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, Japan3Max Planck Institute for Solar System Research, Germany

4Chalmers University of Technology, Sweden

—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.

MMars EExploration with LLander-OOrbiter SSynergy

Japanese Mars Exploration Plan (MELOS)Japanese Mars Exploration Plan (MELOS)

Preliminary Mission DesignPreliminary Mission Design

MELOS-1

LANDERS

trace the global atmospheric motion from near-apocenter (8 Martian radius)

In-situ measurement of escaping atmosphere

MELOS-2

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).

- 1-2 Orbiter(s) and 1 (or more) Lander(s). - detail of the orbiters:

- Now planned to launch in 2019-2022.- Collaborate with USA & European Mars 2010/20's missions.

Concept of MELOS SMM instrumentConcept of MELOS SMM instrument- Concept study has been started in 2008 : focusing on the

water cycle & atmospheric circulation sciences.

• 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

JEM/SMILES (NICT/JAXA)Balloon SMILES (NICT)

Mars SMM

Japan

Europe

USA

High sensitivity, high frequency, large (500kg)

Small (10–30 kg)

Techniques for light receivers with high frequency

ROSETTA/MIRO (NASA/JPL, MPS)

Odin/SMR (Sweden SSC)

MLS (NASA/JPL)

Sounder

2019-2022

Concept of MELOS SMM instrumentConcept of MELOS SMM instrument

Characteristics of SMM observations Characteristics of SMM observations - SMM domain is a treasure of the molecular lines!

Atmospheric state (Temperature, Pressure): CO, CO isotopesWater-cycle: H2O, H2O isotope (HDO, H2

18O, …)

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

A short list of the “potential targets” for the Martian atmospheric research using the SMM wavelength (300 – 900 GHz).

Characteristics of SMM observations Characteristics of SMM observations - SMM domain is a treasure of the molecular lines!

Atmospheric state (Temperature, Pressure): CO, CO isotopesWater-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

A short list of the “potential targets” for the Martian atmospheric research using the SMM wavelength (300 – 900 GHz).

Example of the spectral atlas at SMM domain based on the HITRAN08 [Rothman et al. 2009] database

Characteristics of SMM observations Characteristics of SMM observations

SMM instrument is a very effective tool to investigate the Martian atmospheric chemistry & dynamics.

• 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 !

• Pressure-broadened line shapes of molecular emission can be spectrally resolved in the measured spectra.Sensitive to the vertical profiles of the molecular concentration.

- Very high frequency resolution spectroscopy (/ ~ 10 7–8) with the Heterodyne technique

0.1 mbar [40 km]

0.01 mbar [60 km]

1 bar [75 km]

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.

Complementary to other instrumentsComplementary to other instruments

Ground-based Obs.

Lander, Rover

- Wind at upper mesosphere- D/H, 13C/12C profiles

Vis/NIR imagers

- Complement the detection of minor species; provide

2D maps of minor species.

- Monitoring, Calibration

Plasma Instruments

IR Spectrometer

- T(z), Wind, Compositions at 0–120 km; even under the dusty condition.

(atmospheric escape)

- Thermal property of the surface layer. - Evaporation/Condensation of H2O ice.

SMM instrument

Temperature [K]

[mbar]

[km]

1

0.01

10 -3

10 -6

Better spatial resolution. Better sensitivity to minor species.

Solar occultation can be used as the reference measurements.

Thermosphere（ atmos. escape)

0.1 SMM

(nad

ir)

IR s

pect

rom

eter

IR : Can observe CH4

SMM : Can measure Winds directly

80

120

160

200

40

0150 200100

Boundary layer

e.g. SMM & IR spectrometere.g. SMM & IR spectrometer

Possible to observe up to 130 km (depends on the species). Observe averaged distributions of H2O2, HO2, etc.

Unaffected by dust opacities.SM

M (l

imb

Scan

)

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.

Observes the molecular lines as absorption against the surface emission.

Advantages: Horizontal mapping,Long data integration for minor species.

Simulations of nadir/limb obs. geometriesSimulations of nadir/limb obs. geometries

frequency

frequency

brig

htne

ss te

mpe

ratu

re

brig

htne

ss te

mpe

ratu

re

Spectra from different pointing altitudes

Spectra from different season

Limb geometry

Nadir geometry

• 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)

Daytime column density, by MGS-TES by MEx-SPICAM

Mapping of water vapor distributionsScientific TargetsScientific Targets

[Smith, 2004][Trokhimovskiy et al., 2008]

An example of vertical distributions [ppm] from solar occultation by MEx–SPICAM

[Fedorova et al., 2009]

Detection of the HDO/H2O ratio

Distributions of the HDO/H2O ratio observed from a ground-based infrared

telescope [Villanueva et al., 2008]

• 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.

Scientific TargetsScientific Targets

Detection of HOx ： Key of keeping CO2 stable?

• 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.

Possible catalytic cycles to keep CO2

Distribution of the OH production rate in the MAOAM chemistry

GCM

Scientific TargetsScientific 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

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)

Doppler wind at ~50km height by PdBI telescope [Moreno et al., 2009]

Scientific TargetsScientific Targets

• 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).

SummarySummary

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

Thank you for your attentionThank you for your attention