Adso p ion o wa e on oli ine
and he o igin o Ea h’s wa e
Luca Va uone1
Ma co Sme ie i 2, Le izia Sa io, 2
Abu Md Asaduzzamann 3, K ishna Mu alidha an4
Ma io Rocca 1
1DIFI Uni e si y o Genoa & IMEM-CNR (I aly)
2IMEM-CNR (I aly)
3School o Science, Enginee ing and Technology , Pennsyl ania S a e Uni e si y (USA)
4Dep . O Ma e ial Science and Enginee ing & Luna and Plane a y Obse a o y
Uni e si y o A izona (USA)
I is gene ally ag eed ha i was oo ho a 1 as onomical uni (AU) o hyd ous mine als o be
s able in he acc e ion disc.
Boss A. P. 1998. Tempe a u es in p o oplane a y disks. Annual
Re iews o Ea h and Plane a y Science 26:26–53.
Ea h’s wa e is con en ionally belie ed o ha e been deli e ed by come s o we
as e oids a e he Ea h o med
BUT
•we as e oids and come s ha e elemen al and iso opic p ope ies ha a e inconsis en wi h hose o he Ea h
D ake MJ. 2005 The Leona d medal add ess: o igin o wa e in he e es ial plane s.
Me eo i ics Plane . Sci. 40, 519–527.
•I was hus p oposed ha wa e was in oduced du ing plane g ow h in he acc e ion disc in a o m s able
unde high- empe a u e condi ions.
Be hell T, Be gin E. 2009 Fo ma ion and su i al o wa e apo in he e es ial plane –
o ming egion. Science 326, 1675–1677.
L. Va uone
The p esence o wa e on Ea h is an enigma…
Only ca bonaceous
chond i es con ain
signi ican amoun s o wa e
BUT
Osiso opes in Ea h a e
qui e unlike any hyd ous
ca bonaceous chond i e
me eo i e alling o Ea h
oday.
D/H a io o Ea h’s wa e
no compa ible wi h known D/H aio in come s !
&
The las me eo i es we e anyd ous
(Walke e al.2002 Geochimica
e Cosmochimica Ac a 66:4187–4201)
L. Va uone
The hypo hesis o wa e deli e ing om come s / me eo i es is no sa is ac o y…
Theo e ical Mon eca lo calcula ions
Indica e ha :
1) A signi ican H2O co e age is
possible
2) Such co e age can accoun
o (mo e han) he amoun o
wa e p esen in Ea h’s oceans
L. Va uone
M. D ake’s idea: di ec adso p ion o wa e on o g ains p io o plane a y acc e ion
L. Va uone
An expe imen al es : H2O adso p ion on oli ine 100
1 mm hick slab o na u al Pakis ani
oli ine (Fo90) cu om
a single c ys al pa allel o {100} and
polished on one side only o 1 µm
smoo hness
H2O deli e ed by Supe sonic
Molecula Beam (H2O apou seeded
in He, E=0.30 eV)
Adso p ion on:
non polished
(model o eal oli i e)
polished oli ine S icking p obabili y es ima ed by Tempe a u e P og ammed Spec oscopy
S icking p obabili y es ima ed by King & Wells me hod
L. Va uone e al. 2013
Phil T ans R Soc A 371:
20110585.
L. Va uone
Expe imen al esul s: 300 s H2O (0.30 eV) a 138 K
The peak a 165 K is due o H2O mul ilaye
The peak a lowe T is e iden only on non-polished side and is due
o H2O nuclea ion a de ec s
A e each cycle he sample is lashed o deso b he mul ilaye
and hen exposed o H2O again
The amoun o deso bing H2O dec eases in subsequen
up akes !
S < 0.05
S0.2
Polished side
Non- polished
side
The su ace is passi a ed due o H2O
adso p ion and deso p ion cycles
DISSOCIATIVE ADSORPTION !
L. Va uone
Expe imen al esul s: es ing H2O adso p ion a high T (423 K/ 560 K)
Elec on spec oscopies no sui able due o he insula ing na u e o he su ace
H2O adso p ion a 136 K used as p obe o su ace s a e
I oli ine is exposed o H2O a high T (423 K/560 K )
and hen cooled down and exposed o H2O a 136 K
Fo he polished side: TPD a e he second up ake shows no deso p ion
Fo he non polished side: KW shows no adso p ion in he p obe expe imen
Polished
oli ine
Non- polished
oli ine
H2O adso p ion MUST ha e occu ed du ing he high T up ake:
wi h S > 0.015 o he non polished side
wi h S> 5 10-4 o he polished side
L. Va uone
Hin s om heo e ical calcula ions (DFT)
Vienna ab ini io simula ion package (VASP) wi hin he amewo k o DFT
and he gene alized g adien app oxima ion unc ional PBE .
We ha e used he p ojec ed augmen ed wa e as p o ided wi h he VASP
package . A cu -o ene gy o 400 eV was chosen o he plane-wa e basis.
𝐸𝑑𝑖𝑠𝑠 =𝐸ℎ𝑦𝑑 − (𝐸𝑢ℎ𝑦𝑑 + 𝐸𝑊 )
Ehyd hyd a ed su ace ene gy
Euhyd unhyd a ed su ace ene gy
EWcohesi e ene gy o a single H2O molecule
Ediss=-270 kJ/mol
Fo he molecula (i..e non dissocia i e) adso p ion
on he hyd oxyla ed su ace:
E= - 33.7 kJ/mol , less s able han condensed wa e (-40 kJ/mol)
Thus explaining he ine ness o he hyd oxyla ed su ace
•Signi ican wa e up ake akes place on oli ine when dosing a 138 K, leading o mul ilaye adso p ion.
•When annealing, pa o he wa e laye deso bs and pa o i mus dissocia e o ming OH and H.
Dissocia ion is possible only o molecules in con ac wi h he oli ine su ace.
•Wa e up ake a 560 K (i.e. inside he ange expec ed o he acc e ion disk: 500-1500 K) causes he o ma ion o
a passi a ing laye o hyd oxyls.
The so-p oduced su ace is passi e wi h espec o low T wa e adso p ion and s able up o a leas 900 K,
since annealing o his empe a u e does no es o e he ini ial eac i i y.
A way o p oduce H2O om OH is equi ed o make he acc e ion disk mechanism iable.
Th ee ways can be en isaged:
1)Recombina i e deso p ion wi h H gi en by H2: no sui able since H is weakly adso bed on oli ine (102 kJ/mol)
2) Reac ion wi h p o ons p o ided by he sola wind (s ongly exho e mic by 511 J/mol and ba ie less)
3) Recombina ion o OH wi h OH o o m H2O and libe a e oxygen in plane a y magma (also exho e mic by 66 kJ/mol)
L. Va uone
Conclusions and open issues…
