# Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS

Jean-Yves Chaufray, Majd Mayyasi, Michael Chaffin, Justin Deighan, Dolon Bhattacharyya, John Clarke, Sonal Jain, Nick Schneider, Bruce Jakosky

► To cite this version:

Jean-Yves Chaufray, Majd Mayyasi, Michael Chaffin, Justin Deighan, Dolon Bhattacharyya, et al. Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS. 22nd EGU General Assembly, May 2020, Online, Unknown Region. pp.id.13984, 10.5194/egusphere-egu2020-13984. insu-04417907

HAL Id: insu-04417907

https://insu.hal.science/insu-04417907

Submitted on 30 May 2024

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<figure><img src="image_1.png" /></figure>

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# Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS

Jean-Yves Chaufray, Majd Mayyasi, Michael Chaffin, Justin Deighan, Dolon Bhattacharyya, John Clarke, Sonal Jain, Nick Schneider, Bruce Jakosky

<figure><img src="image_1.png" /></figure>

## To cite this version:

Jean-Yves Chaufray, Majd Mayyasi, Michael Chaffin, Justin Deighan, Dolon Bhattacharyya, et al. Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS. 22nd EGU General Assembly, May 2020, Online, Unknown Region. pp.id.13984, 10.5194/egusphere-egu2020-13984. insu-04417907

HAL Id: insu-04417907

https://insu.hal.science/insu-04417907v1

Submitted on 30 May 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS

Chaufray, J-Y., M. Mayyasi, M. Chaffin, J. Deighan, D. Bhattacharyya, J. Clarke, S. Jain, N. Schneider, B. Jakosky

EGU 2020

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

LATMOS

<figure><img src="image_5.png" /></figure>

SORBONNE
UNIVERSITÉS

UNIVERSITÉ DE
VERSAILLES
ST-QUENTIN-EN-YVELINES

université PARIS-SACLAY

<figure><img src="image_6.png" /></figure>

Laboratory for Atmospheric and Space Physics
University of Colorado Boulder

BOSTON
UNIVERSITY
# Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS

Chaufray, J-Y., M. Mayyasi, M. Chaffin, J. Deighan, D. Bhattacharyya, J. Clarke, S. Jain, N. Schneider, B. Jakosky

EGU 2020

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

LATMOS

<figure><img src="image_6.png" /></figure>

SORBONNE
UNIVERSITÉS

UNIVERSITÉ DE
VERSAILLES
ST-QUENTIN-EN-YVELINES
université PARIS-SACLAY
Large seasonal variations of deuterium observed with IUVS/echelle mode with a peak near Ls = 270° (Clarke et al. 2017)

Chaffin et al. (2015) show some Lyman-alpha profiles observed with the « low resolution » mode not reproduced with only H population, especially at morning near Ls = 270°

The expected D emission should be present in the low resolution Lyman-alpha profile (also in SPICAM, Hubble Space Telescope,...) near Ls = 270° and could explain the discrepancy.
Large seasonal variations of deuterium observed with IUVS/echelle mode with a peak near Ls = 270° (Clarke et al. 2017)

Chaffin et al. (2015) show some Lyman-alpha profiles observed with the « low resolution » mode not reproduced with only H population, especially at morning near Ls = 270°

The expected D emission should be present in the low resolution Lyman-alpha profile (also in SPICAM, Hubble Space Telescope,...) near Ls = 270° and could explain the discrepancy.
<figure><img src="image_7.png" /></figure>

**Period 1:** Feb 2015 (Ls ~290°-300°)

Bright limb.

No echelle observations

**Period 2:** Jul 2017 (Ls ~14-17°)

No bright limb

Echelle observations : no D detected

**Period 3:** Dec 2016 (Ls ~287°-290°)

Bright limb

Echelle observations : D detected

**Systematic observations of bright limb near southern summer**
<figure><img src="image_7.png" /></figure>

**Period 1:** Feb 2015 (Ls ~290°-300°)

Bright limb.

