Thermogravimetry: a technique for planetary in-situ missions A. Longobardo 1,F. Dirri 2, E. Palomba 1, A. Zinzi 3, E. Zampetti 4, S. Pantalei 4, D. Biondi 1, B. Saggin 5, A.Bearzotti 4 and A. Macagnano 4 1 IAPS-INAF, Via Fosso del Cavaliere 100, Rome, Italy 2 Dipartimento di Fisica, Università La Sapienza, Rome, Italy 3 DISAM, Università Parthenope, Naples, Italy 4 IMM-CNR, Rome, Italy 5 Politecnico di Milano, Milan, Italy

Outline i.Introduction to Thermogravimetry ii.Planetary applications iii.The VISTA project iv.Laboratory measurements v.Conclusions 23/10/2015EPSC 2012, Madrid2

Basic principles Thermogravimetry is a widely used technique to study absorption, sublimation and condensation processes. The instrument core is a Piezoelectric Crystal Microbalance (PCM), whose oscillation frequency increases at decreasing deposited mass: once the material is deposited onto the sensor it is possible to measure the amount of weight change as a function of increasing temperature due to the release of more volatile species. The temperature is increased by an appropriate heater. Abundance volatile compound Composition volatile compound 23/10/2015EPSC 2012, Madrid3

Application fields Detection and analysis of volatiles compounds in the studied samples, i.e. adsorbed/included in the molecular structure, or in the studied environment Analysis of condensable species, i.e. discrimination between different phases (gas/liquid/solid). The Thermo-Gravimetric Analysis (TGA) can be performed in two temperature regimes, depending on the purpose: ACT (Ambient to Cryogenic Temperatures Regime): <300 K AHT (Ambient to High Temperatures Regime): >300 K 23/10/2015EPSC 2012, Madrid4

Techniques for volatile measurements Attenuated Total Reflectance (ATR) - mass not lower than 200 g - power of few watts required Gas Cromatography/Mass Spectroscopy (GC-MS) /  GC-MS - instrument size of cm 3 - problems about interface between GC and MS ThermoGravimetric Analysis (TGA) /  TGA - low mass (25 g) - low size (cm 3 ) - low requested power (<1 W) 23/10/2015EPSC 2012, Madrid5

Outline i.Introduction to Thermogravimetry ii.Planetary applications iii.The VISTA project iv.Laboratory measurements v.Conclusions 23/10/2015EPSC 2012, Madrid6

Moon Water ice detection Measurement of water, organics and other volatiles content in the lunar regolith Analysis of electrical properties of regolith Scientific goals in a lunar lander scenario 23/10/2015EPSC 2012, Madrid7

Asteroids and comets Measurement of water and organic content in the asteroid regolith (asteroid taxonomy) Detection of cometary activity (measuring flux and dust/ice ratio) Scientific goals in a in-situ mission on asteroids or comets 23/10/2015EPSC 2012, Madrid8

Icy satellites Discrimination between water ice and clathate hydrates (not possible by means of spectral analysis) Determination of non-ice materials composition (solphates, carbonates, H 2 O 2 ), characterised by different sublimation temperatures Detection of possible organic presence Scientific goals in a in-situ mission on a icy satellite (e.g. Europa and Ganimede) 23/10/2015EPSC 2012, Madrid9

Mars Measurement of water frost point, i.e. relative humidity Detection of possible ice falls Measurement of dust settling rate Measurement of water, organics and carbonates content in the Martian dust (related to habitability of the planet) Scientific goals in a martian lander scenario 23/10/2015EPSC 2012, Madrid10

Venus Scientific goals in a aerostatic balloon mission on Venus Dew point (i.e. partial pressure) measurement of cloud condensable species Discrimination of volatile and refractory species in aerosols Analysis of areosol electrical properties 23/10/2015EPSC 2012, Madrid11

Titan Scientific goals in a aerostatic balloon mission on Titan Measurement of methan dew point (i.e. mixing ratio) Measurement of organics content (e.g. ethane, acetylene, benzene) in cloud aerosols (possible thanks to their different volatility and partial pressure) 23/10/2015EPSC 2012, Madrid12

