Deep Trek: Missions Concepts for Exploring Subsurface Habitability &

Deep Trek : Missi o n Concepts f or Exploring Subsurface H a bit a bilit y & Lif e o n M ars A Windo w into Subsurface Life i n the Solar Syste m

L e a d A ut hor : Charles D. Ed wards (Jet Propulsion Laboratory, California Institute of Technology ).

C o ntact : Charles. D. Ed wards @j pl. . g o v

C o -A ut hors : 1. Vlada Sta men kovi ć Jet Propulsion Laboratory, California Institute of Technology 2. Penelope Boston N A S A A mes 3. Kennda Lynch L PI / USR A 4. Jesse Tarnas Bro wn Uni versity 5. Barbara Sher wood -Lollar University of Toronto 6. Sushil Atreya University of Michigan 7. Ale xis Te mpleton University of Colorado 8. Anthony Free man Jet Propulsion Laboratory, California Institute of Technology 9. Wood ward Fischer California Institute of Technology 1 0. Til man Spohn International Space Science Institute 1 1. Chris Webster Jet Propulsion Laboratory, California Institute of Technology 1 2. Alberto G. Fairén Centro de Astrobiología ( C SI C -I N T A) 1 3. John (Jac k) Mustard Bro wn University 1 4. Michael Mischna Jet Propulsion Laboratory, California Institute of Technology 1 5. Tullis C. Onstott Princeton University 1 6. Magdalena Rose Osburn North western University 1 7. Tho mas Kieft N M T 1 8. Robert E. Gri m m S w RI 1 9. Willia m B. Brinc kerhoff N AS A Goddard 2 0. Sarah Johnson Georgeto wn University 2 1. Luther Beegle Jet Propulsion Laboratory, California Institute of Technology 2 2. Ja mes Head Bro wn University 2 3. Albert Halde mann ES A/ EST EC 2 4. Charles Coc kell University of Edinburgh 2 5. John Hernlund E L SI, To kyo Tech 2 6. Brian Wilco x J P L / Marine Bio mass 2 7. David Paige UCL A 2 8. Giuseppe Etiope Istituto Nazionale di Geofisica e Vulcanologia, Ro ma, Italy 2 9. Daniel Glavin N A S A Goddard Space Flight Center 3 0. Maria -Paz Zorzano Centro de Astrobiología ( C SI C -I N T A) 3 1. Yasuhito Se kine E L SI, To kyo Tech 3 2. Stalport Fabien LIS A 3 3. Joseph Kirschvin k California Institute of Technology 3 4. Cara Magnabosco E T H 3 5. Roberto Orosei Istituto Nazionale di Astrofisica

A Windo w into Subsurface Life in the Solar Syste m i © 2 0 2 0. All ri g hts reser ve d.

Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

3 6. Matthias Grott D L R 3 7. John D. Ru m mel Friday Harbor Partners L L C 3 8. Atsu ko Kobayashi Earth -Life Science Institute, To kyo institute of Technology 3 9. Fu mio Inaga ki J A MSTEC 4 0. Janice Bishop S E TI Institute 4 1. Vincent Chevrier University of Ar kansas 4 2. Mary Sue Bell Jacobs @ N AS A / 4 3. Beth N. Orcutt Bigelo w Laboratory for Ocean Sciences 4 4. Jennifer McIntosh University of Arizona 4 5. Katarina Milj kovic Curtin University 4 6. Doris Breuer D L R 4 7. To mohiro Usui J A X A 4 8. Kris Zacny Honeybee Robotics 4 9. Essa m Heggy University of Southern California 5 0. Edgard G. Rivera -Valentín Lunar and Planetary Institute ( U S R A) 5 1. Nathan J. Barba Jet Propulsion Laboratory, California Institute of Technology 5 2. Ryan Woolley Jet Propulsion Laboratory, California Institute of Technology 5 3. Oliver Warr University of Toronto 5 4. Mi ke Malas ka Jet Propulsion Laboratory, California Institute of Technology 5 5. Jennifer G. Blan k N A S A A mes / Blue Marble Space Institute of Science 5 6. Donald F. Ruffatto Jet Propulsion Laboratory, California Institut e of Technology 5 7. Haley M. Sapers Caltech / U S C /J P L 5 8. Larry H. Matthies Jet Propulsion Laboratory, California Institute of Technology 5 9. Le wis Ward Harvard University 6 0. Svetlana Sh kolyar N AS A GSFC/ USR A 6 1. Cedric Sch melzbach E T H Zurich, S witzerland 6 2. Travis S.J. Gabriel Arizona State University 6 3. Ceth Par ker Jet Propulsion Laboratory, California Institute of Technology 6 4. Her mes Hernan Bolivar -Torres Universidad Nacional Autóno ma de Mé xico 6 5. Bernadett Pál CSFK KT M CSI 6 6. Dir k Schulze -Ma kuch Technical University Berlin 6 7. Jorge Andres Torres Celis Universidad Nacional Autóno ma de Mé xico 6 8. A kos Kereszturi Research Centre for Astrono my and Earth Sciences 6 9. J. Andy Spry S E TI Institute 7 0. Kyle Uc kert Jet Propulsion Laboratory, California Institute of Technology 7 1. Marc A. Hesse The University of Te xas at Austin 7 2. Rachel Harris Harvard University 7 3. A na -C atalina Plesa D L R 7 4. Renyu Hu Jet Propulsion Laboratory, California Institute of Technology 7 5. Ali -a kbar Agha -moha m madi Jet Propulsion Laboratory, California Institute of Technology 7 6. Brian D. Wade Michigan State University 7 7. Sneha moy Chatterjee Michigan Technological University 7 8. Patric k Mc Garey Jet Propulsion Laboratory, California Institute of Technology 7 9. Heather Valeah Graha m N AS A GSFC 8 0. Shino Suzu ki J A MSTEC 8 1. Matt Schren k Michigan State University 8 2. Kristopher Sherrill Jet Propulsion Laboratory, California Institute of Technology 8 3. Scott Ho we Jet Propulsion Laboratory, California Institute of Technology

