A very remarkable mission has finally been brought to pass by the European Space Agency! Set to be launched in 2022, the JUICE (JUpiter ICEy moons Explorer) will venture into the Jovian system, with planned flybys at Jupiter’s moons Europa, Callisto, and finally Ganymede! A very ambitious project to reconnoiter the basic lay of these fascinating worlds and venture upon a voyage of discovery in hopes of finding locations of extraterrestrial life, the mission is set to arrive eight years after launch and last for three years!

The Giant of the Solar System: A Quick Glimpse

Jupiter is indeed quite a fascinating world because it is the largest planet of the solar system. A gas giant, it does not have a solid surface that we can observe. In fact, it has clouds made up of hydrogen and helium.  This is because of Jupiter’s great mass and its surface gravity that is 2.4 times that of Earth. In addition, owing to Jupiter’s relatively great distance from the sun, sunlight hitting it is 25 times weaker than it is on Earth. For all of these aforementioned reasons, hydrogen and helium molecules on Jupiter are not accorded enough energy or escape velocity to break free of Jupiter’s gravity and there they remain. The atmosphere is adjourned by churning colourful cloud top structures, belts, and zones that move about with high speeds and immense convective patterns. Nonexistent landmasses on Jupiter also mean hurricane-like storms cannot be broken up, leading to spectacular features, like the Great Red Spot. Temperatures at the cloud tops are relatively cool at -148 Celsius but as you go into the solid core which is layered by metallic liquid hydrogen, temperatures get increasingly hot at about 30,000 Celsius degrees! At such depths, the temperatures and pressures are increasingly immense that they smash out the hydrogen and helium into this remarkable liquid substance. Quite remarkably also, the bands at Jupiter’s equatorial region rotate 5 minutes faster than the bands at the equator. This astronomical phenomenon of differential rotation is indicative of the fluid nature of the Jovian surface. Jupiter, itself, also rotates in only 9 hours and 55 minutes which is quite a distinguishable thing, considering Jupiter’s immense size. The intriguing spin exerts forces on the planet which causes the equator to bulge and the poles to slightly flatten.

The Jovian System

With 28 moons and a giant planet, the Jovian system is well a solar system, figuratively speaking. In fact, Jupiter has often been dubbed “a failed star” — as it does share the mainly hydrogen composition of the Sun but it failed as a star since it was not massive enough to initiate a fusion reaction as that of the Sun. It settled rather well for a planet indeed, however.

Four of Jupiter’s moons (Io, Europa, Callisto, and Ganymede) are of particular interest. On the moon Io, Jupiter’s gravitational pull and the ensuing tidal energy result in phenomenal sulfur-rich magma fountains being ejected to immense heights of hundreds of kilometres. Io, however, does not make a particularly good candidate for alien life due to the immense energies generated on its surface, owing to its close proximity to Jupiter’s magnetic fields that blast it with charged particles. Io’s surface is coated by layers of erupted sulphur and sulphur dioxide frost. It possesses subterranean oceans of molten lava. Any potential organic molecules would have long been destroyed by Io’s hostile environment and any water would have long by ejected by the immense volcanism. The possibility of life however is not entirely precluded and if discovered, would lend intriguing implications about life elsewhere in this hostile solar system of ours.

Ganymede might offer a slightly more intriguing scenario for life. Jupiter’s moon Ganymede is the largest moon and satellite in the solar system, even exceeding planets like Mercury and Pluto in size. Ganymede’s relatively low density is indicative of considerable quantities of water and points to a mixture of icy and rocky material on the moon that are positioned in distinct layers. The icy surface is intricately patterned by geologically inactive highly cratered dark regions and lighter, younger grooved terrains permeated considerably with tectonics, indicating a history of tidal flexing and internal heating. Ganymede is also the only moon in our solar system that has its own self-generated magnetic field, and data has suggested its possession of a molten iron core, surrounded by a rocky mantle. Even though the geology of Ganymede’s surface does not show any effects of a subsurface liquid layer, the magnetic fields however are most probable indication of a thick layer of salty water deep below Ganymede’s icy surface. Ganymede’s oceans however are sandwiched between ice layers and are not associated with any hydro-thermal sources that can supply biogenic elements to power living processes, so the prospect of life in Ganymede also remains a bit unlikely. The possibility of earlier lifeforms in Ganymede’s 4 billion year history however cannot be precluded entirely and further exploratory missions might possibly yield interesting results and shed insights on the evolution of this remarkable Jovian system.

