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THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN. E. D. Young1, T. D. Swindle2, S. P.
Schwenzer3, and the MSR Gas Sampling Science Team, 1Earth, Planetary, and Space Sciences, UCLA, USA
(eyoung@epss.ucla.edu), 2 University of Arizona, Lunar and Planetary Laboratory, USA, 3 Open University, UK.
Introduction: The return of a sample of near-surface
atmosphere from Mars would facilitate answers to sev-
eral first-order science questions surrounding the forma-
tion and evolution of the planet. One of the impor-
tant aspects of terrestrial planet formation in general is
the role that primary atmospheres played in influencing
the chemistry and structure of the planets and their an-
tecedents. Studies of the martian atmosphere can be used
to investigate the role of a primary atmosphere in its his-
tory. Atmosphere samples would also inform our un-
derstanding of the near-surface chemistry of the planet,
and ultimately the prospects for life. High-precision iso-
topic analyses of constituent gases are needed to address
these questions, requiring that the analyses are made on
returned samples rather than in situ.
Prospects for a Return Sample: The Roubion sam-
ple core from Jezero Crater provides the opportunity to
return a near-surface atmosphere sample. Between sols
159 and 168, Perseverance attempted to obtain a core
from the Roubion target. The sample was disaggregated
and virtually no rock was retained [1, 2]. However, this
empty sample tube offers the chance to bring back an at-
mosphere sample that will have had minimal exchange
with regolith in comparison to headspace gases in other
sample tubes. This is important because degassing and
exchange will likely alter the headspace gas chemically
and isotopically [2]. The viability of the sample against
leakage has been assessed recently [3] and the conclu-
sion is that the sample will be viable against contami-
nation for many years. Witness tubes will provide other
opportunities for atmosphere return.
The total gas available in the Roubion tube is 12.55
cm3 at ∼ 7.4 mbar. This is equivalent to about 0.1 mi-
cromoles of N2 gas, 1 × 10−5 micromoles of Ne, and 3.9
micrmoles of CO2. These yields compare favorably with
present requirements for isotopic analyses of about 0.1
micromoles, 1 × 10−10 micromoles, and 0.1 micromoles
for relevant isotopic analyses of N2, Ne, and CO2 (TLS),
respectively.
Is there Solar Gas in the Interior of Mars? Previ-
ous analyses of 20Ne/22Ne from trapped atmosphere de-
gassed from SNC meteorites have yielded two distinct re-
sults, with values of ∼ 10.21±1 [4] and 7.3±0.2 [5]. This
difference leads to entirely different interpretations of the
significance of Ne isotopes in the martian atmosphere.
A transfer function relating atmosphere 20Ne/22Ne val-
ues to mantle values [6] suggests that the higher Ne iso-
tope ratio is consistent with incorporation of a solar-like
gas in the interior of Mars, while the lower value is con-
solid
liquid
No primary atmosphere
Primary atmosphere
Mars, no primary atmosphere while molten
Magma
ocean
H2
Magma
ocean
Figure 1: The relationship between maximum surface
temperature for retention of an H2-rich atmosphere and
planet mass. A solidus for surface pressures is shown
for comparison. Mars is only massive enough to have
retained an atmosphere at subsolidus surface conditions
[7].
sistent with a chondritic source. Previous work [7] has
shows that Mars, a stranded planetary embryo, is mas-
sive enough to have had a primary atmosphere of solar-
like composition but only if the surface temperature did
not exceed approximately 700◦ C, i.e., the surface was
subsolidus (Figure 1). In view of the recent suggestion
that Earth was built from embryos with H2-rich atmo-
spheres in contact with magma oceans (and thus with
masses ≥ 0.2MÉ [7], a definitive answer as to the pres-
ence or absence of solar gas in the interior Mars becomes
a crucial arbiter for models of terrestrial planet forma-
tion.
Seasonal vs. Secular Changes in Atmosphere
Composition: Martian atmospheric Kr/Xe ratios ex-
hibit differences between present-day measurements, as
deduced from shergottite meteorites and Viking lan-
der data, and the “fractionated” values obtained from
nakhalites and the martian meteorite ALH84001 (age
> 4 Ga). Is this difference the result of a secular evolu-
tion from the atmosphere trapped in older rocks, or is it
some sort of local seasonal variation [8]? An actual sam-
ple from a well-characterized locality would go a long
way towards understanding the meaning of this variabil-
ity.