A Windo w into Subsurface Life in the Solar Syste m ii Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

8 4. Raju Manthena Jet Propulsion Laboratory, California Institute of Technology 8 5. Mari ko Burgin Jet Propulsion Laboratory, California Institute of Technology 8 6. Kalind Carpenter Jet Propulsion Laboratory, California Institute of Technology 8 7. Louis Giersch Jet Propulsion Laboratory, California Institute of Technology 8 8. Velibor Cor mar kovic Jet Propulsion Laboratory, California Institute of Technology 8 9. Nigel S mith Snolab 9 0. Jeffrey J. Mc Donnell University of Sas katche wan 9 1. Joseph Michals ki University of Hong Kong 9 2. Devanshu Jha M VJ College of Engineering 9 3. Morgan L. Cable Jet Propulsion Laboratory, California Institute of Technology 9 4. Elodie Gloesener U C Louvain 9 5. Varun Paul Mississippi State University 9 6. Ste wart Gault University of Edinburgh 9 7. Sharon Kedar Jet Propulsion Laboratory, California Institute of Technology 9 8. Eloise Marteau Jet Propulsion Laboratory, California Institute of Technology 9 9. Or kun Te mel Royal Observatory of Belgiu m 1 0 0. Seth Krieger U S C 1 0 1. Ryan Ti money University of Glasgo w

LI N K t o List of C o -A ut hors & C o -Si g n at ori es: https://drive.google.co m/file/d/1qogP3k AubSt918v1 MSo Bvqt Tl Y N Q E_cS/view?usp =sharing

A Windo w into Subsurface Life in the Solar Syste m iii Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

1. M otivati o n : A n Unprecedented Scientific Opportunity A c o m pa ni o n w hite pa per e ntitle d “ Dee p Tre k: Scie nce of S u bs urface Ha bita bility & Life o n Mars ” highlights the i m mense sc ience return potential of Mars subsurface exploration. Here we focus on missi o n c o nce pts, dri vi n g scie nce o bjecti ves, a n d technologies t hat e na ble access t o a maj or ne w fr o ntier i n pla netary scie nce , the Martian subsurface , wit h a f oc us o n m o der n s u bs urface ha bita bility & life. Differe nt missi o n arc hitect ur es spanning s mall spacecraft (SS C) , Discovery, Ne w Fr o nti ers, t o Fl a gs hi p cl ass es will ge nerate maj or disc o veries relati n g t o t he p ote ntial f or life i n t he Martia n su bsurface. find the water explore the (bio)geoche mistry Fi g . 1: E xploration of the Martian subsurface with S S Cs, Ne w Frontiers & Flagship mission concept s using the V ALKYRIE concepts . S S Cs with liquid water sounders can detect ground water to depth s of many kilo meters (a) . Ne w Frontiers -type mission concept s would allo w more advanced & co mplete characterization of subsurface habitability with drills accessing sa mples to depths of 1 0 -1 0 0 m (b) . a) b) T h e arc hitect ures sho wn here b el o n g t o a cl ass of missi o n co nce pts c all e d VALKYRIE : “ V olatiles A n d L ife: K eY R econnaissance & In-Situ E x pl orati o n ”. Building a bridge over four decades fro m t he first dari n g missi o n t hat searc h e d f or si g ns of e xta nt life on Mars wit h t he 1 9 7 6 Vi king la nders , the V AL K Y RI E mission concepts re -address the question of whether there could be habitable environ ments and/ or life o n Mars t o day. H o wever , VAL KYRIE f ocus es o n t he m ost li kely p ote ntial m o der n habitable environ ment , the Martian subsurface , im ple me nti n g c utti n g -e d ge tec h n ol o gies & leveragi ng o ur scie ntific understan d i n g o f Mars a n d terrestrial s u bs urface life , all of w hic h ha ve greatly i mproved si nce t he Vi king missi o n era .

