Meeting Information

Where Has All the Atmosphere Gone? Isotope Ratios and Atmosphere Loss from Mars

April 21, 2021

Date: April 21, 2021
Speaker: Timothy A. Livengood, University of Maryland and CRESST, NASA Goddard Space Flight Center
Title: Where Has All the Atmosphere Gone? Isotope Ratios and Atmosphere Loss from Mars
Time: 1:00 PM Eastern Time (US and Canada). Attendees can sign in anytime after 12:30 p.m.

Abstract: We have measured a key feature of Mars’ atmosphere that supports the conclusion that Mars once had much more atmosphere than today, and which can provide constraints on how much more atmosphere it once had. What makes this measurement significant is that it comes decades after the first such measurements failed to detect the same property, and measurements since then have been inconclusive and often disagreed with each other. Atmospheric loss happens due to ultraviolet sunlight breaking up (photolyzing) molecules, releasing constituent atoms to escape to space if they have high enough thermal velocity. The lighter the atom, the more readily it escapes; the heavier the atom, the more of it is retained. As a result, in atoms of the same species, lighter isotopes tend to escape more rapidly than the heavier isotopes, resulting in an enrichment of heavy isotopes. In mass spectrometer measurements on Mars as far back as Viking (1976) this pattern was observed in an enrichment of deuterium, in N-15 compared to N-14, and in Argon isotopes. In the major atmospheric constituent, carbon dioxide, the pattern broke down: the carbon and oxygen isotope ratios were essentially terrestrial. Four decades later, there have finally been two more mass spectrometers landed on Mars, as well as three published efforts to measure isotope ratios spectroscopically from Earth – including ours. Some measurements agree with terrestrial ratios, some show enrichments in one atomic species but not the other, and our measurements show isotope ratios varying with time of day. 40 years after Viking, we have a hypothetical solution to the inconsistency and unreasonable nature of many Mars isotope ratio measurements, and a guide to discerning the true isotope ratios in Mars CO2. With improved isotope ratios, yet to be measured, we will have a way to deduce the density of Mars’ primordial atmosphere and a better handle on how Earthlike an atmosphere has to be to support Earthlike features such as flowing liquid water.

Biography: Dr. Tim Livengood is an Associate Research Scientist in the University of Maryland Department of Astronomy. He came to NASA Goddard Space Flight Center in 1991 as a National Research Council postdoctoral fellow, after completing his PhD in ultraviolet spectroscopy of Jupiter’s aurorae at The Johns Hopkins University (the “The” is critical). Since then, he has been affiliated with several local institutions while conducting research in planetary atmospheres at Goddard, including three stints with UMD and five years at the Challenger Center for Space Science Education. He is currently in his third and final employment run with UMD (promise!). He has worked on projects all over the Solar System with infrared, ultraviolet, and visible spectroscopy and spectrophotometry. He is a co-investigator with the Lunar Exploration Neutron Detector instrument on NASA’s Lunar Reconnaissance Orbiter, to study water on the Moon. and is leading the development at Goddard Space Flight Center of the Submillimeter Solar Observation Lunar Volatiles Experiment (SSOLVE). He is a minor player in additional spaceflight instrument projects for submillimeter, ultraviolet, and neutron remote sensing methods.

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