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Measu ing Elec ical Conduc i i y o S udy he Fo ma ion
o B ines Unde Ma ian Condi ions
Mi acle Is ael Naza ious*,1,4, Abhilash Vakkada Ramachand an*,1, Ma ia-Paz Zo zano*,2,4, Ja ie Ma in-To es*,3,4
1G oup o A mosphe ic Science, Depa men o Compu e Science, Elec ical and Space Enginee ing, Luleå Uni e si y o Technology 2Cen o de
As obiología (INTA-CSIC) 3Ins i u o Andaluz de Ciencias de la Tie a (UGR-CSIC) 4School o Geosciences, Uni e si y o Abe deen
*These au ho s con ibu ed equally
Co esponding Au ho
Mi acle Is ael Naza ious
[email p o ec ed]
Ci a ion
Naza ious, M.I., Ramachand an, A.V.,
Zo zano, M.P., Ma in-
To es, J. Measu ing Elec ical
Conduc i i y o S udy he Fo ma ion o
B ines Unde Ma ian Condi ions. J. Vis.
Exp. (173), e61217, doi:10.3791/61217
(2021).
Da e Published
July 28, 2021
DOI
10.3791/61217
URL
jo e.com/ ideo/61217
Abs ac
This pape desc ibes a p o ocol o design expe imen s o s udy he o ma ion o
b ines unde Ma ian condi ions and moni o he p ocess wi h elec ical conduc i i y
measu emen s. We used he Enginee ing Quali ica ion Model (EQM) o Habi abili y:
B ines, I adia ion, and Tempe a u e (HABIT)/ExoMa s 2022 ins umen o he
expe imen se up bu we p o ide a b ie accoun o cons uc ing a simple and
inexpensi e elec ical conduc i i y measu emen se up. The p o ocol se es o
calib a e he elec ical conduc i i y measu emen s o he sal deliquescence in o b ine
in a simula ed Ma ian en i onmen . The Ma ian condi ions o empe a u e (-70 °C o
20 °C), ela i e humidi y (0% o 100%) and p essu e (7 - 8 mba ) wi h ca bon-dioxide
a mosphe e we e simula ed in he SpaceQ Ma s simula ion chambe , a acili y a he
Luleå Uni e si y o Technology, Sweden. The hyd a e o m o he known amoun o
sal accommoda ed be ween a pai o elec odes and hus he elec ical conduc i i y
measu ed depends p edominan ly on i s wa e con en and he empe a u e and
ela i e humidi y o he sys em. Elec ical conduc i i y measu emen s we e ca ied
ou a 1 Hz while exposing sal s o a con inuously inc easing ela i e humidi y ( o
o ce ansi ioning h ough a ious hyd a es) a di e en Ma ian empe a u es. Fo
demons a ion, a day-nigh cycle a Oxia Planum, Ma s ( he landing si e o ExoMa s
2022 mission) was ec ea ed.
In oduc ion
One o he main esea ch opics o plane a y explo a ion
is he wa e cycle, bu i is di icul o design a gene al,
obus and scalable p ocedu e, ha allows o moni o he
in e ac ion o he a mosphe e wi h he g ound. Labo a o y
simula ions can ec ea e he plane a y a mosphe es, su aces
and he in e ac ions wi hin. Howe e , i comes wi h a
challenge, om p ocu ing necessa y equipmen o aining
pe sonnel. This pape desc ibes a p o ocol o design
expe imen s o s udy he o ma ion o b ines unde
Ma ian condi ions o empe a u e, ela i e humidi y and
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ca bon-dioxide a mosphe e, and moni o s he p ocess wi h
elec ical conduc i i y measu emen s. We also p o ide a
b ie accoun o cons uc ing a simple and inexpensi e
elec ical conduc i i y measu emen se up. The p o ocol may
be adap ed o design simila expe imen s in acuum o o he
plane a y a mosphe es.
Impo ance o b ine o ma ion s udies
Hyg oscopic sal s can abso b a mosphe ic wa e apo o
o m liquid solu ions in a p ocess called deliquescence. This
p ocess c ea es b ine unde a o able condi ions on he
su ace o Ea h and Ma s ha is likely o exis in ce ain
imes and places. The e e se p ocess called e lo escence
is also possible when he b ines dehyd a e unde un a o able
condi ions. The plausible exis ence o b ines on he su ace
o subsu ace o Ma s has se e al implica ions on he cu en
e es ial and Ma ian s udies. Addi ionally, sal s can hyd a e,
hold and elease wa e molecules, which also a ec s he
wa e cycle and he p ope ies o he egoli h.
