CaltechAUTHORS
  A Caltech Library Service

Retrieval of Chemical Abundances in Titan's Upper Atmosphere from Cassini UVIS Observations with Pointing Motion

Fan, Siteng and Shemansky, Donald E. and Li, Cheng and Gao, Peter and Wan, Linfeng and Yung, Yuk L. (2019) Retrieval of Chemical Abundances in Titan's Upper Atmosphere from Cassini UVIS Observations with Pointing Motion. Earth and Space Science, 6 (7). pp. 1057-1066. ISSN 2333-5084. https://resolver.caltech.edu/CaltechAUTHORS:20190522-105635213

[img] PDF - Published Version
Creative Commons Attribution Non-commercial No Derivatives.

1MB
[img] PDF - Accepted Version
See Usage Policy.

2MB
[img] MS Word - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

1MB
[img] Postscript (Figure S1) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

72kB
[img] Postscript (Figure S2) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

531kB
[img] Postscript (Figure S3) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

337kB
[img] Postscript (Figure S4) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

317kB
[img] Postscript (Figure S5) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

50kB
[img] MS Excel (Data Set S1) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

26kB
[img] MS Excel (Data Set S2) - Supplemental Material
Creative Commons Attribution Non-commercial No Derivatives.

7kB

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20190522-105635213

Abstract

Cassini/UVIS FUV observations of stellar occultations at Titan are well suited for probing its atmospheric composition and structure. However, due to instrument pointing motion, only five out of tens of observations have been analyzed. We present an innovative retrieval method that corrects for the effect of pointing motion by forward modeling the Cassini/UVIS instrument response function with the pointing motion value obtained from the SPICE C‐kernel along the spectral dimension. To illustrate the methodology, an occultation observation made during flyby T52 is analyzed, when the Cassini spacecraft had insufficient attitude control. A high‐resolution stellar model and an instrument response simulator that includes the position of the point source on the detector are used for the analysis of the pointing motion. The Markov Chain Monte‐Carlo method is used to retrieve the line‐of‐sight abundance profiles of eleven species (CH_4, C_2H_2, C_2H_4, C_2H_6, C_4H_2, C_6H_6, HCN, C_2N_2, HC_3N, C_6N_2 and haze particles) in the spectral vector fitting process. We obtain tight constraints on all of the species aside from C_2H_6, C_2N_2 and C_6N_2, for which we only retrieved upper limits. This is the first time that the T52 occultation was used to derive abundances of major hydrocarbon and nitrile species in Titan's upper and middle atmosphere, as pointing motion prohibited prior analysis. With this new method, nearly all of the occultations obtained over the entire Cassini mission could yield reliable profiles of atmospheric composition, allowing exploration of Titan's upper atmosphere over seasons, latitudes, and longitudes.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1029/2018EA000477DOIArticle
https://arxiv.org/abs/1906.02230arXivDiscussion Paper
ORCID:
AuthorORCID
Fan, Siteng0000-0002-3041-4680
Shemansky, Donald E.0000-0001-7168-871X
Li, Cheng0000-0002-8280-3119
Gao, Peter0000-0002-8518-9601
Wan, Linfeng0000-0002-3762-5034
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2019 American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Received 18 SEP 2018; Accepted 8 MAY 2019; Accepted article online 22 MAY 2019. This research was supported in part by the Cassini/UVIS program via NASA grant JPL.1459109 to the California Institute of Technology, and was partially supported by funding from NASA’s Astrobiology Institute’s proposal “Habitability of Hydrocarbon Worlds: Titan and Beyond” (PI R.M. Lopes). All the data and tools in this work are publicly available. Cassini/UVIS data is available on NASA PDS (pds.nasa.gov). The python package emcee is available at dfm.io/emcee/current. We thank Dr. Tommi T. Koskinen and Dr. Karen Willacy for sharing results.
Group:Astronomy Department
Funders:
Funding AgencyGrant Number
NASAJPL.1459109
Issue or Number:7
Record Number:CaltechAUTHORS:20190522-105635213
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190522-105635213
Official Citation:Fan, S., Shemansky, D. E., Li, C., Gao, P., Wan, L., & Yung, Y. L. (2019). Retrieval of chemical abundances in Titan's upper atmosphere from Cassini UVIS Observations with pointing motion. Earth and Space Science, 6, 1057–1066. https://doi.org/10.1029/2018EA000477
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95696
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 May 2019 21:59
Last Modified:20 Apr 2020 08:47

Repository Staff Only: item control page