DOI: 10.1126/science.1065569. Detection of Molecular Hydrogen in the Atmosphere of Mars

Detection of Molecular Hydrogen in the Atmosphere of Mars

10.1126/science.1065569

Crossref journal-article

American Association for the Advancement of Science (AAAS)

Science (221)

Abstract

Four hydrogen (H 2 ) lines have been detected in a spectrum of Mars observed with the Far Ultraviolet Spectroscopic Explorer. Three of those lines are excited by the solar Lyman β photons. The line intensities correspond to a column H 2 abundance of 1.17 (±0.13) × 10 13 per square centimeter above 140 kilometers on Mars. A photochemical model for the upper atmosphere that simulates the observed H 2 abundance results in an H 2 mixing ratio of 15 ± 5 parts per million in the lower atmosphere. The H 2 and HD mixing ratios agree with photochemical fractionation of D (deuterium) between H 2 O and H 2 . Analysis of D fractionation among a few reservoirs of ice, water vapor, and molecular hydrogen on Mars implies that a global ocean more than 30 meters deep was lost since the end of hydrodynamic escape. Only 4% of the initially accreted water remained on the planet at the end of hydrodynamic escape, and initially Mars could have had even more water (as a proportion of mass) than Earth.

Bibliography

Krasnopolsky, V. A., & Feldman, P. D. (2001). Detection of Molecular Hydrogen in the Atmosphere of Mars. Science, 294(5548), 1914â1917.

Authors 2

Vladimir A. Krasnopolsky (first)
Paul D. Feldman (additional)

References 58 Referenced 161

10.1029/JS082i028p04341
10.1029/JS082i028p04635
10.1006/icar.1994.1137
10.1029/94JE03283
The basic data on the chemical composition of Mars' atmosphere were obtained from the mass spectrometers on the Viking 1 and 2 landing probes that were used to study the upper (1) and lower (2) atmospheres. However those mass spectrometers had been designed for masses exceeding 10 and could not detect H 2 .
An attempt to detect H 2 on Mars by summing the Mariner 9 ultraviolet spectra resulted in an upper limit of 1.5 R to the line at 1607.5 Å that corresponded to the H 2 density of 1.1 × 10 5 cm −3 at 560 km (53). One R (Rayleigh) corresponds to a column production of 10 6 photons cm −2 s −1 (4π ster) −1 .
Spectroscopic detection of H 2 presents some difficulties. Despite the low H 2 dissociation energy of 4.48 eV dissociation to the ground-state H atoms is parity-forbidden and H 2 absorbs photons only below 1108 Å in the lines of the Lyman and other band systems. The Lyman system converges to the dissociative continuum at 845 Å which corresponds to the formation of one of the H atoms in the excited state n = 2. The solar radiation is weak below 1108 Å and the fluorescence of H 2 is weak as well. Fortunately three absorption lines of the H 2 Lyman band system are exceptionally close to the strong solar Lyman β 1025.72 Å Lyman γ 972.54 Å and C ii 1037.02 Å lines. The differences in the wavelengths are smaller than the widths of the solar lines and the H 2 emission lines from these three levels are much stronger than other H 2 emission lines. This effect was first observed and explained using the Apollo 17 ultraviolet spectrometer (54).
B. Blair B. G. Anderson Eds. The FUSE Observer's Guide (version 3.0 January 2001; ).
1 AU (astronomical unit) is the distance between Earth and the Sun (1.5 × 10 8 km).
10.1029/1999JE001232
Eight spectra of Mars and eight foreground spectra were observed at each of six orbits. Wavelengths in each spectrum were adjusted using strong unblended lines of H O N and Ar. Only one of the four telescopes was exactly pointed to Mars and pointing of the other telescopes was less accurate because of thermal flexture. Exposures intensities of strong lines and the known instrument effective areas were used to determine statistical weights for averaging.
10.1086/177168
Some other lines were considered in (12) for Jupiter but should be very weak on Mars.
The population α was calculated as α(J)=(2J+1)gs exp−hcBJ(J+1)kTΣ (2J+1)gs exp−hcBJ(J+1)kT where g s is the nuclear spin statistical weight B = 60.853 cm −1 is the H 2 ground-state rotational constant h and k are the Planck and Boltzmann constants respectively and c is the speed of light.
The absorption cross sections σ were calculated as σ (cm2Å)=108 Aλ4 (2J′+1)8πc(2J"+1) Nuclear spins are the same for upper and lower states and cancel out A is the transition probability and λ is the wavelength in cm.
Abgrall H., Roueff E., Launay F., Roncin J.-Y., Subtil J.-L., Astron. Astrophys. Suppl. Ser. 101, 273 (1993). / Astron. Astrophys. Suppl. Ser. by Abgrall H. (1993)
10.1086/313151
The H 2 line at 1037.15 Å is near the solar lines at 1036.34 1037.02 and 1037.61 Å. We fitted the observed maxima and minima of this structure in (55) with Gaussians and took into account the instrument resolution of 84 mÅ in (55) to obtain the solar intensity at 1037.15 Å.
10.1029/94JA00518
10.1029/JA076i028p06666
Nakata R. S., Watanabe K., Matsunaga F. M., Sci. Light 14, 54 (1965). / Sci. Light by Nakata R. S. (1965)
J. W. Chamberlain D. M. Hunten Theory of Planetary Atmospheres (Academic Press Orlando FL 1987).
This term was calculated as 0.93 (R+160 km)(2πRH)1/2 (1+9/8λ)R2(1+2/λ) where H = R /λ = 331 km is the H 2 scale height at 160 km for 270 K λ = γ Mm /( RkT ) = 10.73 is the structure parameter γ is the gravitational constant M and m are the masses of Mars and H 2 respectively and 0.93 is a ratio of H 2 column abundances at 160 and 140 km.
We deduced the following relation between τ and τ 0 : τ=2√π¯∫0∞1−exp[−τ0 exp(−x2)]dx which is applicable for τ 0 < 1.
V. A. Krasnopolsky in preparation.
10.1126/science.280.5369.1576
The heliocentric distance of Mars was 1.67 AU F 10.7 cm = 70 and T ∞ = 200 K during the observation (26). These values are similar to those from Viking 1 and Viking 2 (1 2).
10.1006/icar.2000.6534
HDO/H 2 O = 2 D/H.
10.1126/science.240.4860.1767
10.1029/96JE03766
10.3402/tellusa.v22i6.10278
10.1029/1999GL008367
10.1006/icar.1999.6264
10.1126/science.280.5369.1545
10.1029/JB095iB02p01475
10.1126/science.284.5419.1495
10.1029/2000JE001315
10.1126/science.259.5099.1294
10.1029/94JE02801
10.1126/science.265.5168.86
10.1016/0016-7037(96)00122-6
10.1029/1999GL008455
H. Nair Y. L. Yung Bull. Am. Astron. Soc. 27 (1995).
We obtained 10 m by integrating the data from table 1 in (56) and adding the data for nonthermal escape from (57).
D. M. Kass thesis California Institute of Technology (1999).
10.1029/1999JE001058
10.1038/338487a0
10.1016/0019-1035(83)90212-9
10.1016/0019-1035(90)90050-J
This is a standard assumption for calculations of deuterium enrichment in the inner solar system.
10.1016/0019-1035(87)90148-5
10.1029/JA079i019p02887
10.1086/181330
10.1051/aas:1997265
10.1006/icar.1994.1145
10.1029/96JE03440
Supported by the NASA FUSE Guest Investigator Program. V.A.K. thanks A. Dalgarno for consultation.

