Mercury Science Goals, Objectives and Investigations - Version 1.0

Author: Stephen, Parman; Ernst, Carolyn; Dewey, Ryan; DiBraccio, Gina; Kinczyk, Mallory; Klimczak, Christian; Plattner, Alain; Raines, Jim; Vervack, Ron; Wright, Jack

Publisher: Zenodo

DOI: 10.5281/zenodo.17664618

Source: https://zenodo.org/records/17664618/files/MExAG_Science_Goals_V1.0.pdf

Me cu y Science Goals, Objec i es, and
In es iga ions
Me cu y Explo a ion Assessmen G oup (MExAG)
Ve sion 1.0
Ve sion eleased on Sep embe 3 d, 2025
The MExAG Science Goals, Objec i es, and In es iga ions documen is he ﬁ s o h ee MExAG goals
documen s: Science, Technology, and Communi y. This documen is ecommended o be ci ed as:
“The Me cu y Explo a ion Assessmen G oup Science Goals, Objec i es, and In es iga ions, MExAG
(2025). Ve sion 1.0, XX pp., <inse LPI Link>”.
The pu pose o his documen is o p o ide an o e iew o he science goals o he MExAG communi y
o unde s anding and explo ing Me cu y. The in ended audiences o he documen a e: (1)NASA, as a
means o communica ing he communi y-d i en goals, and (2) he plane a y science communi y, as a
mechanism o sha ing knowledge abou impo an hemes o unde s anding and explo ing Me cu y.
This documen will be upda ed e e y h ee yea s, o main ain ele ance and u ili y. Communi y membe s
wishing o p o ide inpu can do so a any ime by emailing me[email p o ec ed].
The science goals we e de ised by he MExAG S ee ing Commi ee a e communi y discussions du ing
he Feb ua y 2021 MExAG Annual Mee ing. This documen was concep ualized and compiled be ween
2022 and 2025 by he MExAG Goals Wo king G oup, including con ibu ions om many membe s o he
MExAG and Me cu y science communi y. The ex was edi ed by he MExAG Science Goals Wo king
g oup and MExAG s ee ing commi ee eleased o commen by he communi y in Janua y 2025.
Communi y commen s we e inco po a ed and he ﬁnal documen (Ve sion 1.0) was eleased on Augus
1, 2025.
Cu en and P e ious MExAG Goals Wo king G oup Membe s:
Ryan Dewey, Gina DiB accio, Ca olyn E ns , Mallo y Kinczyk, Ch is ian Klimczak, S ephen Pa man, Alain
Pla ne , Jim Raines, Ron Ve ack, Jack W igh
Con ibu o s:
Sae Aizawa, B endan Anzu es, Da id Bake , Jeﬀ Balce ski, Océane Ba aud, Sébas ien Besse, Paul
By ne, Nancy Chabo , Cla k Chapman, Ma Clemen , Kelsey C ane, Gab iele C emonese, B e Dene i,
A iel Deu sch, Ryan Dewey, Ma hieu Dumbe y, Nick Dyge , Den on Ebel, Ca olyn E ns , Caleb Fasse ,
Sande Goossens, S e en Hauck, Robe He ick, Daniel Heyne , Lon Hood, Dana Hu ley, Suzanne
Imbe , Pe e James, Xianzhe Jia, Ca he ine Johnson, Rosema y Killen, Mallo y Kinczyk, Misha
K esla sky, Lau a La k, Da id Law ence, F ancois Leblanc, Vale ia Mangano, Simone Ma chi, Elena
Ma ella o, E wan Maza ico, Tim McCoy, Jeﬀ Mo gen hale , Liam Mo issey, Megan Mouse , La y Ni le ,
S ephen Pa man, Michael Phillips, Alain Pla ne , Gangkai Poh, Pe Poko ný, Anne Pommie , Pa a hy
P em, Jim Raines, Edga d Ri e a-Valen in, Da e Ro he y, Daniel Sa in, Ca l Schmid , Jim Sla in, G ego
S einb ügge, Weijie Sun, Nicola Tosi, Ron Ve ack, Thomas Wa e s, Shoshana Weide , Jack W igh
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MExAG Science Goals
O e iew
The documen is s uc u ed in o goals and objec i es, wi h objec i es b oken in o se e al mo e-speciﬁc
sub-objec i es. The goals a e he high-le el ou comes o be achie ed and should emain ai ly s able
o e ime. The objec i es iden i y s a egies o achie e he goals. The objec i es a e in ended o be
b oad, so ha he ways in which hey can be conduc ed a e no o e ly cons ained. Once he
Technology Goals Documen has been published, he in en ion is o e ise he Science Goals documen
o include speciﬁc in es iga ions. These in es iga ions will desc ibe speciﬁc missions o s udies ha
could be unde aken o achie e an objec i e. Goals and objec i es a e lis ed in he ou line below.
Goal 1 is ocused on how Me cu y can be used o add ess scien iﬁc ques ions abou ou sola sys em
and beyond. I demons a es how Me cu y is a keys one o unde s anding he o igin and
e olu ion o ou sola sys em, he plane s wi hin i , and he p ocesses ha aﬀec hem.
Goals 2–4 a e mo e di ec ly ocused on unde s anding he e olu ion o Me cu y i sel . These goals
include all aspec s o Me cu y’s o ma ion and e olu ion, and a e in ended o be a comp ehensi e
esou ce o p opose s.
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MExAG Science Goals
Ou line
Documen
Goals
Objec i es
Science
1) Es ablish Me cu y’s con ex in ou
sola sys em and beyond
1.1) Use Me cu y’s uniqueness as a composi ional and physical
end-membe o cons ain he o ma ion o he sola sys em
1.2) Apply ou knowledge o Me cu y o unde s and o he plane a y
bodies and ice e sa
1.3) In o m ou unde s anding o ocky exoplane s
2) Unde s and he o igins o
Me cu y, om acc e ion o
solidiﬁca ion
2.1) In es iga e composi ional building blocks
2.2) Explo e o ma ion scena ios
2.3) Unde s and global diﬀe en ia ion/e olu ion
3) Cha ac e ize Me cu y’s e olu ion
since solidiﬁca ion
3.1) S udy pas geological p ocesses
3.2) Unde s and p ocesses behind he chemical and mine alogical
di e si y o he c us
3.3) In es iga e he o igin and e olu ion o he pola deposi s
3.4) Explo e he his o y o he in insic magne ic ﬁeld
3.5) In e long- e m eﬀec s o a ia ions in exosphe ic and
magne osphe ic sou ce and loss mechanisms
4) In es iga e p ocesses cu en ly
ongoing a Me cu y
4.1) Cha ac e ize p esen -day geologic ac i i y
4.2) In es iga e magne osphe ic dynamics
4.3) Unde s and exosphe ic and magne osphe ic sou ce and loss
p ocesses
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MExAG Science Goals
Table o con en s (click on opic o go o ex )
Ou line 4
Execu i e Summa y 8
Abb e ia ions 9
1. Es ablish Me cu y’s con ex in ou sola sys em and beyond 10
1.1 Use Me cu y’s uniqueness as a composi ional and physical end-membe o cons ain he
o ma ion o he sola sys em 10
a) Cosmochemis y: Is Me cu y he missing piece? 10
b) Dynamics o he p o oplane a y disk: Why is Me cu y so small and so dense? 10
1.2 Apply ou knowledge o Me cu y o unde s and o he plane a y bodies and ice e sa 10
a) Obse ed su ace geology 10
b) Impac c a e ing eco d and ﬂux 11
c) Pola deposi s 12
d) Exosphe ic and magne osphe ic p ocesses 12
e) Co e s uc u e and e olu ion 13
1.3 In o m ou unde s anding o ocky exoplane s 14
a) Me cu y as an exoplane 14
b) Exoplane exosphe es and magne osphe es 14
2. Unde s and he o igins o Me cu y, om acc e ion o solidiﬁca ion 15
2.1 In es iga e composi ional building blocks 15
a) Unde s anding me eo i ic con ibu ions 15
b) O igin and e en ion o ola iles du ing o ma ion 16
c) Cons ain s on bulk composi ion om su ace chemis y 16
2.2 Explo e o ma ion scena ios 17
a) Dynamics o ea ly acc e ion o ma e ials (dus o plane esimals) 17
b) O igin scena ios (plane esimal collisions, o bi mig a ion and la ge co e/man le a io) 17
c) Vola ile eco d (be o e and a e gas loss om he inne disk) 18
2.3 Unde s and global diﬀe en ia ion/e olu ion 18
a) Ini ial diﬀe en ia ion (co e and man le) 18
b) Solidiﬁca ion o he magma ocean and p oduc ion o a p ima y c us 19
c) Co e s uc u e and dynamics du ing magma ocean solidiﬁca ion 20
3. Cha ac e ize Me cu y’s e olu ion since solidiﬁca ion 20
3.1 S udy pas geological p ocesses 20
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MExAG Science Goals

a) C a e ing eco d 20
b) Timing and s yles o olcanism 21
c) Timing and s yles o ec onics 22
d) Rela ionships be ween olcanism, ec onism, ola iles 23
e) Long-wa eleng h opog aphy 23
) S uc u e o he c us and li hosphe e 24
g) Hea ﬂow 24
h) Regoli h o ma ion and mixing 25
3.2 Unde s and p ocesses behind he chemical and mine alogical di e si y o he c us 25
a) Geochemical a ia ions 25
b) Va ia ions in mine alogy 26
c) In e io ola iles 27
d) Low- eﬂec ance ma e ial 27
e) Low c us al i on 27
3.3 In es iga e he o igin and e olu ion o he pola deposi s 28
a) Dis ibu ion and olume 28
b) Composi ion 28
c) Vola ile anspo 29
3.4 Explo e he his o y o he in insic magne ic ﬁeld 30
a) Remanen magne ism 30
b) Dipole ﬁeld s eng h 31
3.5 In e long- e m eﬀec s o a ia ions in exosphe ic sou ce and loss mechanisms 31
a) O igin o he exosphe e 31
b) Space wea he ing p ocesses and a es 32
4. In es iga e p ocesses cu en ly ongoing a Me cu y 33
4.1 Cha ac e ize p esen -day geologic ac i i y 33
a) P esen -day c a e ing a e 33
b) Recen /cu en olcanic ac i i y 33
c) Recen /cu en ec onic ac i i y 34
d) Hollows 35
e) Pola deposi s 35
4.2 In es iga e magne osphe ic dynamics 36
a) Gene a ion o he cu en magne ic ﬁeld 36
b) Magne ic econnec ion 37
c) Induc ion eﬀec s 38
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MExAG Science Goals
d) Dawn-dusk asymme ies 38
e) Magne osphe ic cu en s 39
) Flux ope o ma ion 40
g) Eﬀec o sola e en s on he sys em 40
4.3 Unde s and exosphe ic and magne osphe ic sou ce and loss p ocesses 41
a) Magne osphe ic ions 41
b) Dis ibu ions o neu al and ionized species and hei empo al / spa ial a ia ions 42
5. Re e ences 44
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MExAG Science Goals
Execu i e Summa y
The ongoing ad ances in cosmochemis y and plane o ma ion dynamics places Me cu y ﬁ mly a he
cen e o unde s anding how ou sola sys em o med. I s composi ion is likely a key geochemical
end-membe in he sola sys em, bu i is as ye unsampled. Measu ing i s composi ion would no only
e olu ionize ou unde s anding o Me cu y’s o ma ion, bu also shed ligh on he makeup o he Ea h
and o he plane s, he o igin o li e-essen ial ola iles in he inne sola sys em, and how plane s acc e ed
in he ea ly p o oplane a y disk.
