NASA Technical Reports Server (NTRS) 20110016140: Observations of Al, Fe and Ca(+) in Mercury's Exosphere

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Observations of AI, Fe and Ca+ in Mercury's exosphere
Thomi1~ A. . Bida (1), Rosemary:Vi. Killen (2)
(1) L<)we!! Observatory, Flagstaff, AL XoCK)l CSA (2) Planetary \'lagnclOSphGfcs Lab,milory, Solar System
Expk)nlliull Dtvisi<m, NASA Guddard Space Flight Center, GreenbelL MD 2{177!, USA (tDJdai1 Iil\\c1Ledu)
Abstract and 4S()U K, rc~pectivdy rhj~ small observed
column ahundan..:t' of atomic Ai is (m!l' )'% of that
predicted frOIll impact vaporinltion of ,\ regulith
\Vc rertm 5-(r tangent column detections ,)j" Al and c\)lltaining 5% A! We ,>mducic thOil impact
Fe, and strict 3-<..1 tangem .;:<)]umn upper iimilS for Ca vap"rization "1t'dS Ai primarily in moicwJar form,
in Mercury's cx,)sphcrc chtained USing the' IIlRFS similar (0 Ca [6] and that vt'ry little of thi~ (':I.jdc
spCClmmeter ()Il the Kcck I tckscopc. 'Ibcse are the di~sociates in the exc)sphere
Hrst din;c! detections of AI and h: in Mercury's
3.lroo
c"(,,sphere Our Ci'I- observatiun is c(lUsislcnt with
that reported by the The Mercury Almospheric and
Surfa<:e Cornpositwll Spectromeler (~"fASCS) dll the Iron ha~ also been observed in \-kreury's tx,)sphcn:
Mcrc\Jf) SurL1ce, Space ENl'irunmcm, using th..: HIRES spectmmeter on the Kcck I
GEuchemistry, and Rangmg (MESSENGER) tdes(;('pc_ Column abundances of iron are more than
spacccnlft i j i :TIrorclcr Df ma~-nitm:kftrrgentr,jJj thm;-c of At in-spite
(If predictions <)f smail iron ah-und:m~e in the regolith
1. Introduction Tprhoims owteudu ldi ntiom ptlhye (heaxto spir\hl1elr, e unplriikmea riAlyJ, i:n~ nlhuei 1I! Cdaenof 1am!l\,cmbdr eeandtt af:itr isMoTn ;;i miiPl,l p aa&bnbR arIebld,,ta'r"t aiiOnd !t idh5Oc s ethe5exju,t,.l, dtD mhdeel enti nthgi s
l'wo :nomic specics were detected in \'1ercury's m,)k(:uiJr roml, Of that it el1sity diSS()~iak~ Ir ,toed. [\'\Ihy all E/>sC Jhdnld n""d,; its ()wn
eMxaorsipnheer relO (wfli,t ha ndt hHe e) LwVith as pmccatrrg,'mJnaelt edrd eclltniuhlola ordf Hobo~ewTveavteir(,) nths,(: (/2e_n9i !-h8 c.(2.)l uxm 1n0 a" bcumn-d2 awncats' cinaflecrurleadte fdr oomn 0:a~b_n'ra:d:;:;L;: _ z_l_w_t_lw_ r~ _qll_H U~D~J,<,~ { _,n_e ~ j c a_n_l_lo_t_ ,~ _____ /
o Three additional dcments tvere discovered the assumption of a Chamberlilin exosphere, The
previuusly oy gr,JUnd-baseU tcickopic searche~: 'a, ubserved altitude distrihmion of Fe, if com:ec w{;uld
K, and Ca 12, 31. More recently rvlg has ht'en lead us to inler that Fe is partially the produ..:t of
ohst'rved in the exosphere by the MASCS t;v f1h}leeular breakup in the exosphut', and the surface
speetromettr onboard MESSENGER i4] Each of abundance of r~ in the atomic form is less than
these species has its ,)wn unique spatiaJ and ttmporal inft'rrcd on the basis c)f a Chamberlain exosphere
variability, arguing that the physics of the gas-surraet'
mteractlOn, the plasma interaction with the 4. Summary and Conclusions
magnt'tospheft' and suriil..:e, the solar radiatiun for..:t'
a~ wtll as gravitational J<)fces, arc important in \1/<': fCport new, Hrst-tim(: dett'eli(lIls <)f t\I'O n",w
promoting the atoms into the ex<)spherc and in ncutr:d spccic~ in Menury'" t'xosphcre by ground
redj~tributi.ng them ab,)ut the t'xospht'n:; and surface based observations AI, with ~n observtd tangent
W t' repon the dctco.:tion of two new species, A1 and .;oJumn Jen~ily (j( 2,4 x 10': ~m-;, and Fe, measur",d
Fc, in Mercury's ex()~phere, and the c()nlinnation PI' at 6 2 x 109 ~lll-? In addition, important clue~ lO the
Ca' pbysical pr,)ccSS(S at \vork arc given by the altitude
distributions ;)f tht'sc dements the very low,
2. Aluminum d..:ereilsing Jt'n~ity <If AJ argues t~)r a mokcular
source, while the high, increasing J(nsity of Fe
Aluminum has been observed at the Kcck I tdes(\)pc implies a reduced SUrra(,; density compared v'
using the I1iRES high-rcsolu!i(lf) sptelromCler A mudeh and significant secondary production from
zcnith column <'1' (1.4 • 2) x JU7 cnf" was inferred molecular dissociation
Bidj and Killen 15], assuming a temperature of
Acknowledgements
This. re~ellfch Wih supp<)rted by a gram fronJ :-.Jf\;;'A
Planetary ;\stmnomy (fAll) and by the NASA.
Participating Scientist Program (RMK), The ground·
bused data wen: obtained at the \Y.M Ked;:
Obsc[vatuy, whieh i~ operated in a partncrship
bettveen the California Institute of fcchnology. the
Cnh-crsily \If Cctlihmlia, and k\SA
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