2. Science Goals & Objectives The mission concepts proposed here ai m t o r es p o n d t o s o m e or t o all of t h e t w o s ci e n c e g o als specified in our co mpanion paper. These science goals are: (G 1) quantify modern Martian s u bs urf a c e h a bit a bilit y a n d ( G 2) s e ar c h f or e vi d e n c e of e xt a nt s u bs urface lif e . O ur Missi o n G oal (1), s u bs urface ha bita bility e x pl orati o n , has t hree o bjecti ves ( s e e o ur Scie nce Tracea bility M atri x, S T M i n Fi g . 3 ): ( A) l ocate & c haracterize li q ui d w at er, ( B) i d e ntif y e ner gy & n utri e nt s o ur c es, a n d ( C) assess m ol e c ul ar a n d c ell ul ar st a bilit y p ot e nti al wit h de pt h . W het her li q ui d water e xists o n Mars t o day is e x pl ore d wit h t he first o bjecti ve. T he sec o n d o bjecti ve f oc uses o n t he a vaila bility of re d o x n utrie nts a n d e ner gy gra die nts t hat c o ul d dri ve micr o bial meta b olic acti vity by deter mi ni n g t he ( bi o) ge oc he mical a n d mi neral o gical state of t he s u bs urface. T he t hir d o bjecti ve i n vesti gates m olec ular a n d cell ular sta bility, by deter mi ni n g h o w dee p i o nizi n g ra diati o n a n d o xi dizi n g ra dicals penetrate into the Martian subsurface. This leads t o a f o urt h o bjecti ve , directly a d dressi n g Missi o n G oal 2 , t o ( D) searc h for si g ns of exta nt s u bs urface life by l o o ki n g f or bio markers & si g ns of meta b oli c acti vity . Landing sites have been discussed in our co mpanion paper “ Deep Trek: Science of S u bs urface Ha bita bility & Life o n Mars ”. O ur missi o n c o nce pts are als o li n ke d t o secondary science g oals s uc h as see ki n g si g ns of e xti nct life, rec o nstr ucti n g cli mate hist ory, ge o p hysical structure of t he cr ust , resource prospecting & hu man exploration (see Sta menkovi ć et al., 2 0 1 9).

A Windo w into Subsurface Life in the Solar Syste m 1

Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

3. Scie nce Tracea bility & O bj e cti v es 3.1. O bj e cti v e A : Is T h er e Ground water To day ? Li q ui d w at er wit h s uffi ci e ntl y hi g h w at er a cti vit y is ess e nti al f or lif e as w e k n o w it. O n M ars, foll o wi n g t h e (li q ui d) w at er l e a ds us t o de pt hs of m a n y kilo meters . The proposed investigations would deter mine the a mount of adsorbed subsurface water as a function of depth, as well as t he de pt h , t hick ness , a n d c he mistry of t he p utati ve gr o u n d water ta ble hy p ot hesize d t o e xist ma ny kil o meters bel o w t he surface ( A 1 , A 2). T his may be ac hie ve d by usi n g a tra nsie nt electr o m a g netic s o u n der ( T E M) fro m the surface without any drilling , w hic h meas ures t he electrical c o n d ucti vity of t he s u bs urface a n d i n verts t h ose data i nt o pr ofiles of li q ui d water abundance , hy drati o n a n d sali ni ty a n d has bee n o ne of the most co m mon techniques to search for ground water on the Earth in the last three decades . T he electrical c o n d ucti vity will hel p us t o deter mi ne t he c o nce ntrati o n of i o ns i n t he ground water by relati n g the meas ure d electrical c o n d ucti vity t o p ote ntial i o nic c o m p ositi o ns . Measure ments o f t he subsurface geother mal gradient wit h de pt h ( A 5 à M 3, M 7) will hel p f urt her c o nstrai n t he c o m p ositi o n of the ground water through co mparison with d ata f or freezi ng -p oi nt depression in the presence of salts . Meas uri n g t he p or osity c ha n ge wit h de pt h will all o w us t o e xtra p olate , beyond the accessible drilli n g de pt h , t he water st ora ge ca pacity a n d t he p hysically ha bita ble s pace a vaila ble ( A 3) . It is i m porta nt to note t hat eve n i n t he u nlikely case of a l o c al n o n -detecti o n of ground w at er, t his fi n di n g w o ul d all o w us t o p ut c o nstr ai n ts on global water inventories (i n c o m bi n ati o n wit h measure ments of the porosity, the unaltered hydration state and the salt content with depth ) a n d b e a si g nifi c a nt a n d s ur prisi ng discovery b y its elf.

