THE DIURNAL TEMPERATURE REGIME OF THE SURFICIAL REGOLITH OF PHOBOS IN THE LANDING SITE REGION OF THE FOBOS-GRUNT LANDER FOR DIFFERENT SEASONS: THE MODEL PREDICTION.

R.O. Kuzmin1,2, E.V. Zabalueva1

1 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 2 Space Research Institute, Russian Academy of Sciences.

IKI RAS, Moscow 10-13 October, 2011IKI RAS, Moscow 10-13 October, 2011

The main factors determining the peculiarities of the thermal The main factors determining the peculiarities of the thermal regime of the surface regolith on the Phobos:regime of the surface regolith on the Phobos:

An atmosphereless body;An atmosphereless body;

Short duration of the Phobos’s day (7.7 hours);Short duration of the Phobos’s day (7.7 hours);

Highly porous and low-density surface regolith of the Highly porous and low-density surface regolith of the impact origin with low thermal inertia ( 25–84 J mimpact origin with low thermal inertia ( 25–84 J m-2-2 s s-1/2-1/2 K K-1 -1 ););

Low surface albedo (average 0.05);Low surface albedo (average 0.05);

Repeated eclipses of the Phobos by Mars;Repeated eclipses of the Phobos by Mars;

Reflected and thermal radiation of Mars;Reflected and thermal radiation of Mars;

The ellipsoidal shape of the Phobos figure;The ellipsoidal shape of the Phobos figure;

The absence of internal heat sources.The absence of internal heat sources.

Location of the former (1) and new (2) potential landing sites for FOBOS-GRUNT mission

Topography of Phobos based on HRSC stereo images

1

2

III

Suggested new landing sites (option I and II)

Viking-1 image VO1_246a68

240 210

15°N, 230°W

Phobos albedo map based on the Viking Orbiter observations(from Simonelli et al., 1998) Shklovsky

Laga

do P

lani

tia

Thermal Model of Phobos’s surfaceThermal Model of Phobos’s surfaceIn developing the computer code we used as a basis the thermal model of In developing the computer code we used as a basis the thermal model of the surface layer of Phobos (Kuhrt and Giese, 1989), which take into the surface layer of Phobos (Kuhrt and Giese, 1989), which take into account:account:

Ellipsoidal shape of PhobosEllipsoidal shape of Phobos Eclipses of Phobos by MarsEclipses of Phobos by Mars Reflected and thermal radiation of MarsReflected and thermal radiation of Mars Variable thermal conductivity and specific heat of materialVariable thermal conductivity and specific heat of material Absence of internal heat sourcesAbsence of internal heat sources Phobos albedo: 0.07Phobos albedo: 0.07 Surface regolith density: 1100 kg m-3Surface regolith density: 1100 kg m-3 Thermal conductivity and specific heat are temperature dependentThermal conductivity and specific heat are temperature dependent with values analogous to lunar regolithwith values analogous to lunar regolith (Thermal conductivity range: 8x10(Thermal conductivity range: 8x10-5-5 –2.2 x10 –2.2 x10-3-3 W m W m-1-1KK Specific heat range: 260-772 J kgSpecific heat range: 260-772 J kg-1-1K)K) For complete model description, see Kuzmin and Zabalueva (2003)For complete model description, see Kuzmin and Zabalueva (2003) Solar System Research, 37, 480-488Solar System Research, 37, 480-488

The main characteristics of the computational procedure:The main characteristics of the computational procedure:

(1) The consecutive orbital positions of Mars are taken with a step equal to 1/100 (1) The consecutive orbital positions of Mars are taken with a step equal to 1/100 of its annual period (6.9 days); of its annual period (6.9 days);

(2)(2) For each Mars position, the computation is made for one spin of Phobos For each Mars position, the computation is made for one spin of Phobos around Mars (the satellite begins its motion at local noon foraround Mars (the satellite begins its motion at local noon forthe given point on Phobos); the given point on Phobos);

(3)(3) The step in the Phobos orbit is taken to be 7.5° away from the eclipse and 0.5° The step in the Phobos orbit is taken to be 7.5° away from the eclipse and 0.5° within the eclipse zone. within the eclipse zone.

(4)(4) The results of the calculation of the temperature as a function of time and The results of the calculation of the temperature as a function of time and depth were considered only after 5.5 Martian years.depth were considered only after 5.5 Martian years.The model deals with a 40-cm-thick regolith layer, which isThe model deals with a 40-cm-thick regolith layer, which isdivided into sublayers, the first being 0.08 mm thick.divided into sublayers, the first being 0.08 mm thick.The thickness of the subsequent sublayers increases asThe thickness of the subsequent sublayers increases asthe progression with a geometric ratio of 1.26. the progression with a geometric ratio of 1.26. The regolith layer is assumed isothermal at the initial timeThe regolith layer is assumed isothermal at the initial timeand its temperature is taken to be 200 K. and its temperature is taken to be 200 K.

The computations start at the perihelion of the Martian orbit.The computations start at the perihelion of the Martian orbit.