As he closes plane o he Sun, Me cu y p o ides a unique an age poin o s udy a ange o key
plane a y p ocesses, including: acc e ion in he p o oplane a y disk, pas and cu en c a e ing a es,
space wea he ing, and ola ile deli e y o he inne plane s. I s p oximi y o he Sun also p o ides a
unique window in o many exoplane s, a subs an ial ac ion o which o bi as close, o close , o hei
hos s a s han Me cu y. Due o i s p oximi y o he Sun, Me cu y o med in an oxygen-poo , ca bon- ich
en i onmen , dis inc om all o he e es ial plane s. Many exoplane s also o med in such low-oxygen
condi ions, making Me cu y uniquely sui ed o unde s anding hei o ma ion and e olu ion. Me cu y is
uly an ‘exoplane in ou backya d’.
The la ge ( ela i e) size o Me cu y’s co e is also unique wi hin he sola sys em. The co e p oduces
a global magne ic ﬁeld ha leads o complex in e ac ions be ween he Sun and he plane ’s su ace. This
in e ac ion p o ides insigh s in o he dynamics o plane a y magne osphe es, exosphe es, and space
wea he ing.
Su p isingly, he e is hough o be mo e wa e ice on Me cu y han on he Moon. As wi h he
Moon, i has been ound in pe manen ly shadowed egions o c a e s a Me cu y’s poles, bu in
Me cu y’s case, he e a e ac ually la ge a eas o exposed ice. How and when his ice o med is
unknown, bu i is clea ly a unique eco d o ola ile deli e y and deposi ion in he inne sola sys em.
By ad ancing he unde s anding o Me cu y, key con ibu ions o many o he P io i y Science Ques ions
iden iﬁed in he Na ional Academies O igins, Wo lds, and Li e Decadal Su ey* will be made, including:
Q1) E olu ion o he p o oplane a y disk, Q3) O igin o he Ea h and inne sola sys em bodies, Q4)
Impac s and dynamics, Q5) Solid body in e io s and su aces, Q6) Solid body a mosphe e, exosphe es,
magne osphe es and clima e e olu ion, and Q12) Exoplane s.
* Na ional Academies o Sciences, Enginee ing, and Medicine. 2023. O igins, Wo lds, and Li e: A
Decadal S a egy o Plane a y Science and As obiology 2023-2032. Washing on, DC: The Na ional
Academies P ess. h ps://doi.o g/10.17226/26522.
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MExAG Science Goals
Abb e ia ions
CSFD - c a e size equency dis ibu ion
CMB - co e man le bounda y
ESD - elec on s imula ed deso p ion
EUV - ex eme ul a iole
FAC - ﬁeld-aligned cu en
O2 - oxygen ugaci y
FR - ﬂux ope
S - sul u ugaci y
FTE - ﬂux ans e e en
GRAIL - G a i y Reco e y And In e io Labo a o y (mission)
HMR - high magnesium egion
ICME - in e plane a y co onal mass ejec ion
IMF - in e plane a y magne ic ﬁeld
IW - I on-wüs i e oxygen buﬀe
IR - in a ed
JWST - James Webb Space Telescope
KPLO - Ko ea Pa hﬁnde Luna O bi e (mission)
LCROSS - Luna CRa e Obse a ion and Sensing Sa elli e (mission)
LRM - low- eﬂec ance ma e ial
MASCS - Me cu y A mosphe ic and Su ace Composi ion Spec ome e (ins umen )
MDIS - Me cu y Dual Imaging Sys em (ins umen )
MDM - Me cu y Dus Moni o (ins umen )
MERTIS - ME cu y Radiome e and The mal In a ed Spec ome e (ins umen )
Mio - Me cu y Magne osphe ic O bi e (mission)
MORE - Me cu y O bi e Radio-science Expe imen (ins umen )
MPO - Me cu y Plane a y O bi e (spacec a )
MESSENGER - ME cu y Su ace, Space EN i onmen , GEochemis y and Ranging (mission)
NEO - nea -Ea h o bi
PSD - pho on s imula ed deso p ion
PSR - pe manen ly shadowed egion
SEP - sola ene ge ic pa icle
SIMBIO-SYS - Spec ome e and Imaging o MPO BepiColombo In eg a ed Obse a o y SYS em
(ins umen )
UVVS - Ul a iole and Visible Spec ome e (ins umen )
VISTIR - isible- o- he mal in a ed
VNIR - isible- o-nea -In a ed
XRF - X- ay ﬂuo escence
XRS - X-Ray Spec ome e (ins umen )
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MExAG Science Goals
b) O igin and e en ion o ola iles du ing o ma ion
To explain many o Me cu y’s unusual ea u es, including i s high bulk-Fe con en , many models
in oke a high- empe a u e o ma ion o he plane , and he e o e p edic a ola ile-deple ed composi ion.
MESSENGER esul s demons a ed, howe e , ha Me cu y appea s no o be ola ile deple ed. Fo
example, i s K/Th a io ( ola ile elemen /non- ola ile elemen ) is he same as ha o Ea h and Ma s. In
addi ion, Me cu y’s su ace is ich in S, Na, and Cl, and py oclas ic deposi s (d i en by ola iles) abound.
How Me cu y e ained i s ola iles while o ming so close o he Sun is no unde s ood. I may be due o
changing geochemical beha io unde educing condi ions whe e nominally li hophile elemen s become
mo e chalcophile and side ophile (McCubbin e al. 2012; Wohle s and Wood 2015; Boujiba e al. 2019;
Pi o e e al. 2023; McCubbin and Anzu es 2025). Reduced ens a i e chond i es a e also en iched in
mode a ely ola ile li hophiles such as Na and K (Fogel e al. 1989; Keil 2010; Weisbe g and Kimu a
2012; Wilbu e al. 2022; Hammouda e al. 2022). Be e analysis o mode a ely ola ile elemen s
on Me cu y’s su ace, as well as mo e de ailed s udies o ola iles in educed me eo i es, will
p o ide insigh in o how he inne mos plane e ained i s ola ile- ich su ace.
The specia ion o ola ile elemen s du ing Me cu y’s o ma ion would ha e depended on
condi ions in he ea ly ho inne disk. Modeling and expe imen s on ola ile pa i ioning and specia ion a
ele an condi ions would help o de e mine hei chalcophile/li hophile cha ac e and how e ac o y hei
hos solids a e as a unc ion o O2. P elimina y calcula ions indica e ha a leas some elemen s (S, Cl,
K) become mo e e ac o y in sola -sys em apo en iched in ca bon (low O2) (Ebel and Sack, 2013). A
landed mission wi h he abili y o analyze ola ile elemen concen a ions in-si u would
p o ide in aluable insigh in o he building blocks o Me cu y. Addi ionally, a sample e u n
mission would allow de ailed iso opic analysis o ola ile elemen s as well as analysis o ola iles in
polyc ys alline ma e ial.
c) Cons ain s on bulk composi ion om su ace chemis y
As wi h all o he e es ial plane s, he bulk composi ion o Me cu y mus be in e ed om a combina ion
o geophysical measu emen s (some o which can sample o he cen e o he plane ), geochemical
measu emen s (which a e es ic ed o he su ace), and labo a o y expe imen s a ele an p essu e and
empe a u e (P, T) alues and composi ions (Ni le e al., 2018; Ca ie and Wood, 2019). Geologic
p ocesses, including c a e ing and aul ing, can exhume ma e ial om dep h, allowing di ec analysis o
in e io ma e ials. Howe e , much o ou unde s anding o he in e io composi ion o plane s, including
hei o e all bulk composi ion, comes om he analysis o e up ed la as combined wi h unde s anding o
mel ing p ocesses h ough expe imen s and he modynamic modeling (Cha lie e al., 2013; Namu e
al., 2013, 2016a; Boujiba e al., 2014, 2025). Thus, imp o ed analysis o he composi ion o
Me cu y’s su ace, in bo h spa ial esolu ion and accu acy o geochemical and mine alogical
measu emen s, will di ec ly lead o imp o ed cons ain s on he composi ional s uc u e o he
plane ’s in e io .
Landed missions wi h he capabili y o analyze majo and ace elemen composi ion, mine alogy, and
iso opic composi ion, would p o ide a huge leap o wa d in ou unde s anding o Me cu y’s su ace
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MExAG Science Goals

chemis y. Key a ge s migh be a eas whe e ma e ial om dep h is exhumed by impac c a e s and
a eas whe e la a ﬂows wi h a ange o composi ions could be accessed wi h a o e . Me cu y’s
high-magnesium egion (HMR) could also be a key a ge o a landed mission as i may ep esen pa o
he man le exhumed by an ea ly, la ge, impac o an a ea co e ed by highly-magnesian (and sul u - ich)
la as (Weide e al., 2015). Landed missions would also p o ide c i ical ‘g ound u h’ o emo ely
sensed composi ional and mine alogical da ase s.
High-p essu e expe imen s will also be key o in e p e ing he su ace composi ional and mine alogical
a ia ions, bu o da e, ela i ely ew expe imen s ha e been conduc ed unde Me cu y- ele an
condi ions. Expe imen s explo ing a wide ange o composi ions, O2, and ola ile con en s a e hus
equi ed. As he magmas undoub edly unde wen cooling and ac iona ion as hey mig a ed om he
man le o he su ace, models o how me cu ian magmas would diﬀe en ia e a e also needed. A ange o
man le composi ions, magma ocean solidiﬁca ion scena ios, and mel ing models should be explo ed
h ough a combina ion o expe imen s, he modynamic modeling, and physical modeling o mel ing
p ocesses.
2.2 Explo e o ma ion scena ios
a) Dynamics o ea ly acc e ion o ma e ials (dus o plane esimals)
Unde s anding he dynamics o acc e ion— om dus , o plane esimals, o plane s—is c i ical
o cons aining he building blocks o Me cu y. Mos dynamical collision models p edic Me cu y
should ha e a subs an ially la ge mass and a less inclined/eccen ic o bi (Nes o ny e al., 2021; Woo e
al., 2022; Clemen e al., 2023). The mass deﬁci and o bi a e explained by pos - o ma ion s ipping o
mass by one o mo e la ge collisions o by he inwa d mig a ion o Me cu y om a he ou in he disk.
Each o hese models has implica ions o he composi ion o Me cu y, he iming o i s o ma ion, and
he size o he o he e es ial plane s. Imp o ed dynamical models a e hus needed ha explo e longe
pe iods o ea ly sola sys em e olu ion, mo e ealis ic collision physics, and he eﬀec s o mass-deple ed
zones wi hin he disk.
b) O igin scena ios (plane esimal collisions, o bi mig a ion and la ge co e/man le a io)
Me cu y’s la ge co e, diminu i e mass, and dynamically isola ed o bi a e a ely ep oduced in
e es ial acc e ion models (Chambe s, 2001; Clemen e al., 2023; Lykawka and I o, 2023) and
ha e long been in e p e ed o imply a unique o ma ion his o y (Mo gan and Ande s, 1980; Chapman,
1988). Me cu y’s mys e ious o igin is e en mo e enigma ic when iewed wi hin he con ex o nume ous
exoplane sys ems; as many as 50% o Sun-like s a s possess >Ea h-mass plane s wi h o bi al pe iods
much less han ~100 days (Howa d e al., 2012; Pe igu a e al., 2018). In ligh o MESSENGER’s
ﬁndings, wo b oad classes o models aiming o explain Me cu y’s la ge co e mass ac ion emain iable.
In he ﬁ s , he man le o a p imo dially la ge Me cu y is s ipped in one o mo e iolen collisions wi h
ano he p o o-plane (a “chao ic” o igin: Benz e al., 2007; Asphaug and Reu e , 2014). Howe e , in such
an e en , Me cu y would likely e-acc e e subs an ial amoun s o he los ma e ial (Gladman and Coﬀey,
2009). Mo eo e , such an e en would equi e imp obably la ge impac eloci ies (Jackson e al., 2018).
