Subsurface probing of planetary bodies

Marek BanaszkiewiczSpace Research Centre PAS

in cooperation with: B. Dabrowski, J. Grygorczuk, K. Seweryn, R. Wawrzaszek

Outline

Surface and subsurface thermal physicsMissions with subsurface scienceThermal sensors Models and measurementsHeat transport in granular media

Why to go under the surface

To take samples and analyse their chemical & mineralogical compositionTo perform measurements of physical properties (seismometry, thermal properties, mechanical properties, structure)To reach deep layers of the body (subsurface ocean on Europe)To collect minerals and precious materials (e.g. He3 on the Moon)

Techniques of surface and subsurface exploration

Taking samples

Drilling

Hammering

Penetrating mole

AnchoringMelting in

Thermal processes in planetary bodies

Heat sources- hot interior - surface irradiation

Thermal transport processes- heat conduction (in solid, liquid and gas phases)- radiative transfer - advection/convection (mass motion)

Quantities to be determined:

Temperature profile T(z)Heat flow K rTthermal 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 & 17Mars-Express: Beagle Rosetta: MUPUS (Philae)Phobos-GrundExo-Mars: HP3

Apollo: thermal probes inserted into boreholes 2m deep, but sensors not properly deployed, therefore heat flow values, 28-33 mW / m^2 questioned => the uncertainty in the lunar core temperature is 250 - 400º

Penetrators

Penetrators MUPUS on Philae (Rosetta Lander) PI – Tilman Spohn (DLR)

Penatrator designed & manufacturedin SRC, Warsaw

Penetrators: moles

HP3 (Exo-Mars) – Beagle heritage

SRCDesign

Thermal sensors

Resistance thermometers

Thermal sensors

Principle of operationHot rod method

MUPUS measurements on Earth

Potential problems

Conductivity of thin sensors (titanium, copper) is different than the conductivity of the bulk materialCalibration: precise K(T) dependence should be takenAging effects => recalibration 12 years after sensor manufacturing should be doneTwo wire method used => reference current should be measured before each measurementHeating and temperature measurements must be done sequentially

New sensors

SM

SL

SH

sample

(wires to measure- and-power-supply system)

a) b) c)

New sensors

15 mm

14 mm

10 mm

17,5 mm

173 473373273

99.6

99.4

99.8

100.2

100.0

T [K]

Resistance [Ω]

b)

ISOTAN

Resistance [Ω]

173 473373273

100

50

150

200

T [K]a)

PLATINUM

platinum sensor circuit

isotan heater circuit

Connection to datalogger using 4 wire resistance

measurement method

Electric power supplied andcontrolled by datalogger.

sensor

Copper wires

Thermal measurements

Cometary material & asteroid regolith analoguesTeflon and delrin as reference materials

Measurements in thermaland thermal-vacuum chambers

Models

Analytical: applicable for simple geometries and quite complicatedSemi analyical based

on Green functionsNumerical: FEM

Measurements: calibration

Measurements

Measurements

In thermal chamber => K in the narrow range0.2 -0.4 W/m/K

Granular media

Different transport processes (Slavin etal.)

Gs

GcGi

GrGo

Unit cell

R

Granular media (2)

When the parameters of cometary/asteroid analogues are used then K ≈ 0.2 W/m/K at atmospheric pressure

Slavin et al., 1 mm aluminum spheres

Future research

Different sensor designs should be testedModeling needs improvement => granularity of medium taken into accountThermal resistance between the sensors and the medium is the main experimental problem

Between not too frequent space missions most of the planetary research will be done in the lab

0 100 200 300 400 500 600 700 800 900 1000-40

-30

-20

-10

0

10

20

30

T ime [s]

Tem

per

atu

re [C

]S tanda rd diam ete rStandard diamete r+0.02 m m

S tanda rd d iame ter+0 .04 m m

Standa rd d iameter+0.0 6 mm

Thank you for your attention