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Title: Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko

Abstract

Because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminum and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon, or carbon monoxide during their accretion phase in the protosolar nebula (PSN). Here, we investigate how heat generated by the radioactive decay of {sup 26}Al and {sup 60}Fe influences the formation of comet 67P/Churyumov–Gerasimenko, as a function of its accretion time and the size of its parent body. We use an existing thermal evolution model that includes various phase transitions, heat transfer in the ice-dust matrix, and gas diffusion throughout the porous material, based on thermodynamic parameters derived from Rosetta observations. Two possibilities are considered: either, to account for its bilobate shape, 67P/Churyumov–Gerasimenko was assembled from two primordial ∼2 km sized planetesimals, or it resulted from the disruption of a larger parent body with a size corresponding to that of comet Hale–Bopp (∼70 km). To fully preserve its volatile content, we find that either 67P/Churyumov–Gerasimenko’s formation was delayed between ∼2.2 and 7.7 Myr after that of Ca–Al-rich Inclusions in the PSN or the comet’s accretion phase took place over themore » entire time interval, depending on the primordial size of its parent body and the composition of the icy material considered. Our calculations suggest that the formation of 67P/Churyumov–Gerasimenko is consistent with both its accretion from primordial building blocks formed in the nebula or from debris issued from the disruption of a Hale–Bopp-like body.« less

Authors:
; ; ;  [1];  [2]; ;  [3]; ; ; ;  [4]; ; ; ;  [5];  [6];  [7]; ;  [8];  [9] more »; « less
  1. Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France)
  2. Department of Astronomy and Carl Sagan Institute, Space Sciences Building Cornell University, Ithaca, NY 14853 (United States)
  3. Université de Toulouse, UPS-OMP-CNRS, IRAP, Toulouse (France)
  4. Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Ringlaan 3, B-1180 Brussels (Belgium)
  5. Physikalisches Institut, University of Bern, Sidlerstr. 5, CH-3012 Bern (Switzerland)
  6. LATMOS/IPSL-CNRS-UPMC-UVSQ, 4 Avenue de Neptune F-94100, Saint-Maur (France)
  7. Department of Space Science, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228 (United States)
  8. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany)
  9. Centre de Recherches Pétrographiques et Géochimiques, CRPG-CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, F-54501 Vandoeuvre lès Nancy (France)
Publication Date:
OSTI Identifier:
22654500
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 839; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALUMINIUM; ARGON; CARBON MONOXIDE; COMETS; COMPUTERIZED SIMULATION; IRON; LOSSES; NITROGEN; PLANET-SYSTEM ACCRETION; SOLAR NEBULA; SPACE; SPACE VEHICLES