 

A similar moon to Ganymede in size and composition is Callisto. Callisto has a battered icy and rocky surface, covered considerably with craters. In fact, it is the most extensively cratered moon in the solar system. Furthermore, Callisto is quite a primitive world and very geologically inactive. Because it is the farthest moon from Jupiter, it experiences very little tidal heating. It is a cold, dead world with no volcanism or grooved terrains. It only shows a degree of partial differentiation. But since Callisto’s density is the lowest of all the four previously mentioned moons, it is therefore quite likely that there is a liquid layer beneath the layer. Movement of Callisto through Jupiter’s gravitational fields also shows signs of a magnetic induction signature which is indicative of a subterranean conductive liquid layer. It is an interesting possibility that  Callisto might hide an salty ocean abode capable of supporting primitive lifeforms.

 

Perhaps one of the best candidates for an alien ecosystem in the solar system is Jupiter’s moon Europa. Europa has a craterless icy surface interlaced with long features that crack into it, leading to many choatic icy blocks on the surface that move about and slide over deeper layers below the surface (first extraterrestrial ice bergs!). This is suggestive of tectonic plate activity occurring on Europa. The fractured appearance of Europa’s surface is suggestive of a tidal flexing mechanism that possibly squeezes icy material from beneath and onto the surface leading to those crack-like features that run through Europa. The tidal heating also lends reasonable credence to the notion of a subsurface ocean below Europa capable of harboring an alien abode. The tidal heat would keep the internal seas liquid enough and warm enough below the icy cap of Europa’s gleaming surface ice. Europa also has some evidence of warm material rising up to the surface, suggesting volcanism at the bottom of the ocean. Europa’s ice is too thick to allow sunlight to pass through the subterranean oceans and power life via photosynthesis but still one of the reasons why Europa is a great candidate for life is because here on Earth, life is still to thrive without sunlight when it comes to underwater seafloor volcanoes that supply  chemical energy and nutrients. Observations of Europa’s bright surface indicate asteroid impacts that may have possibly delivered organic compounds (hence the bright colour). Perhaps the persisting conundrum here for Europa is whether it might have enough chemical energy to power life. For many moons, radiation of the ice on the surface can produce oxidants. But for Europa, can any potential oxidants produced find their way into the subsurface ocean? Europa is continually hit by harsh radiation levels, increasing the possibility of oxidants on the surface. And, Europa’s icy surface is not too thick so as to ward off tectonic activity to stir the icy plates. So, it is quite possible indeed the active geologic activity of Europa could deliver the surface oxidants into the deep ocean waters of Europa and power the chemical reactions needed for life. Models also indicate the presence of silicates below the subsurface ocean which could leach important elements for life. But, it is not quite certain, however, whether Europa could have accumulated enough compounds in its early stages of formation so as to allow for life to develop. Of course, the only way to know for sure is to go and look!

 

The JUICE Mission

The JUICE spacecraft set to launch in 2022 might offer intriguing answers to the questions so far posed. The main goal of this ambitious mission is to study the icy moons Ganymede, Europa, and Callisto. The mission will explore the subsurface oceans of these moons in an attempt to look for chemical, thermal, or tidal energy sources that could power life. The GALA instrument on board (Ganymede laser altimeter) will be employed to gain information about the surface and topography of the moon Ganymede and also during flybys of Europa and Callisto. The GALA altimeter will also be employed to detect the subsurface ocean of Ganymede. The surface slopes of the icy moons will also be characterized to gain insights on the formation and evolution of these fascinating worlds.

The main goals of the JUICE mission are first to determine the composition of the non-icy materials on these moons. The instruments will attempt to determine what those materials are, analyze their spectra, and also characterize their origins and where they come from (subsurface oceans?). The second goal which is to search for liquid water will be accomplished using radio waves from the spacecraft’s radar. The radio waves will penetrate deep below the surface to study the subsurface structures and lakes. Finally, the third goal of the mission is to study the active geologic process that shape the surface of these moons. In particular, the spacecraft will attempt to study the underlying processes that continually repave the surface of the icy worlds and chaotically rearrange its jagged, chaotic terrains.

The mission itself is set to last 3.5 years. The spacecraft will use the gravity wells of the four Galilean moons to propel itself along. In the process, the spacecraft will monitor Jupiter’s atmosphere and magnetosphere. It will make two flybys of Europa and one flyby of Callisto and then possibly and finally attempt a landing at Ganymede to study the moon and its interactions with Jupiter. For Europa and Ganymede, moons where a lot of volatile material is thought to seep from the subsurface oceans and onto the surface, it will be easy to observe such processes. Doing so will yield tremendous insight on the internal oceans of these moons. Currently, the JUICE payload does not harbor any landers for the characterization process but suggestions are being made to employ something of the sort. However, with the cameras, spectrometers, and radars on board, this mission will certainly provide unprecedented information, tremendous insights, and most importantly will settle the question of lunar subsurface oceans once and for all. Exciting times ahead!

 

Featured image courtesy of: European Space Agency. Artist’s impression of JUICE spacecraft.