N2 Cycling on Mars: On Earth, N2 in air has a 19.2
h excess of 15N15N [9] relative to stochastic (expressed
as ∆30 = 30) caused by upper-atmosphere ion-molecule
reactions involving N and O. This signature of atmo-
2620.pdf
55th LPSC (2024)
spheric chemistry serves as a unique tracer for cycling of
N2 [10] between the surface and the mantle because all
other sources of dinitrogen have ∆30 values of between
0 and ∼ 1 h. In the case of Earth, the ∆30 tracer has
been used to infer that nitrogen in the mantle has been
isolated from the surface throughout most of the history
of the planet. Return of a martian atmosphere sample
will enable us to investigate whether a similar signal can
be used as a tracer on Mars.
The Origin of Methane on Mars: Methane gas
has great potential as a tracer of geochemical and at-
mospheric chemical processes on Mars, in part because
its potential biogenicity offers the attractive prospect of
a biosignature [11]. The power of methane as a tracer
stems not merely from its presence or absence, although
this is important, but also because it comprises a large
number of isotopologues (isotopic varieties); the pres-
ence of two elements with two relatively abundant sta-
ble isotopes each, in a molecule composed of 5 atoms,
results in a large information content. Following the ini-
tial ground-based detections that were seemingly in con-
flict with one another, the subsequent in-situ discovery
of CH4 gas on Mars by Curiosity [12] was described as a
“eureka moment” in planetary exploration [11]. The ori-
gin of martian methane can one day be addressed using
the rare, mass-18 isotopologues 13CH3D and 12CH2D2 .
One approach is to combine inferences from bulk isotope
ratios, 13C/12C and D/H , to provide a “prior” probabil-
ity for biogenicity (e.g., Figure 2), with the the abun-
dances of the rare isotopologues relative to stochastic
values, expressed as ∆13CH3D and ∆12CH2D2 values, as
a likelihood function (e.g., Figure 3) to yield a posterior
probability that a gas sample is biogenic in origin. In the
example shown here, the prior probability of just 0.008
based on bulk isotopes, combined with the likelihood
function of 0.995 from the rare isotopologues, yields a
posterior probability for biogenicity of 0.621. The key
advantage of ∆13CH3D and ∆12CH2D2 values is that, un-
like bulk isotope ratios, they are sensitive to process but
not source material, the latter being largely unknown on
Mars. While any trace methane that may be present in a
return atmosphere sample will be too low in concentra-
tion to afford measurements with current technologies,
future developments may one day permit measurements
of such small samples.
References: [1] J. I. Simon, et al., JGR: Planets
128, (2023). [2] T. D. Swindle, et al., Astrobiology 22,
(2022). [3] J. T. Osterhout, K. A. Farley, M. Wadhwa,
J. Treffkorn, E. Kulczycki, Astrobiology 24, 1, (2023).
[4] R. Wiens, R. Becker, R. Pepin, EPSL 77, 149
(1986). [5] J. Park, et al., LPSC, no. JSC-CN-38725
(2017). [6] H. Kurokawa, et al., Icarus 370, 114685
Figure 2: Probability density map of δ13C vs.
δD isotope ratio space showing the prior probability for
biogenicity for the datum shown as the white point.
Translucent points represent the data used to create the
prior map. All data collected at UCLA.
Figure 3: Probability density map of ∆13CH3D vs.
∆12CH2D2 isotopologue space showing the likelihood
for biogenicity for the datum shown as the white point.
Translucent points represent the data used to create the
Likelihood function map. All data collected at UCLA.
(2021). [7] E. D. Young, A. Shahar, H. E. Schlichting,
Nature 616, 306 (2023). [8] U. Ott, T. D. Swindle, S. P.
Schwenzer, Volatiles in the Martian Crust, J. Filiberto,
S. P. Schwenzer, eds. (Elsevier, 2019), pp. 35–70.
[9] L. Y. Yeung, et al., Science Advances 3, (2017).
[10] J. Labidi, et al., Nature 580, 367, (2020).