Citation Formats

Mousis, O., Drouard, A., Vernazza, P., Le Deun, T., Lunine, J. I., Monnereau, M., Rème, H., Maggiolo, R., Cessateur, G., De Keyser, J., Gasc, S., Altwegg, K., Balsiger, H., Rubin, M., Tzou, C.-Y., Berthelier, J.-J., Fuselier, S. A., Korth, A., Mall, U., Marty, B., E-mail: olivier.mousis@lam.fr, and and others. Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA6839.
Mousis, O., Drouard, A., Vernazza, P., Le Deun, T., Lunine, J. I., Monnereau, M., Rème, H., Maggiolo, R., Cessateur, G., De Keyser, J., Gasc, S., Altwegg, K., Balsiger, H., Rubin, M., Tzou, C.-Y., Berthelier, J.-J., Fuselier, S. A., Korth, A., Mall, U., Marty, B., E-mail: olivier.mousis@lam.fr, & and others. Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko. United States. doi:10.3847/2041-8213/AA6839.
Mousis, O., Drouard, A., Vernazza, P., Le Deun, T., Lunine, J. I., Monnereau, M., Rème, H., Maggiolo, R., Cessateur, G., De Keyser, J., Gasc, S., Altwegg, K., Balsiger, H., Rubin, M., Tzou, C.-Y., Berthelier, J.-J., Fuselier, S. A., Korth, A., Mall, U., Marty, B., E-mail: olivier.mousis@lam.fr, and and others. Mon . "Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko". United States. doi:10.3847/2041-8213/AA6839.
@article{osti_22654500,
title = {Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko},
author = {Mousis, O. and Drouard, A. and Vernazza, P. and Le Deun, T. and Lunine, J. I. and Monnereau, M. and Rème, H. and Maggiolo, R. and Cessateur, G. and De Keyser, J. and Gasc, S. and Altwegg, K. and Balsiger, H. and Rubin, M. and Tzou, C.-Y. and Berthelier, J.-J. and Fuselier, S. A. and Korth, A. and Mall, U. and Marty, B., E-mail: olivier.mousis@lam.fr and and others},
abstractNote = {Because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminum and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon, or carbon monoxide during their accretion phase in the protosolar nebula (PSN). Here, we investigate how heat generated by the radioactive decay of {sup 26}Al and {sup 60}Fe influences the formation of comet 67P/Churyumov–Gerasimenko, as a function of its accretion time and the size of its parent body. We use an existing thermal evolution model that includes various phase transitions, heat transfer in the ice-dust matrix, and gas diffusion throughout the porous material, based on thermodynamic parameters derived from Rosetta observations. Two possibilities are considered: either, to account for its bilobate shape, 67P/Churyumov–Gerasimenko was assembled from two primordial ∼2 km sized planetesimals, or it resulted from the disruption of a larger parent body with a size corresponding to that of comet Hale–Bopp (∼70 km). To fully preserve its volatile content, we find that either 67P/Churyumov–Gerasimenko’s formation was delayed between ∼2.2 and 7.7 Myr after that of Ca–Al-rich Inclusions in the PSN or the comet’s accretion phase took place over the entire time interval, depending on the primordial size of its parent body and the composition of the icy material considered. Our calculations suggest that the formation of 67P/Churyumov–Gerasimenko is consistent with both its accretion from primordial building blocks formed in the nebula or from debris issued from the disruption of a Hale–Bopp-like body.},
doi = {10.3847/2041-8213/AA6839},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 839,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}
  • We report Spitzer Space Telescope observations of comet 67P/Churyumov-Gerasimenko at 5.5 and 4.3 AU from the Sun, post-aphelion. Comet 67P is the primary target of the European Space Agency's Rosetta mission. The Rosetta spacecraft will rendezvous with the nucleus at heliocentric distances similar to our observations. Rotationally resolved observations at 8 and 24 {mu}m (at a heliocentric distance, r{sub h} , of 4.8 AU) that sample the size and color-temperature of the nucleus are combined with aphelion R-band light curves observed at the Very Large Telescope (VLT) and yield a mean effective radius of 2.04 {+-} 0.11 km, and anmore » R-band geometric albedo of 0.054 {+-} 0.006. The amplitudes of the R-band and mid-infrared light curves agree, which suggests that the variability is dominated by the shape of the nucleus. We also detect the dust trail of the comet at 4.8 and 5.5 AU, constrain the grain sizes to be {approx}<6 mm, and estimate the impact hazard to Rosetta. We find no evidence for recently ejected dust in our images. If the activity of 67P is consistent from orbit to orbit, then we may expect the Rosetta spacecraft will return images of an inactive or weakly active nucleus as it rendezvous with the comet at r{sub h} = 4 AU in 2014.« less
