Seeking out life forms on Jupiter’s moons

The Euro­pean Space Agen­cy’s JUICE (Jupiter Icy Moons Explor­er) mis­sion was launched on 14^th April aboard an Ari­ane 5 rock­et from Kourou in French Guiana. The pur­pose of the mis­sion is to test the con­di­tions that could have led to the emer­gence of hab­it­able envi­ron­ments on three of Jupiter’s four icy moons (Europa, Ganymede and Cal­lis­to, all of which have oceans). It is sched­uled to reach the gas giant in July 2031. JUICE will be the first space­craft to orbit a moon in the out­er Solar Sys­tem, arriv­ing in Decem­ber 2034 in the orbit of Ganymede, the only moon in the Solar Sys­tem with a mag­net­ic field. Olivi­er La Mar­le, Head of Uni­ver­sal Sci­ence Pro­grammes at CNES, tells us the sto­ry of the mis­sion’s devel­op­ment and the role of CNES in the project.

At CNES, we are not involved in sci­en­tif­ic research as such, but we are respon­si­ble for ensur­ing France’s par­tic­i­pa­tion in inter­na­tion­al space mis­sions. In return, French sci­en­tists have access to the data obtained dur­ing these mis­sions and can then pub­lish arti­cles in sci­en­tif­ic jour­nals. These researchers do not come from CNES, but from CNRS, CEA and uni­ver­si­ty lab­o­ra­to­ries, for exam­ple. They are moti­vat­ed by their own research pri­or­i­ties – pri­or­i­ties that are com­mu­ni­cat­ed and refined dur­ing reg­u­lar fore­sight exer­cis­es coor­di­nat­ed by their research organ­i­sa­tions and CNES. The aim of these exer­cis­es is to iden­ti­fy projects that mer­it future fund­ing, and then to help them to be select­ed by the major agencies.

As the sci­en­tif­ic com­mu­ni­ty is inter­na­tion­al by nature, we col­lab­o­rate with oth­er major space agen­cies – such as ESA, NASA, the Chi­nese Space Agency (CNSA), the Japan Aero­space Explo­ration Agency (JAXA), and of course the oth­er Euro­pean nation­al agen­cies. We decide togeth­er which coun­try will be respon­si­ble for what. These col­lab­o­ra­tions are nec­es­sary because large-scale mis­sions like JUICE can­not be fund­ed by the CNES bud­get alone, nor by the French space com­mu­ni­ty in gen­er­al. The most tra­di­tion­al way of organ­is­ing such mis­sions is to entrust each coun­try with the task of devel­op­ing and build­ing part of the sci­en­tif­ic instru­men­ta­tion that will be car­ried on board. CNES’s role in this phase is to posi­tion France’s con­tri­bu­tion to the instru­ments in line with our nation­al areas of expertise.

The devel­op­ment of these major sci­en­tif­ic mis­sions involves a whole series of tests, mod­el­ling, and sim­u­la­tions to help define and devel­op a real­is­tic mis­sion that can be launched. Sci­en­tists play an essen­tial role in this exer­cise, as they alone can advise the agen­cies and their indus­tri­al part­ners to work towards a mis­sion that is both achiev­able and of suf­fi­cient sci­en­tif­ic inter­est. Cling­ing to unat­tain­able objec­tives can only lead to a dead end and the mis­sion being abandoned.

Our role here extends from finan­cial and tech­ni­cal sup­port for our nation­al lab­o­ra­to­ries, to coor­di­na­tion with part­ner space agen­cies and, ulti­mate­ly, to prepar­ing for the exploita­tion of the huge quan­ti­ties of data that will be obtained. This involves devel­op­ing extreme­ly reli­able mod­els, sim­u­la­tions, and soft­ware to inter­pret the huge quan­ti­ty of images and spec­tra that will be obtained. For exam­ple, for Euclid¹, anoth­er ESA mis­sion, images of one bil­lion pix­els will be obtained every ten min­utes. These data will also have to be com­bined with those from exist­ing tele­scopes, such as the James Webb telescope.

There is a lot of prepara­to­ry work to be done, and a cer­tain amount of sci­en­tif­ic com­pe­ti­tion, the researchers who pub­lish their results first will be the most vis­i­ble. If a mis­sion from anoth­er agency is not on the list of top pri­or­i­ties for French sci­en­tists, we will work on a more mod­est instru­men­tal con­tri­bu­tion. On the oth­er hand, on space mis­sions such as JUICE, we are heav­i­ly involved, being entire­ly respon­si­ble for one of the 10 instru­ments on board. This is the infrared spec­trom­e­ter, a large, com­pli­cat­ed, and expen­sive instru­ment. We have also con­tributed to the devel­op­ment of half a dozen oth­er instru­ments. This is by far the largest con­tri­bu­tion of any Euro­pean coun­try. The com­po­nents of the oth­er instru­ments were sup­plied by oth­er Euro­pean agen­cies, in addi­tion to NASA and JAXA. These include an opti­cal cam­era, var­i­ous spec­trom­e­ters, an altime­ter, a radar, par­ti­cle detec­tors and a magnetometer.

As head of the astro­physics theme at CNES at the time, my role includ­ed defin­ing and set­ting up the French con­tri­bu­tions to Euclid and to SVOM (a joint Fran­co-Chi­nese mis­sion ded­i­cat­ed to the detec­tion and detailed study of phe­nom­e­na known as gam­ma-ray bursts, to be launched in 2024). For Euclid, this involved numer­ous meet­ings with the CNRS, the CEA and the main agen­cies involved (ESA, the Ital­ian Space Agency, and the UK Space Agency in par­tic­u­lar). For SVOM, we col­lab­o­rat­ed with the CNSA, which required numer­ous trips to Shang­hai and Bei­jing to reach agree­ment on a text incor­po­rat­ing every­one’s con­tri­bu­tions. This goes as far as know­ing how many French or Chi­nese sci­en­tists authors of the result­ing sci­en­tif­ic pub­li­ca­tions will be. The ques­tion of the bud­get is of course essen­tial: how much will the French con­tri­bu­tion cost, and will we have the nec­es­sary resources?