Outline i.Introduction to Thermogravimetry ii.Planetary applications iii.The VISTA project iv.Laboratory measurements v.Conclusions 23/10/2015EPSC 2012, Madrid13

Volatile In-Situ Thermogravimetry Analyser VISTA is the thermogravimeter developed by a consortium of Italian institutes, led by IAPS-INAF and coordinated by Dr. Ernesto Palomba. Light (25 grams) Small (2x2x3 cm 3 ) Low power-consuming (60 mW for  T=60° K in vacuum) High sensitivity ( ppm) 23/10/2015EPSC 2012, Madrid14

Instrument concept VISTA has a heater and a thermistor integrated onto the crystal. The thermistor can act as additional heater, in parallel to the other heater. In this configuration the required voltage to obtain a certain  T decreases of 50%. Simulation: V=1 V, I=50 mA P=50 mW in air 23/10/2015EPSC 2012, Madrid15

The lunar version: MOVIDA MOon Volatile, Ice and Dust Analyser Legend Lunar surface Capacitor Microbalance Dust particle The microbalance is placed inside a capacitor held at a voltage  V. Dust particles passing through the capacitor will deposit on the PCM in a time t depending on their charge-to-mass ratio q/m: q/m= 2/(  V t 2) 23/10/2015EPSC 2012, Madrid16

VISTA and ESA Cosmic Vision Different VISTA configurations have been studied for Phase A of the following ESA Cosmic Vision ( ) missions: MARCO POLO Target: primitive asteroid MARCOPOLO-R Target: primitive asteroid Penetrator for EJSM Target: Europa and Ganimede 23/10/2015EPSC 2012, Madrid17

Outline i.Introduction to Thermogravimetry ii.Planetary applications iii.The VISTA project iv.Laboratory measurements v.Conclusions 23/10/2015EPSC 2012, Madrid18

Water desorption from clay (1) The mass of a clay sample has been measured 1.Before the controlled hydration 2.After the controlled hydration 3.After the  TGA In the two performed tests, the TGA measures show a very good agreeement between the amount of water absorbed from clay during its hydration and the amount of released water after the heating (Zinzi et al., Sensor and Actuators A, 2011). Controlled hydration camera 23/10/2015EPSC 2012, Madrid19

Water desorption from clay (2) Three kinds of experiments performed, differing on humid flux exposure time Exposition time (hours) Adsorbed water (% wt.) Desorbed water (% wt.) Measure ± ± 0.2 Measure ± ± 0.2 Measure ± 0.2 Average ± ± 0.2 No dependence on exposure time Images from Zinzi et al., Sensor and Actuators A, /10/2015EPSC 2012, Madrid20

23/10/2015EPSC 2012, Madrid Enthalpy of sublimation of adipic acid in vacuum (1) Adipic acid has been heated at different temperatures and hence deposited on a cold PCM (T PCM = -25°C) 21

23/10/2015EPSC 2012, Madrid Enthalpy of sublimation of adipic acid in vacuum (1) Adipic acid has been heated at different temperatures and hence deposited on a cold PCM (T PCM = -25°C) Becker containing adipic acid PCM Copper shield Plate 22

Enthalpy of sublimation of adipic acid in vacuum (2) Deposition rates of adipic acid at different temperatures have been measured. Enthalpy of sublimation has been inferred by Van’t Hoff relation:  H : enthaply of sublimation T 1 and T 2 : adipic acid temperatures R 1 and R 2 : deposition rates at temperatures T 1 and T 2 R : gas constant 23/10/2015EPSC 2012, Madrid23 We found  H = 131 kJ/mol, in agreement with the literature value (129.3±2.5) kJ/mol

Outline i.Introduction to Thermogravimetry ii.Planetary applications iii.The VISTA project iv.Laboratory measurements v.Conclusions 23/10/2015EPSC 2012, Madrid24

Conclusions Thermogravimetry can find application in many planetary environments An instrument based on TGA (i.e. VISTA) is under study and development for space applications: it is very light, small and low-power consuming A VISTA laboratory breadboard has been tested by performing measurements of water desorption and enthalpy of sublimation 23/10/2015EPSC 2012, Madrid25