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Title: OXIDIZING PROTO-ATMOSPHERE ON TITAN: CONSTRAINT FROM N{sub 2} FORMATION BY IMPACT SHOCK

Abstract

Titan is the only satellite that possesses a thick atmosphere, composed mainly of N{sub 2} and CH{sub 4}. However, its origin and evolution remain largely unknown. Knowledge of the acquirement of a N{sub 2} atmosphere on Titan would provide insights into nitrogen evolution in planetary atmospheres as well as the formation of satellite systems around gas giants. Previous studies have proposed that the atmospheric N{sub 2} would have been converted from NH{sub 3} via shock heating by accreting satellitesimals in the highly reducing proto-atmosphere composed of NH{sub 3} and CH{sub 4}. Nevertheless, the validity of this mechanism strongly depends on both the composition of the proto-atmosphere and kinetics of shock chemistry. Here, we show that a CO{sub 2}-rich oxidizing proto-atmosphere is necessary to form N{sub 2} from NH{sub 3} efficiently by atmospheric shock heating. Efficient shock production of N{sub 2} is inhibited in a reducing proto-atmosphere composed of NH{sub 3} and CH{sub 4}, because CH{sub 4} plays as the coolant gas owing to its large heat capacity. Our calculations show that the amount of N{sub 2} produced in a CO{sub 2}-rich proto-atmosphere could have reached {approx}20 times that on the present Titan. Although further quantitative analysis are required (especially, themore » occurrence of catalytic reactions), our results imply that the chemical composition of satellitesimals that formed the Saturnian system is required to be oxidizing if the current atmospheric N{sub 2} is derived from the shock heating in the proto-atmosphere during accretion. This supports the formation of regular satellites in an actively supplied circumplanetary disk using CO{sub 2}-rich materials originated from the solar nebula at the final stage of gas giant formation.« less

Authors:
;  [1];  [2];  [3]
  1. Planetary Exploration Research Center (PERC), Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan)
  2. Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561 (Japan)
  3. Institut UTINAM Universite de Franche-Comte, CNRS/INSU, UMR 6213, Besancon Cedex 25030 (France)
Publication Date:
OSTI Identifier:
21565350
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 741; Journal Issue: 1; Other Information: DOI: 10.1088/2041-8205/741/1/L10; Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIA; CARBON DIOXIDE; EVOLUTION; IMPACT SHOCK; METHANE; NITROGEN; OXIDATION; PLANETARY ATMOSPHERES; SATELLITE ATMOSPHERES; SHOCK HEATING; ALKANES; ATMOSPHERES; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; CHEMICAL REACTIONS; ELEMENTS; HEATING; HYDRIDES; HYDROCARBONS; HYDROGEN COMPOUNDS; NITROGEN COMPOUNDS; NITROGEN HYDRIDES; NONMETALS; ORGANIC COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; PLASMA HEATING

Citation Formats

Ishimaru, Ryo, Matsui, Takafumi, Sekine, Yasuhito, and Mousis, Olivier. OXIDIZING PROTO-ATMOSPHERE ON TITAN: CONSTRAINT FROM N{sub 2} FORMATION BY IMPACT SHOCK. United States: N. p., 2011. Web. doi:10.1088/2041-8205/741/1/L10.
Ishimaru, Ryo, Matsui, Takafumi, Sekine, Yasuhito, & Mousis, Olivier. OXIDIZING PROTO-ATMOSPHERE ON TITAN: CONSTRAINT FROM N{sub 2} FORMATION BY IMPACT SHOCK. United States. doi:10.1088/2041-8205/741/1/L10.
Ishimaru, Ryo, Matsui, Takafumi, Sekine, Yasuhito, and Mousis, Olivier. Tue . "OXIDIZING PROTO-ATMOSPHERE ON TITAN: CONSTRAINT FROM N{sub 2} FORMATION BY IMPACT SHOCK". United States. doi:10.1088/2041-8205/741/1/L10.
@article{osti_21565350,
title = {OXIDIZING PROTO-ATMOSPHERE ON TITAN: CONSTRAINT FROM N{sub 2} FORMATION BY IMPACT SHOCK},
author = {Ishimaru, Ryo and Matsui, Takafumi and Sekine, Yasuhito and Mousis, Olivier},
abstractNote = {Titan is the only satellite that possesses a thick atmosphere, composed mainly of N{sub 2} and CH{sub 4}. However, its origin and evolution remain largely unknown. Knowledge of the acquirement of a N{sub 2} atmosphere on Titan would provide insights into nitrogen evolution in planetary atmospheres as well as the formation of satellite systems around gas giants. Previous studies have proposed that the atmospheric N{sub 2} would have been converted from NH{sub 3} via shock heating by accreting satellitesimals in the highly reducing proto-atmosphere composed of NH{sub 3} and CH{sub 4}. Nevertheless, the validity of this mechanism strongly depends on both the composition of the proto-atmosphere and kinetics of shock chemistry. Here, we show that a CO{sub 2}-rich oxidizing proto-atmosphere is necessary to form N{sub 2} from NH{sub 3} efficiently by atmospheric shock heating. Efficient shock production of N{sub 2} is inhibited in a reducing proto-atmosphere composed of NH{sub 3} and CH{sub 4}, because CH{sub 4} plays as the coolant gas owing to its large heat capacity. Our calculations show that the amount of N{sub 2} produced in a CO{sub 2}-rich proto-atmosphere could have reached {approx}20 times that on the present Titan. Although further quantitative analysis are required (especially, the occurrence of catalytic reactions), our results imply that the chemical composition of satellitesimals that formed the Saturnian system is required to be oxidizing if the current atmospheric N{sub 2} is derived from the shock heating in the proto-atmosphere during accretion. This supports the formation of regular satellites in an actively supplied circumplanetary disk using CO{sub 2}-rich materials originated from the solar nebula at the final stage of gas giant formation.},
doi = {10.1088/2041-8205/741/1/L10},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 1,
volume = 741,
place = {United States},
year = {2011},
month = {11}
}