3. 2. O bj e cti v e B : Geoche mical Gradients with Depth T he pr o p ose d i n vesti gati o ns w o ul d all o w us t o deter mi ne t he ge oc he mical ( B 1) a n d mi neral o gical ( B 2) pr o perties of the Martia n s u bs urface t o de pt hs of at least 1 0 m ( threshold ) b ut ai mi n g f or 1 0 0 m (baseli ne ). Drilli n g t o 1 0 m w o ul d be s ufficie nt t o miti gat e s urficial te m perat ure variati o ns ( bel o w ~ 5 m), t o test hy p ot heses o n cell ular de gra dati o n as a f u ncti o n of de pt h d ue t o prese nce of c ha otr o pic o xi da nts (e.g., perc hl orates) a n d i o nizi n g ra diati o n, a n d t o be c o nser vati vely far e n o u g h fr o m t he hi g hly o xi dizi n g a n d ra diati o n -i nte nse s urface e n vir o n me nt t o o bser ve p hysic o -c he mical c o n diti o ns m ore re prese ntative of a n is olate d dee per su bsurface. H o w e v er, dril li n g t o ~1 0 0 m w o ul d i ncrease scie ntific ret ur n co nsi dera bly by per mitti n g meas ure me nts of lar ger -s c al e re d o x gr a di e nts, which would enable develop ment of ne w water inventor y a n d s u bs urface ha bita bility m o d els . T his will f or m t h e b asis f or extrapolating me asure ments a n d m o d els do wn to regions at k m - de pt hs w here gr o u n d w at er wit h a hi g h er w at er a cti vit y is m or e li k el y ( which V AL K Y RI E would not access p h ysi c all y ). Of partic ular f oc us will be t he c haracterizati o n of c he mical re d o x gra die nts a n d dise q uili bria , a n d s pecifically t he o xi dati o n state s of S, Fe , N a n d M n co mpounds i n s oil ( M 8) a n d mi nerals ( M 9) as a f u ncti o n of de pt h, u naltere d fr o m h ostile s urface c o n diti o ns . T he Fe -M n pair pr o vi des es pecially good constraints on redox conditions a n d water a vaila bility wit h de pt h, as Fe a n d M n nee d very differe nt c o nce ntrati o ns of o xi da nts a n d li q ui d water to be o xi dize d. Exposed scarps on the surface and shallo w caves are continuously altered by the at mosphere and d o , h e n c e, n ot pr o vi d e t h e i nsi g ht t h at d e e p v erti c al drilli n g pr o vi d es .

3. 3. O bj e cti v e C : C ell ul ar St a bilit y wit h D e pt h P r o p ose d i n vesti gati o ns w o ul d test e xisti n g hy p ot heses a n d m o dels o f t he abundance of o xi da nts ( C 1) a n d i o nizi n g ra diati o n ( C 2) as a f u ncti o n of de pt h. By accessi n g sa m ples t o at least ~ 1 0 m, we i ncl u de t he w orst -case pre dicti o n s of t he de pt h w here cells c o ul d still sustain da mage ( Dart nell et al., 2 0 0 7) .

3. 4. O bj e cti v e D : W hiffs & Fi nger pri nts of Exta nt Life We pr o p ose a t hree f ol d strate gy f or searc hi n g f or si g ns of e xta nt life i n t he Martia n s u bs urface. T his f ocus es o n or ga nic ( D 1) a n d i n or ga nic ( D 2) i n dicat ors of life, by measuri ng the relative abundances

A Windo w into Subsurface Life in the Solar Syste m 2

Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars of a mi n o aci ds, li pi ds, bi o m olec ules, meta b olic by pr o d ucts, is ot o pic si g nat ures i n m ulti ple or ga nic a n d inorganic carbon c o m p o u n ds, a n d bi o mi nerals a n d micr ostr uct ures. T he c ha n ge in de pt h of these bi osi g nat ures, es pecially i n relati o n t o variati o ns i n mi n eral hy drati o n states, will hel p us e x pl ore w het her we see i n dicati o ns of a dee p bi os p here. A d di n g sa m pli n g of trace gases or v olatile meta b olic by pr o d ucts ( D 3) a n d t heir varia bility wit h de pt h a n d ti me will pr o vi de f urt her infor mation regard i n g t he li keli h o od of o bservi ng t he first evide nce of exta nt su bsurface life.

4. Instru ments 4.1. Ground water Sounders : Fi n d t h e Li q ui d S u bs urface W at er Wit h o ut Drilli n g T he m ost pla usi ble met h o d at prese nt f or gr o u n d water detecti o n to de pt hs of ma ny kil o meters is tra nsie nt electr o m a g netic ( T E M) s o u n di n g fr o m a pla net’s s urface ( or biti n g assets ca n n ot a d dress t he existence of ground water on Mars at the sounding depths that are needed) , which operate s at l o wer frequencies than radar measure ments , t here by pe netrati n g f ar dee per . T he T ra ns missi ve H 2 O R econnaissance ( T H 2 O R) T E M i nstr u me nt u n der de vel o p me nt at J P L has ac hie ve d a T R L of 4 wit h a ntici pate d T R L of 6 by 2 0 2 3 , < 1 0 k g, 3 u, < 5 0 0 W h /s ol ). T his lo w -mass instr u me nt is key f or a subsurface mission to Mars of any budg et class, as it will r o b ustly test f or t he prese nce of gr o u n d water a n d deter mi ne t he p hysical a n d c he mical pr o perties of gr o u n d water reser v oirs t hat e xta nt Martia n life c o ul d i n ha bit. Pe netrati o n de pt h i n t o the Martian subsurface by the orbiting radar M A RS I S o n Mars Express and S H A R A D on M R O has likely been li mited to depths of ~100 -2 0 0 m, e xce pt f or “re gi o ns wit h fa v ora ble s u bs urface c o n diti o ns ” wit h ice or v olca nic as h (see Still ma n & Gri m m, 2 0 1 1) . Ground pe netrati ng surface ra dar a n d a seis mic stati o n ca n assist T E M s o u n ders t o better c o nstrai n ground water inventories, by deter mining distinct subsurface layers .