No echelle observations

**Period 2:** Jul 2017 (Ls ~14-17°)

No bright limb

Echelle observations : no D detected

**Period 3:** Dec 2016 (Ls ~287°-290°)

Bright limb

Echelle observations : D detected

**Systematic observations of bright limb near southern summer**
<figure><img src="image_8.png" /></figure>

Average of 6
observations done
with echelle mode
and 8 observations
with the FUV detector
for Period 3 (Dec
2016)

Average of low resolution mode vs echelle mode
Difference ~ 10% in total brightness. The agreement is reasonable
<figure><img src="image_8.png" /></figure>

Average of 6
observations done
with echelle mode
and 8 observations
with the FUV detector
for Period 3 (Dec
2016)

Average of low resolution mode vs echelle mode
Difference ~ 10% in total brightness. The agreement is reasonable
<figure><img src="image_9.png" /></figure>

1D density and temperature profile (spherical symmetry)

Free parameters : hydrogen and deuterium density and temperature at the exobase (200 km)

Temperature (K)

<figure><img src="image_10.png" /></figure>

Example of parametrized density profile of H and D

## Models 1

$T(z)$ from Krasnopolsky 2002 f(Texo)

nH and nD derived from the diffusion equation between 120 – 200 km

nH and nD constant below 120 km represent the photochemical profile if the dominant source is ion – neutral reactions near 110 km.

Above 200 km : Chamberlain's profile

Consider interplanetary lyman-alpha emission = 500R
## 1D density and temperature profile (spherical symmetry)

## Free parameters : hydrogen and deuterium density and temperature at the exobase (200 km)

Temperature (K)

<figure><img src="image_9.png" /></figure>

Example of parametrized density profile of H and D

## Models 1

$T(z)$ from Krasnopolsky 2002 f(Texo)

nH and nD derived from the diffusion equation between 120 – 200 km

nH and nD constant below 120 km represent the photochemical profile if the dominant source is ion – neutral reactions near 110 km.

Above 200 km : Chamberlain's profile

Consider interplanetary lyman-alpha emission = 500R
1D density and temperature profile (spherical symmetry)

Free parameters : hydrogen and deuterium density and temperature at the exobase (200 km)

<figure><img src="image_11.png" /><figcaption>Temperature (K)</figcaption></figure>

Example of parametrized density profile of H and D

Models 2

If the main source of H and D is water photodissociation in the mesosphere, we could expect this profile.

Consider interplanetary lyman-alpha emission = 500R
1D density and temperature profile (spherical symmetry)

Free parameters : hydrogen and deuterium density and temperature at the exobase (200 km)

<figure><img src="image_10.png" /><figcaption>Temperature (K)</figcaption></figure>

Example of parametrized density profile of H and D

Models 2

If the main source of H and D is water photodissociation in the mesosphere, we could expect this profile.

Consider interplanetary lyman-alpha emission = 500R
<figure><img src="image_12.png" /></figure>

Simulated D/H profiles for models 1 and 2.

$$D_{mol}(z) \left( \frac{dn}{dz}(z) + n(z) \left( \frac{m_{eff}(z)g}{kT} + \frac{1 + \alpha \frac{dT}{dz}}{T} \right) \right) = 0$$
$$m_{eff} = m_H + m_a \frac{w(z)}{w_l(z)} = m_H + \frac{F_H kT}{bgX_H}$$

Below ~130 km, the hydrogen scale height is reduced due to escape → D/H increases
<figure><img src="image_11.png" /></figure>

Simulated D/H profiles for models 1 and 2.

<figure><img src="image_12.png" /></figure>

Below ~130 km, the hydrogen scale height is reduced due to escape → D/H increases
<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

Validation of the method:
Simulated data

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

Monte Carlo simulated D +H
(black) profile (D/H brightness
peak = 0.14)

Simulated Noise :

0.8 kR below 300 km

0.4 kR above 300 km

(chosen from data due to
different integration time)

Best fit derived from the models
(D blue, H green, D+H red)

Given the IUVS noise, D/H ratio better than 50% could be expected
But Larger systematic uncertainties due to model assumptions
Validation of the method:
Simulated data

<figure><img src="image_13.png" /></figure>

Monte Carlo simulated D +H
(black) profile (D/H brightness
peak = 0.14)

Simulated Noise :

0.8 kR below 300 km

0.4 kR above 300 km

(chosen from data due to
different integration time)

Best fit derived from the models
(D blue, H green, D+H red)

Given the IUVS noise, D/H ratio better than 50% could be expected
But Larger systematic uncertainties due to model assumptions
Source of systematic uncertainties from model assumptions

o Exospheric temperature (T estimated between 160 – 200K)

D/H ratio at 200 km : factor 10

D/H ratio at 80 km : factor 2

o Shape of density profile (model 1 vs model 2)

D/H ratio at 200 km : factor 1.3

D/H ratio at 80 km : factor 2.5

o Absolute calibration (estimated ~ 10%)

D/H ratio at 200 km : factor 1.4

D/H ratio at 80 km : factor 1.4

o Interplanetary hydrogen emission (estimated between 0.2 – 0.8 kR)

D/H ratio at 200 km : factor 1.3

D/H ratio at 80 km : factor 1.3
Source of systematic uncertainties from model assumptions

o Exospheric temperature (T estimated between 160 – 200K)