General characteristics of Phobos and Mars employedGeneral characteristics of Phobos and Mars employedin the computer codin the computer code

Parameters Phobos

Mars

Albedo 0.07 0.25

Surface layer density, kg/m3 1100

Spin period of Phobos aboutMars, s 2.76 ´ 104

Spin period of Mars about the Sun, s

5.94 ´ 107

Semimajor axis of Mars’ orbit, AU

1.52

Solar radiation on Mars’ orbitat 1.52 AU, W/m2 600

Inclination of equator planeto plane of ecliptic, deg 25.2 25.2

Eccentricity 0.093

Angle (w ) between ascending node and perihelion of Mars’ orbit, deg

70

Ratio d of Mars’ radius (RM) to distance between Mars andPhobos (2.76 RM)

Emissivity,

0.361

1.0

Parameters obtained from the Parameters obtained from the numericalnumerical modeling:modeling:

The diurnal course of the surface temperature for different seasons;The diurnal course of the surface temperature for different seasons;

The diurnal variation of the temperature in the surfaceThe diurnal variation of the temperature in the surface

layer of the Phobos regolith;layer of the Phobos regolith; Max and min values of the diurnal surface temperature;Max and min values of the diurnal surface temperature;

The diurnal temperature’s amplitude on the surface and in the depth;The diurnal temperature’s amplitude on the surface and in the depth;

The thermal skin depth of the Phobos regolith;The thermal skin depth of the Phobos regolith;

The depth with the temperature’s amplitude < 1°.The depth with the temperature’s amplitude < 1°.

The diurnal course of the temperature of the The diurnal course of the temperature of the Phobos surface during the spring Phobos surface during the spring

The diurnal variation of the temperature in the surfaceThe diurnal variation of the temperature in the surface layer of the Phobos regolith during the springlayer of the Phobos regolith during the spring

Spring, Ls=45.7°

The diurnal variation of the temperature in the surfaceThe diurnal variation of the temperature in the surface layer of the Phobos regolith during the summer layer of the Phobos regolith during the summer

The diurnal course of the temperature of the The diurnal course of the temperature of the Phobos surface during the summer Phobos surface during the summer

Summer, Ls=135.9°

The diurnal course of the temperature of the The diurnal course of the temperature of the Phobos surface during the autumnPhobos surface during the autumn

The diurnal variation of the temperature in the The diurnal variation of the temperature in the surface layer of the Phobos regolith during surface layer of the Phobos regolith during the autumnthe autumn

Autumn, Ls=224.2°

The diurnal variation of the temperature in the The diurnal variation of the temperature in the surface layer of the Phobos regolith during surface layer of the Phobos regolith during the winterthe winter

The diurnal course of the temperature of the The diurnal course of the temperature of the Phobos surface during the winterPhobos surface during the winter

Winter, Ls=316.8°

Spring

Summer

Autumn

Winter

2013.15.02, Ls=263.07°2013.15.02, Ls=263.07°late autumnlate autumn

The diurnal thermal regime in the The diurnal thermal regime in the surface layer of the Phobos regolith surface layer of the Phobos regolith on the date of the landing.on the date of the landing.

Comparison of the diurnal course of the temperature on the opposite Comparison of the diurnal course of the temperature on the opposite and sub-Martian hemispheres of the Phobos during the winter and sub-Martian hemispheres of the Phobos during the winter

15°N 230°W15°N 230°W

15°N 310°W15°N 310°W

Seasonal thermal parameters of the surface regolith layer in the Seasonal thermal parameters of the surface regolith layer in the potential landing site for potential landing site for Fobos–Grunt mission Fobos–Grunt mission derived from the derived from the numerical modeling numerical modeling

SeasonsSeasons(northern (northern hemisphere hemisphere of Mars)of Mars)

Max Max T (K)T (K)

Min Min T(K)T(K)

DailyDailyamplitudeamplitude (deg.) (deg.)

ThermalThermal skin skin depth depth (cm) (cm)

Depth, Depth, where where amplitudeamplitude<1<1o o

(cm) (cm)

Spring, LSpring, Lss=45.7=45.7oo 297.8297.8 115.6115.6 182.6182.6 ~0.33~0.33 ~1.7~1.7

Summer, Summer, LLss=135.9=135.9 o o

305.1305.1 117.1117.1 188.1188.1 ~0.33~0.33 ~1.8~1.8

Autumn, Autumn, LLss=224.2=224.2oo

Autumn,Autumn,Ls=265Ls=265oo

(Date of landing)(Date of landing)

300.8300.8

291.3291.3

112.2112.2

109.1109.1

188.6188.6

182.2182.2

~0.32~0.32

~0.31~0.31

~1.7~1.7

~1.8~1.8

Winter LWinter Lss=316.8=316.8oo 294.6294.6 109.2109.2 185.4185.4 ~0.32~0.32 ~1.5~1.5The results of conducted numerical modeling maybe useful at analysis of the The results of conducted numerical modeling maybe useful at analysis of the measurements data from the instrument Thermophob (see Marov et al., 2010) measurements data from the instrument Thermophob (see Marov et al., 2010) which will work underneath of one of the Fobos-Grunt Lander’s legs.which will work underneath of one of the Fobos-Grunt Lander’s legs.

Thank you for your attentionThank you for your attention