scholarly journals Comet 67P/Churyumov-Gerasimenko rotation changes derived from sublimation-induced torques

2019 ◽  
Vol 630 ◽  
pp. A3 ◽  
Author(s):  
T. Kramer ◽  
M. Läuter ◽  
S. Hviid ◽  
L. Jorda ◽  
H. U. Keller ◽  
...  
Keyword(s):  
Rotation Axis ◽  
Rotation Period ◽  
Rigid Body Dynamics ◽  
The Body ◽  
Active Fraction ◽  
Sublimation Rate ◽  
Rosetta Mission ◽  
Surface Active ◽  
Induced Changes ◽  
Comet 67P

Context. The change in rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P) can be deduced with high precision from images taken by the scientific imaging instruments on board the Rosetta mission. Non-gravitational forces are a natural explanation for these data. Aims. We describe observed changes in orientation of the rotation axis and the rotation period of 67P. We explain them based on a sublimation model with a best fit for the surface active fraction (model P). Torque effects of periodically changing gas emissions on the surface are considered. Methods. We solved the equation of state for the angular momentum in the inertial and the body-fixed frames and provide an analytic theory of the rotation changes in terms of Fourier coefficients, which are generally applicable to periodically forced rigid-body dynamics. Results. The torque-induced changes in rotation state constrain the physical properties of the surface, the sublimation rate, and the local active fraction of the surface. Conclusions. We determine a distribution of the local surface active fraction in agreement with the rotation properties, period, and orientation of 67P. The torque movement confirms that the sublimation increases faster than the insolation toward perihelion. The derived relatively uniform activity pattern is discussed in terms of related surface features.

scholarly journals Outgassing-induced acceleration of comet 67P/Churyumov-Gerasimenko

2019 ◽  
Vol 630 ◽  
pp. A4 ◽  
Author(s):  
T. Kramer ◽  
M. Läuter
Keyword(s):  
Rotation Axis ◽  
Gravitational Acceleration ◽  
Axis Orientation ◽  
Fourier Decomposition ◽  
Sublimation Process ◽  
Rosetta Mission ◽  
Position Data ◽  
Comet 67P ◽  
Local Noon

Context. Cometary activity affects the orbital motion and rotation state through sublimation-induced forces. The availability of precise rotation-axis orientation and position data from the Rosetta mission allows us to accurately determine the outgassing of comet Churyumov-Gerasimenko/67P (67P). Aims. We derived the observed non-gravitational acceleration of 67P directly from the trajectory of the Rosetta spacecraft. From the non-gravitational acceleration, we recovered the diurnal outgassing variations and study a possible delay of the sublimation response with respect to the peak of the solar illumination. This allowed us to compare the non-gravitational acceleration of 67P with expectations based on empirical models and common assumptions about the sublimation process. Methods. We used an iterative orbit refinement and Fourier decomposition of the diurnal activity to derive the outgassing-induced non-gravitational acceleration. The uncertainties of the data reduction were established by a sensitivity analysis of an ensemble of best-fit orbits for comet 67P. Results. We find that the Marsden non-gravitational acceleration parameters reproduce part of the non-gravitational acceleration, but need to be augmented by an analysis of the nucleus geometry and surface illumination to draw conclusions about the sublimation process on the surface. The non-gravitational acceleration closely follows the subsolar latitude (seasonal illumination), with a small lag angle with respect to local noon around perihelion. The observed minor changes of the rotation axis do not favor forced precession models for the non-gravitational acceleration. Conclusions. In contrast to the sublimation-induced torques, the non-gravitational acceleration does not place strong constraints on localized active areas on the nucleus. We find a close agreement of the orbit-deduced non-gravitational acceleration and the water production that is independently derived from Rosetta in situ measurements.

scholarly journals Investigating the Rosetta/RTOF observations of comet 67P/Churyumov-Gerasimenko using a comet nucleus model: influence of dust mantle and trapped CO

2020 ◽  
Vol 638 ◽  
pp. A106
Author(s):  
M. Hoang ◽  
P. Garnier ◽  
J. Lasue ◽  
H. Rème ◽  
M. T. Capria ◽  
...  
Keyword(s):  
Numerical Models ◽  
Bulk Composition ◽  
The Body ◽  
Comet Nucleus ◽  
Near Surface ◽  
Highly Sensitive ◽  
Thermophysical Model ◽  
Rosetta Mission ◽  
Comet 67P ◽  
Range Of Values