Dates

Type	When
Created	23 years, 1 month ago (July 27, 2002, 5:47 a.m.)
Deposited	1 year, 7 months ago (Jan. 9, 2024, 5:35 p.m.)
Indexed	1 week, 3 days ago (Aug. 19, 2025, 6:06 a.m.)
Issued	23 years, 8 months ago (Nov. 30, 2001)
Published	23 years, 8 months ago (Nov. 30, 2001)
Published Print	23 years, 8 months ago (Nov. 30, 2001)

Funders 0

None

BibTeX

@article{Krasnopolsky_2001, title={Detection of Molecular Hydrogen in the Atmosphere of Mars}, volume={294}, ISSN={1095-9203}, url={http://dx.doi.org/10.1126/science.1065569}, DOI={10.1126/science.1065569}, number={5548}, journal={Science}, publisher={American Association for the Advancement of Science (AAAS)}, author={Krasnopolsky, Vladimir A. and Feldman, Paul D.}, year={2001}, month=nov, pages={1914–1917} }

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  "abstract": "<jats:p>\n            Four hydrogen (H\n            <jats:sub>2</jats:sub>\n            ) lines have been detected in a spectrum of Mars observed with the Far Ultraviolet Spectroscopic Explorer. Three of those lines are excited by the solar Lyman \u03b2 photons. The line intensities correspond to a column H\n            <jats:sub>2</jats:sub>\n            abundance of 1.17 (\u00b10.13) \u00d7 10\n            <jats:sup>13</jats:sup>\n            per square centimeter above 140 kilometers on Mars. A photochemical model for the upper atmosphere that simulates the observed H\n            <jats:sub>2</jats:sub>\n            abundance results in an H\n            <jats:sub>2</jats:sub>\n            mixing ratio of 15 \u00b1 5 parts per million in the lower atmosphere. The H\n            <jats:sub>2</jats:sub>\n            and HD mixing ratios agree with photochemical fractionation of D (deuterium) between H\n            <jats:sub>2</jats:sub>\n            O and H\n            <jats:sub>2</jats:sub>\n            . Analysis of D fractionation among a few reservoirs of ice, water vapor, and molecular hydrogen on Mars implies that a global ocean more than 30 meters deep was lost since the end of hydrodynamic escape. Only 4% of the initially accreted water remained on the planet at the end of hydrodynamic escape, and initially Mars could have had even more water (as a proportion of mass) than Earth.\n          </jats:p>",
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      ]
    ]
  },
  "references-count": 58,
  "journal-issue": {
    "issue": "5548",
    "published-print": {
      "date-parts": [
        [
          2001,
          11,
          30
        ]
      ]
    }
  },
  "alternative-id": [
    "10.1126/science.1065569"
  ],
  "URL": "http://dx.doi.org/10.1126/science.1065569",
  "relation": {},
  "ISSN": [
    "0036-8075",
    "1095-9203"
  ],
  "subject": [],
  "container-title-short": "Science",
  "published": {
    "date-parts": [
      [
        2001,
        11,
        30
      ]
    ]
  }
}