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Subsurface probing of planetary bodies
Marek Bana szki ewicz Space Research Centre PAS in cooperation with: B. Dabrowski, J. Grygo rczuk, K. Seweryn, R. Wa wrzaszek


Outline
Surf ace and su bsurf ace thermal ph ysics Missions with subsurf ace scienc e Thermal s ensors Models and measurem ents Heat transport in granular media


Why to go under the surface
To t ak e sam ples an d an alys e their chemical & mineralogical com position To perf orm measurements of physic al properties (seism ometr y, thermal properties, mechanic al pr operties, structure) To r each deep layers of the body (subsurf ace oc ean on Europe) To c ollect minerals an d pr ecious mat erials (e.g. He3 on the Moon)


Techniques of surface and subsurface exploration

T aking samples

Penetrating mole

Hammering Drilling Anchoring Melting in


Thermal processes in planetary bodies
Heat sources
- hot interior - surfac e irradiation

Thermal trans port proc ess es

- heat conduction (in solid, liquid and gas phases) - radiative transfer - advection/con vection (mass motion)

Quantities to be determined: Temperature profile T(z) Heat flow K rT thermal conductivity K, thermal diffusivity, thermal inertia


Example: heat transport in comets

Heat transport equation (Prialnik & Podolak) Koemle Conduction

Advection

Amorph. ice <=> cryst. ice

Sublimation


Missions with subsurface thermal experiments
Apollo 15 & 17 Mars-Express: Beagle Ros etta: MUPUS (Philae) Phobos-Grund Exo-Mars: HP3 Apollo: thermal probes ins erted into bor eholes 2m deep, but sens ors not properly deployed, theref ore heat f low valu es, 28-33 mW / m^2 question ed => the uncertaint y in the lunar core t emperature is 250 - 400є


Penetrators
Pen etrat ors
MUPUS on Philae (Rose tta Lande r) PI ­ Tilm an Spohn (DLR) Pe natrator de signe d & m anufacture d in SRC, Warsaw


Penetrators: moles
HP3 (Exo-Mars) ­ Beagle h eritage

SRC Design


Thermal sensors
Resist ance thermom eters


Thermal sensors
Principle of oper ation
Hot rod method


MUPUS measurements on Earth


Potential problems
Conductivit y of thin sensors (titanium, copper) is dif f erent than the conductivit y of the bulk mat erial Calibration: pr ecis e K(T) depen dence sh ould be tak en Agin g ef f ects => recalibr ation 12 years af ter sensor manuf acturing should be done Two wire meth od us ed => ref erenc e current should be measured bef ore each measurem ent Heating and t emperature m easurem ents must be don e sequentially


New sensors
(w ires to meas ure- andpow er-s upply s ystem)

SH SM SL sa mp le

a)

b)

c)


New sensors
17, 5 m m
C opper wires

100

a)

50 173

273

T [K ]

373

Resist ance [ ]

Resist ance [ ]

10 m m

14 m m

15 mm

Connect io n t o dat alo gger usin g 4 wire resistan ce m easur em ent met ho d

platinum sensor ci rcu it

i s ot an h eat er ci rcu it

Ele ct ric p ower supp lied and cont rolled by dat alo gger.

sensor 100.2 PLAT INUM 150 100.0 99.8 99.6 99.4 173 ISOT AN

200

473

b)

273

T [K ]

373

473


Thermal measurements
Comet ar y material & ast eroid regolith analogues Tef lon an d delrin as ref erence m aterials

Measurem ents in thermal and thermal- vacuum chambers


Models
Analytic al: applic able f or simple geometries and quite c omplicat ed Semi analyic al based on Green f unctions Numerical: FEM


Measurements: calibration


Measurements


Measurements
In thermal chamber => K in the narrow range 0.2 -0.4 W/m/K


Granular media
Diff erent transport pr ocess es (Slavin et al.)
Gs

Unit cell

Gr

Go Gi

Gc

R


Granular media (2)
Slavin et al., 1 mm alu minu m spheres

Whe n the parameters of cometary/asteroid analo g ues are used then K 0.2 W/m/K at atmospheric pressure


Future research
Different sensor designs should be tested Modeling needs improvement => granularit y of medium taken into account Thermal resistanc e bet ween the sensors and the medium is the main experimental problem
30
m 6m 0. 0 r+ et e

20
a rd nd Sta

m d ia

10 Te mp eratu re [ C]
4 mm er+ 0 .0 ia m e t d a rd d S ta n

0

-1 0

-2 0

mm t e r+ 0. 0 2 rd di a me St an d a er rd di am et S ta n da

-3 0

Between not too f requent s pac e missions most of the planet ary r esearch will be done in the lab

-4 0 0

10 0

20 0

30 0

40 0

500 T ime [s]

60 0

700

80 0

900

1000


Thank yo u for yo ur attentio n