Context. Cometary outgassing is induced by the sublimation of ices and the ejection of dust originating from the nucleus. Therefore measuring the composition and dynamics of the cometary gas provides information concerning the interior composition of the body. Nevertheless, the bulk composition differs from the coma composition, and numerical models are required to simulate the main physical processes induced by the illumination of the icy body. Aims. The objectives of this study are to bring new constraints on the interior composition of the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by comparing the results of a thermophysical model applied to the nucleus of 67P and the coma measurements made by the Reflectron-type Time-Of-Flight (RTOF) mass spectrometer. This last is one of the three instruments of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), used during the Rosetta mission. Methods. Using a thermophysical model of the comet nucleus, we studied the evolution of the stratigraphy (position of the sublimation and crystallisation fronts), the temperature of the surface and subsurface, and the dynamics and spatial distribution of the volatiles (H2O, CO2 and CO). We compared them with the in situ measurements from ROSINA/RTOF and an inverse coma model. Results. We observed the evolution of the surface and near surface temperature, and the deepening of sublimation fronts. The thickness of the dust layer covering the surface strongly influences the H2O outgassing but not the more volatiles species. The CO outgassing is highly sensitive to the initial CO/H2O ratio, as well as to the presence of trapped CO in the amorphous ice. Conclusions. The study of the influence of the initial parameters on the computed volatile fluxes and the comparison with ROSINA/RTOF measurements provide a range of values for an initial dust mantle thickness and a range of values for the volatile ratio. These imply the presence of trapped CO. Nevertheless, further studies are required to reproduce the strong change of behaviour observed in RTOF measurements between September 2014 and February 2015.

Further constraints on activity models of comet 67P/Churyumov-Gerasimenko with Rosetta data

2020 ◽  
Author(s):  
Nicholas Attree ◽  
Laurent Jorda ◽  
Olivier Groussin ◽  
Raphael Marschall
Keyword(s):  
Rotation Axis ◽  
Pure Water ◽  
Reaction Force ◽  
Rotation Period ◽  
Parametric Models ◽  
Back Reaction ◽  
Astronomical Society ◽  
Royal Astronomical Society ◽  
Geological Unit ◽  
Comet 67P

<p>Cometary outgassing produces a back-reaction force on a nucleus that can alter its trajectory and rotation state. Understanding this activity is key to exploring the physics of the upper layers of cometary surfaces, with implications for their formation and subsequent evolutionary history, and can be constrained by observing the orbit and rotation changes. For comet 67P/Churyumov-Gerasimenko, detailed measurements have been made by the Rosetta spacecraft and various attempts have been made to model the activity (see, e.g. [1,2]).</p><p>Here we will present updated work using the activity model of [2] to fit to Rosetta outgassing, trajectory, and rotation data. We test a number of different activity distributions over the surface of the comet by varying the Effective Active Fraction (EAF), relative to pure water ice, of facets on a shape model. The previous work has shown that, in order to fit the fast ramp-up and fall-off in outgassing either side of perihelion, 67P’s EAF must vary with time. We therefore investigate a number of different EAF curves to see if different parametric models can be ruled out. The objective here is to constraint the shape of the activity curve that a more advanced thermo-physical model (see, for example [3,4]) must produce in order to fit the data. We also investigate different spatial patterns in EAF, and attempt to correlate them to physical features on the cometary surface. Here we are able, for the first time, to achieve a good fit to the Rosetta data by parameterizing EAF in terms of the different geological unit types on 67P (Fig. 1). This may have important implications for understanding how activity works on the different types of surface observed on cometary nuclei, including ‘rough’, ‘smooth’, ‘dusty’ and ‘rocky’ surface morphologies. Finally, in addition to the changes in rotation period examined in [2], we also compute changes in the rotation axis in order to compare with the observations.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.a40b65df80fe55673282951/sdaolpUECMynit/0202CSPE&app=m&a=0&c=f8cb6140092ce98ec083408a35de649e&ct=x&pn=gnp.elif" alt=""></p><p><strong>References</strong></p><ol><li>Nongravitational Effects of Cometary Activity. S. Mottola, N. Attree, L. Jorda, H.U. Keller, R. Kokotanekova, D. Marshall. Space Science Reviews 216 (1), 1-20</li> <li>Constraining models of activity on comet 67P/Churyumov-Gerasimenko with Rosetta trajectory, rotation, and water production measurements. N. Attree, L. Jorda, O. Groussin, S. Mottola, N. Thomas, Y. Brouet, E. Kührt. Astronomy & Astrophysics 630, A18</li> <li>On the activity of comets: understanding the gas and dust emission from comet 67/Churyumov-Gerasimenko’s south-pole region during perihelion. B. Gundlach, M. Fulle, J. Blum. Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 3, April 2020, Pages 3690–3715</li> <li>Near-perihelion activity of comet 67P/Churyumov–Gerasimenko. A first attempt of non-static analysis. Yu. Skorov, H. U. Keller, S. Mottola and P. Hartogh. Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 3, May 2020, Pages 3310–3316</li> </ol>