4. 2. Drills : A c c ess S u bs urf a c e ( Bio) Geoche mi cal Gra die nts T he drill o n Curiosity has been used to access depths of ~ 7 c m a n d t he drill is desi g ne d t o reac h si milar de pt hs. Drills reac h i n g 1 – 1 0 m i n ty pical Mars subsurface materials (c o m pete nt & fria ble r ocks ) have been de monstrated u n der si m ulate d or Mars a nal o g ue c o n diti o ns at T R L s of 5 -6 a n d are c o m pati ble wit h Ne w Frontiers -clas s lander missions (e.g. , Exo Mars Drill , Icebrea ker , M ART E , Pla netary Dee p Drill [P D D ]). The P D D wireli ne d rill (at T R L 5 a n d 7 0 k g ) fro m Honeybee R o b otics has drille d 1 3. 5 m i n t o g y ps u m ( drilling could have progressed Fig . 2 : (a) Wireline drill ASG AR D . Drilling is feasible to 1 0 0 m with deeper but was halted due to li mited Ne w Frontiers cap on In Sight -li ke platfor m. (b) M obile P D D. funding ). T o get t o de pt hs of ~ 1 0 0 m and more , w hil e still re mai ni n g c o m pati ble wit h a Ne w Fr o ntiers class lander mission , wireli ne drilli n g a p pr oac hes are a p peali n g: P D D, f or e xa m ple, was teste d s uccessf ully i n 2 0 1 9 t o a de pt h of 1 1 1 m i n ice (Es hel ma n n et al., 2 0 1 9 ; B hartia et al., 2 0 1 9 ), w hic h has a si milar hardness to rocks in Gale crater . J P L’s A res S u bs urface G reat A ccess & R esearc h D rill ( A S G A R D , Fi g . 2 a, T R L 5 targeted in 2020 ) is a n ot her mi niat urize d wireli ne drill wit h a tar get mass bel o w 5 0 k g , us i n g o n average less tha n 1 0 0 W of s olar p o wer a n d c o m presse d C O 2 harveste d in situ fr o m the Martia n at m os p here as drilli n g fl ui d. F or b ot h wireli ne drills , c utti n gs w o ul d be deli vere d i n stratigra p hic or der wit h a res ol uti o n ca pa bility of ~ ce nti meters . Usi n g i n -borehole instru men ts (as f or a n enhanced missi o n sce nari o) ca n i ncrease t his strati gra p hic res ol uti o n t o m m (t his has bee n de m o nstrate d by P D D i n Gree nla n d). T h e a d v a nt a g e of wir eli n e drills is t h at drilli n g c a n pr o c e e d to depths much greater than ~1 0 0 m wit h o ut a n y si g nifi c a nt i ncrease i n i nstr u ment mass —

A Windo w into Subsurface Life in the Solar Syste m 3

Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars providing the opportunity to go beyond 100 m in an extended missi o n mo de (t he o nly c ost t o go deeper is the mass of the tether , w hic h is <1 kg/k m of tether , a n d t he ti me f or drilli n g). O n e c h all e n g e of wir eli n e syste ms is t hat drilli n g m ust occ ur i n ge ol o gically c o m pete nt material t o pre ve nt b ore h ole c olla pse. F ort u nately, ( i) s u c h m at eri als (including volcanic and sedi mentary lit h ol o gi es) are co m mon and widespread on Mars , ( ii ) t h e y ar e w ell -s uit e d t ar g ets f or astro biological s u bs urface scie nce , a n d ( iii ) b or e h ol e st a bilit y i s g e n er all y n ot a n iss u e i n s u c h r o c ks. F or e xa m ple, t he 1 3. 5 m b ore h ole drille d by P D D i n a gy ps u m q uarry i n 2 0 1 5 is still o pe n. Boreholes in petroleu m/natural g as i njecti o n a n d pr o d ucti o n wells, a n d t h ose fr o m e x pl orati o n drilli n g in the mining sector, often re main open for decades . O n Mars , d ue t o t he l o wer gra vity a n d t he l o wer seis mic stresses, b ore h ole s s h o ul d re mai n sta ble t o de pt h s of hu ndreds of meters ( Zacny & Bar - C o he n, 2 0 0 9) . Lastly, all t he 1 0 0 + m drills discusse d here, i ncl u di n g c oile d t u bi n g drills li ke Re d Water t hat ca n drill i n a ny ki n d of s oil, are c o m pati ble wit h Curiosity -class r o vers t hat w o ul d be Fla gs hi p class missi o ns (Fi g. 2 b for P D D ). N ot e : In Sight ’s H P 3 mole ( Spohn et al., 2 0 1 8) was designed for penetration through loose soil. A mole is not baselined for any of the missions propose d here .