17
MExAG Science Goals
In he al e na i e class o models, Me cu y o ms wi hin a ese oi o objec s wi h Fe/Si a ios ha a e
boos ed as a esul o a p ocess ha diﬀe en ially aﬀec ed he in an Sun’s p o oplane a y disk (an
“o de ly” o igin: Ebel and Alexande , 2011; Wu m e al., 2013; K uss and Wu m, 2018; Johansen and
Do n, 2022). Howe e , i emains diﬃcul o en ision how his p ocess only aﬀec ed Me cu y because o
he high deg ee o mixing known o occu du ing he epoch o e es ial plane o ma ion (Raymond e
al., 2006; Woo e al., 2022).
An “o de ly” o igin o Me cu y axioma ically implies ha i o med much close o he Sun, wi hin a
diﬀe en ese oi o ma e ial han Ea h and Venus. In con as , he mos likely impac scena io would be
one whe e Me cu y o igina ed in he icini y o Ea h and Venus, and was sca e ed ou o he egion a e
i s co e mass ac ion was al e ed (Clemen e al., 2019; F anco e al., 2022; Izido o e al., 2022). Thus,
imp o ed cons ain s on he age o Me cu y’s su ace and i s bulk and iso opic composi ions
om high- esolu ion su ace images, in-si u lande measu emen s, and/o age-da ing o
e u ned samples o he oldes c us could b eak degene acies be ween hese models. I is
also possible ha an as-ye uniden iﬁed me cu ian me eo i e cu en ly exis s in ou collec ion. Indeed,
he e a e undiﬀe en ia ed me eo i es wi h simila ly low O2 whose o igins emain mu ky (Ebel and
Alexande , 2011; Weisbe g and Kimu a, 2012), and in-si u elemen al and iso opic measu emen s could
be used o es ablish such a link.
c) Vola ile eco d (be o e and a e gas loss om he inne disk)
Me cu y is su p isingly ola ile- ich bo h in i s in e io (Peplowski e al., 2012). The in e io
composi ion indica es ha Me cu y e ained ola iles h oughou i s o ma ion and solidiﬁca ion, despi e
i s p oximi y o he Sun. Expe imen s on ola ile solubili y in man le and co e phases a e needed, as well
as physical models o magma ocean diﬀe en ia ion, o cons ain how Me cu y could ha e e ained i s
ola iles. Analysis o samples on he su ace would cons ain how much o Me cu y’s ola ile in en o y
was los , as well as hei dis ibu ion in he in e io , bo h in he silica e and me allic po ions o he plane .
Imp o ed models o he ea ly e olu ion o Me cu y’s magne ic ﬁeld a e also needed o cons ain he
ex en o which i could ha e shielded Me cu y om ola ile s ipping by he Sun (Johnson e al., 2015).
2.3 Unde s and global diﬀe en ia ion/e olu ion
a) Ini ial diﬀe en ia ion (co e and man le)
Models o he o ma ion o Me cu y’s co e a e s ongly linked o he o ma ion o Me cu y i sel . I
Me cu y o med di ec ly om me al- ich building blocks, hen he e was li le man le o he co e- o ming
me al o eac wi h, possibly p omo ing a man le and co e ha a e no in chemical equilib ium wi h each
o he . Whe eas i Me cu y we e la ge , hen co e- o ma ion p ocesses may ha e been simila o hose
hypo hesized o Ea h, whe e he a e se o me al h ough a sizable man le induced equilib ium, a leas
a he s a (T ønnes e al., 2019).
T aces o Me cu y’s ini ial diﬀe en ia ion should be eco ded in he composi ion o
Me cu y’s man le (and la as), in hei ace elemen s and iso opic composi ions, including o he
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MExAG Science Goals
side ophile elemen s, as well as W, Si, and Fe iso opes (Righ e , 2003; Hel ich e al., 2019).
Measu emen s ei he in si u o on e u ned samples would hus p o ide aluable insigh s in o co e
o ma ion on Me cu y. Expe imen al s udies o cons ain pa i ioning o hea -p oducing elemen s
be ween man le and co e analogs a p essu e and empe a u e condi ions ele an o Me cu y a e
needed o in e p e he geochemical obse a ions and p o ide aluable insigh s in o co e o ma ion
(Boujiba e al., 2019; Pi o e e al., 2023). Geophysical cons ain s on he size o he co e and pu a i e
inne co e, as well as he co e densi y also in o m o ma ion models, because hey help cons ain he
concen a ions o he ligh elemen s in he co e (e.g. S, Si, C) and hea loss. Imp o ed geodynamic
models a e needed o unde s and he po en ial eﬀec s o Me cu y’s hin man le on co e seg ega ion.
These should include he eﬀec s o low O2 on he physical p ope ies o silica e mel s (Anzu es e al.,
2020; Mouse e al., 2021; Pommie e al., 2023) and me allic mel s (e.g., Pommie e al., 2019; Be ada
e al., 2022).
b) Solidiﬁca ion o he magma ocean and p oduc ion o a p ima y c us
The solidiﬁca ion o Me cu y’s magma ocean es ablished i s ini ial in e nal s uc u e and se
he s age o i s subsequen e olu ion. Due o he high-S and low-Fe solubili y in he magma ocean,
and he p esence o C, he solidiﬁca ion and diﬀe en ia ion o Me cu y’s magma ocean is e y diﬀe en
om ha o he Moon (Bouka é e al., 2019). Cons aining wha phases o med om Me cu y’s magma
ocean, as well as hei chemical and physical p ope ies (Anzu es e al., 2020; Mouse e al., 2021;
Pommie e al., 2023), is key o add essing se e al ques ions abou Me cu y’s ea ly e olu ion, including:
Did g aphi e and/o Ca-Mg sulﬁde ﬂoa o o m a p ima y c us (Vande Kaaden and McCubbin, 2015)?
A e sulﬁdes abundan in he man le (La k e al., 2022)? Was he e enough densi y inc ease du ing
ac iona ion o d i e subsequen o e u n, as sugges ed o he Moon (Mouse and Dyge , 2023)? Did
he ini ial laye ing p oduced by magma ocean solidiﬁca ion su i e o p oduce he a ie y o magmas
seen on Me cu y’s su ace, o was i homogenized by con ec ion (Cha lie e al., 2013)?
Expe imen s unde Me cu y- ele an condi ions a e needed o cons ain how Me cu y’s magma ocean
diﬀe en ia ed. C i ical measu emen s include phase composi ions as well as hei physical p ope ies
(e.g., densi y, elec ical and he mal conduc i i y, iscosi y, su ace ene gy), whe e i is c i ical o
unde s and he beha io o silica e magmas unde highly educing condi ions. Models o c ys al/mel
sepa a ion in he magma ocean a e needed o deﬁne laye ing and mel e en ion in he man le.
Geophysical measu emen s (e.g., g a i y, opog aphy, shape, and hea ﬂow) can cons ain cu en
man le densi y and s uc u e, which may help o in o m magma ocean models. New measu emen s o
la a composi ion o la as (majo / ace elemen s and iso opic) and di e si y would g ea ly inc ease ou
unde s anding o how he magma ocean o med and c ys allized.
c) Co e s uc u e and dynamics du ing magma ocean solidiﬁca ion
Once Me cu y’s co e o med, subsequen cooling was con olled by hea loss h ough he co e–man le
bounda y (CMB) and in e nal hea p oduc ion. As he magma ocean cooled and solidiﬁed, he co e
would ha e esponded o he changing bounda y condi ions, which would ha e aﬀec ed he he mal
g adien and he possible o ma ion o a sulﬁde- ich laye a he CMB (Smi h e al., 2012). Such a laye
19
MExAG Science Goals
migh ha e inco po a ed some amoun o adioac i e hea -p oducing elemen s (U, Th, K) in he sulﬁdes
(Bouka é e al., 2019; Pi o e e al., 2023). Howe e , cooling models o he plane showed ha his FeS
laye should ha e negligible eﬀec s on co e dynamics and he magne ic ﬁeld (Da ies e al., 2024).
Fu u e obse a ions om BepiColombo will help o imp o e ou exis ing models o co e
con ec ion, and u he ou unde s anding o he e y ea ly s ages o Me cu y’s co e. Be e
cha ac e iza ion o he iming and ex en o plane con ac ion may cons ain he ea lies co e his o y. The
disco e y o a c us al magne ic ﬁeld spa ially associa ed wi h Calo is Plani ia may indica e magne ic
emanence acqui ed du ing he Calo is impac (3.8 o 3.9 Ga) and ha he co e ﬁeld was ac i e ea ly in
Me cu y’s his o y (Johnson e al., 2015). Combined geoch onologic and paleomagne ic analysis o
mine als (e.g., zi con) o ock agmen s in egoli h, ei he in si u o in a e u ned sample, could cons ain
he ea ly e olu ion o he co e. S udies o emnan magne ism in he c us and de e mina ion o i s
geological con ex could u he elucida e he his o y o Me cu y’s dynamo.
3. Cha ac e ize Me cu y’s e olu ion since solidiﬁca ion
3.1 S udy pas geological p ocesses
a) C a e ing eco d
A ue unde s anding o Me cu y’s impac ﬂux h ough ime, which o ms he basis o Me cu y’s
ch onology (Spudis and Gues , 1988), equi es measu ing he absolu e age om a known geological
e ain on Me cu y ia in si u age da ing o sample e u n. In he absence o such measu emen s, ou
unde s anding is ex apola ed om he Moon, compensa ing o Me cu y’s dis inc g a i y and impac
eloci y. Obse ed p ima y c a e size equency dis ibu ions (CSFDs) a e ansla ed in o a p oduc ion
unc ion and absolu e ch onology h ough assumed models o impac ﬂux and c a e scaling
ela ionships (e.g., Spudis and Gues , 1998; Ma chi e al., 2009; Le Feu e and Wieczo ek, 2011). The
iming o geological e en s, including s a ig aphic ma ke s like Tols oj and Calo is, can be signiﬁcan ly
aﬀec ed by wha models a e used (e.g., Dene i e al., 2018). Fu he , seconda y c a e s may con amina e
he CSFDs o diame e s <10 km (Bie haus e al., 2018). Thus, c a e -based da ing o he younges o
smalles uni s and unde s anding o he p ima y impac ﬂux ha elies on hese small c a e sizes
equi es an unde s anding o seconda y c a e p oduc ion and dis ibu ion.
To imp o e knowledge o Me cu y’s impac ﬂux h ough ime, one aim is o s udy he
cha ac e is ics and dynamics o small-body popula ions in he sola sys em, o unde s and he
sou ces o he impac o s. Fu he esea ch on luna and ma ian ch onology, along wi h heo e ical
s udies o he e olu ion o small-body popula ions in he sola sys em, could na ow he unce ain ies
conce ning Me cu y’s geological e olu ion. De ailed sea ches, especially by spacec a o bi ing nea
Me cu y, o small body popula ions in e io o Me cu y’s o bi would de e mine he po en ial ole o such
impac o s in aﬀec ing he changing a e o c a e o ma ion on he plane . Geophysical and geochemical
20
MExAG Science Goals
s udies could shed ligh on he eﬀec ha basin- o ming impac s ha e on modi ying he geological and
geochemical cha ac e is ics o he su ace.
Ano he aim is o be e cha ac e ize p ima y c a e -size equency dis ibu ions and he
con ibu ion o seconda y c a e s o he c a e ing eco d. By in es iga ing he mo phology o small
impac c a e s and he a ia ions in pos - o ma ion modiﬁca ion p ocesses, we may be e unde s and
he diﬀe ences in he seconda y c a e dis ibu ion on Me cu y compa ed wi h o he bodies such as he
Moon. Addi ionally, he spa ial a ia ion o c a e modiﬁca ion will elucida e he p ocesses ha ha e
shaped diﬀe en pa s o he su ace. High- esolu ion o bi al images and digi al e ain models o e a
la ge pe cen age o he su ace, such as will be acqui ed om SIMBIO-SYS on he BepiColombo
mission (Da Deppo e al., 2017; C emonese e al., 2020), will allow de ailed cha ac e iza ion o c a e
mo phology and imp o e he abili y o iden i y seconda y c a e s.