D/H ratio at 200 km : factor 10

D/H ratio at 80 km : factor 2

o Shape of density profile (model 1 vs model 2)

D/H ratio at 200 km : factor 1.3

D/H ratio at 80 km : factor 2.5

o Absolute calibration (estimated ~ 10%)

D/H ratio at 200 km : factor 1.4

D/H ratio at 80 km : factor 1.4

o Interplanetary hydrogen emission (estimated between 0.2 – 0.8 kR)

D/H ratio at 200 km : factor 1.3

D/H ratio at 80 km : factor 1.3
<figure><img src="image_17.png" /></figure>

Example of fit during period 3

good fit for T = 180 K

Derived D and H brightness in
reasonable agreement with
echelle average profile
(differences ~ 10% expected
due to differences between
small differences between
echelle and FUV brightness).

Simultaneous observations from echelle and low spectral mode

Average D/H at 80 km : 2.5 – 4.7 x 10⁻³ (water vapor : 9 ± 4 x 10⁻⁴)

Average D/H at 200 km : 2.5 – 14.0 x10⁻³
<figure><img src="image_14.png" /></figure>

Example of fit during period 3

good fit for T = 180 K

Derived D and H brightness in
reasonable agreement with
echelle average profile
(differences ~ 10% expected
due to differences between
small differences between
echelle and FUV brightness).

Simultaneous observations from echelle and low spectral mode

Average D/H at 80 km : 2.5 – 4.7 x 10⁻³ (water vapor : 9 ± 4 x 10⁻⁴)

Average D/H at 200 km : 2.5 – 14.0 x10⁻³
<figure><img src="image_18.png" /></figure>

Example of fit during period 2

good fit for T = 200 K

The profile can be fitted without
deuterium

Assuming D/H = 10⁻³ → D density at 200 km ~ 80 – 150 cm⁻³

The observed profile can be well fitted without deuterium in agreement with a low
deuterium brightness (< 300R) from echelle mode
<figure><img src="image_15.png" /></figure>

Example of fit during period 2

good fit for T = 200 K

The profile can be fitted without
deuterium

Assuming D/H = 10⁻³ → D density at 200 km ~ 80 – 150 cm⁻³

The observed profile can be well fitted without deuterium in agreement with a low
deuterium brightness (< 300R) from echelle mode
<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

Example of fit during period 1

good fit for T = 180 K

The shape of the profile can
be reproduced with H and D.
No echelle observations, but
the D brightness (peak ~ 1
kR) is comparable to
observations done during
period 3.

Average D/H at 80 km : 0.6 – 3.4 x 10⁻³ (water vapor : 9 ±4 x10⁻⁴)

Average D/H at 200 km : 1 – 16.0 x10⁻³
<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>

Example of fit during period 1

good fit for T = 180 K

The shape of the profile can be reproduced with H and D. No echelle observations, but the D brightness (peak ~ 1 kR) is comparable to observations done during period 3.

Average D/H at 80 km : 0.6 – 3.4 x 10⁻³ (water vapor : 9 ±4 x10⁻⁴)

Average D/H at 200 km : 1 – 16.0 x10⁻³
☐ Systematic presence of a bright limb observed with the low spectral resolution mode (FUV detector) of MAVEN/IUVS at southern summer (dayside) when large deuterium brightness is observed with echelle mode

☐ We can reproduce the shape of the Lyman-alpha profile observed with the FUV detector of MAVEN/IUVS when D Lyman-alpha emission is included

☐ The major source of uncertainty is not the data noise, but the model assumptions used to derive the D/H values, particularly the density shape profile and exospheric temperature.

→ Possibility to improve the retrieved values with more accurate models (e.g. 3D empirical, validated numerical models).

☐ A source of H and D below the homopause could provide better fit of the total brightness increase.

Future Work

☐ Need to study other observations

☐ Improve models to derive more accurate values.
☐ Systematic presence of a bright limb observed with the low spectral resolution mode (FUV detector) of MAVEN/IUVS at southern summer (dayside) when large deuterium brightness is observed with echelle mode

☐ We can reproduce the shape of the Lyman-alpha profile observed with the FUV detector of MAVEN/IUVS when D Lyman-alpha emission is included

☐ The major source of uncertainty is not the data noise, but the model assumptions used to derive the D/H values, particularly the density shape profile and exospheric temperature.

→ Possibility to improve the retrieved values with more accurate models (e.g. 3D empirical, validated numerical models).

☐ A source of H and D below the homopause could provide better fit of the total brightness increase.

Future Work

☐ Need to study other observations

☐ Improve models to derive more accurate values.