Dr. Alexander ("Xander") Thelen is a NASA Astrobiology Postdoctoral Program fellow associated with the NASA Goddard Space Flight Center Planetary Systems Laboratory. Dr. Thelen's research pertains to the chemical composition and dynamics of planetary atmospheres; in particular, Dr. Thelen's work is focused on Titan and other outer solar system moons. Using high spatial and spectral resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA), Dr. Thelen has begun investigating seasonal variations in Titan's atmospheric composition to continue the legacy of the Cassini-Huygens mission. Additionally, Dr. Thelen is interested in the study of other solar system objects using ALMA, the development of interplanetary CubeSats, and the investigation of Ocean World analogues.
Alexander Edouard Thelen
(Associate Research Scientist)
| Email: | alexander.e.thelen@nasa.gov |
| Phone: | 301.286.8797 |
| Org Code: | 693 |
| Address: |
NASA/GSFC Mail Code 693 Greenbelt, MD 20771 |
| Employer: | CALIFORNIA INSTITUTE OF TECHNOLOGY |
Brief Bio
Research Interests
Chemical Composition and Dynamics of Titan's Atmosphere
Solar System: MoonsThe study of Titan's atmospheric composition through spatially resolved observations using the ALMA interferometer. Submillimeter spectra are modeled using the Non-linear optiMal Estimator for Multi-variatE spectral analySIS (NEMESIS) radiative transfer code to determine the vertical and latitudinal distribution of Titan's trace atmospheric constituents - many of which are hydrocarbon (CxHy) and nitrile (CxHy[CN]z) species. These results will allow us to understand how Titan's atmosphere responds to seasonal changes during the moon's northern summer, after the end of the Cassini-Huygens mission. Additionally, the distribution of trace atmospheric species, and the search for previously undetected species, may be important for astrobiology studies of Titan.
Submillimeter Investigation of Planetary Atmospheres
Solar System: AtmospheresThe investigation of other planetary atmospheres, including Mars, Neptune, and Jupiter, using techniques developed for studying Titan with ALMA. Through the wide range of chemical species observable in the submillimeter – including CO, hydrocarbons, and nitriles – measurements of chemical abundance, temperature, and atmospheric winds can be derived. With the newest generation of ground-based facilities such as ALMA, observations can be made with high spatial resolution allowing for unprecedented studies of atmospheric dynamics and composition from the ground.
Europa CubeSats
Solar System: MoonsPrevious work involved a concept study of a Europa CubeSat to ride along with the Europa Clipper spacecraft. The Deployable Atmospheric Reconnaissance CubeSat with Sputtering Ion Detector at Europa (DARCSIDE) mission concept was developed at New Mexico State University in cooperation with JPL. The spacecraft would utilize an accelerometer and solid state particle telescope to monitor the atmospheric drag imparted upon the CubeSat from Europa's tenuous atmosphere, and determine the heavy ion flux at the moon from Jupiter's magnetosphere. These results could help to elucidate the connection between the origin and composition of Europa's atmosphere, and the harsh Jovian radiation environment.
Positions/Employment
Postdoctoral Scholar
California Institute of Technology - Pasadena, CA
October 2022 - Present
NPP Astrobiology Fellow
NAI/USRA - NASA Goddard Space Flight Center, Greenbelt, MD
December 2019 - October 2022
Research Associate
Catholic University of America/NASA GSFC - Washington, DC
October 2018 - December 2019
NASA ASTAR/JGFP Graduate Fellow
New Mexico State University - Las Cruces, NM
2015 - 2018
Education
Ph.D., Astronomy
New Mexico State University
2013-2018
Dissertation: "The Chemical Composition and Dynamics of Titan's Atmosphere as Revealed by ALMA"
Advisors: Dr. Nancy Chanover, Dr. Conor Nixon
B.S., Physics (Astrophysics)
University of California, Santa Cruz
2008-2012
Thesis: "The Kinematics of Andromeda's DIG Disk"
Advisor: Dr. Puragra Guha Thakurta
Professional Societies
American Astronomical Society
2012 - Present
AAS/Division for Planetary Sciences
2014 - Present
American Geophysical Union
2016 - Present
Professional Service
AGU Fall Meeting Planning Committee: 2021–2022
Primary Convener: 'Phosphine in the Venusian Atmosphere: Observations and Implications', AGU 2020 Fall Meeting; 'Outer Planets and Beyond', AGU 2021 Fall Meeting; 'Outer Planets and Beyond', AGU 2022 Fall Meeting
Convener: 'Asteroids, Meteoroids, and Moons: Inner Solar System Processes', AGU 2021 Fall Meeting
Session Chair: DPS 2020, AGU Fall Meeting 2021
Proposal Panelist/External Reviewer: NASA ROSES, CDAP, FINESST, Keck TAC
Proposal Executive Secretary: NASA CDAP
Manuscript Referee: Astrophysical Journal Letters, Planetary Science Journal, Acta Astronautica, Astronomy & Astrophysics
Awards
ALMA Student Observing Support Award
2020 ALMA Ambassador
2021 ALMA Ambassador
Grants
Submillimeter Observations of Titan's Atmosphere: Implications for Astrobiology
NASA Astrobiology Postdoctoral Program (NPP) Fellowship - NASA/NAI - Awarded: 2019-03-01
Dates: 2020-01-02 - 2022-01-02
Global Measurements of the Atmospheric Temperatures on Mars Using ALMA, and the Comparison to Climate Models and Spacecraft Datasets
FLaRe - NASA GSFC - Awarded: 2019-06-07
Dates: 2019-06-07 - 2019-12-31
Coverage: 0.25
The Chemical History and Evolution of Titan's Atmosphere as Revealed by ALMA
NASA ASTAR/JGFP Fellowship - NASA/NMSU - Awarded: 2015-09-01
Dates: 2015-09-01 - 2018-09-01
Amount 165,000
Other Professional Information
Articles and Press Releases:
- "How Scientists Are Searching for Life on Titan" - July 15th, 2019
NASA Astrobiology feature story.