4. 3. Bi o -geoche mical/ R a di ati o n A n al ysis S uit e A m ulti -a nalytical a p pr oac h t o assessi n g t he s patially c orrelate d mi neral o gical, c he mical, a n d m olec ular c o m ple xity of a pr os pective ha bita ble e n vir o n me nt re mai ns t he m ost pr o misi n g strate gy f or bi osi g nat ure detecti o n. Mass s pectr o metry, ofte n c o u ple d wit h gas c hr o mat o gra p hy, is a pr o ve n technique for detection of volatile and refractory organics in planetary environ ments. Mass spectro metry can be coupled with various front -end sa mple introduction techniques including lasers f or s patially res ol ve d c o m p ositi o nal meas ure me nts a n d ca pillary electr o p h oresis f or water s ol u ble or ga nics. T he m ost rece nt e xa m ples of mass s pectr o meters desi g ne d f or fli g ht are t he Sa m ple A nalysis at Mars ( S A M) i nstr u me nt ( Ma haffy et al. , 2 0 1 2) o n Curiosity a n d t he Mars Organic Molecul e A nalyzer Mass Spectro meter ( M O M A -M S, Bri nc ker h off et al. , 2 0 1 3) , w hic h is fli g ht q ualifie d ( T R L 8). Mass s pectr o metry als o detects t he l o wer m olec ular wei g ht v olatiles re prese nti n g pr o d ucts of res pirati o n of e xta nt life such as C H 4 , C O 2 , N 2 , H 2 , O 2, a n d n o n -methane hydrocarbons ( Fi g . 3 , B 1, M 8; C 1, M 8). T he S A M quadrupole mass spectro meter has de monstrated stable isotopic measure ments of carbon ( Ma haffy et al. , 2 0 1 3) , nitr o ge n ( W o n g et al. , 2 0 1 3) , a n d s ulf ur ( Fra nz et al. , 2 0 1 7) , t h us meeti n g t he sta ble i s ot o pe s measure ment require ment ( Fig . 3 , D1, M12). I R spectroscopy, such as the Tunable Laser Spectroscopy ( T LS) on the S A M instru ment, is a high T R L, proven technique for meas uri ng t he abundance and isotopic co mposition of trace gases of biological intere st (e. g., We bster et al., 2 0 1 8 ) that co mple ments mass spectro metry and other co mpositional analyzers . A d diti o nal i nstr u me nts may i ncl u de the Wet Che mistry Laboratory ( W C L) deployed on Phoeni x f or re d o x c he mistry i de ntificati o n, che mical mapping through X -ray a n d fl u oresce nce s pectr o metry s uc h as PI X L, c he mical a nalysis t hr oug h laser -induced breakdo wn spectroscopy ( LI BS) ( Che m Ca m, Super Ca m), organic mapping wit h Ra ma n s pectr o meters ( S H E R L O C) a n d mi neral o gy wit h i ma gi n g s pectr o meters. D ee p U V Ra man spectrosco py is es pecially i ntri g ui n g d ue t o its a bility t o detect s mall c o nce ntrati o ns of ar o matic or ga nics. A n o n -board radio meter / hi g h -e nergy particle tracker w o ul d all o w f or c haracterizati o n of i o nizi n g ra diati o n le vels wit h de pt h.

5. Missi o n Co nce pt Arc hitect ures Beca use t he ( bi o) ge oc he mistry of t he s u bs urface of Mars has never bee n ex pl ore d in detail, t he afore mentioned instru ments can be mixed -a n d -matched dep e n di n g o n t he le vel of f u n di n g a vaila ble for a given mission. All budget classes have the capacity for significant discovery and advance ment of kno wledge regarding subsurface habitable environ ments on Mars and the possibility of extant su bsurface life. T h e infor mation belo w on mission cost is an outco me of an architecture Tea m X st u d y at J P L a n d work by o ur i nter nal J P L S S C T e a m perfor med i n 2018 -2 0 2 0 ( B ar b a et al. , 2 0 2 0).

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Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

5.1. S S C s: Find the Ground water W e c a n assess t he prese nce of gr o u n d w at er fr o m t h e M arti a n s urf a c e at l o w c ost i n t his d eca de . As descri be d i n t he Deca dal W hite pa per by Bar ba et al. (2 0 2 0), s mall s pacecraft are a n especially i mportant opportunity for Mars subsurface science. We have found that, using fully hosted pi g gyback o p p ort u nities, s uc h as wit h Mars Sa mple Return or Ice Mapper planned for 2026, we can ans wer s o me of t he lea di n g o bjecti ves ( gr o u n d water detecti o n & c haracterizati o n [ A 1 -A 2] as well as trace gas l ocalizati o n [ D 3]) at a n A -D c ost of ~ $ 1 2 0 M t otal. T o ac hie ve s uc h g oals, as a pri ority , t h is missi o n w o ul d deli ver a T E M li q ui d water s o u n der t o t he Martia n s urface wit h a rough lander such as S HI E L D (see Bar ba et al. 2 0 2 0) or t he si milar T R L 6 Fi n nis h La n der. If launched as a secondary , or pri mary payl oa d o n a de dicate d la u nc h ve hicle such as Falcon 9 , i n de pe n de ntly ma ki n g its way t o Mars, t he n A -D c osts f or o ne s mall la n der mis si o n w o ul d be ~ $ 1 5 0 -2 0 0 M wit h o ut la u nc h ( pl us u p t o ~ $ 6 0 M f or la u nc h c osts, e.g., wit h Falc o n 9) . If three S HI E L D landers, carrying the payload mentioned above, would be merged on a Falcon 9 under Class D require ments, then the costs for A -D w o ul d m o u nt t o ~ $ 3 0 0 M + la u nc h c osts. T his m ulti -u nit o pti o n i m proves o ur a bility to extra polate local res ults t o gl o b al w at er i n v e nt ori es a n d f a cilit at es a price / u nit dr o p b y ~ $ 5 0 -10 0 M — w hi c h c o ul d open up doors for sharing with international a n d c o m m er ci al part ners.

