H&lt;sub&gt;2&lt;/sub&gt;O line emission was detected, we obtained sensitive 3&amp;#963; water production rate upper limits of Q(H&lt;sub&gt;2&lt;/sub&gt;O)&lt; 4.1&amp;#215;10&lt;sup&gt;26&lt;/sup&gt; molecules s&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; for Themis and Q(H&lt;sub&gt;2&lt;/sub&gt;O) &lt;7.6 &amp;#215; 10&lt;sup&gt;26&lt;/sup&gt; molecules s&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; for the case of Cybele. Using a thermophysical model, we merged data from the Subaru/Cooled Mid-Infrared Camera and Spectrometer and the Herschel SPIRE (Spectral and Photometric Imaging Receiver) instrument with the contents of a multi-observatory database and thus derived new radiometric properties for these two asteroids. For Themis, we obtained a thermal inertia G = 20 &lt;sup&gt;+25&lt;/sup&gt;&lt;sub&gt;-10&lt;/sub&gt; J m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt; s&lt;sup&gt;&amp;#8722;1/2&lt;/sup&gt; K&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;, a diameter 192 &lt;sup&gt;+10&lt;/sup&gt;&lt;sub&gt;-7&lt;/sub&gt; km, and a geometric V-band albedo p&lt;sub&gt;V&lt;/sub&gt;=0.07&amp;#177;0.01. For Cybele, we found a thermal inertia G = 25&lt;sup&gt;+28&lt;/sup&gt;&lt;sub&gt;-19&lt;/sub&gt; J m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt; s&lt;sup&gt;&amp;#8722;1/2&lt;/sup&gt; K&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;, a diameter 282&amp;#177;9 km, and an albedo pV=0.042&amp;#177;0.005. Using all inputs, we estimated that water ice intimately mixed with the asteroids&amp;#8217; dark surface material would cover &lt;0.0017% (for Themis) and &lt;0.0033% (for Cybele) of their surfaces, while an areal mixture with very clean ice (Bond albedo 0.8 for Themis and 0.7 for Cybele) would cover &lt;2.2% (for Themis) and &lt;1.5% (for Cybele) of their surfaces. Based on these very low percentage coverage values, it is clear that while surface (and subsurface) water ice may exist in small localized amounts on both asteroids, it is not the reason for the observed 3.1 &amp;#956;m absorption feature.&lt;/p&gt;

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