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