The e is an inc easing in e na ional in e es on de e mining
he empe a u e, ela i e humidi y and p essu e condi ions
ha a e a o able o he o ma ion o b ines due o
deliquescence o sal s and sal mix u es, bo h o Ea h and
Ma s. Field obse a ions o he da k s eep-sloped wa e
acks nea Don Juan Pond (DJP) wa e shed and he
o ma ion o we pa ches in he McMu do D y Valleys in
An a c ica ha e been a ibu ed o he b ine o ma ion in he
calcium-chlo ide ich sedimen s1.
These esul s ha e also been alida ed wi h labo a o y
expe imen s simula ing he low empe a u es be ween -30
°C and 15 °C and a ela i e humidi y be ween 20% and
40%2. Chlo ide-bea ing e apo i es in he Yungay egion in
he hype -a id co e o he A acama Dese , Chile can abso b
wa e and ha bo mic obial li e3. The p ocesses occu ing in
he DJP and he d ies places on Ea h such as he A acama
Dese may be analogous o se e al o he Ma ian s udies
sugges ing ha simila p ocesses could be happening on
he p esen -day Ma s1,2,4,5,6,7,8,9,10,11,12,13,14,15,16.
Recen emo e sensing obse a ions o he Sala de Uyuni
(Boli ian Al iplano) ha e desc ibed a simila p ocess o wha
is obse ed on Ma s om o bi 17. Despi e ha sh condi ions,
he deliquescence-d i en b ine o ma ion p ocess can sus ain
liquid wa e in quan i ies la ge enough o allow colonies o
bac e ia o h i e deep wi hin he sal nodules3. This is o
in e es o as obiologis s and plane a y scien is s.
Diu nal abso p ion and deso p ion o he a mosphe ic
mois u e by he deliquescen sal s in he Ma ian egoli h
has been epo ed4,5. The b ine o ma ion p ocess o
pe chlo a es exis ing on Ma s ha e al eady been s udied,
obse ing he changes in phase o hyd a ion s a e o
indi idual sal pa icles1,9,18.Di e en b ine ela ed s udies
ha e also been pe o med unde Ma s- ele an condi ions o
de e mine he ela i e humidi y alues a which Ma s ele an
sal s and sal mix u es will unde go deliquescence and
e lo escence19,20,21. O he s ha e used hese expe imen
condi ions o s udy he e apo a ion a es o b ines a
Ma ian empe a u e, ela i e humidi y and ca bon-dioxide
a mosphe e22.
Me hods o b ine o ma ion de ec ion and moni o ing
Se e al me hods exis o moni o he b ine o ma ion p ocess.
Visual obse a ion and images in he isible wa eleng hs
a e he simples . Weighing he sal s o moni o he inc ease
in mass could well be used23. Usually he en i onmen al
pa ame e s such as empe a u e, ela i e humidi y and
p essu e a e moni o ed o p ope ly in e p e he obse a ions.
Some s udies used a hyg ome e . The hyg oscopic p ope ies
o he sal s can also be measu ed wi h di e en ial mobili y
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analyze s o elec odynamic balances, bu hei ope a ion is
no accu a e enough beyond a ela i e humidi y o 90%24.
In ecen s udies, ansmission and scanning elec on
mic oscopes (TEM and SEM) ha e been widely u ilized.
Bo h hese mic oscopes ha e en i onmen al cells ha
enable s udying he in e ac ion o wa e wi h indi idual sal
pa icles24. The phase changes and ansi ions in indi idual
sal pa icles a e gene ally de ec ed wi h op ical, in a ed
(IR) o Raman spec oscopy inco po a ed in he expe imen al
se up8,13,19,20,25. Exis ing spec oscopic me hods o e
good obse a ion limi s and a clea de ec ion o phase
changes, bu hey a e no compa ible o moni o bulk
sal samples and o he con inuous moni o ing o he
b ine o ma ion p ocess h ough he in e media e s ages o
phase ansi ions. Fu he mo e, he lase -based mic oscopic
de ices such as he 'Raman mic oscope' a e expensi e and
may equi e a complex expe imen al se up.
We use elec ical conduc i i y as he measu emen
echnique. Measu emen s o de e mine he ela i e humidi y
a which he sal s unde go deliquescence ha e been
pe o med using elec ical conduc i i y whe e he de i ed
alues we e in good ag eemen wi h hose de e mined using a
s anda d hyg ome e 26. The ime se ies o he b ine o ma ion
p ocess o he deliquescen sal s has been s udied using
elec ical conduc i i y ea lie by Heinz e al.27. He e, hey
used a mix u e o JSC Ma s-1a simulan and pe chlo a es
o chlo ides. The elec ical conduc i i y echnique has also
been used o de ec liquid o ozen wa e in soils28,29. The
ad an age o his me hod is ha , i can be applied bo h
o small and medium-sized samples, as long as hey a e
con ained in he space be ween he wo elec odes.
This p o ocol could be use ul o design simila expe imen s
ha in ol es con olling he empe a u e and ela i e humidi y
in acuum o simula ing he ex a e es ial a mosphe es such
as Ma s and o he s.