[11] Y. L. Yung, et al., Astrobiology 18, 1221, (2018).
[12] C. R. Webster, P. R. Mahaffy, S. K. Atreya,
G. Flesch, AGU Fall Meeting Abstracts (2015), vol.
2015, pp. P43B–2110.
2620.pdf
55th LPSC (2024)

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THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.

  • 1. THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN. E. D. Young1, T. D. Swindle2, S. P. Schwenzer3, and the MSR Gas Sampling Science Team, 1Earth, Planetary, and Space Sciences, UCLA, USA (eyoung@epss.ucla.edu), 2 University of Arizona, Lunar and Planetary Laboratory, USA, 3 Open University, UK. Introduction: The return of a sample of near-surface atmosphere from Mars would facilitate answers to sev- eral first-order science questions surrounding the forma- tion and evolution of the planet. One of the impor- tant aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their an- tecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its his- tory. Atmosphere samples would also inform our un- derstanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision iso- topic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ. Prospects for a Return Sample: The Roubion sam- ple core from Jezero Crater provides the opportunity to return a near-surface atmosphere sample. Between sols 159 and 168, Perseverance attempted to obtain a core from the Roubion target. The sample was disaggregated and virtually no rock was retained [1, 2]. However, this empty sample tube offers the chance to bring back an at- mosphere sample that will have had minimal exchange with regolith in comparison to headspace gases in other sample tubes. This is important because degassing and exchange will likely alter the headspace gas chemically and isotopically [2]. The viability of the sample against leakage has been assessed recently [3] and the conclu- sion is that the sample will be viable against contami- nation for many years. Witness tubes will provide other opportunities for atmosphere return. The total gas available in the Roubion tube is 12.55 cm3 at ∼ 7.4 mbar. This is equivalent to about 0.1 mi- cromoles of N2 gas, 1 × 10−5 micromoles of Ne, and 3.9 micrmoles of CO2. These yields compare favorably with present requirements for isotopic analyses of about 0.1 micromoles, 1 × 10−10 micromoles, and 0.1 micromoles for relevant isotopic analyses of N2, Ne, and CO2 (TLS), respectively. Is there Solar Gas in the Interior of Mars? Previ- ous analyses of 20Ne/22Ne from trapped atmosphere de- gassed from SNC meteorites have yielded two distinct re- sults, with values of ∼ 10.21±1 [4] and 7.3±0.2 [5]. This difference leads to entirely different interpretations of the significance of Ne isotopes in the martian atmosphere. A transfer function relating atmosphere 20Ne/22Ne val- ues to mantle values [6] suggests that the higher Ne iso- tope ratio is consistent with incorporation of a solar-like gas in the interior of Mars, while the lower value is con- solid liquid No primary atmosphere Primary atmosphere Mars, no primary atmosphere while molten Magma ocean H2 Magma ocean Figure 1: The relationship between maximum surface temperature for retention of an H2-rich atmosphere and planet mass. A solidus for surface pressures is shown for comparison. Mars is only massive enough to have retained an atmosphere at subsolidus surface conditions [7]. sistent with a chondritic source. Previous work [7] has shows that Mars, a stranded planetary embryo, is mas- sive enough to have had a primary atmosphere of solar- like composition but only if the surface temperature did not exceed approximately 700◦ C, i.e., the surface was subsolidus (Figure 1). In view of the recent suggestion that Earth was built from embryos with H2-rich atmo- spheres in contact with magma oceans (and thus with masses ≥ 0.2MÉ [7], a definitive answer as to the pres- ence or absence of solar gas in the interior Mars becomes a crucial arbiter for models of terrestrial planet forma- tion. Seasonal vs. Secular Changes in Atmosphere Composition: Martian atmospheric Kr/Xe ratios ex- hibit differences between present-day measurements, as deduced from shergottite meteorites and Viking lan- der data, and the “fractionated” values obtained from nakhalites and the martian meteorite ALH84001 (age > 4 Ga). Is this difference the result of a secular evolu- tion from the atmosphere trapped in older rocks, or is it some sort of local seasonal variation [8]? An actual sam- ple from a well-characterized locality would go a long way towards understanding the meaning of this variabil- ity. N2 Cycling on Mars: On Earth, N2 in air has a 19.2 h excess of 15N15N [9] relative to stochastic (expressed as ∆30 = 30) caused by upper-atmosphere ion-molecule reactions involving N and O. This signature of atmo- 2620.pdf 55th LPSC (2024)