To imp o e Me cu y-speciﬁc c a e scaling models, an aim is o be e unde s and he composi ional and
physical a ibu es o he su ace (s eng h, bulk densi y, po osi y, laye ing) and how hey change la e ally
ac oss he su ace and as a unc ion o dep h (e.g., Geno a e al., 2021). O bi al spec oscopic
obse a ions and in si u sample analysis would imp o e ou unde s anding o he composi ion o he
su ace and i s in e ed mechanical p ope ies. Expe imen al and nume ical impac s udies would also
imp o e models o how a ge p ope ies, highe p ojec ile eloci ies, and highe a ge empe a u es
migh aﬀec c a e size.
b) Timing and s yles o olcanism
An aim is o be e unde s and he composi ion, ola ile con en , and specia ion ha d o e he
esicula ion, e up ion, and iming o olcanic deposi s ac oss Me cu y. Volcanic deposi s on
Me cu y a e gene ally cha ac e ized as ei he smoo h plains o explosi e/py oclas ic deposi s. Smoo h
plains occupy abou a qua e o he plane 's su ace. The as majo i y by olume o hese uni s we e
emplaced as eﬀusi e olcanic p oduc s by ~3.5 billion yea s ago. Subsequen ly, global con ac ion
appea s o ha e supp essed la ge eﬀusi e olcanic episodes (By ne e al., 2016). Some deposi s ha e
mo phological and spec al cha ac e is ics o la as, whe eas o he s may be ponded impac mel (Dene i
e al., 2013). Many smoo h plains uni s a e colloca ed wi h impac ea u es, sugges i e o a causal
ela ionship (By ne e al., 2018b) ha needs o be u he in es iga ed. O he aims a e o iden i y i he
spec al cha ac e is ics o smoo h plains ha e sys ema ic empo al o spa ial a ia ions, and e up ion
a es and composi ions.
Py oclas ic deposi s ha e been ound o be long-li ed, wi h some o hem less han 1 billion yea s old
(Thomas e al., 2014b), bu he e is an in iguing pauci y o cons uc ional olcanic ea u es such as
shield o cone-like olcanoes (W igh e al., 2018). De e mining he iming, a e, and ola ile
specia ion o explosi e olcanic e up ions and how hey con inued a e he cessa ion o
majo eﬀusi e ac i i y and he onse o global con ac ion is an impo an aim. Ca bon and
sul u in such deposi s a e deple ed ela i e o Me cu y’s su ace (Weide e al., 2016), which has been
in e p e ed as indica ing ha C and S we e he d i ing ola ile species, bu he key species ha d o e he
explosi e olcanism s ill emain o be conﬁ med (Iaco ino e al., 2023).
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MExAG Science Goals

To achie e hese aims, high- esolu ion images and spec al da a, oge he wi h de ailed mapping o uni
supe posi ion and onlap ela ions and imp o ed c a e p oduc ion models o Me cu y, a e
equi ed—some o which will be p o ided by BepiColombo (C emonese e al., 2020; Bunce e al., 2020;
Hiesinge e al., 2020). Mo eo e , mo e expe imen s a e needed o cons ain he solubili y o ola iles in
magmas a ele an composi ions and O2 and wha gas species magmas would emi as hey e up .
New he modynamic models o low- O2 and high-sul u - ugaci y ( S) condi ions will need o be
de eloped. Ul ima ely in si u geochemical and geoch onological analysis o smoo h plains, o e u ned
samples om hese egions and/o si es o explosi e olcanism would answe open ques ions ela ed o
hese aims.
c) Timing and s yles o ec onics
Me cu y has unde gone global con ac ion since a leas he Calo ian e a, e inced by he global
dis ibu ion o c us al sho ening ea u es (By ne e al., 2018a) and supe posi ion ela ionships wi h
c a e s o a ious deg ada ion s ages (C ane and Klimczak, 2017). Tec onic ac i i y p io o ha phase o
global sho ening, howe e , is no well unde s ood. Me cu y was likely much mo e ac i e— olcanically,
ec onically, and o he wise—ea ly in i s geologic his o y. I is he e o e an aim o iden i y, desc ibe,
and model he oldes p ese ed ( h us ) aul s on he body o unde s and hei s uc u al s yle
and subsu ace geome y, iming, and loca ions. I is also an aim o unde s and he opog aphic
exp essions o h us s, hei ec onic pa e ns, and hei ela ionship o o he long-wa eleng h a ia ions
in he li hosphe e. This is impo an o cons aining he o al ec onic his o y wi h indi idual con ibu ions
om con ac ion, changes in o a ion, e ical loads on he li hosphe e, and he spa ial pa e n o
a ia ions in hickness and s eng h o he c us and li hosphe e. To achie e his aim, high- esolu ion
opog aphy measu emen s wi h global co e age a e needed, as well as de ailed es ima es o he iming
o aul ing. Fu he mo e, model-de i ed geologically easonable in e p e a ions o subsu ace geome ies
o h us aul s a e needed o cons ain es ima es o Me cu y’s adial con ac ion. These geologically
easonable subsu ace geome ies migh also illumina e he physical p ope ies o Me cu y’s ocks and
i s c us al s uc u e. I will be impo an o alida e he model solu ions o subsu ace geome ies a
app op ia e Ea h analogue si es.
Ex ensional de o ma ion on Me cu y is much mo e spa ially es ic ed han sho ening and is mos ly
ound in olcanically ﬂooded impac basins (F eed e al., 2012) associa ed wi h slumps on c a e walls, o
along he old axes o majo sho ening s uc u es (Man e al., 2023). Howe e , Me cu y may ha e
unde gone an ea ly phase o plane a y expansion leading o i ing and gian dike o ma ion, simila o
wha is ound on he Moon (And ews-Hanna e al., 2013). To add ess his opic, high- esolu ion g a i y
ﬁeld measu emen s, compa able o ha e u ned by he GRAIL mission, a e equi ed o de ec linea
g a i y anomalies associa ed wi h ancien i s o dikes. Fu he , only limi ed ins ances o s ike-slip
de o ma ion ha e been epo ed on Me cu y (e.g., Galluzzi e al., 2015). High- esolu ion images and
opog aphic da ase s a e equi ed o de e mine i his kind o de o ma ion is mo e widesp ead and o
elucida e he na u e o ancien ec onic ac i i y global.
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MExAG Science Goals
d) Rela ionships be ween olcanism, ec onism, ola iles
Connec ing olcanism and ec onism on Me cu y is key o unde s anding he o ma ion and
spa ial dis ibu ion o olcanic en s, he emplacemen o he smoo h plains ma e ials, and he
connec ion be ween in usi e and ex usi e igneous p ocesses. Since ac u es in uma ole
sys ems se e as condui s o gases (Muna e o e al., 2023), i is impo an o unde s and he in e play
o ac u e sys ems and uma olic ac i i ies o Me cu y- ele an condi ions. To achie e ha , i is essen ial
o conduc ﬁeld wo k a analog si es on Ea h a pe ma os e ains o sul u - ich olcanic c a e
o ma ions like sol a a as and hei connec ion o ac u es (Phillips e al., 2021). To connec in usi e and
ex usi e olcanism, analysis o upcoming da a om he Me cu y O bi e Radio Science Expe imen
(MORE) (Iess e al., 2021) and geologic mapping using SIMBIO-SYS (C emonese e al., 2020) on
BepiColombo will be needed. G a i y anomaly mapping can be used o: de ec in usi e bodies;
de e mine he loca ion, o ien a ion, and cha ac e is ics o olcanic condui s ha p oduced he smoo h
plains; mo e igh ly cons ain models o c us al hickness; and add ess why smoo h plains a e
concen a ed in he no he n hemisphe e. Imp o ed spec al and spa ial obse a ions om o bi e s,
oge he wi h in-si u sampling o Me cu y’s c us , will ul ima ely cons ain he composi ional a ia ions
be ween he explosi e and eﬀusi e olcanic uni s, de e mine he ola iles d i ing olcanism, and u he
elucida e he ela ionship be ween ec onics and olcanism.
e) Long-wa eleng h opog aphy
MESSENGER-de i ed opog aphy o Me cu y’s no he n hemisphe e e eals b oad egions o undula ing
elie , which appea o be gene ically independen o o he , majo opog aphic modiﬁca ions such as
aul ing, c a e ing, and olcanism. These a ia ions occu a a ange o scales om he deg ee 2 shape o
he plane (Phillips e al., 2018) o he undula o y pa e ns in he Calo is basin o b oad, isola ed ises, he
mos p ominen o which is seen in Bo ealis Plani ia ( he No he n Rise) (Zube e al., 2012; Klimczak e
al., 2013). The supe posi ion ela ionships o geologic ea u es indica e ha long-wa eleng h opog aphic
changes occu ed subsequen o he c a e s and olcanically esu aced a eas ha hey aﬀec . The e is
minimal co ela ion be ween g a i y and opog aphy, sugges ing ha he obse ed opog aphy is
suppo ed by mul iple p ocesses. Modeling indica es ha olding is unlikely o ha e been p oduced by
global con ac ion (Kay and Domba d, 2019). Such p ocesses may include op loading o an elas ic
li hosphe e, bo om loading, c us al hickening, and/o dynamic opog aphy. I is an aim o elucida e how,
whe e, and when each o hese p ocesses ope a ed. Because o Me cu y’s hin man le, p ocesses a he
co e-man le bounda y (CMB) may ha e an obse able eﬀec on long-wa eleng h opog aphy. Thus, i is
an aim o cha ac e ize how plausible diﬀe en CMB p ocesses a e and how hey aﬀec he
long-wa eleng h opog aphy. To achie e hese aims, some imp o emen s in obse a ions on opog aphy
and g a i y om BepiColombo, especially o he sou he n hemisphe e, and ul ima ely majo such
imp o emen s by a mission simila in design o GRAIL, will p o ide u he insigh in o he dis ibu ion o
he long wa eleng h undula ions. Thei causes mus be u he s udied by modeling plausible CMB
p ocesses and hei exp essions in g a i y, opog aphy and he magne ic ﬁeld (Pla ne and Johnson,
2021).
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MExAG Science Goals
) S uc u e o he c us and li hosphe e
Cha ac e izing he s uc u e o he c us and li hosphe e, and hei ela ionship o geologic
ea u es and su ace composi ions, is i al o unde s anding how he plane ’s c us o med
and he endogenic and exogenic p ocesses ha ha e shaped he su ace. MESSENGER
p o ided a ﬁ s look a he opog aphy, c us al hickness, and c us al densi y o e Me cu y’s no he n
hemisphe e (e.g., James e al., 2015; Pado an e al., 2015; So i, 2018; Beu he e al., 2020.). Imp o ed
cha ac e iza ion o enigma ic ea u es o he li hosphe e, such as long-wa eleng h opog aphic a ia ions,
will p o ide new insigh s in o man le s uc u e and he mal s a e. Cons aining li hosphe ic hickness
h ough ime is impo an o pu obse ed su ace ea u es in con ex and o es ima e how in e io hea
has declined wi h ime. Like he Moon, Me cu y’s shape and g a i y ﬁgu e a e no in hyd os a ic
equilib ium. The eason o his is ye unexplained bu is impo an o o ma ion and ea ly e olu ion
scena ios. Global high- esolu ion g a i y and opog aphy da a a e impo an o e ealing he suppo
mechanisms o majo ea u es such as he No he n Rise and he Calo is basin, he his o y o hea ﬂow,
and he o igin o he global, non-hyd os a ic shape o he plane .
g) Hea ﬂow
The loss o hea h ough he su ace o a plane is a c ucial window in o he cu en and his o ical
ope a ion o he plane ’s in e io . Unde s anding how Me cu y has los hea is di ec ly ela ed o
he composi ion o he plane , i s ec onic and olcanic ac i i y, and how he magne ic ﬁeld is
gene a ed. The p ima y long- e m sou ce o hea in Me cu y is he decay o adioac i e elemen s in he
in e io (e.g., Hauck e al., 2004). Cons aining he dis ibu ion o hea -p oducing elemen s ac oss and
below he su ace is he e o e essen ial o unde s anding how he in e io has e ol ed. This could be
accomplished h ough imp o ed measu emen o hea p oducing elemen s a a a ie y o scales ac oss
he su ace, de e mina ion o su ace ock and mine al composi ions ha hos hea -p oducing elemen s,
de e mina ion o pa i ioning ela ionships o hea -p oducing elemen s in Me cu y analog ma e ials, and
iden iﬁca ion and composi ional analysis o any Me cu y me eo i es.