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Figu e 1: Cons uc ion o he expe imen se up. A block diag am showing a simple elec ical conduc i i y measu emen
se up comp ising o he main componen s such as elec odes, measu ing ci cui s and an A duino. Please click he e o iew a
la ge e sion o his igu e.
Elec ical conduc i i y o b ines can be measu ed wi h
a simple inexpensi e se up as shown in Figu e 1. The
speci ic p oduc s o cons uc he se up is gi en in Table
o Ma e ials. The se up p ima ily consis s o a pai o
me al elec odes o same dimensions sepa a ed by a known
dis ance wi hin which he sal o sal mix u es o he s udy a e
accommoda ed. A PT1000 esis ance empe a u e de ec o
can be used o measu e he empe a u e o he sal s.
One o he la ends o he elec odes can be solde ed o
each e minal o a shielded coaxial cable. Simila ly, he wo
e minals o he senso can be solde ed o ano he shielded
coaxial cable. The o he ends o each o hese coaxial
cables can be connec ed o he ci cui s o measu e elec ical
conduc i i y and empe a u e, espec i ely. An A duino boa d
and a simple se ial da a moni o can be used o e ie e he
da a and s o e i .
In he con ex o his expe imen , we use he Enginee ing
Quali ica ion Model (EQM) o he HABIT/ExoMa s 2022
ins umen , he closes eplica o he Fligh Model (FM) ha
will be lown o Ma s in 2022. HABIT s ands o Habi Abili y:
B ines, I adia ion, and Tempe a u e. I is one o he wo
Eu opean payloads in he ExoMa s 2022 Su ace Pla o m
Kazachok and has he objec i e o s udy he habi abili y
condi ions a he landing si e, Oxia planum, Ma s. The B ine
Obse a ion T ansi ion To Liquid Expe imen (BOTTLE) is
one o he componen s o HABIT ins umen wi h a pu pose o
demons a e he liquid wa e s abili y on Ma s31. The p o ocol
desc ibed he e se es o calib a e he elec ical conduc i i y
measu emen s as a unc ion o b ine o ma ion unde
Ma ian condi ions o empe a u e, ela i e humidi y and
ca bon-dioxide a mosphe e31. This is applied o e ie e he
calib a ed elec ical conduc i i y measu emen s o BOTTLE
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ha aids wi h he de ec ion o liquid b ine o ma ion p ocess
on Ma s, which is one o i s p ima y mission objec i es18.
By calib a ion, he e we e e o expe imen -le el calib a ion.
Ins umen -le el calib a ion is pe o med wi h de e mining he
geome ical cell cons an s o each elec ode pai and wi h
calib a ion s anda ds o known elec ical conduc i i y31.
P o ocol
1. Cons uc ion o he expe imen se up o
measu ing elec ical conduc i i y
1. Choose he dimensions o he elec odes and he
dis ance be ween he elec ode pai . The dimensions o
he elec odes depend on he dimensions o he sample
con aine and he eby he amoun o sal s used. The
dimensions o he HABIT BOTTLE con aine dimensions
men ioned below can be aken as e e ence o he
sample con aine and he amoun o sal s can be e e ed
om S ep 2.1. The geome ical cell cons an can be
de i ed om equa ion (1).
(1)
whe e, d - dis ance be ween he elec ode pai , and
A - A ea o he elec odes (= Leng h x B ead h).
The geome ical cell cons an , K decides he elec ical
conduc i i y ange o which he measu emen se up is
sensi i e. Fo example, K = 1 cm-1 can measu e in 5 -
200, 000 µScm-1 ange while K = 10 cm-1 can measu e
in 10 µScm-1 - 1 Scm-1 ange. The e may be a ious
le els o elec ode pai s. The choice o ma e ial could
be om coppe , pla inum, gold, e c. Se e al long- e m
expe imen s a Omnisys Ins umen AB, Sweden acili y
wi h gold and pla inum elec odes, passing di ec cu en
(DC) in b ine medium has shown ha gold elec odes a e
p e e ed in e ms o be e co osion esis ance o his
ope a ion.
NOTE: HABIT has a o al o 16 elec ode pai s wi h a
possibili y o s udy six di e en sal s a h ee le els ( wo
co ne cells measu e only wi h low and mid elec ode
pai s) sepa a ed wi hin a con aine o dimensions 25
mm x 15 mm x 15 mm (L x W x H). BOTTLE uses
h ee le els o elec ode pai s o dimensions: Low: 1.6
x 0.4, Mid: 1.6 x 0.2, High: 1.6 x 0.2, sepa a ed a
2.5 cm p oducing a cell cons an o 3,9062 cm-1 and
7.8125 cm-1. The measu emen s we e pe o med using
an op ical measu emen sys em (e.g., Mi u oyo MF 176).
