The Surface and Atmosphere of Mercury

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The Surface and Atmosphere of Mercury

• F.W. Taylor
• University of Oxford

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(88 days)
D 28.5 to 43.5 million miles
(59 days)
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Caloris Basin
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Caloris Antipode
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Size Comparisons
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Composition of Mercury

• 75of the radius of Mercury is Fe-S core
• What is the rest made of, and can we use surface
  measurements to find out?
• Vilas (in "Mercury" Vilas, Chapman, and Matthews,
  eds., University of Arizona Press, 1988 ) asserts
  we can.

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Mercury is different from the moon
Mercury is systematically brighter the smooth
plains on Mercury are twice as reflective as the
lunar maria. The bright rays surrounding
relatively fresh craters also typically have
twice the albedo of their equivalents on the
Moon, and tend to be bluish rather than reddish
in colour. This implies a difference in
composition, less iron in the mercurian crust,
for example, or more titanium, or both.
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Infrared spectroscopy is diagnostic
Near -IR (0.7 to 3 µm)
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Thermal -IR (7 to 14 µm) Sprague et al. (Icarus,
147, 421-432, 2000)
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Results from Sprague et al. (2000)
Mercury spectrum can be fitted by a mixture
of Picrite, a mafic olivine-rich rock
consisting of 24.3 MgO, 7.66 CaO, 11.24
FeO and Sodalite, a soda-rich aluminium silicate
Na8Al6Si6O24Cl2 Are these found together in
nature? Only in the Teschenite Sills, Shiant
Isles
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Shiant Islands
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Teschenite Sills, Shiant (Wm Daniell, 1819)
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Mercury Atmosphere

• Surface Pressure 10-15 bar (0.001 picobar)
• Average temperature 440 K (range 80-725 K)
• Atmospheric composition
• 42(44) oxygen, 29(22) sodium, 6(33) helium
• 22(0.33) hydrogen, 0.5(0.22) potassium
• possible amounts (undetected) of Argon (Ar),
  Carbon Dioxide (CO2), Water (H2O), Nitrogen (N2),
  Xenon (Xe), Krypton (Kr), Neon (Ne)
• cm-3. From Hunten et al in "Mercury" Vilas,
  Chapman, and Matthews, eds., University of
  Arizona Press, 1988 (cm-2 from Killen Ip,
  Rev.Geophys., 1999)

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Atmosphere-Surface Processes

• Trapped solar wind
• Meteoritic cometary debris
• Bakeout from surface
• Diffusion/exhalation through regolith
• Atoms hop about 50 times on average between
  source loss
• A hop takes 250 s for Na, may reside on surface
  between hops, or bounce
• Radiation pressure, Jeans (c.) escape

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POLAR VOLATILES

• (H2O is stable if Tlt112K models show T as low
  as 60K in shadows, so CO2 could be trapped as
  well)
• Killen et al.(1996) estimate 0 to 60m of ice
  could accumulate
• Some craters Tgt150K

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MERCURY KEY OBJECTIVES

• Nature Origin of the Surface
• Sources Sinks of the Atmosphere
• Volatile Component?
• Polar Deposits
• Interior Source of the Magnetic Field

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Nature Origin of the Surface

• Morphology
• Composition
• Thermophysical Properties

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Thermophysical Properties

• Temperature (sza, from Sun,...)
• Deviations from model
• Look for ice
• Look for thermal anomalies (hot spots)
• Emissivity reflectivity (angle, l?)
• Scattering Properties ?(???????
• Energy Balance (Solar - thermal sensible)
• Thermal Conductivity C
• Thermal Inertia Idensity, depth,...)

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ESA Thermal Model
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Thermal IR observations of polar volatiles on
Mars by the THEMIS on Mars Odyssey (Oct 30, 2001)
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Interior Heat Source of the Magnetic Field

• The night side is very cold (80K)
• We should be able to detect hot spots, due to
  core cooling local escape
• Model of Mercurys interior Schubert et al.,
  1988 predicts 10-30 mW/m2
• A x100 anomaly would be at 120K

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Themal inertia is very diagnostic

• I
• (k conductivity r density c heat
  capacity)
• Varies a lot with type of surface (e.g. dust vs.
  soil vs. rock)
• Reveals layering

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thermal Inertia maps of Mars(from MGS TES,
Mellon et al., Icarus 148, 437-455, 2000)
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Thermal Inertia maps of Mars 2
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ESA Advanced Planetary Mission Studies Venus
Sample Return and Mercury Sample ReturnLebreton
J.-P. (1), Scoon G. (2), Lognonné Ph. (3), Masson
Ph. (4), Taylor F. W. (5), Wänke H., (6),
Coradini M. (7), and the VSR and MeSR Study Teams
(1) ESA/ESTEC, Space Science Department (2)
ESA/ESTEC, Future Project Study Office (3) IPG,
Paris (F) (4) Univ. Paris-Sud (F) (5) Univ. of
Oxford (UK) (6) MPI Mainz (D) (7) ESA/HQ , Paris
(F) VSR MeSR Study Teams (ESA/ESTEC and
ESA/ESOC)
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Mercury Sample Return Scientific Objectives

• Scientific goals understanding the structure,
  the chemical composition and the isotopic
  composition of the surface of Mercury.
• Sampling Site selection
• In this preliminary study, one of the mission
  design drivers wrt the selection of the sampling
  site
• Benign thermal environment (-50/50 C)
• Adequate solar illumination for generation of
  photovoltaic energy during extended sampling
  phase ( 7 days considered)
• A high-latitude region ( 85 deg lat.) fulfils
  those thermal constraints and at the same time
  ensures enough solar illumination for surface
  operations on solar cells.
• Geological and geochemical mapping of the planet
  as pre-requisite objectives for landing site
  selection - orbital phase prior to sampling
  phase other ESA precursor mission e.g. MeCS.

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Mercury Sample Return sampling strategy

• Primary mission goal acquire surface rock and
  soil samples from a single landing site. Limited
  surface mobility is provided by a robotic arm and
  a short-range mobile element. Mobility around the
  Lander allows flexibility for sample pre-analysis
  and pre-selection.
• Sample type surface rocks and dust samples (lt 1
  kg total)
• In-situ identification and categorisation of the
  samples (including its orientation for magnetism
  studies)
• Sample isolation/separation to avoid
  cross-contamination between the samples.

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Mercury Sample Return
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Mercury Sample Return
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Mercury Sample Return
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Mercury Sample Return
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MeSR Overall Mission timeline
(7yrs 10 mo.)
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Comprehensive Study

• High-resolution visible imaging (morphology)
• near-ir reflectance /thermal emission
  spectroscopy (surface composition)
• UV spectroscopy (atmospheric composition)
• Thermal ir imaging (surface physical properties,
  heat flow, polar ice)
• Microwave/radar mapping

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Mariner 10 Venus- Mercury 1974
(Boeing)
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Mariner 10 (1974)
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• Mercury Dual Imaging System (MDIS) 
• Gamma-Ray and Neutron Spectrometer (GRNS) 
• Magnetometer (MAG)
• Mercury Laser Altimeter (MLA) 
• Atmospheric and Surface Composition Spectrometer
  (ASCS) 
• Energetic Particle and Plasma Spectrometer
  (EPPS) 
• X-Ray Spectrometer (XRS) 
• Radio Science (RS) uses telecommunication system 

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BepiColombo
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The Mercury Infrared Surface Temperature,
Emissivity, Reflectivity and Inertia Experiment
(MISTERIE).

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THE END