https://nai.nasa.gov/articles/2019/7/15/how-earth-based-scientists-are-searching-for-life-on-titan/
- "How to Plan a Space Mission" - July 12th, 2020
New Yorker article on the 2019 Planetary Science Summer Seminar:
- "NASA Scientists Discover ‘Weird’ Molecule in Titan’s Atmosphere" - October 27th, 2020
NASA article on the detection of c-C3H2 in the atmosphere of Titan using ALMA
Special Experience
Accepted Observing Proposals:
Apache Point 3.5 m
- Observations of Jupiter's Atmosphere at Visible Wavelengths [DIS] (PI: A. E. Thelen) - 2012, 2013
Atacama Large Millimeter/submillimeter Array
- Elucidating Titan's High-Altitude Nitrogen Chemistry [Main Array] (PI: M. A. Cordiner) - Cycle 7 2019
- Mapping Trace Gases in Jupiter's Atmosphere [ACA, TP] (PI: A. E. Thelen) - Cycle 7 Supplemental Call 2020
- An Investigation of Latitudinal Variations in Titan's Atmospheric CH4 [Main Array] (PI: A. E. Thelen) - Cycle 8 2021
- Unlocking Titan's Atmospheric Chemistry with ALMA [Main Array] (PI: A. E. Thelen) - Cycle 8 2021
- Blowing in the Wind: Temporal Variability of Titan's High-Altitude Circulation System [Main Array] (PI: M. A. Cordiner) - Cycle 8 2021
- Titan's Atmospheric Asymmetry [Main Array] (PI: N. A. Teanby) - Cycle 8 2021
Other Facilities:
- Titan's stratospheric winds from disk-resolved occultation imaging - Gemini South 2022
- Co-I: Gemini North, Keck
International Astrobiology Summer School - 2016
Astrobiology Graduate Conference Proposal Writing Workshop - 2017
JPL Planetary Science Summer School
Development of BRIDGE mission concept to interstellar objects or long-period comets - 2019
GSFC Planetary Science Winter School
Participation in flight instrument design study - 2020
Field Experience
Measurements and sample collection in Yellowstone National Park hot springs - 2019
Publications
Refereed
2024. "Observations of Titan’s Stratosphere during Northern Summer: Temperatures, CH3CN and CH3D Abundances." The Planetary Science Journal 5 (5): 125 [10.3847/psj/ad47bd] [Journal Article/Letter]
2024. "Measurements of Titan’s Stratospheric Winds during the 2009 Equinox with the eSMA." The Planetary Science Journal 5 (4): 98 [10.3847/psj/ad3355] [Journal Article/Letter]
2024. "Subsurface Thermophysical Properties of Europa’s Leading and Trailing Hemispheres as Revealed by ALMA." The Planetary Science Journal 5 (2): 56 [10.3847/psj/ad251c] [Journal Article/Letter]
2023. "Author's Reply to Comment by Greaves et al. on “Phosphine in the Venusian Atmosphere: A Strict Upper Limit From SOFIA GREAT Observations”." Geophysical Research Letters 50 (23): [10.1029/2023gl106136] [Journal Article/Letter]
2023. "Thermal Properties of the Leading Hemisphere of Callisto Inferred from ALMA Observations." The Planetary Science Journal 4 (8): 142 [10.3847/psj/aceb68] [Journal Article/Letter]
2022. "Phosphine in the Venusian Atmosphere: A Strict Upper Limit From SOFIA GREAT Observations." Geophysical Research Letters 49 (22): [10.1029/2022gl101055] [Journal Article/Letter]
2022. "Variability in Titan’s Mesospheric HCN and Temperature Structure as Observed by ALMA." The Planetary Science Journal 3 (6): 146 [10.3847/psj/ac7050] [Journal Article/Letter]
2021. "No evidence of phosphine in the atmosphere of Venus from independent analyses." Nature Astronomy 5 (7): 631-635 [10.1038/s41550-021-01422-z] [Journal Article/Letter]
2021. "Titan: Earth-like on the Outside, Ocean World on the Inside." The Planetary Science Journal 2 (3): 112 [10.3847/psj/abf7c9] [Journal Article/Letter]
2021. "Observations of Mars with ALMA: potential for future constraints of global circulation models." Journal of Astronomical Telescopes, Instruments, and Systems 7 (02): [10.1117/1.jatis.7.2.025001] [Journal Article/Letter]