  • 2. spheric chemistry serves as a unique tracer for cycling of N2 [10] between the surface and the mantle because all other sources of dinitrogen have ∆30 values of between 0 and ∼ 1 h. In the case of Earth, the ∆30 tracer has been used to infer that nitrogen in the mantle has been isolated from the surface throughout most of the history of the planet. Return of a martian atmosphere sample will enable us to investigate whether a similar signal can be used as a tracer on Mars. The Origin of Methane on Mars: Methane gas has great potential as a tracer of geochemical and at- mospheric chemical processes on Mars, in part because its potential biogenicity offers the attractive prospect of a biosignature [11]. The power of methane as a tracer stems not merely from its presence or absence, although this is important, but also because it comprises a large number of isotopologues (isotopic varieties); the pres- ence of two elements with two relatively abundant sta- ble isotopes each, in a molecule composed of 5 atoms, results in a large information content. Following the ini- tial ground-based detections that were seemingly in con- flict with one another, the subsequent in-situ discovery of CH4 gas on Mars by Curiosity [12] was described as a “eureka moment” in planetary exploration [11]. The ori- gin of martian methane can one day be addressed using the rare, mass-18 isotopologues 13CH3D and 12CH2D2 . One approach is to combine inferences from bulk isotope ratios, 13C/12C and D/H , to provide a “prior” probabil- ity for biogenicity (e.g., Figure 2), with the the abun- dances of the rare isotopologues relative to stochastic values, expressed as ∆13CH3D and ∆12CH2D2 values, as a likelihood function (e.g., Figure 3) to yield a posterior probability that a gas sample is biogenic in origin. In the example shown here, the prior probability of just 0.008 based on bulk isotopes, combined with the likelihood function of 0.995 from the rare isotopologues, yields a posterior probability for biogenicity of 0.621. The key advantage of ∆13CH3D and ∆12CH2D2 values is that, un- like bulk isotope ratios, they are sensitive to process but not source material, the latter being largely unknown on Mars. While any trace methane that may be present in a return atmosphere sample will be too low in concentra- tion to afford measurements with current technologies, future developments may one day permit measurements of such small samples. References: [1] J. I. Simon, et al., JGR: Planets 128, (2023). [2] T. D. Swindle, et al., Astrobiology 22, (2022). [3] J. T. Osterhout, K. A. Farley, M. Wadhwa, J. Treffkorn, E. Kulczycki, Astrobiology 24, 1, (2023). [4] R. Wiens, R. Becker, R. Pepin, EPSL 77, 149 (1986). [5] J. Park, et al., LPSC, no. JSC-CN-38725 (2017). [6] H. Kurokawa, et al., Icarus 370, 114685 Figure 2: Probability density map of δ13C vs. δD isotope ratio space showing the prior probability for biogenicity for the datum shown as the white point. Translucent points represent the data used to create the prior map. All data collected at UCLA. Figure 3: Probability density map of ∆13CH3D vs. ∆12CH2D2 isotopologue space showing the likelihood for biogenicity for the datum shown as the white point. Translucent points represent the data used to create the Likelihood function map. All data collected at UCLA. (2021). [7] E. D. Young, A. Shahar, H. E. Schlichting, Nature 616, 306 (2023). [8] U. Ott, T. D. Swindle, S. P. Schwenzer, Volatiles in the Martian Crust, J. Filiberto, S. P. Schwenzer, eds. (Elsevier, 2019), pp. 35–70. [9] L. Y. Yeung, et al., Science Advances 3, (2017). [10] J. Labidi, et al., Nature 580, 367, (2020). [11] Y. L. Yung, et al., Astrobiology 18, 1221, (2018). [12] C. R. Webster, P. R. Mahaffy, S. K. Atreya, G. Flesch, AGU Fall Meeting Abstracts (2015), vol. 2015, pp. P43B–2110. 2620.pdf 55th LPSC (2024)