2. P epa e a con aine wi h la su aces o hold he sal s o
s udy as shown in Figu e 1. The con aine size can be
chosen depending on he geome ical dimensions o he
elec odes and he dis ance be ween he elec ode pai
whe e he sal s a e accommoda ed. Mul iple con aine s
con igu a ion may be adap ed. The con aine s may be
3D p in ed in PLA o p e e ably milled wi h aluminum o
o he me al, hey should be p o ec ed agains wa e loss
as apo o liquid leakage h ough he walls.
3. P epa e he epoxy 2216 esin coa ing and apply i on he
walls o he con aine (s). Lea e i o an hou o i o se
and cu e he coa ed con aine (s) a 66 °C o 2 hou s.
NOTE: The epoxy coa ing can be dissol ed in a sol en
and sp ayed o bes esul s.
4. Accommoda e he elec ode pai on he opposi e walls o
he con aine (s) and glue hem wi h he epoxy 2216 esin
ha was al eady applied.
5. Use a long shielded coaxial cable and solde he ends
on one side o he con ac poin o each o he elec ode
in a pai .

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6. Connec he o he end o he shielded coaxial cable o
he wo e minals o he elec ical conduc i i y measu ing
ci cui .
NOTE: A simple elec ical conduc i i y measu ing ci cui
can be buil wi h one e minal o an AC ol age sou ce
o gene a e elec ic pulses a a speci ied equency and
he o he e minal o a ol age di ide ci cui o ead he
ol age d op ac oss he elec ode pai . The digi al ou pu
pins o A duino can be used in Pulse Wid h Modula ed
(PWM) mode o gene a e he equi ed AC ol age. AC
ol age is used o p e en co osion o he elec odes.
The ol age d op ac oss he elec ode pai can also be
measu ed wi h he analog inpu pins o he A duino wi h
i s in-buil 10-bi analog- o-digi al con e e (ADC). O he
comme cial ci cui s a e also a ailable.
7. Simila ly, use he mal pas e o glue he PT1000
Resis ance Tempe a u e De ec o (RTD) on one o he
walls o he con aine (s).
8. Use ano he long shielded coaxial cable o connec he
one side o he wo e minals o he PT1000 senso and
he o he side o a empe a u e measu ing ci cui .
NOTE: A simple empe a u e measu ing ci cui can be
buil wi h one e minal o an DC ol age sou ce and he
o he e minal o a ol age di ide ci cui o ead he
ol age d op ac oss he PT1000 senso which can be
measu ed wi h he analog inpu pins o he A duino wi h
i s in-buil 10-bi analog- o-digi al con e e (ADC). O he
comme cial ci cui s a e also a ailable.
1. To p epa e he HABIT ins umen o he
expe imen al se up, sepa a e he cable connec ion
be ween he BOTTLE componen and he
Elec onics Uni (EU). Then, unsc ew he 8x M3 bol s
o he BOTTLE, o emo e he op lid and he HEPA
il e holde in o de o expose he six open cells.
Be o e eeding in he sal s o s udy, clean he cells
and elec odes o he BOTTLE, p e e ably using an
elec ode cleaning solu ion and a s e ile co on swab
o ee o any pa icles o liquids.
2. Ca y ou calib a ion o he elec ical conduc i i y
measu emen s o he se up p io o eeding in
he sal s, using a se o calib a ion s anda ds wi h
known elec ical conduc i i y alues o de e mine he
calib a ion unc ion coe icien s o each elec ode
pai . Use he elec ical conduc i i y measu emen o
0.0364 µScm-1 (as ze o o d y poin ) when BOTTLE
was subjec ed o acuum condi ions in a he mal
acuum chambe and main ained a 25 °C as he
absolu e ze o elec ical conduc i i y o he sys em.
Fu he , use wo calib a ion s anda ds: 84 µScm-1
and 1413 µScm-1 o de i e a wo-poin calib a ion
unc ion as shown in equa ion (2).
(2)
whe e, σcalib a ed - Calib a ed ac ual elec ical
conduc i i y,
σmeasu ed - Raw measu ed elec ical conduc i i y,
and
a2,a1,a0 - Polynomial cons an s
3. Fi he aw elec ical conduc i i y measu ed by he
se up in o he de i ed calib a ion unc ion o achie e
a ue elec ical conduc i i y measu emen .
NOTE: The ini ial calib a ion is achie ed while
main aining he empe a u e o he sys em a 25
°C. Howe e , as he empe a u e changes du ing
he expe imen , he elec ical conduc i i y alues
change. As i ge s complex o de i e empe a u e
s elec ical conduc i i y unc ions a di e en
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empe a u es, we use empe a u e da a only o
de e mine he phase s a e o he b ine. Naza ious e
al.31 has discussed his aspec in de ail.