De e mining a ia ions in li hosphe ic hickness a a a ie y o scales (e.g., h ough s udies o li hosphe ic
de o ma ion a aul s, cha ac e iza ion o high- esolu ion g a i y and opog aphy da a, de e mina ion o
he dep h o seismogenic ac i i y) can also place cons ain s on pas hea ﬂow om he man le (e.g.,
G o e al., 2011; By ne e al., 2014). In addi ion, es ima ing he he mal s uc u e o he shallow
subsu ace (e.g., ia di ec measu emen wi h hea ﬂow p obes on a landed mission, high esolu ion
he mal mapping, es ima ion o su ﬁcial po osi y ia high- esolu ion g a i y measu emen s, and modeling
based on su ace p ope ies, e c.) is c i ical o cons aining mode n hea ﬂow, ec onic ac i i y, and he
seques a ion and libe a ion o ola iles.
h) Regoli h o ma ion and mixing
Unde s anding o Me cu y’s egoli h can beneﬁ om ou knowledge o he Moon’s egoli h,
bu he e a e signiﬁcan diﬀe ences in me eo oid, mic ome eo oid, and p o on ﬂuxes, su ace
composi ion, and day ime empe a u e be ween he wo bodies. By cha ac e izing he diﬀe ences
in egoli h p oduc ion a Me cu y in compa ison o he Moon, we may be e unde s and he
24
MExAG Science Goals
en i onmen al and composi ional ac o s ha inﬂuence egoli h de elopmen on ai less bodies in gene al.
In si u analyses o Me cu y egoli h om a landed in es iga ion (akin o in o ma ion gleaned om e u ned
Apollo d ill co es) would in o m unde s anding o he a e o impac ga dening and he dep h o which
p ocesses aﬀec he egoli h. Regoli h o ma ion and mixing models can be imp o ed by unde s anding
he mass, eloci y, and ﬂux o he me eo oid popula ion nea Me cu y. Regoli h models can also be
imp o ed h ough obse a ions o deg ading ea u es (e.g., dep h-diame e a io and he shape o ejec a
blanke s a ound esh c a e s on Me cu y) and models o opog aphic diﬀusion such as hose conduc ed
o he Moon (Fasse and Thomson, 2014; Fasse e al., 2017). Such s udies a e mos obus when
emo e sensing echniques co e ing se e al dep h scales a e used oge he (e.g., ada obse a ions on
he decame e scale and isible ligh on he su ace). I is also necessa y o unde s and he mechanical
p ope ies o Me cu y’s egoli h and how i may diﬀe om o he ai less bodies. Remo e he mal in a ed
adiome y (e.g., om MERTIS on BepiColombo; Hiesinge e al., 2010; 2020) will allow analysis o
he mophysical p ope ies. Fu u e landed images o egoli h g ains could be used o in es iga e pa icle
size, s eng h, cohesion, and po osi y.
Space wea he ing a Me cu y is hough o be domina ed by he o ma ion o agglu ini ic deposi s
h ough mic ome eo i e bomba dmen and o be lacking in sola wind ion spu e ing (Hapke, 2001).
Addi ionally, Me cu y’s ex eme empe a u e ange has implica ions o he diﬀusion in glass and c ys al
g ow h p ocesses in he egoli h (Noble and Pie e s, 2003). These p ope ies ha e impo an eﬀec s on
he spec al p ope ies o he soil. Pho ome ic modeling has ound ha Me cu y’s egoli h is likely
smoo he a mic ome e scales and has a smalle mean pa icle size dis ibu ion compa ed wi h luna
egoli h, which is consis en wi h a la ge ﬂux and highe eloci y o impac o s han a he Moon
(Domingue e al., 2016). The in ense space wea he ing en i onmen may ha e esul ed in a highe
abundance o agglu ina es, leading o smoo he g ains he eby educing su ace oughness. While
Me cu y’s deﬁcien 1-mic on band could be due o a lack o i on, i is plausible ha he lack o a
1-mic on band is he esul o an amo phous su ace ich in agglu ina es (McClin ock e al., 2008;
Robinson e al., 2008). Colo imaging and analysis be o e and a e a physical in e ac ion wi h he egoli h
(e.g., wi h a lande a m) would help o elucida e he eﬀec s o space wea he ing on Me cu y’s egoli h as
well as egoli h dep h. Cha ac e izing egoli h op ical ma u a ion a es on Me cu y (and on ai less bodies
in gene al) is essen ial o in e p e ing mul ispec al eﬂec ance measu emen s (B aden e al., 2013).
3.2 Unde s and p ocesses behind he chemical and mine alogical di e si y o he c us
a) Geochemical a ia ions
Da a om MESSENGER’s geochemical ins umen s e ealed he p esence o geochemical e anes in
Me cu y’s no he n hemisphe e— egions wi h geog aphically dis inc composi ions (e.g., McCoy e al.,
2018; Peplowski and S ocks ill-Cahill, 2019) ha a e hough o be p ima ily igneous in o igin. Se e al
pe ologic s udies ha e been conduc ed o asce ain he condi ions ha p oduced he geochemical
e anes (Cha lie e al., 2013; Ca ie e al., 2014; Namu e al., 2016a, Vande Kaaden e al., 2016;
Boujiba e al., 2025), bu u he p og ess in unde s anding Me cu y’s geochemical di e si y
equi es imp o emen s in he expe imen al (mel ing/c ys alliza ion) da a a ailable o di e se,
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MExAG Science Goals
no quan i a i ely explain he obse ed spa ial and empo al a ia ions obse ed in hese elemen s.
Pa hways o ma e ial loss om he su ace o c ea e each o hese exosphe ic elemen s a e
no ully unde s ood. Imp o ed obse a ions o Me cu y’s exosphe e and imp o ed heo e ical and
nume ical modeling a e needed.
The link be ween me eo oid impac s and diﬀe en species in Me cu y’s exosphe e has been es ablished
hanks o MESSENGER da a. BepiColombo is expec ed o p o ide a a ie y o new measu emen s and
cons ain s ha would p o ide a igh e connec ion o he Ca, CaO, and Mg exosphe e s uc u e o he
imp in o he me eo oid inﬂux a Me cu y om bo h he spo adic me eo oid backg ound (Poko ný e al.
2018) and he indi idual pa en bodies such as come 2P/Encke (Ch is ou e al 2015, 2024).
b) Space wea he ing p ocesses and a es
Pa icles, pho ons, and mic ome eo i es can deso b ma e ial om he su aces o egoli h g ains and
cause changes in hei chemical composi ion, op ical p ope ies, and mo phologic s uc u e,
cumula i ely known as space wea he ing. Mic ome eo oid impac s apo ize egoli h g ains, p oduce
impac ga dening o he egoli h, con amina e he su ace wi h exogenic ma e ials, and cause
elec os a ic eﬀec s on su ace p ocesses. Pho on and elec on s imula ed deso p ion (PSD and ESD,
espec i ely) can d i e elease o Na, K, and H2O, and po en ially o he mode a ely ola ile species
including Ca and S, h ough elec onic exci a ions. Sola wind ion impac s lose ene gy h ough bina y
collisions wi h he a ge ma e ial and elease a oms, molecules, and ions om he op-mos laye s o he
solid su ace in a p ocess known as spu e ing.
Open ques ions ela ing o hese space wea he ing eﬀec s include: Wha is he ela i e impo ance o
each o he abo e-desc ibed space wea he ing p ocesses o he a ious su ace species ound on
Me cu y? Wha a e he binding ene gies o ola ile ma e ials adso bed on o he su aces o egoli h
g ains, and how do hese change when he species a e inco po a ed in o he c ys alline s uc u e o he
g ains? How a e binding ene gies aﬀec ed by he p esence o oids, c acks, and o he su ace de ec s?
How do binding ene gies change he deso p ion ene gies o ola ile species (and hus hei exosphe ic
densi ies)? Wha a e he deli e y a es o ola iles o he poles? How does he empe a u e o he su ace
inﬂuence he ela i e impo ance o he a ious deso p ion p ocesses? These ques ions can be
add essed wi h labo a o y space wea he ing expe imen s, combined wi h mo e de ailed obse a ions o
spa ial and empo al a ia ions in Me cu y’s exosphe e.
4. In es iga e p ocesses cu en ly ongoing a Me cu y
4.1 Cha ac e ize p esen -day geologic ac i i y
a) P esen -day c a e ing a e
Es ima es o he cu en impac ﬂux a Me cu y ha e been de i ed using nume ous echniques including
dynamical calcula ions (Ma chi e al., 2005; Poko ný e al., 2018), ex apola ing measu emen s om he
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MExAG Science Goals

Moon (Ma chi e al., 2009), and by sea ching o su ace changes in spacec a images (Speye e e al.,
2022). The la e obse a ional analysis iden iﬁed 19 su ace changes ha we e a ibu ed o he
o ma ion o c a e s >100 m. I his es ima e is co ec , he implied c a e o ma ion a e is a ac o
o 1000 imes highe han exis ing p oduc ion models, necessi a ing u he wo k o
unde s and he disc epancy be ween obse a ions and models.
Unde s anding he ole dus impac s play in shaping Me cu y’s su ace and exosphe e is an
impo an ongoing ﬁeld o wo k. To da e, s udies ha e been conduc ed o unde s and he dus
popula ion (<10 mic on pa icles) using measu emen s in he inne sola sys em om Pa ke Sola P obe
and Sola O bi e (e.g., Mann e al., 2019; K üge e al., 2024) and mo e speciﬁcally a Me cu y (K üge
e al., 2024). Fo pa icle sizes up o 10 mic ome e s, he Me cu y Dus Moni o (MDM) on BepiColombo
will p o ide a di ec measu emen . In he u u e, an o bi e hos ing a dedica ed dus de ec o wi h a mass
spec ome e (e.g., S e no sky e al., 2011) could be used o de i e pa icle impac eloci y ec o ,
mass, and composi ion. Fo pa icle sizes om 10 mic ome e s o 1 cen ime e , wo k could be done o
indi ec ly es ima e he ﬂux by be e unde s anding he exci a ion o he Me cu y’s exosphe e ia
mic ome eo oid impac s (Killen and Hahn, 2015; Poko ný e al., 2018). Fu he wo k is needed o
imp o e ou knowledge o collisional p ocesses be ween pa icles, he inﬂuence o dus /me eo oid
shapes on magni udes o adia i e eﬀec s, and hype eloci y chemis y (mel ing, apo iza ion, ioniza ion
o diﬀe en species).