Growth Hormone-Induced Changes in Myofibrillar Protein Breakdown in Hypopituitary Children

1983 ◽  
Vol 64 (3) ◽  
pp. 315-320 ◽  
Author(s):  
F. J. Ballard ◽  
J. L. Burgoyne ◽  
F. M. Tomas ◽  
J. L. Penfold
Keyword(s):  
Growth Hormone ◽  
Hormone Treatment ◽  
Myofibrillar Protein ◽  
The Body ◽  
Protein Breakdown ◽  
Older Children ◽  
Breakdown Rate ◽  
Fractional Rate ◽  
Excretion Rates ◽  
Induced Changes

1. Creatinine and Nτ-methylhistidine excretion rates have been measured in 13 hypopituitary children to calculate the body muscle contents and rates of myofibrillar protein breakdown. Analyses have been made during periods of growth hormone withdrawal and subsequent administration. 2. The creatinine excretion rate was lower in the hypopituitary children, indicating a lower muscle content per kg body weight. This difference persisted even in children who had received growth hormone for several years. 3. Excretion of Nτ-methylhistidine was reduced by the administration of growth hormone. 4. The fractional breakdown rate of myofibrillar protein, as calculated from the Nτ-methylhistidine to creatinine molar excretion ratio, averaged 1.76%/day in the four youngest children during growth hormone withdrawal. This was significantly higher than for control children of a similar age (P < 0.02) and was reduced to the normal rate of 1.47%/day by growth hormone administration. 5. in older children the fractional rate of myofibrillar protein degradation remained in the normal range irrespective of growth hormone treatment. 6. These results are discussed in the context of the anabolic effects of growth hormone on muscle being partly explained by its action to decrease rates of protein breakdown.

WING MOVEMENTS AND LIFT REGULATION IN THE FLIGHT OF DESERT LOCUSTS

1993 ◽  
Vol 182 (1) ◽  
pp. 57-69 ◽  
Author(s):  
M. Wortmann ◽  
W. Zarnack
Keyword(s):  
Body Weight ◽  
Unsteady Aerodynamics ◽  
Movement Patterns ◽  
The Body ◽  
Three Dimensions ◽  
Body Angle ◽  
Wing Movement ◽  
Induced Changes ◽  
Lift Body

1. We simultaneously recorded lift/body weight, flight speed, body angle and 12 variables of wing movement for locusts performing tethered long-term flight with low movement scatter. The movements of the forewings and hindwings were recorded in three dimensions by means of miniature induction coils. 2. By adjusting the body angle, we could reproducibly manipulate lift generation as a consequence of induced changes in the wings' movement patterns. We were therefore able to analyse various relationships between the movement patterns and lift. 3. The most prominent variations of kinematic variables were observed for the forewing movements. The relative lift and the steady angle of pitch were positively correlated but there was a negative correlation between relative lift and pitching amplitude. We found no correlation between relative lift and flapping amplitude. Our results seem to correspond to a new theory about unsteady aerodynamics of oscillating aerofoils. 4. We sometimes observed variations in lagging. 5. The forewing downstroke was delayed by 0–8 ms following the hindwing downstroke. Relative lift was positively correlated to this delay.

scholarly journals The changing rotation period of comet 67P/Churyumov-Gerasimenko controlled by its activity