2. Manipula ion o he deliquescen sal samples
1. Weigh a speci ic amoun o sal o sample ha is
conside ed o he s udy. We weighed 1.5 g each o ou
di e en sal s: calcium-chlo ide CaCl2, e ic-sulpha e
Fe2(SO4)3, magnesium-pe chlo a e Mg(ClO4)2, and
sodium-pe chlo a e NaClO4in indi idual con aine s.
CAUTION: Some sal s pa icula ly pe chlo a es a e
co osi e and he e o e any con ac wi h skin o eye mus
be a oided.
1. Use p ope chemical ga men s, goggles and ni ile
glo es while handling he sal s. In case o con ac
wi h skin o eye, immedia ely inse wi h plen y o
wa e and consul a doc o .
NOTE: In addi ion o he sal s, we added 0.75 g
o sodium sal o alginic acid (Supe Abso ben
Polyme , SAP) in o each o he ou con aine s
wi h sal and mixed ho oughly o ob ain a uni o m
sal -SAP mix u e. We used SAP as a solidi ying
agen as a sa e y measu e o a oid he b ine
o ise by capilla i y and un o om he ligh
model ins umen . While he sal s abso b gaseous
wa e om he a mosphe ic en i onmen , he SAP
abso bs wa e om a liquid s a e, om he liquid
b ine o sal s once i is in con ac wi h i . Adding
SAP was pu ely due o he enginee ing limi a ions
o s o ing he sal s in Ea h condi ions (p io o
ExoMa s launch in 2022) and has less meaning o
he expe imen i sel . Consequen ly, he elec ical
conduc i i y measu emen is a esul om he
mix u e o sal +SAP+wa e which is expec ed.
Since he goal o his expe imen is o moni o
he abso p ion o wa e in he whole sys em,
he changes in elec ical conduc i i y om he
d y s a e o sal +SAP o he hyd a ed s a es is
deemed ele an o in e p e a ion. The calib a ion
p ocedu e was also ca ied ou o he same sal
+SAP combina ion.
2. Use he same sal and SAP mix u es and weigh s
ha we e used o he ligh model o BOTTLE
componen o he HABIT/ExoMa s ins umen .
3. Feeding he sal samples in he expe imen
se up
1. Ca e ully ans e he en i e y o he p e iously weighed
sal in s ep 2 in o he expe imen con aine (s).
NOTE: The p e iously weighed sal -SAP mix u e was
ca e ully ans e ed in o he ou cells o BOTTLE
in he ollowing o de : Cell-2: calcium-chlo ide CaCl2,
Cell-3: e ic-sulpha e Fe2(SO4)3, Cell-4: magnesium-
pe chlo a e Mg(ClO4)4, Cell-5: sodium-pe chlo a e
NaClO4. Cell-1 and Cell-6 we e le emp y.
1. Follow he same o de in he ligh model o BOTTLE,
so his con igu a ion and expe imen is a ge ed
owa ds he calib a ion and in e p e a ion o i s
ope a ion on Ma s.
2. Le el he op su ace o he sal s such ha hey co e he
elec odes. Choose he amoun o sal s o achie e his
c i e ion.
NOTE: Each sal -SAP mix u e o BOTTLE weighed 2.25
g in o al and co e ed he low elec ode in each cell.
This amoun was chosen so ha he b ine o med will no
o e low.
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3. Use a HEPA il e o co e he op o he con aine (s).
This will allow in e ac ion o sal s wi h he ambien ela i e
humidi y o he simula ed en i onmen .
NOTE: A nylon based HEPA il e wi h a holde ame
was used o co e he sal -SAP mix u es in BOTTLE and
he op lid o BOTTLE was secu ed wi h 8x M3 bol s.
4. Ins alla ion o he expe imen se up in he
simula ion chambe
1. Place he expe imen con aine (s) in he simula ion
chambe 32. Make su e o a good he mal con ac
be ween he wo king able o he chambe and he
con aine (s).
2. Place he elec ical conduc i i y and empe a u e
measu emen ci cui ou side he chambe . This will a oid
any empe a u e induced noises in he ci cui s ha migh
comp omise he measu emen s.
3. Make he powe and da a connec ion be ween he
measu ing ci cui s and he con aine (s) h ough an
in e media e connec o o he simula ion chambe .
NOTE: BOTTLE uses a dedica ed spli cable o i s
2x DB-9 connec o s o he EU o he in e io DB-25
connec o o he chambe . The spli cable is a cus omized
powe and da a connec ion cable speci ic o his
pu pose. F om he ex e io o he DB-25 connec o o he
chambe , ano he spli cable wi h he powe connec ions
was plugged o a DC powe supply and he 2x USB da a
connec ions o a lap op wi h he HABIT EQM LabView
so wa e ins alled.