Fo pa icle sizes om 1 cen ime e and abo e, mo e insigh s wi h change de ec ion (e.g., in e
MESSENGER–BepiColombo high- esolu ion image compa isons) will aid in u he cha ac e izing he
p esen -day me eo oid impac ﬂux. Telescopic o o bi al obse a ions o impac ﬂashes on Me cu y’s
su ace (c. . luna obse a ions Suggs e al., 2014) o de ec ion wi h seismic ins umen s o in asound
echniques (Silbe and B own, 2018) on a lande could help o es ima e he p esen -day impac o ﬂux,
mass, and ene gy. Addi ionally, cha ac e izing he cu en impac a e on Me cu y will shed ligh on he
dynamical e olu ion o he nea -Ea h o bi (NEO) popula ion in o Me cu y c osse s.
b) Recen /cu en olcanic ac i i y
Iden i ying ecen eﬀusi e olcanism is challenging as i can be diﬃcul o dis inguish smoo h la a ﬂows
om impac mel s. Finding olcanic en s would be diagnos ic, howe e loca ing en s o eﬀusi e la as
is o en diﬃcul because hey end o sel -seal. I is he e o e an aim o iden i y and ob ain s e eo image
pai s o candida e en a eas a he sub-10 m/pixel-scale and iden i y and cha ac e ize he mos
ecen eﬀusi e olcanism by deﬁning spec ally homogeneous a eas as small as abou 400 km2.
C a e coun s down o c a e diame e s o 1 km should be done on hese a eas o es whe he spec al
uni s ha e diﬀe en CSFDs and o quan i y hese as ages using a c a e p oduc ion unc ion. To achie e
his aim, high- esolu ion spec al imaging o smoo h plains uni s is needed, as well as absolu e age
calib a ions ha can be achie ed ia sample e u n o in si u adiome ic da ing. In addi ion, geologic
con ex can help dis inguish be ween small young eﬀusi e olcanism and impac mel , bu composi ional
in o ma ion om X- ay ﬂuo escence (XRF) and isible- o- he mal in a ed (VISTIR) spec oscopy will
ul ima ely only p o ide he impo an disambigua ion.
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MExAG Science Goals
Me cu y has mo e han 100 candida e si es o explosi e e up ion. Two o he younges explosi e en s
ha e been da ed as Kuipe ian (<280 Ma) on he basis o a supe posi ion ela ionship wi h c isp c a e s
(Thomas e al., 2014b; Jozwiak e al., 2018). The e up i e li e ime o each explosi e en si e is poo ly
deﬁned, bu many en s consis o mul iple closely spaced loci o e up ion, sugges i e o mul iple
e up ions spaced o e pe haps long in e als. Mos explosi e deposi s ( aculae) could be a cumula i e
p oduc o many sepa a e e up ions (Pegg e al. 2021). The composi ion and a e a which aculae lose
hei spec al dis inc i eness wi h age emains unknown. I is hus an aim o be e deﬁne he iming and
du a ion o he explosi e e up ions. To achie e his aim, high- esolu ion imaging can p o ide ﬁne-scale
supe posi ional ela ionships and ex u al diﬀe ences wi hin compound en s, whe eas composi ional
in o ma ion ia high- esolu ion XRF and VISTIR spec oscopy and space wea he ing expe imen s can
p o ide in o ma ion on composi ion and longe i y o spec al dis inc i eness o aculae.
c) Recen /cu en ec onic ac i i y
La ge h us aul - ela ed sca ps, 100s o km long, c osscu impac c a e s as old as p e-Tols ojan (> ~4
Ga) bu as young as Kuipe ian (< 280 Ma). Despi e such e idence o a long du a ion o con ac ion, i is
no known how ac i e ec onics on Me cu y a e a p esen (C ane and Klimczak, 2017). The c osscu ing
o sca ps wi h small c a e s and e y small-scale h us aul sca ps sugges s ha ec onic ac i i y
occu ed geologically ecen ly and is pe haps ongoing (Wa e s e al., 2016). Ve y small g abens on la ge,
old loba e sca ps also sugges long-li ed and/o ecen ec onism on Me cu y (Man e al., 2023). To
unde s and how geologically ecen he land o ms a e, an aim is o unde s and hei spa ial and
kinema ic ela ions o la ge sho ening s uc u es, and wha p ocess(es) d i e hei o ma ion. Ano he
aim is o iden i y he cu en a e o ec onic de o ma ion o speci y how ec onically ac i e Me cu y is a
p esen .
The mechanisms d i ing he ec onic ac i i y on Me cu y a e no ully quan iﬁed. I is c ucial o
unde s and he espec i e oles o con inuing global con ac ion, opog aphic elaxa ion,
he mally and idally induced de o ma ion, seismic su ace modiﬁca ion leading o mass
was ing, and e en local-scale de o ma ion om magma ascen o impac bomba dmen .
Unde s anding he ela i e con ibu ion o hese p ocesses will p o ide insigh s in o he e olu ion o
Me cu y’s in e io . Cha ac e iza ion o ela ionships be ween ec onic ea u es and impac c a e s,
ca aloging o indica o s o ecen su ace change such as landslides and boulde ails om
highe - esolu ion- han-cu en ly-a ailable images, and de e mina ion o po en ial su ace changes
be ween da a om MESSENGER, BepiColombo, and u u e o bi e s a e app oaches ha can indica e
ec onic sou ces o geologic ac i i y. Fu he mo e, using ec onic obse a ions o in o m modeling o he
po en ial o seismici y om Me cu y’s solid body (sola ) ides—sugges ed o be as much as 17 imes
la ge han hose on he Moon (Van Hols and Jacobs, 2003)—as well as modeling coseismic slip on
h us aul s will in o m cu en de o ma ion a es. A Me cu y lande con aining one (o mo e)
seismome e (s) would ul ima ely p o ide in o ma ion on de o ma ion a es by measu ing magni udes,
equencies, and sou ces o quakes.
Finally, he in es iga ion o Me cu y's ec onic and olcanic ac i i y equi es unde s anding o i s in e io ,
especially he composi ion and s uc u e o he silica e po ion o he plane . New insigh om
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MExAG Science Goals
BepiColombo's ins umen s as well as new labo a o y measu emen s on c us and man le analogs and
nume ical modeling will help o cons ain he mine alogy and he mal s a e o he silica e po ion. Fo
ins ance, induc ion da a can be used o ob ain an elec ical conduc i i y-dep h p oﬁle o he man le
(Geno a e al., 2021), which can be used o place cons ain s on he mine alogy and he mal s a e (e.g.,
Pommie e al., 2025). Elucida ing he in e io o he plane is necessa y o model he diﬀe en
de o ma ion p ocesses and ela ed olcanism ha shaped he su ace.
d) Hollows
Al hough much p og ess has been made in unde s anding hollows, how hey o m emains an
open ques ion. I is gene ally ag eed ha he hollows a e young (Blewe e al., 2011, 2013), ha
sublima ion o space wea he ing p ocesses a e in ol ed in hollow o ma ion (Blewe e al., 2011, 2013;
Vaughan e al., 2012; Phillips e al., 2021), and ha hollows a e associa ed wi h Me cu y’s Low
Reﬂec ance Ma e ial (LRM) (Blewe e al., 2013; Thomas e al., 2014a). Mos hollows occu wi hin
impac c a e s o ma e ial exca a ed by impac s (Thomas e al., 2014a; Blewe e al., 2018); howe e ,
whe he impac s simply exca a e ma e ial o play some addi ional ole, such as p o iding necessa y hea
o mel p oduc s, is unknown. I has also been p oposed ha ejec a blocks om Calo is ha ha e been
modiﬁed by long- e m and ongoing mass was ing had subs an ial ola ile con en s and may be ela ed o
hollows (W igh e al., 2020). A ﬁ s aim is o de e mine he iden i y o he ola ile-bea ing phase ha is
los in he hollow- o ma ion p ocess. High- esolu ion composi ional and eﬂec ance o bi al
measu emen s o hollows and LRM could help o un eil hei composi ion and ela ionship o one
ano he . Landed elemen al (e.g., sul u and ca bon) and mine alogical (e.g., sulﬁde, ca bide)
measu emen s will be c i ical o unde s anding he ola ile-bea ing phase. A second aim is o cons ain
he mechanism by which hollows o m. High- esolu ion images o hollow mo phology could shed ligh on
hollow o ma ion. High- esolu ion image co e age o Me cu y’s sou he n hemisphe e would allow a
mapping o he global dis ibu ion o hollows and hei associa ions wi h o he land o ms. A hi d aim is o
cons ain he ages, o ma ion imescales, and g ow h- a es o hollows. Highe esolu ion imaging o he
su ace would de e mine he ages o hos uni s and could e eal “ ossil” hollows (no b igh compa ed o
hei su oundings). Change-de ec ion imaging ( isible o ada ) o hollows could illumina e whe he
hollows a e ac i ely g owing and a wha a e.
e) Pola deposi s
The pola ice deposi s in Me cu y PSRs ha e ew c a e s and so appea o be ecen and/o ac i e
ea u es. In addi ion, hei co e ing o da k, possibly o ganic, ma e ial appea s o co ela e closely wi h
he ex en o he pe manen ly shadowed a eas (Chabo e al., 2014a). Po en ial cu en p ocesses ac ing
on he deposi s include sublima ion/de-sublima ion, mic ome eo oid impac , space wea he ing, ion
implan a ion and in e ac ion wi h he magne ic ﬁeld.
To imp o e ou unde s anding o he p ocesses cu en ly aﬀec ing he pola deposi s, along wi h hei
cu en accumula ion and loss a es, a numbe o key measu emen s a e needed. These include de ailed
measu emen s o pola he mal en i onmen s, measu emen s o sola wind ﬂux a mul iple loca ions
(including a la i udes whe e wa e ice is exposed a he su ace and a la i udes whe e wa e ice is
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MExAG Science Goals
insula ed by a laye o low-albedo ma e ials), and measu emen s o he ongoing egoli h ga dening a es.
High- esolu ion measu emen s o he g a i y ﬁeld would p o ide key insigh s in o he dis ibu ion o ice,
and be e measu emen s o magne ic ﬁelds a he poles would imp o e cons ain s on ice o ma ion and
loss p ocesses. A lande (e en one no a he pola egions) would p o ide key cons ain s on ongoing
ac i i y. High- esolu ion images, eﬂec ance measu emen s, and opog aphic measu emen s o he pola
deposi s a e also impo an , pa icula ly i hey can be made epea edly o e long imespans, o di ec ly
measu e changes and a es o changes. Addi ionally, measu emen s o pola deposi pu i y as a unc ion
o dep h (e.g., by ada sounding) would p o ide insigh in o ice e olu iona y his o y.
A a ie y o expe imen s and model imp o emen s would also imp o e ou unde s anding o ongoing
p ocesses a he pola deposi s, including expe imen s and models o space wea he ing a es a
Me cu y’s pola condi ions, expe imen s o come a y-like ola iles o es wha low- eﬂec ance ola iles
may o m a e exposu e o Me cu y-like en i onmen al condi ions, and expe imen s o de e mine how
he mal lag deposi s may de elop and e ol e in Me cu y-like condi ions.
4.2 In es iga e magne osphe ic dynamics
a) Gene a ion o he cu en magne ic ﬁeld
The global magne ic ﬁeld o Me cu y is likely gene a ed by a con ec ion-d i en dynamo in he co e (e.g.,
Ch is ensen, 2006) ha is hough o ha e ope a ed ea ly in he plane 's his o y (~ 3.7–3.9 billion yea s;
Johnson e al., 2015). Using magne ic and geode ic measu emen s, i has been sugges ed ha he
me allic co e is a leas pa ially liquid a p esen (e.g., S einb ügge e al., 2021). Co e cooling models
ha e shown ha i on snow is unlikely o occu in Me cu y's co e, and he g ow h o a solid inne co e is
he only expec ed c ys alliza ion mechanism (Knibbe and an Wes enen, 2018; Da ies e al., 2024).