5. 2. Dis c o v er y Cl ass: M ulti pl e S S C s Rough La n ders or O n e I nSi g ht -t y p e L a n der

T he latter 3 -u nit rough lander concept , for exa mple , carrying a ground water sounder like T H 2 O R, w o ul d fit as well u n der the Discovery cap e ve n if syste m assurance is increased to a Class B mission. O ne si n gle herita ge -base d In Sight -type lander could also deliver one ground water sounder within the Disc o very b u d get. T he In Sight -ty pe c o nce pt le vera ges a hi g h herita ge a n d lo w ris k la n di n g syste m, w hile the S S C rough la n der c o nce pt has the a d va nta ge of deli veri n g the sa me instr u me nt at t hree differe nt l ocati o ns f or a si milar price as o ne si n gle In Sight la n der , probing the unexplored subsurface in different geologic contexts and enhancing the science return by pr o vi di n g a m ore gl o bal pers pecti ve on ground water distri b uti o n .

5. 3. Ne w Frontiers Class: Physical Access to the Subsurface is F e asi bl e T E M sounding fro m the surface for ground water is a critical objective for the V A L K Y RI E mission c o nce pts b ut t he scie nce ret ur n is si g nifica ntly e n ha nce d o nce a drill is a d de d t o sa mple subs urface redox gradients, going beyond objectives A1 and A2. We consider a basic instru ment suite such as o ne T E M, t wo I C C surface context ca meras, a M O M A G C -M S, a T L S, a M E T Stati o n, a Hi g h E ner gy Particle Trac ker a n d a heat pr o be c o n necte d t o t he drill. T o mi ni mize pla netary pr otecti o n pr ot oc ols a n d t otal mass, we ass u me t hat all baseli ne i nstr u me nts will be o n the surface as part of a n a nalysis s uite, wit h sa m ples bei n g deli vere d as t hey are bei n g drille d. W e fi n d t h at b y usi n g a n I nSi g ht -t y p e platfor m, we can address all the science goals of V A L K Y RI E, within a Ne w Frontiers -t y p e b u d g et. H o we ver, it is cr ucial t hat t he drill re mai ns bel o w 5 0 k g. T his is feas i ble f or a 1 0 m H o ney bee c oil t u bi n g drill li ke Re d Water, w hic h c o ul d o perate i n a ny ki n d of gr o u n d. T his mass li mit is als o i n reac h f or a 1 0 0 m wireli ne drill li ke J P L’s A S G A R D wit h near -ter m i n vest me nts ( Fi g. 2a).

5. 4. Fl a gs hi ps: V erti c al E x pl or ati o n wit h M o bilit y M o bilit y off ers t h e a d v a nt a g e of m ulti pl e drill sit es b ut m o v es t h e c ost i nt o t h e Fl a gs hi p Cl ass d o m ai n. T he class of drills pr o p ose d here ( 1 0 m a n d 1 0 0 m) is c o m pati ble wit h Curiosity / Perseverance - type rovers (see Fig . 2 b f or a 1 0 0 m P D D drill syste m). T he c o m plete enhanced V AL K YRI E sa mple a nalysis payl oa d, as descri be d i n Fi g. 3, is i n ma ny ways si milar t o t he payl oa d o n Curiosity / Perseverance . In co mparison to our Ne w Frontiers -type baseline scenario, our Flagship bas eli ne payl oa d i ncl u des a d diti o nally a Dee p U V Ra ma n i nstr u me nt ( S H E R L O C) a n d t he I C C ca mera is re place d wit h Che m Ca m/Super Ca m. In an enhanced missi o n sce nari o, a n a d diti o nal T L S ca n be a d de d as a do wn -

A Windo w into Subsurface Life in the Solar Syste m 5

Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars b ore h ole de vice t o pr ovide better c o nstrai nts o n su bsur face trace gases gra die nts . A d diti o nal i nstr u me nts as s h o w n i n Fi g. 3 ca n be i ncl u de d f or a n enhanced missi o n sce nari o .

Fig . 3 : Science Traceability Matri x ( S T M) . Identical measure ments are needed for a fe w objective s; if so, they are sho wn in brac kets, e.g., ( M 3, M 8 & M 1 2 ) for A 5 , C 1 & D 2 . The red bo xes indicate investigations that can be addressed without drilling with S S C s (ground water characterization with sounders and trace gas localization ). All other investigations require drilling of 1 0 -1 0 0 m (1 0 0 m being the baseline target ).