5. Con ols o he simula ion chambe
Figu e 2: Con ols o he simula ion chambe 32. Rep esen a ion o he Ma s simula ion chambe wi h i s a ious sys ems
o con olling empe a u e, ela i e humidi y, and ca bon-dioxide p essu e. Powe and da a connec ion ou le s a e also
shown. Please click he e o iew a la ge e sion o his igu e.
1. Main aining he empe a u e o he wo king able
be ween 20 °C and -30 °C
NOTE: The empe a u e o he wo king able is egula ed
using he liquid ni ogen (LN2) eed h ough sys em as pe
he p o ocol shown in Figu e 2. Ini ially he chambe is
main ained a he labo a o y ambien empe a u e.
1. Open he al e o he low o LN2. The empe a u e
will s a o dec ease.
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2. Se he desi ed empe a u e on he eedback
con olle . The PT100 empe a u e senso i ed on
he wo king able ac s as a eedback loop.
3. Once he desi ed empe a u e is eached, close he
al e o shu he low o LN2.
2. Main aining he ca bon-dioxide p essu e
1. Tu n ON he acuum pump un il he p essu e inside
he chambe eads acuum.
2. Once he chambe is in acuum, u n he acuum
pump OFF, and injec he chambe wi h CO2 gas
un il i eaches he p essu e o 7-8 mba .
3. Main aining he ela i e humidi y
1. Injec he wa e in inc emen s o 0.5 mLusing a
s ainless-s eel Swagelok sy inge i ed on o he
chambe . This will inc ease he ela i e humidi y
g adually.
NOTE: The sy inge is in u n connec ed o a ball
al e so he sy inge can be used o injec wa e
mul iple imes.
2. Ensu e he p essu e is wi hin he limi s. O he wise,
elease he p essu e by adjus ing he al e.
6. Elec ical conduc i i y s ela i e humidi y
expe imen
Figu e 3: Elec ical conduc i i y s ela i e humidi y expe imen . S eps o he expe imen p o ocol o pe o ming he
calib a ion expe imen o de i e he ela ionship o elec ical conduc i i y as a unc ion o ela i e humidi y. Please click he e
o iew a la ge e sion o his igu e.
1. Tu n he o a y acuum pump ON o lush ou all he
ai om inside he chambe . The p essu e inside he
chambe will educe o an o de o 10-3 mba .
NOTE: The ela i e humidi y will be close o ze o.
The ambien empe a u e o he wo king able o
he chambe is a ound 20 °C. The e may be an
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wi h he wo king able o he chambe ) showing no elec ical
conduc i i y.
As a demons a ion p ac ice o HABIT ope a ion on Ma s
ollowing a success ul landing in ea ly 2021, we simula ed
one Sol o he en i onmen condi ions a Oxia Planum, he
planned landing si e o he ExoMa s 2022 mission. The
ob ained esul s mimic he day-nigh cycle o he BOTTLE
ope a ion on Ma s and p o ides a i s -hand da a in ele an
condi ions. Figu e 6 shows ha du ing he simula ion o he
Ma ian day-nigh cycle, deliquescence has been obse ed in
all he sal -SAP mix u es. Figu es 6C-6F show he elec ical
conduc i i y alues o he ou di e en sal -SAP mix u es,
calcium-chlo ide CaCl2- SAP, e ic-sulpha e Fe2(SO4)3 -
SAP, magnesium-pe chlo a e Mg(ClO4)2 - SAP, and sodium-
pe chlo a e NaClO4- SAP, espec i ely.

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Figu e 6: Calib a ed elec ical conduc i i y measu emen s o he Ma s Sol simula ion. (A) P essu e and ela i e
humidi y, (B) g ound and ai empe a u e, (C) calcium-chlo ide, (D) e ic sulpha e, (E) magnesium-pe chlo a e, (F) sodium-
pe chlo a e elec ical conduc i i ies (in log scale wi h base 10), and (G) Elec onics Uni (EU) and Con aine Uni (CU)
o BOTTLE empe a u es a e shown. Ve ical lines wi h ci cled numbe s indica e a ious phases o he simula ion. 0-1:
Pumping ou ai o a ain acuum and ca bon-dioxide injec ion o main ain a 7-8 mba p essu e a cons an empe a u e,
1-2: wa e injec ion o inc ease he ela i e humidi y a cons an empe a u e, 2-3: wo king able cooling ON o dec ease
he empe a u e (day-nigh ansi ion), accompanied by a ela i e humidi y dec ease, and 3-4: wo king able cooling OFF
o inc ease he empe a u e (nigh -day ansi ion), accompanied by a ela i e humidi y inc ease. Please click he e o iew a
la ge e sion o his igu e.