2021. "Bridge to the stars: A mission concept to an interstellar object." Planetary and Space Science 197 105137 [10.1016/j.pss.2020.105137] [Journal Article/Letter]
2020. "Detection of Dynamical Instability in Titan’s Thermospheric Jet." The Astrophysical Journal 904 (1): L12 [10.3847/2041-8213/abc688] [Journal Article/Letter]
2020. "Detection of CH3C3N in Titan’s Atmosphere." The Astrophysical Journal 903 (1): L22 [10.3847/2041-8213/abc1e1] [Journal Article/Letter]
2020. "Detection of Cyclopropenylidene on Titan with ALMA." The Astronomical Journal 160 205 [10.3847/1538-3881/abb679] [Journal Article/Letter]
2020. "Propionitrile in the two lowest excited vibrational states in the laboratory and on Titan." Journal of Molecular Spectroscopy 372 111324 [10.1016/j.jms.2020.111324] [Journal Article/Letter]
2019. "ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale." The Astronomical Journal 158 (2): 76 [10.3847/1538-3881/ab2d20] [Journal Article/Letter]
2019. "Measurement of CH3D on Titan at Submillimeter Wavelengths." The Astronomical Journal 157 (6): 219 [10.3847/1538-3881/ab19bb] [Journal Article/Letter]
2019. "Abundance measurements of Titan’s stratospheric HCN, HC3N, C3H4, and CH3CN from ALMA observations." Icarus 319 417-432 [10.1016/j.icarus.2018.09.023] [Journal Article/Letter]
2018. "Spatial variations in Titan’s atmospheric temperature: ALMA and Cassini comparisons from 2012 to 2015." Icarus 307 380-390 [10.1016/j.icarus.2017.10.042] [Journal Article/Letter]
2018. "The Origin of Titan’s External Oxygen: Further Constraints from ALMA Upper Limits on CS and CH2NH." The Astronomical Journal 155 (6): 251 [10.3847/1538-3881/aac172] [Journal Article/Letter]
2017. "A Europa CubeSat Concept Study for Measuring Atmospheric Density and Heavy Ion Flux." Journal of Small Satellites 6 (2): 591-607 [Journal Article/Letter]
Talks, Presentations and Posters
Invited
Investigating Titan's Atmospheric Chemistry with ALMA
July 16, 2022
American Astronomical Society 240th/Laboratory Astrophysics Division Meeting
Exploring Titan's Atmospheric Chemistry and Dynamics with ALMA
2021
Kapteyn Astronomical Institute Colloquium, University of Groningen
The Search for New Molecular Species in the Atmosphere of Titan
2, 2020
Astrochemistry Discussions online talk series.
https://discussions.astrochem.net/videos
ALMA Observations of Titan's Dynamic Atmosphere into the Post-Cassini Era
August 15, 2020
Japanese Geophysical Union - American Geophysical Union Joint Virtual Meeting 2020
Other
Titan's Variable Mesospheric Thermal Structure as Measured by ALMA
2020
American Geophysical Union Fall Meeting
Detection of CH3C3N in Titan's Atmosphere
November 2020
AAS/Division of Planetary Sciences 52nd Meeting
The Temporal Variability of Titan’s Atmosphere During Northern Summer
2019
American Geophysical Union Fall Meeting
Submillimeter Detection of CH3D on Titan
October 2019
AAS/Division of Planetary Sciences + EPSC Joint Meeting
Titan's Atmospheric CH3D Measured in the Submillimeter with ALMA
June 2019
New Horizons in Planetary Systems
Titan's Atmospheric Dynamics Revealed Through Temperature and Chemical Abundance Measurements from 2012-2015 ALMA Observations
November 2018
AAS/Division for Planetary Sciences 50th Meeting
ALMA and Cassini Comparisons of Titan's Stratospheric Temperature from 2012-2015
November 2017
AAS/Division for Planetary Sciences 49th Meeting
Measuring Spatial and Temporal Variations in Titan's Atmosphere with ALMA
May 2017
Titan Through Time 4
Spatial Variations of Chemical Abundances in Titan's Atmosphere as Revealed by ALMA
November 2016
AAS/Division for Planetary Sciences 48th Meeting