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