  • The cometary coma is a unique phenomenon in the solar system being a planetary atmosphere influenced by little or no gravity. As a comet approaches the sun, the water vapor with some fraction of other gases sublimate, generating a cloud of gas, ice and other refractory materials (rocky and organic dust) ejected from the surface of the nucleus. Sublimating gas molecules undergo frequent collisions and photochemical processes in the near-nucleus region. Owing to its negligible gravity, comets produce a large and highly variable extensive dusty coma with a size much larger than the characteristic size of the cometary nucleus.The Rosettamore » spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. Both, interpretation of measurements and safety consideration of the spacecraft require modeling of the comet's dusty gas environment.In this work we present results of a numerical study of multispecies gaseous and electrically charged dust environment of comet Chyuryumov-Gerasimenko. Both, gas and dust phases of the coma are simulated kinetically. Photolytic reactions are taken into account. Parameters of the ambient plasma as well as the distribution of electric/magnetic fields are obtained from an MHD simulation of the coma connected to the solar wind. Trajectories of ions and electrically charged dust grains are simulated by accounting for the Lorentz force and the nucleus gravity.« less
  • The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. With a limited amount of available observational data, planning of the mission as well as the interpretation of measurements obtained by instruments on board the spacecraft requires modeling of the dusty/gas environment of the comet. During the mission, the collision regime in the inner coma will change starting from transitional to fully collisionless. As a result, a physically correct model has to be valid at conditions that are far from equilibrium and account for the kinetic nature of the processesmore » occurring in the coma. A study of the multi-species coma of comet 67P/Churyumov-Gerasimenko is presented in our previous paper, where we describe our kinetic model and discuss the results of its application to cases that correspond to the different stages during the mission. In this work, we focus on numerical modeling of the dust phase in the coma of comet 67P/Churyumov-Gerasimenko and its interaction with the surrounding gas. The basic phenomena that govern the dynamics and energy balance of the dust grains are outlined. The effect of solar radiation pressure and the nucleus gravity in limiting the maximum liftable mass of the grains is discussed. The distribution of the terminal velocity of the dust grains as a function of subsolar angle is derived in the paper. We have found that in the regions with high gradients of the gas density, spike-like features can form in the dust flow. The obtained results represent the state of the coma in the vicinity of the nucleus for a series of stages throughout the Rosetta mission. The implications of the model results for future measurements by the GIADA instrument are discussed.« less
  • We present a one-dimensional ion chemistry model of the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko, the target comet for the ESA Rosetta mission. We solve the continuity equations for ionospheric species and predict number densities of electrons and selected ions considering only gas-phase reactions. We apply the model to the subsolar direction and consider conditions expected to be encountered by Rosetta at perihelion (1.29 AU) in 2015 August. Our default simulation predicts a maximum electron number density of {approx}8 Multiplication-Sign 10{sup 4} cm{sup -3} near the surface of the comet, while the electron number densities for cometocentric distances r > 10more » km are approximately proportional to 1/r {sup 1.23} assuming that the electron temperature is equal to the neutral temperature. We show that even a small mixing ratio ({approx}0.3%-1%) of molecules having higher proton affinity than water is sufficient for the proton transfer from H{sub 3}O{sup +} to occur so readily that other ions than H{sub 3}O{sup +}, such as NH{sub 4} {sup +} or CH{sub 3}OH{sub 2} {sup +}, become dominant in terms of volume mixing ratio in part of, if not throughout, the diamagnetic cavity. Finally, we test how the predicted electron and ion densities are influenced by changes of model input parameters, including the neutral background, the impinging EUV solar spectrum, the solar zenith angle, the cross sections for photo- and electron-impact processes, the electron temperature profile, and the temperature dependence of ion-neutral reactions.« less
  • We approach the complicated phenomena of gas-dust interactions in a cometary ionosphere, focusing in particular on the possibility of significant depletion in electron number density due to grain charging. Our one-dimensional ionospheric model, accounting for grain charging processes, is applied to the subsolar direction and the diamagnetic cavity of 67P/Churyuomov-Gerasimenko, the target comet for the ESA Rosetta mission, at perihelion (∼1.25-1.30 AU). We argue on the one hand that grains with radii >100 nm are unlikely to significantly affect the overall ionospheric particle balance within this environment, at least for cometocentric distances >10 km. On the other hand, if nanograins with radii inmore » the 1-3 nm range are ejected to the coma at a level of ∼1% with respect to the mass of the sublimated gas, a significant electron depletion is expected up to cometocentric distances of several tens of kilometers. We relate these results to the recent Cassini discoveries of very pronounced electron depletion compared with the positive ion population in the plume of Enceladus, which has been attributed to nanograin charging.« less