The ini ial amp in he elec ical conduc i i y may be a ibu ed
o he apid p essu e dec ease while ela i e humidi y
emained high, accele a ing he p ocess o wa e cap u e
ollowed by ou gassing o he emaining wa e in he mix u e.
This was also consis en wi h he exo he mici y o wa e
cap u e p ocess by he sal s. The empe a u e inc ease in
he Elec onics Uni (EU) and BOTTLE may be a combina ion
o a apid dep essu iza ion (unde cons an olume) and he
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exo he mic beha io o sal -wa e in e ac ion. The p essu e
dip obse ed a ound 13:00 could be associa ed wi h eaching
he lowes empe a u e in he wo king able, which is
also coinciden wi h a small up ick in he RH. A colde
empe a u es, he wo king able beha ed as a wa e sink
eezing he wa e d ople s and hence he ela i e humidi y
o he ai was low. Du ing his phase o Ma ian day-nigh
ansi ion, he e we e less signi ican signs in he elec ical
conduc i i y cu es. Bu , du ing he nigh -day ansi ion, when
he empe a u e inc eased and so did he ela i e humidi y,
he sal -SAP mix u e began cap u ing wa e s eadily as
indica ed by he inc ease in elec ical conduc i i y in he
la e pa o he expe imen also mi o ed by he sudden
inc ease in he BOTTLE empe a u e. The inal elec ical
conduc i i y alues indica ed he ex en o wa e cap u e by
each o he ou sal -SAP mix u es as shown in Figu e 7.
All he sal -SAP mix u es cap u ed wa e and pa icula ly,
calcium-chlo ide sal -SAP mix u e p oduced liquid b ine. The
maximum elec ical conduc i i y alue o he CaCl2 b ine o
100 µScm-1 is cohe en wi h he li e a u e31.
Figu e 7: Images o he sal -SAP mix u es. (A) be o e and (B) a e he Ma s Sol simula ion. Le o igh : Ini ial condi ions
o 1.5 g each o calcium-chlo ide, e ic sulpha e, magnesium-pe chlo a e, sodium-pe chlo a e wi h 0.75 g SAP in each sal .
Calcium-chlo ide in he le co ne p oduced liquid b ine also showing ele an elec ical conduc i i y alues o 100 µScm-1.
All o he sal -SAP mix u es also cap u ed conside able amoun s o wa e as appea ing we in he images. Please click he e
o iew a la ge e sion o his igu e.
Discussion
This is he maiden a emp o cha ac e ize he elec ical
conduc i i y o he b ine o ma ion p ocess in acuum
o Ma ian p essu e condi ions. The key elemen o his
expe imen is o simula e he Ma ian day-nigh cycle wi h he
Ma s simula ion chambe o s udy he sal s. The esul s o
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he sal deliquescence a e shown as a ep esen a i e esul
while he ocus is mo e on achie ing he equi ed condi ions
o simula e Ma ian en i onmen . Wi h his i s expe imen ,
we now unde s and he p ocess and he limi a ions o he
chambe as men ioned in he discussion sec ion o he
manusc ip . In he u u e expe imen s, we will ollow his
p o ocol o a ious science expe imen s ha is ele an
o p ocess on Ma s. Ea lie s udies ha e ca ied ou he
elec ical conduc i i y measu emen s in ambien labo a o y
p essu es27,28,29. Measu ing in lowe p essu es poses a
challenge and hus demanded a modi ica ion o he p o ocol
used o he Ea h p essu e condi ions. Du ing a p e ious
calib a ion campaign in a clima e chambe unde ambien
p essu es, di e en hyd a es we e p epa ed by adding
de ined amoun s o sal and wa e , p io o each se o he
expe imen s o de i e he ela ionship be ween he elec ical
conduc i i y and he sal hyd a e o m a di e en Ma ian
empe a u es31. Bu , wi h Ma ian p essu es, he added wa e
used o o m hyd a es will e en ually ou gas when educing
he p essu e, hus we s a ed o e e y expe imen wi h a
d y sal -SAP mix u e and egula ed he ela i e humidi y o
ansi ion h ough a ious hyd a e o ms.
Pas s udies moni o ing he b ine o ma ion p ocess using
Raman spec oscopic me hods, gene ally we e pe o med
wi h an indi idual g anule o he sal pa icle in an
en i onmen al cell and obse ing he phase ansi ions in
he O-H s e ching egion o he Raman spec a1,9,18. The
elec ical conduc i i y cha ac e iza ion o he b ine o ma ion
p ocess deemed o be mo e sensi i e o in e media e
phase ansi ions han he exis ing Raman spec oscopy and
p o ided a con inuous ime se ies o he b ine o ma ion
p ocess27. F om ou expe imen s, we also demons a ed
elec ical conduc i i y as a iable measu emen op ion o bulk
sal samples wi h good p ecision.
