1 st Moscow Solar System Symposium, 14/10/2010, IKI, Moscow

1. 1st Moscow Solar System Symposium, 14/10/2010, IKI, Moscow Development of the Sub-millimeter Instrument onboard the Japanese Mars Orbiter Yasuko Kasai1, *Takeshi Kuroda2, Hideo Sagawa1, Paul Hartogh3, Donal Murtagh4, MELOS SMM Sounder Team 1National Institute of Information and Communications Technology, Japan2Institiute of Space and Astronautical Science, JAXA, Japan 3Max Planck Institute for Solar System Research, Germany 4Chalmers University of Technology, Sweden

2. Japanese Mars Exploration Plan (MELOS) Mars Exploration with Lander-Orbiter Synergy —Why does Mars appear Reddish? Why is the current Martian surface covered by the hematite? To answer this question, we have to understand the evolution of Martian atmosphere, the current climate system, and the interaction between the surface and atmosphere. Japanese new Mars mission, MELOS, will carry on dedicated explorations on - Meteorology - Atmospheric Escape - Interior Structure & Surface Environment.

3. Preliminary Mission Design MELOS-1 - 1-2 Orbiter(s) and 1 (or more) Lander(s). - detail of the orbiters: trace the global atmospheric motion from near-apocenter (8 Martian radius) MELOS-1, a meteorological orbiter, targets the global mapping of atmospheric motions with multi-wavelengths imaging cameras from an equatorial elliptic orbit (heritages from Planet-C/Akatsuki). MELOS-2 explores the atmospheric escape with in-situ measurements from a near Mars polar orbit by using plasma instruments (heritages from Nozomi). LANDERS MELOS-2 In-situ measurement of escaping atmosphere - Now planned to launch in 2019-2022.- Collaborate with USA & European Mars 2010/20's missions.

4. Concept of MELOS SMM instrument • Concept study has been started in 2008 : focusing on the water cycle& atmospheric circulationsciences. • 2 frequency bands (500 GHz and 600 GHz) •  to observe different opacity H2O lines (weak H2O line sounds deeper altitudes) • Chirp-Transform spectrometer  clean baselines • Polarization  to observe thermal property of the surface • 40 – 50 cm-diameter antenna, Passive cooling system • Roughly estimated mass & power = 10-20 kg & 50 W Developed in an international collaboration: - Antenna & quasi-optics : Japan - Local Oscillator, Amp., Mixer : Sweden - Spectrometer : Germany

5. Concept of MELOS SMM instrument Japan JEM/SMILES (NICT/JAXA) Balloon SMILES (NICT) 2019-2022 High sensitivity, high frequency, large (500kg) Mars SMM Sounder Small (10–30 kg) Europe Odin/SMR (Sweden SSC) Techniques for light receivers with high frequency ROSETTA/MIRO (NASA/JPL, MPS) USA MLS (NASA/JPL)

6. Characteristics of SMM observations • SMM domain is a treasure of the molecular lines! A short list of the “potential targets” for the Martian atmospheric research using the SMM wavelength (300 – 900 GHz). • Atmospheric state (Temperature, Pressure): CO, CO isotopes • Water-cycle: H2O, H2O isotope (HDO, H218O, …) • Photochemistry: H2O2, HO2, O3, O3 isotopes, HCl, ClO, • (ClO)2, OCS, H2CO, etc. • Evolution/Escape of the atmosphere: HDO/H2O • Volcanic activity: SO2, SO • Evidence of life: H2S, NO, NO2, N2O, NH3

7. Characteristics of SMM observations • SMM domain is a treasure of the molecular lines! A short list of the “potential targets” for the Martian atmospheric research using the SMM wavelength (300 – 900 GHz). • Atmospheric state (Temperature, Pressure): CO, CO isotopes • Water-cycle: H2O, H2O isotope • Photochemistry: H2O2, HO2, O3, O3 isotopes, HCl, ClO, • (ClO)2, OCS, H2CO, etc. • Evolution/Escape of the atmosphere: HDO/H2O • Volcanic activity: SO2, SO • Evidence of life: H2S, NO, NO2, N2O, NH3 Example of the spectral atlas at SMM domain based on the HITRAN08 [Rothman et al. 2009] database

8. Characteristics of SMM observations • Very high frequency resolution spectroscopy (n/Dn ~ 10 7–8) with the Heterodyne technique • Pressure-broadened line shapes of molecular emission can be spectrally resolved in the measured spectra. • Sensitive to the vertical profiles of the molecular concentration. 1 mbar [75 km] 0.01 mbar [60 km] 0.1 mbar [40 km] • The frequency of the molecular lines are shifted (~100 kHz at 500 GHz band) due to Doppler shift caused by the line-of-sight velocity of the wind. • Such a small shift can be detected; i.e. the wind can be directly measured ! 1 mbar [20 km] Typical line shape of Martian molecular line. The line shape varies depends on the pressure. Observed spectrum is the integral of the different line shaped spectra along the line-of-sight.  SMM instrument is a very effective tool to investigate the Martian atmospheric chemistry & dynamics.