2015 ◽  
Vol 579 ◽  
pp. L5 ◽  
Author(s):  
H. U. Keller ◽  
S. Mottola ◽  
Y. Skorov ◽  
L. Jorda
Keyword(s):  
Rotation Period ◽  
Comet 67P

The Forced Oscillations of Submerged Bodies

2003 ◽  
Vol 125 (4) ◽  
pp. 710-715
Author(s):  
Angel Sanz-Andre´s ◽  
Gonzalo Tevar ◽  
Francisco-Javier Rivas
Keyword(s):  
Rigid Body ◽  
Small Amplitude ◽  
Center Of Mass ◽  
Rigid Body Dynamics ◽  
The Body ◽  
Central Point ◽  
Modal Testing ◽  
Forced Oscillations ◽  
Motion Equations ◽  
Marine Applications

The increasing use of very light structures in aerospace applications are given rise to the need of taking into account the effects of the surrounding media in the motion of a structure (as for instance, in modal testing of solar panels or antennae) as it is usually performed in the motion of bodies submerged in water in marine applications. New methods are in development aiming at to determine rigid-body properties (the center of mass position and inertia properties) from the results of oscillations tests (at low frequencies during modal testing, by exciting the rigid-body modes only) by using the equations of the rigid-body dynamics. As it is shown in this paper, the effect of the surrounding media significantly modifies the oscillation dynamics in the case of light structures and therefore this effect should be taken into account in the development of the above-mentioned methods. The aim of the paper is to show that, if a central point exists for the aerodynamic forces acting on the body, the motion equations for the small amplitude rotational and translational oscillations can be expressed in a form which is a generalization of the motion equations for a body in vacuum, thus allowing to obtain a physical idea of the motion and aerodynamic effects and also significantly simplifying the calculation of the solutions and the interpretation of the results. In the formulation developed here the translational oscillations and the rotational motion around the center of mass are decoupled, as is the case for the rigid-body motion in vacuum, whereas in the classical added mass formulation the six motion equations are coupled. Also in this paper the nonsteady motion of small amplitude of a rigid body submerged in an ideal, incompressible fluid is considered in order to define the conditions for the existence of the central point in the case of a three-dimensional body. The results here presented are also of interest in marine applications.

Ion energy and momentum flux near the cometopause of Comet 67P/Churyumov-Gerasimenko

2021 ◽  
Author(s):  
Hayley Williamson ◽  
Hans Nilsson ◽  
Anja Moslinger ◽  
Sofia Bergman ◽  
Gabriella Stenberg-Wieser
Keyword(s):  
Solar Wind ◽  
Complex Dynamics ◽  
Distribution Functions ◽  
Transitional Period ◽  
Ion Energy ◽  
Rosetta Mission ◽  
Before And After ◽  
Composition Analyzer ◽  
Energy And Momentum ◽  
Comet 67P

&lt;p&gt;Defined as the region where the plasma interaction region of a comet goes from being solar wind-dominated to cometary ion-dominated, the cometopause is a region of comingling plasmas and complex dynamics. The Rosetta mission orbited comet 67P/Churyumov-Gerasimenko for roughly two years. During this time, the cometopause was observed by the Ion Composition Analyzer (ICA), part of the Rosetta Plasma Consortium (RPC), before and after the spacecraft was in the solar wind ion cavity, defined as the region where no solar wind ions were measured. Data from ICA shows that solar wind and cometary ions have similar momentum and energy flux moments during this transitional period, indicating mass loading and deflection of the solar wind. We examine higher order moments and distribution functions for the solar wind and cometary species between December 2015 and March 2016. The behavior of the solar wind protons indicates that in many cases these protons are deflected in a sunward direction, while the cometary ions continue to move predominately antisunward. By studying the distribution functions of the protons during these time periods, it is possible to see a non-Maxwellian energy distribution. This can inform on the nature of the cometopause boundary and the energy transfer mechanisms at play in this region.&lt;/p&gt;

scholarly journals The Rosetta Mission and the Chemistry of Organic Species in Comet 67P/Churyumov–Gerasimenko

Elements ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Monica M. Grady ◽  
Ian P. Wright ◽  
Cécile Engrand ◽  
Sandra Siljeström
Keyword(s):  
Organic Species ◽  
Rosetta Mission ◽  
Comet 67P
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