Du ing he design o he elec ical conduc i i y measu emen
sys em o he HABIT ins umen , we had challenges o
sol e. Selec ion o he elec ode ma e ial was based on i s
esis ance o co osion and he su ace smoo hness o a oid
spo adic gli ches in he elec ical conduc i i y measu emen s.
The hyg oscopic sal s some imes climb up along he walls o
he con aine by capilla i y and hence a choice o hyd ophobic
coa ing is essen ial. We used a coa ing based on an epoxy
esin composi ion ha p e en ed he b ine om capilla y ise.
Also, he elec ical cha ac e is ics such as he ol age o he
elec ic pulse, i s equency and he cu en sense e e ence
esis o we e c ucial o he design. BOTTLE uses a ±2.048
V bias ol age wi h an elec ic pulse o ±70 mV and ±700 V
o low and high conduc ance modes. The elec ic pulses a 1
kHz passes h ough a gold elec ode, and ia he sal samples
o s udy, and a e ead-ou a a gold elec ode on he o he
side wi h 10 k-ohm and 100-ohm e e ence esis o s o low
and high conduc ance modes espec i ely.
Since each o he expe imen s o cha ac e ize he elec ical
conduc i i y as a unc ion o ela i e humidi y, equi ed a
cons an and s able empe a u e, he p o ocol is designed
o accommoda e wi hin he empe a u e s abili y limi s o
he Ma s simula ion chambe . The e is an obse able
di e ence in he wo king able empe a u e ( egula ed by he
LN2 eed h ough sys em o he chambe ) and he BOTTLE
empe a u e due o he he mal isola ion. This means ha
he wo king able empe a u e is no always iden ical wi h he
BOTTLE empe a u e and he di e ence mus be conside ed
o an op imal expe imen condi ion.
Fu u e expe imen s in he Ma s simula ion chambe
will include de i ing a ela ionship be ween he ai
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elec ical conduc i i y and he ela i e humidi y a di e en
empe a u es. Du ing he Ma s Sol simula ion, we obse ed
a possible co ela ion be ween he ela i e humidi y o he
ai and i s elec ical conduc i i y. This may be ele an o
calib a ing he wo emp y cells a he wo ends o BOTTLE
and inco po a e i wi h he calib a ion o he sal -SAP mix u es
o mo e p ecise in e p e a ion o hei hyd a ion le el. To
ca y ou his expe imen , emp y expe imen con aine (s) can
be adap ed wi hou any sal samples ollowing he same
expe imen p o ocol.
The desc ibed expe imen p o ocol p o ides a simple , easily
adap able al e na i e way o moni o he b ine o ma ion
p ocess which can also be applied o o he samples ha may
in e ac wi h a mosphe ic mois u e. I could be complimen a y
o s udies on unde s anding he physical and chemical
p ope ies o he b ines o med by sea-sal mix u es ha will
be applicable o de ine condi ions unde which b ines may
eac wi h cannis e su aces gene ally used o s o e nuclea
uel and nuclea was es33,34. The co osi e p ope ies o
b ines o di e en ma e ials can be s udied unde di e en
en i onmen condi ions by adap ing he p o ocol. We applied
his p o ocol o s udy he deliquescen p ope ies o ou
mix u es o sal and SAP ha we ca y o Ma s onboa d he
HABIT ins umen . Howe e , he hyg oscopic p ope ies o
sal o sal mix u es in any o m, o example, smoke pa icles
can be analyzed o hei cloud-nuclea ing po en ial24. The
expe imen p o ocol could also be applied o simula e
a ious a mosphe e-su ace ela ed phenomenon on Ma s
and elsewhe e inside a labo a o y.
Disclosu es
The au ho s ha e no hing o disclose.
Acknowledgmen s
The HABIT Enginee ing Quali ica ion Model (EQM) ha
was used o he expe imen s was ab ica ed by Omnisys,
Sweden, as pa o he HABIT p ojec de elopmen , unde
he supe ision o MPZ and JMT, and unded by he Swedish
Na ional Space Agency (SNSA). HABIT and BOTTLE
a e he o iginal ideas o MPZ and JMT. SpaceQ Ma s
simula ion chambe is a Luleå Uni e si y o Technology
acili y si ua ed in Luleå, Sweden. The Kempe Founda ion
unded he design and ab ica ion o he SpaceQ chambe .
The SpaceQ chambe was manu ac u ed by Ku J. Leske
Company, U.K., unde he supe ision o MPZ. MPZ has
been pa ially unded by he Spanish S a e Resea ch Agency
(AEI) P ojec No. MDM-2017-0737 Unidad de Excelencia
“Ma ía de Maez u”- Cen o de As obiología (INTA-CSIC)
and by he Spanish Minis y o Science and Inno a ion
(PID2019-104205GB-C21). AVR and JMT acknowledge
suppo om he Wallenbe g Founda ion.
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