Models ha bes ep oduce he exis ing obse a ional cons ain s a e ob ained o a laye ed co e made
o a mol en ou e po ion, composed o a hick he mally s able laye and a con ec ing egion whe e he
dynamo is gene a ed, and a solid inne co e. The p esence o a hypo he ical mol en FeS laye a op he
co e would ha e minimal eﬀec on Me cu y's long- e m he mal and magne ic e olu ion (Da ies e al.,
2024). The size o he expec ed solid inne co e is deba ed (up o 1500 km; e.g., Geno a e al., 2019),
pa ly due o he lack o cons ain s on co e chemis y, and new da a om BepiColombo's Me cu y
O bi e Radio Science Expe imen (MORE) (Iess e al., 2021) a e expec ed o shed ligh on he s uc u e
and e olu ion o he co e.
Cha ac e izing he composi ional and physical p ope ies o Me cu y’s co e is key o modeling
co e dynamics and he o igin o he magne ic ﬁeld. In o ma ion abou he chemis y o he me allic
co e has been ob ained by he combina ion o su ace composi ion da a and labo a o y expe imen s.
The low-Fe and high-S con en s in me cu ian la as sugges ha he co e o med unde highly educing
condi ions (e.g., McCubbin e al., 2012). A hese O2 condi ions, high-p essu e and high- empe a u e
expe imen s showed ha only small amoun s (<~2.0 w .%) o sul u a e expec ed in he co e, whe eas Si
could alloy wi h Fe in signiﬁcan p opo ions (>10 w .%; e.g., Knibbe and an Wes enen, 2018;
Goossens e al., 2022). A non-negligible amoun o Ni (se e al w .%) is expec ed, based on i on
me eo i e cosmochemis y, and subs an ial amoun s o C migh also be p esen in he co e (e.g., Vande
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MExAG Science Goals
Kaaden e al., 2020). In addi ion, pa i ioning expe imen s o Si be ween liquid and solid Fe alloys
indica ed ha la ge amoun s o silicon a e expec ed o pa i ion o he solid inne co e (e.g., Tao and Fei,
2021).
Cu en unde s anding o he physical p ope ies o Me cu y’s co e es s la gely on MESSENGER-based
de e mina ions o he o a ional s a e (i.e., ampli ude o he physical lib a ion and he o ien a ion o he
plane ), he second-deg ee ha monics o he g a i y ﬁeld (e.g., Ma go e al 2018, Be one e al., 2021)
and labo a o y measu emen s o he physical p ope ies (e.g., Pommie e al., 2019). Be e
measu emen s o Me cu y’s g a i y ﬁeld, along wi h highe p ecision opog aphy would g ea ly ad ance
ou unde s anding o he o igin o Me cu y’s magne ic ﬁeld, as would expe imen al s udies ocused on
he ele an co e composi ions and condi ions.
b) Magne ic econnec ion
Me cu y and Ea h bo h ha e econnec ion-d i en magne osphe es, wi h ene gy and momen um om
he sola wind d i ing he ci cula ion o magne ic ﬂux h ough he sys em. The ela i e econnec ion a es
on he dayside and in he magne o ail go e n he change in open magne ic ﬂux con en o he sys em,
and hus a e impo an pa ame e s o desc ibing he global magne osphe ic dynamics (Imbe and
Sla in, 2017; Sla in e al., 2021), he dis ibu ion and accele a ion o magne osphe ic plasma (e.g.
Dewey e al., 2018), and he loca ion o pa icle p ecipi a ion o he su ace (e.g. Poh e al., 2016;
Lindsay e al., 2016; Raines e al., 2022). Al hough MESSENGER a ely obse ed econnec ion si es
di ec ly (e.g., Zhong e al., 2018), i eco ded ample e idence o he equency and impo ance o
econnec ion o Me cu y’s magne osphe e. Due o he single-poin na u e o MESSENGER’s in si u
plasma and magne ic ﬁeld obse a ions, many ou s anding ea u es o magne ic econnec ion
in Me cu y’s magne osphe e emain, including: he numbe and loca ions o simul aneous
econnec ion si es a he magne opause and/o in he magne o ail; he inﬂuence o plane a y ions on
econnec ion occu ence and s eng h; he ela i e impo ance o low-la i ude Kel in-Helmhol z wa es o
plasma en y and ﬂux ci cula ion compa ed o magne ic econnec ion; he ela ion be ween econnec ion
and dawn-dusk asymme ies; pa icle ene giza ion (bo h ion and elec on) di ec ly om econnec ion and
om econnec ion p oduc s.
c) Induc ion eﬀec s
The small dimensions o Me cu y’s magne osphe e and he la ge olume occupied by he plane ’s
conduc ing co e esul in elec omagne ic coupling be ween he plane ’s in e io and i s magne osphe e.
Since Me cu y lacks an ionosphe e, changes in he ex e nal magne ic ﬁeld di ec ly aﬀec he plane as, in
esponse, induc i e cu en s o m on he su ace o Me cu y’s highly conduc ing co e o oppose hese
changes. Induc ion cu en s in oduce addi ional magne ic ﬂux o he magne osphe e ha , like he
in insic magne ic ﬁeld, can unde go dynamic p ocesses like magne ic econnec ion. The eﬀec o
induc ion and i s ole in he coupling be ween Me cu y’s magne osphe e and in e io a e no
well unde s ood. Ini ial s udies o induc ion using MESSENGER da a ha e conﬁ med annual and
episodic changes in he plane ’s axial dipole magne ic momen due o changes in sola wind dynamic
37
MExAG Science Goals

p essu e, wi h a ew-pe cen change due o annual dynamic p essu e a ia ion (Johnson e al., 2016)
and eﬀec s as s ong as ~50–100% due o sola wind ansien s (e.g., Sla in e al., 2014). Howe e ,
o he causes o induc ion eﬀec s, such as hose ela ed o magne o ail cu en sys ems and dynamics,
emain unconﬁ med. Fu he , he consequences o he addi ional magne ic ﬂux in he magne osphe e
gene a ed by induc ion cu en s emain poo ly cons ained. Du ing high-p essu e e en s, he ﬂux added
o he dayside helps o p e en he collapse o he dayside magne osphe e o he su ace o he plane .
Howe e , s ong magne opause econnec ion can anspo his ﬂux o he magne o ail, e oding he
dayside magne osphe e anyway.
The in e play be ween induc ion and econnec ion, and hei eﬀec s on he magne osphe e’s s uc u e
and con en , equi e u he in es iga ion. While induc ion is p esen a many sola sys em objec s, such
as he Galilean moons, only Me cu y and Ganymede a e known o possess bo h global magne ic ﬁelds
and a leas weakly conduc ing in e io s. As Ganymede is deeply embedded in Jupi e ’s magne osphe e,
Me cu y is a unique place o s udy induc ion eﬀec s as i s magne osphe e is subjec o he mo e a iable
sola wind. Expec ed da a om BepiColombo's MPO-MAG ins umen ha e he po en ial o answe
se e al ques ions ela ed o Me cu y's magne osphe e (Heyne e al., 2021).
d) Dawn-dusk asymme ies
Me cu y’s magne osphe e exhibi s diﬀe ences be ween i s duskside and dawnside in he cha ac e is ics
and dynamics o i s plasma and magne ic ﬁeld. These dawn-dusk asymme ies a e p esen h oughou
he sys em, bu a e p onounced in he magne o ail, whe e, o example, he dawnside means cu en
shee hickness is g ea e (e.g., Poh e al., 2017; Rong e al., 2018), he plasma densi y is highe (e.g.,
Ko h e al., 2014; Zhao e al., 2020), and signa u es ela ed o magne ic econnec ion a e mo e equen
han on he duskside magne o ail (e.g., Sun e al., 2016; Smi h e al., 2017; Dewey e al., 2017; Dewey
e al., 2020). Some dawn-dusk asymme ies a e simila o Ea h, howe e , o he s a e opposi e in hei
dawn-dusk p e e ence (see, e.g., a e iew by Sun e al., 2022). Cha ac e iza ion o dawn-dusk
asymme ies o da e has elied on s a is ical accumula ion o MESSENGER obse a ions wi hin he
magne osphe e. While hese accumula ions desc ibe a e age local p ope ies, hey in eg a e o e he
ime his o y o he sys em, lack con ex o sola wind d i ing, and compa e empo ally and spa ially
dis an measu emen s. As a esul , he o igins and consequences o hese asymme ies emain
un esol ed.
One aim is he e o e o unde s and he physical o igins o he magne osphe e’s dawn-dusk asymme ies,
while ano he aim is o de e mine he inﬂuence o hese asymme ies on he magne osphe e’s in e nal
dynamics. Cha ac e iza ion o ela ionships be ween dawn-dusk asymme ies and ex e nal sola wind
d i ing condi ions; compa ison o dayside and nigh side magne osphe e mass, ene gy, and momen um
budge s and he ans e o hese quan i ies h oughou he sys em and wi h he sola wind; esolu ion o
meso-scale dynamics (~0.1 o Me cu y’s e e ence adius) and cons aining hei con ibu ion o global
magne osphe e conﬁgu a ion; and acing o pa icles and ﬁeld lines h ough he magne osphe e as a
unc ion o magne osphe ic s a e can each help o esol e he o igins and eﬀec s o dawn-dusk
asymme ies. Such ac i i ies ely on simul aneous mul i-poin in si u measu emen s wi hin o ac oss
38
MExAG Science Goals
magne osphe ic egions, knowledge o ups eam sola wind condi ions, and compa ison be ween global
simula ions and localized spacec a measu emen s.
e) Magne osphe ic cu en s
Me cu y’s majo magne osphe ic cu en s gene ally esemble hose o Ea h, bu he e a e signiﬁcan
diﬀe ences in cu en closu e a Me cu y due o i s lack o a conduc ing ionosphe e. The majo cu en
sys ems a Me cu y include magne opause cu en , c oss-magne o ail cu en shee , a ing-like cu en
abou he plane , and ﬁeld-aligned cu en s. A he dayside magne opause, a Chapman-Fe a o cu en
sepa a es he closed dayside magne osphe e ﬁeld om he magne oshea h. Me cu y’s magne opause is
mo e conduci e o econnec ion han Ea h’s, including ins ances o symme ic econnec ion, and he
esul ing diﬀe ences in magne opause cu en s eng h and cohe ence compa ed o Ea h’s a e cu en ly
unknown. In he magne o ail, he dawn- o-dusk c oss- ail cu en shee is a consequence o he
elonga ion o nigh side ﬁeld lines. The e is some e idence o bi u ca ion o his cu en shee (Al Asad e
al., 2021), bu he o igins and consequences o his bi u ca ion a e no well unde s ood. Close o he
plane , apped pa icles injec ed om he magne o ail in o he dipole-domina ed egion o he
magne osphe e g adien -cu a u e d i abou he plane . Al hough he exis ence and equency o d i
pa hs emain unde deba e, ecen wo k has sugges ed a suﬃcien amoun o plasma d i s o o m he
equi alen o an Ea h-like ing cu en (Shi e al., 2022; Zhao e al., 2022). Howe e , he di ec ion and
p ima y cu en ca ie s canno cu en ly be econciled. A he dayside, his cu en may close abou
equa o ial dayside, bu du ing mode a e magne osphe e o cing he cu en is expec ed o spli in o he
no he n and sou he n hemisphe es in a Shabansky-like conﬁgu a ion.
The cu en sys ems a Me cu y ha a e leas likely o esemble Ea h’s a e i s ﬁeld-aligned cu en (FAC)
sys ems. Since Me cu y lacks a conduc ing a mosphe e, he in e io o he plane is expec ed o p o ide
necessa y closu e o hese ypes o cu en sys ems. While he exac mechanics and loca ion o cu en
closu e in he plane equi e u he cons ain s, concep ual models sugges he cu en s ﬂow adially
h ough he esis i e c us and man le, and close a he highly conduc i e co e-man le bounda y. Cu en
closu e o e he co e and he esis i e c us /man le imposes cons ain s on empo ally- a iable FACs.