9. Complementary to other instruments Plasma Instruments SMM instrument (atmospheric escape) Ground-based Obs. - Monitoring, Calibration - Wind at upper mesosphere - D/H, 13C/12C profiles - Thermal property of the surface layer. - Evaporation/Condensation of H2O ice. - T(z), Wind, Compositions at 0–120 km; even under the dusty condition. - Complement the detection of minor species; provide 2D maps of minor species. IR Spectrometer Lander, Rover Vis/NIR imagers

10. e.g. SMM & IR spectrometer SMM : Can measure Winds directly [km] 200 Possible to observe up to 130 km (depends on the species). Observe averaged distributions of H2O2, HO2, etc. Unaffected by dust opacities. Thermosphere （atmos. escape) 160 [mbar] 10 -6 120 IR : Can observe CH4 10 -3 80 SMM (limb Scan) SMM (nadir) Better spatial resolution. Better sensitivity to minor species. Solar occultation can be used as the reference measurements. 0.01 IR spectrometer 0.1 40 1 Boundary layer 0 100 150 200 Temperature [K]

11. Simulations of nadir/limb obs. geometries Limb geometry Observes the molecular lines as emission against the cold sky. Advantages: Winds. Longer line-of-sight for weak lines. Sensitivity to higher altitudes with a better vertical resolution than the nadir geometry. Spectra from different pointing altitudes brightness temperature frequency Nadir geometry Spectra from different season Observes the molecular lines as absorption against the surface emission. Advantages: Horizontal mapping, Long data integration for minor species. brightness temperature frequency

12. Scientific Targets Mapping of water vapor distributions by MEx-SPICAM Daytime column density, by MGS-TES [Trokhimovskiy et al., 2008] [Smith, 2004] An example of vertical distributions [ppm] from solar occultation by MEx–SPICAM • A lot of daytime column density data have been obtained by the infrared observations from Mars Global Surveyor and Mars Express, but we still do not have the data for changes of density by local time (i.e. diurnal variation) • For the vertical we still have few observational data, from submm telescopes and MEx-SPICAM (observed local time coverage is limited). • Hygropause (cut-off height of water vapor) is a key to investigate the transport of water. (Favorable meridional transport if higher) [Fedorova et al., 2009]

13. Scientific Targets Detection of the HDO/H2Oratio • The D/H ratio is a key to investigate the climate change (escape of atmosphere) on Mars. • Deuterium is heavier than normal hydrogen and difficult to escape to space, so the water from old surface ice or underground should keep lower D/H ratio. (Is there underground water on Mars?) • According to the ground-based infrared observations, D/H ratio on Mars very large variances in space and time, from 2 to 8 times as SMOW (mean terrestrial ocean value). • Ground-based infrared observations can detect only daytime column densities. • The Mars SMM Sounder enables the detailed 3-D mapping of the D/H ratio for day and night. Distributions of the HDO/H2O ratio observed from a ground-based infrared telescope[Villanueva et al., 2008]

14. Scientific Targets Detection of HOx：Key of keeping CO2stable? Possible catalytic cycles to keep CO2 • CO2 divides into CO and O by the photo-dissociation of ultraviolet rays, but the recombination reaction is spin forbidden. Thus after about 6000 years all CO2 should be converted into CO + O. • However in reality there is about 95 % of CO2 and only ~900 ppm of CO. • →What saves the Martian atmosphere and climate? Is OH a catalyst to keep CO2? • The Mars SMM Sounder detects the minor radical species, and try to investigate the mechanism. Distribution of the OH production rate in the MAOAM chemistry GCM

15. Scientific Targets Mapping of wind velocity • There are the observational data of Doppler wind velocities from the ground-based SMM telescopes, but they are sparse (horizontal resolution of ~300km, vertical resolution of ~20km). • Limb-scan from the near Mars orbit (~ 1000 km altitude) enables the direct wind measurements within an error of ~5 m/s (at 40-70km altitude, lower accuracy at lower atmosphere). • →First, epoch-making wind mapping of Martian atmosphere Doppler wind at ~50km height by PdBI telescope [Moreno et al., 2009] Simulations of the wind velocity measurements limb-scanned between 0-120km altitude using 12CO and 13CO (antenna radius of 40cm, from apocenter (8 Mars radius), 100 seconds integration)

16. Summary • A new Japanese Mars mission, MELOS with 1-2 orbiter(s) and 1 (or more) lander(s), is planned to be launched in 2019-2022. • We propose a Sub-millimerer Sounder onboard the MELOS meteorological orbiter, with 2 frequency bands (500 and 600 GHz) and roughly estimated mass/power of 10-20 kg/ 50 W. • We are investigating the 4-dimensional (space+time) chemistry and dynamics of Martian atmosphere through the Nadir and Limb soundings with very high frequency resolution spectroscopy (Heterodyne technique). • Our main targets to observe are the water vapor including the HDO/H2O ratio, minor radical species and wind velocity. The instrument is also sensitive to the sulfur compounds and NH3 (detecting the upper limits).

17. Thank you for your attention We appreciate any comments on the scientific requirements, any other interesting targets, new collaborations, etc. All the input will improve and optimize the instrumental design and bring a fruitful science! feel free to contact: ykasai@nict.go.jp