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Deep Trek: Missions Concepts for Exploring Subsurface Habitability & Life on Mars

6. Pla netary Protectio n Pla netary pr otecti o n w o ul d f oll o w t he rele va nt N A S A p olicies, kee pi n g i n mi n d t he Vi king missi o n g ui deli nes b ut wit h a d diti o nal re q uire me nts t o re m o ve left -over orga nics suc h as a mi n o aci ds, nucle o bases, a n d car b o xylic aci ds t o mi ni mize t he t otal exogenous organic carbon l oa d . By li miti n g t he use of i n -borehole instru ments (as i n o ur baseli ne sce nari o ), o nly t he drill , t he sa m ple deli very syste m , a n d t he C O 2 p u m pi n g syste m (f or wireli nes) w o ul d nee d t o be sterilize d . T his is feasi ble because the co mponents are steel /tita ni u m base d wit h n o electr o nics . Dry Heat Micr o bial Re d ucti o n or vari o us ty pes of gas sterilizati o n ca n als o be use d t o sterilize n o n steel /tita ni u m c o m p o ne nts.

7. Sy nergy wit h C o m m er ci al & H u m a n E x ploratio n Access t o water i n t he f or m of hy drate d salt s, ice or p ote ntially gr o u n d water is key f or e na bli n g h u ma n e x pl orati o n a n d settle me nt of Mars. T he sa me tec h n ol o gies e m pl oye d by scie nce -orie nte d Mars s u bs urface e x pl orati o n missi o ns will als o e na ble c haracteriz ati o n a n d utilizati o n of these key water - bearing resources required by future hu man Mars ex pl orers . Mars s ubsurface science therefore hosts unique potential for collaboration bet ween S M D and H E O M D, as well as c olla b orati o n wit h i nter nati o nal & c o m mercial p art ners w h o are i ntereste d i n e na bli n g h u ma n settle me nt of Mars.

8. Conclusions Decades of Mars exploration by orbital and landed spacecraft , coupled with kno wledge of Dee p Life o n t he Eart h , s uggest t hat t he s u bs urface of Mars may still h ost a l o n g -li v e d habitable environ ment that could co ntai n e xt a nt lif e. E x pl ori n g t his p ote ntially ha bita ble subsurface environ ment, and searching for extant life there, is the natural progression of t he last 2 -3 deca des that have been focused on ancient life , a n d is o pe ni n g u p a ne w e x pl orati o n pat h way t hat is co mple mentary to MS R and t he Perseverance r over’s scie nce g oals . S S C o ptio ns for c haracterizi ng ground water and Ne w Frontiers -type missions with drills to deter mine subsurface (bio)geoche mistry ar e fe asi bl e. Mars is t he nat ural test be d f or su bsurface ex pl orati o n t hat will i ne vita bly be a p plie d t o ot her , tec h n ol o gically m or e a m biti o us , targets suc h as t he su bsurfaces of icy m o o ns or s mall b o dies. T he pro pose d missio n co nce pts are not o nly releva nt to N AS A’s overarching & dri vi n g s ci e ntifi c g o als, b ut t a p i nt o t h e pri m ar y r e as o n t h e p u bli c fi n ds pla netary ex ploratio n exciti ng : t h e p ossi bilit y of e xta nt life o n ot her worl ds .

9. Refere nces Bar ba et al., 2 0 2 0. White Paper to The Decadal Survey in Planetary Science & . B hartia et al., 2 0 1 9. https://ui.adsabs.harvard.edu/abs/2019 A G UF M.P53 D3501 B/abstract Bri nc ker h off, W. et al ., 2 0 1 3 . I E E E . doi: 10.1109/ A E R O.2013.6496942 . Dart nell, L. R. et al., 2 0 0 7 . G R L 3 4 . doi.org/10.1029/2006 GL027494 Es hel ma n, et al., 2 0 1 9. Astrobiology. 1 9. doi.org/10.1089/ast.2018.1925 Fra nz, H. B. et al., 2 0 1 7. Nat. Geo. 1 0. doi.org/10.1038/ngeo3002 Ma haffy, P. et al., 2 0 1 2, Space Sci. Rev. 1 7 0 . doi.org/10.1007/s11214 -0 1 2 -9879 -z Ma haffy m P. et al, 2 0 1 3. Science 3 4 1 . d oi. or g / 10.1126/science.1237966 S p o h n et al., 2 0 1 8. Space Sci. Rev. 2 1 4 . doi.org/10.1007/s11214 -0 1 8 -0531 -4 Sta menkovi ć, et al., 2 0 1 9. Nat. Ast. 3. doi.org/10.1038/s41550 -0 1 8 -0676 -9 Still ma n D. E. & Gri m m, R. E.. J G R 116 . d oi . org / 10.1029/2010J E003661 We bster, C. R., et al. , 2 0 1 8. Sci. 3 6 0. doi.org/10.1126/science.aaq0131 W o n g, M. et al ., 2013 . G R L 4 0 . doi.org/10.1002/2013 GL057840 Zac ny, K. & Bar -C o he n, Y., 2 0 0 9. springer.co m/gp/book/9783642036286

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Ad ministration ( 8 0 N M 0 0 1 8 D 0 0 0 4). Pre -Decisional Infor mation – For Planning and Discussion Purposes Only . A Windo w into Subsurface Life in the Solar Syste m 7