MESSENGER obse a ions in he magne o ail sugges a subs o m cu en wedge may o m ha
connec s he nea - ail egion o he plane a y in e io (e.g., Dewey e al., 2020) bu he small
spa io empo al scales o he magne osphe e and he esis i e egoli h hampe he o ma ion o his
sys em compa ed o Ea h. The equency and simila i y o a subs o m cu en wedge a Me cu y emain
open. In addi ion o ansien FACs, Me cu y’s magne osphe e possesses a mo e pe manen Region-1
s yle cu en ha was consis en ly obse ed by MESSENGER o e Me cu y’s no he n pole (e.g.,
Ande son e al., 2014, 2018). These la ge-scale pola FACs a e quasi-s a iona y and omnip esen . The
exac o igins o his sys em a Me cu y a e unknown, bu ﬂow shea in e io o he magne opause nea
he e mina o is a possible mechanism. A Region-2 s yle FAC sys em has no been obse ed in he
MESSENGER da a o da e. Howe e , i is expec ed o exis o comple e he Dungey cycle by
anspo ing closed magne o ail ﬁeld lines o he dayside. New obse a ions o he magne ic ﬁeld and i s
e olu ion wi h ime a e equi ed.
39
MExAG Science Goals
) Flux ope o ma ion
Flux opes (FRs) a e helical bundles o magne ic ﬂux ha o m be ween magne ic econnec ion si es and
a e con ec ed away om hei loca ion o o ma ion by a combina ion o magne ic ension o ces and
dominan plasma ﬂows in he sys em. Flux opes a Me cu y ha e been obse ed by MESSENGER o
o m in he magne o ail cu en shee and along he dayside magne opause. Dayside magne opause ﬂux
opes a e also known as ﬂux ans e e en s (FTEs) and a e obse ed mo ing an i-sunwa d along he
magne opause whe e hey may anspo signiﬁcan quan i ies o magne ic ﬂux om he dayside
magne opause in o he magne o ail (e.g. Imbe e al., 2014).
‘Flux ans e e en showe s’ appea o be a phenomenon unique o Me cu y (Sla in e al., 2012) and
consis o hund eds o FTEs obse ed o e e y sho ime pe iods. While indi idual FTEs wi hin he
showe s we e esol ed by MESSENGER’s magne ome e , hei small spa ial scale (and co esponding
sho imescale as hey passed o e he spacec a ) has limi ed analysis om plasma obse a ions.
These magne ic ﬁeld obse a ions sugges ha FTEs may play a signiﬁcan o e en dominan ole in ﬂux
anspo om Me cu y’s dayside magne osphe e o he magne o ail. Howe e , wi hou co esponding
de ailed plasma obse a ions, ques ions emain as o he ole o FTEs in ﬂux and pa icle
anspo , he loca ion o pa icle p ecipi a ion o he plane a y su ace and subsequen
con ibu ion o he gene a ion o he exosphe e, and he s o age and dissipa ion o ene gy
wi hin Me cu y’s magne osphe e. Obse a ions o he magne ic ﬁeld o e longe ime pe iods wi h
imp o ed co e age a e needed.
g) Eﬀec o sola e en s on he sys em
In e plane a y Co onal Mass Ejec ions (ICMEs) ha e he s onges eﬀec on Me cu y’s
magne osphe e o any sola e en s. They ypically b ing signiﬁcan inc eases in plasma ﬂux and
magne ic ﬁeld s eng h. They mainly d i e he magne osphe e ia wo mechanisms: inc eased dayside
magne opause econnec ion and inc eased sola wind dynamic p essu e. When dayside econnec ion
domina es, signiﬁcan magne ic ﬂux is s ipped om he dayside magne osphe e and loaded in o he
magne o ail (Imbe and Sla in, 2017), s imula ing magne ic econnec ion ac oss he cen al cu en shee
and inc easing magne osphe ic ci cula ion. In ex eme cases, his e osion o he dayside magne ic ﬁeld
could expose subs an ial po ions o Me cu y’s dayside su ace o di ec sola wind impac (Sla in e al.,
2019). When p essu e domina es, he whole magne osphe e is squeezed, leading o an inc ease in
dayside magne osphe e ﬁeld s eng h om magne ic induc ion on he co e (Sla in e al., 2014). The ne
esul can be simila o he econnec ion-domina ed e en s: in ex eme cases po ions o he dayside
su ace can be exposed o di ec sola wind impac . Inc eased sola wind spu e ing likely inc eases he
densi y o he neu al exosphe e and hea y ion con en o he magne osphe e (Sun e al., 2022), as well
as he space wea he ing o he su ace (Domingue e al., 2015). The combina ion o he wo
BepiColombo o bi e s will p o ide wo-poin measu emen s ha will g ea ly imp o e unde s anding o
hese e en s compa ed wi h he single-spacec a measu emen s o MESSENGER. MPO will
con inuously moni o nea -plane condi ions wi h i s lowe , nea ly ci cula o bi while Mio will ei he be
ups eam moni o ing he sola wind o deep in he magne o ail moni o ing loading and ail econnec ion.
40
MExAG Science Goals
Two o he classes o sola e en s ha e an indi ec and likely much smalle eﬀec on Me cu y’s
magne osphe e: Sola Ene ge ic Pa icle (SEP) e en s and sola ex eme ul a iole (EUV) ﬂa es. SEP
e en s ha e been shown o ain ene ge ic elec ons down on o Me cu y’s pola cap (Ge shman e al.,
2015a). Sola ﬂa es cause inc eases in pho on-s imula ed deso p ion o ma e ial om he su ace as well
as likely p oduce mo e plane a y ions in he magne osphe e, which may p ecipi a e back on o he
su ace a highe ene gies. Bo h o hese eﬀec s likely lead o mo e spu e ing o neu als and ions om
he su ace, bu e idence o his eﬀec has no been epo ed. Fu u e obse a ions using mul iple
spacec a a e needed o imp o e ou unde s anding o he Sun’s inﬂuence on he magne osphe e.
4.3 Unde s and exosphe ic and magne osphe ic sou ce and loss p ocesses
a) Magne osphe ic ions
Because Me cu y’s exosphe e is collisionless, magne osphe ic ion dynamics a e comple ely decoupled
om exosphe ic neu als. The p ima y sou ces o magne osphe ic ions a e en y o he sola wind
h ough dayside magne opause econnec ion and pho oioniza ion o exosphe ic neu als (Zu buchen e
al., 2008; 2011; Raines e al., 2013). Much smalle quan i ies likely come om ioniza ion o ma e ial om
su ace mic ome eo oid impac s in he ho apo iza ion cloud (Poko ný e al., 2017; 2018) as well as
cha ge exchange o exosphe ic neu als wi h sola wind p o ons in he magne oshea h o cusps, hough
he e a e cu en ly no measu emen s o conclusi ely suppo ei he o hese cases.
Magne osphe ic ions a e los p ima ily h ough magne osphe ic ci cula ion and kine ic p ocesses.
Following magne ic econnec ion in he cen al plasma shee , as pa o Dungey Cycle ci cula ion, ions
a e ca ied by helical magne ic s uc u es called plasmoids down he magne o ail and back in o he sola
wind. Plasma is also ca ied owa d he nigh side o he plane by his p ocess, wi h some being los o
p ecipi a ion on he nigh side su ace h ough he plasma shee ho ns o possibly e en ac oss he en i e
nigh side du ing e y ac i e imes (Glass e al., 2022). While plasmoids ha e been obse ed (Sla in e al.,
2008; DiB accio e al., 2015), es ima es o he plasma los ia his p ocess ha e no been made. The
e ained ions will end o d i a ound Me cu y’s nigh side owa d he dusk e mina o . Me cu y’s weak
magne ic ﬁeld esul s in a e y small magne osphe e (Sla in e al., 2007), whe e, on he dayside, he
dis ance be ween he magne opause and he plane a y su ace is o en he same scale as ion gy o adii.
A la ge po ion o ions d i ing h ough his space will be los by gy a ing ei he in o he plane ’s su ace
(p ecipi a ion) o in o he magne opause (magne opause shadowing). The signiﬁcance o his kine ic
p ocess inc eases wi h inc easing ion ene gy and mass, so ha plane a y ions, such as Na+, which ha e
gy o adii mo e han 20 imes ha o p o ons a he same ene gy, can pass h ough his space only a he
lowes ene gies, 100s o eV (Raines e al., 2014). This eﬀec can be obse ed in se e al kine ic models o
Me cu y, wi h some showing ions able o ci cula e all he way a ound he dayside magne osphe e and
hus cons i u ing a leas a pa ial ing cu en , as well as obse a ions ha a e consis en wi h his
in e p e a ion (Shi e al., 2022; Zhao e al., 2022; Hadid e al., 2024). Ions in his egion as well as u he
down he magne o ail can also be los h ough he Kel in-Helmhol z ins abili y, whe e he diﬀe ing ﬂow
speeds ac oss he magne opause bounda y can cause o ices o o m which expel magne osphe e
plasma in o he magne oshea h (Sundbe g e al., 2010; 2012; Liljeblad e al., 2014; Ge shman e al.,
41
MExAG Science Goals
● Deu sch, A.N., Head, J.W., Chabo , N.L., Neumann, G.A. (2018). Cons aining he
hickness o pola ice deposi s on Me cu y using he Me cu y Lase Al ime e and small
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● Deu sch, A.N., Head III, J.W., Neumann, G.A. (2019). Age cons ain s o Me cu y's pola
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h ps://doi.o g/10.1016/j.epsl.2019.05.027.
● Dewey R M, Sla in J A, Raines J M, Bake D N, Law ence D J. (2017). Ene ge ic Elec on
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● Dewey, R. M., Raines, J. M., Sun, W., Sla in, J. A., and Poh, G. (2018). MESSENGER
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Le e s, 45, 10,110. h ps://doi.o g/10.1029/2018GL079056.
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● Dib accio, G. A., Sla in, J. A., Boa dsen, S. A., Ande son, B. J., Ko h, H., Zu buchen, T.
H., Raines, J. M., Bake , D. N., McNu , R. L., and Solomon, S. C. (2013). MESSENGER
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● DiB accio, G. A., Sla in, J. A., Imbe , S. M., Ge shman, D. J., Raines, J. M., Jackman, C.
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● Dob osa lje ic, V. V., Zhang, D., S u hahn, W., Zhao, J., Toellne , T. S., Cha i on, S. ,
P akapenka, V. B., Pa do, O. S., Jackson, J. M. (2022). Mel ing and phase ela ions o
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● Domingue, D. L., Koehn, P. L., Killen, R. M., Sp ague, A. L., Sa an os, M., Cheng, A. F.,
B adley, E. T., and McClin ock, W. E. (2007). Me cu y’s a mosphe e: A su ace-bounded
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● Domingue, D. L., Chapman, C. R., Killen, R. M., Zu buchen, T. H., Gilbe , J. A., Sa an os,
M., Benna, M., Sla in, J. A., Sch i e , D.,T á níček, P. M., O lando, T. M., Sp ague, A. L.,
Blewe , D. T., Gillis-Da is, J. J., Feldman, W. C., Law ence, D. J., Ho, G. C., Ebel, D. S.,
Ni le , L. R., Vilas, F., Pie e s, C. M., Solomon, S. C., Johnson, C. L., Winslow, R. M.,
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● Domingue, D. L., Mu chie, S. L., Dene i, B. W., E ns , C. M., and Chabo , N. L. (2015).
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● Domingue, D. L., Dene i, B. W., Mu chie, S. L., Hash, C. D. (2016). Applica ion o mul iple
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Me cu y’s egoli h cha ac e is ics. Ica us, 268, 172-203.
h ps://doi.o g/10.1016/j.ica us.2015.11.040.
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po ous IDP en iched apo : Implica ions o Me cu y and ens a i e chond i e o igins.
Plane a y and Space Sciences 59, 1888–1894.
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