France is unique in hav­ing a nation­al space agency that also has a tech­ni­cal cen­tre. We can boast expe­ri­enced engi­neers who know how to suc­cess­ful­ly car­ry out space mis­sions and who have built satel­lites from A to Z. When we decide to con­tribute to a mis­sion, we know that we have a pool of CNES engi­neers who will take charge of the tech­ni­cal aspects or entrust them to CNRS or CEA lab­o­ra­to­ries inter­est­ed in the mis­sion, pro­vid­ing them with finan­cial and tech­ni­cal sup­port. Unlike oth­er Euro­pean coun­tries, France does not nec­es­sar­i­ly need to sign a con­tract with indus­try to car­ry out a pre­lim­i­nary study.

The infrared spec­trom­e­ter we have devel­oped for JUICE is the result of more than 15 years of tech­ni­cal development.

We are work­ing on a rel­a­tive­ly long-time hori­zon when we draw up our strate­gies, because the mis­sions we are cur­rent­ly prepar­ing and par­tic­i­pat­ing in will be launched in the 2030s. One of the areas we are work­ing on is minia­tur­i­sa­tion: when we send probes into space, one of the main prob­lems is the mass of the pay­load. On a probe like JUICE, for exam­ple, over 90% of the mass comes from the body of the satel­lite itself and the fuel used to pro­pel it. The on-board instru­ments must there­fore weigh no more than a few tens of kilo­grams. Com­pared with stan­dard lab­o­ra­to­ry equip­ment, this is very light: it is dif­fi­cult to man­u­fac­ture a spec­trum analyser or an infrared spec­trom­e­ter that can with­stand the extreme con­di­tions of space, that fits into a small space and is lim­it­ed in mass.

The infrared spec­trom­e­ter we devel­oped for JUICE weighs around 40 kg and is the result of more than 15 years of tech­ni­cal devel­op­ment in col­lab­o­ra­tion with researchers at the Insti­tut d’As­tro­physique Spa­tiale d’Or­say, experts in this field.

The JUICE mis­sion has been recog­nised by the author­i­ties and researchers as being of the utmost impor­tance. Some of Jupiter’s moons have ice crusts under which there may be liq­uid oceans that could ben­e­fit from tem­per­ate con­di­tions. Although we won’t be able to see what lies beneath the ice, the onboard instru­ments will enable us to probe this envi­ron­ment and analyse its com­po­si­tion. The sci­en­tif­ic com­mu­ni­ty was very enthu­si­as­tic about this prospect and the project was iden­ti­fied very ear­ly on as a top pri­or­i­ty. In fact, it was select­ed by ESA in 2012, ahead of two oth­er can­di­dates: the Advanced Tele­scope for High Ener­gy Astro­physics (ATHENA) and the New Grav­i­ta­tion­al Wave Obser­va­to­ry (NGO, lat­er renamed LISA), which were also sub­se­quent­ly select­ed. It is also the first L‑class probe in ESA’s Cos­mic Vision 2015–2025 programme.

Ulti­mate­ly, JUICE will help us under­stand whether the con­di­tions on Jupiter’s moons are, or were, poten­tial­ly favourable for life. The inter­nal struc­ture, mag­net­ism, the pres­ence of a rocky soil at the bot­tom of liq­uid oceans, its con­tri­bu­tion of min­er­al salts, the thick­ness and topol­o­gy of icy crusts, the pres­ence of pock­ets of water, the seis­mic effects caused by Jupiter’s enor­mous mass, not for­get­ting the study of the giant itself and its atmos­phere, are just some of the results expect­ed from the mission.

Why do the moons of Jupiter have an icy crust when the moons of the oth­er plan­ets in our solar sys­tem do not? Why do some have CO2 atmos­pheres and oth­ers nitro­gen or methane, even though they all formed in the same ini­tial soup? Why did they evolve in com­plete­ly dif­fer­ent ways, and what fuelled this evo­lu­tion? Was it the effect of mag­net­ic fields or the tidal effect of Jupiter? JUICE will answer all these ques­tions, which cur­rent­ly remain unanswered.

The pos­si­bil­i­ty of find­ing forms of life else­where is of course fas­ci­nat­ing. More gen­er­al­ly, every time we vis­it objects in the Solar Sys­tem, we dis­cov­er that each of them is unique. JUICE’s dis­cov­er­ies will not dis­ap­point us in this respect.

Interview by Isabelle Dumé

Ref­er­ences

https://​www​.esa​.int/​S​c​i​e​n​c​e​_​E​x​p​l​o​r​a​t​i​o​n​/​S​p​a​c​e​_​S​c​i​e​n​c​e​/​Juice

https://​www​.esa​.int/​S​p​a​c​e​_​i​n​_​M​e​m​b​e​r​_​S​t​a​t​e​s​/​F​r​a​n​c​e​/​E​u​c​l​i​d​_​u​n​e​_​m​i​s​s​i​o​n​_​d​e​s​t​i​n​e​e​_​a​_​p​e​r​c​e​r​_​l​e​s​_​m​y​s​t​e​r​e​s​_​d​e​_​l​_​e​n​e​r​g​i​e​_​n​o​i​r​e​_​e​t​_​d​e​_​l​a​_​m​a​t​i​e​r​e​_​noire