A very Jovian affair

It’s not just the monstrous gravity which gives Jupiter a unique hold over humankind. It has worked its way into our mythologies and become embedded in our imaginations over hundreds of years – and we are still captivated. Now, two new missions will continue the exploration of Jupiter’s moons – and maybe even help astronomers begin the hunt for life in the Jovian system…  

Raging storms, a colossal magnetic field and that red spot – there is an awful lot to be fascinated by when it comes to the largest plant in the Solar System. But it is the moons of Jupiter – all 67 of them – that have really grabbed the attention of astronomers of late.

Both NASA and the European Space Agency (ESA) will be launching missions in the 2020s to find out more about the incredibly diverse Jovian moons. But they will not, of course, be our first missions to the region. Since the 1970s more than 20 satellites have been successfully sent to the outer reaches of the Solar System sending back reams of data for scientists to analyse.

Water and an atmosphere – these are exactly the things that get astrobiologists very excited

And what jewels there were to uncover. From data sent back from the Galileo mission, launched in 1989, researchers discovered Europa possessed underground lakes, a smooth surface comprised of mainly solid water as well as a very weak atmosphere. Water and an atmosphere – these are exactly the things that get astrobiologists very excited. Then, a few months ago, the publication of an article in Astrophysical Journal2 (along with that of a separate paper published in 20133) suggested the presence of water vapour plumes on Europa. It is thought they rise about 125 miles before, presumably, raining material back down onto Europa’s surface.

This reignited the fascination with Europa because, if it does harbour life, these plumes could well present a sampling short-cut. Astronomers are busily imagining a mission which can swoop through these plumes rather than deal with tricky business of a lander. At the very least it would be a way to examine those enigmatic underground lakes. Certainly this is a tantalising prospect, but it is a way-off yet. Currently NASA and the ESA are planning a mission to research Europa that will leave in the early 2020s. The NASA Europa Mission will solely focus on this moon, while ESA’s will be more encompassing, including Jupiter and some of its other moons.

Dr Nicolas Altobelli, a scientist from the ESA’s solar system science operation division, is part of their JUICE (JUpiter ICy moons Explorer) mission. The mission aims at exploring Europa, Ganymede and Callisto, the magnetosphere and Jupiter. But why visit Jupiter and some of its moons? What’s the appeal compared to other planetary bodies in the Solar System? Dr Altobelli explains: “Jupiter and its icy moons are likely to be very common in our Galaxy. For many years, it has been suspected moons with an icy crust and on a slightly eccentric orbit around their host planet can maintain liquid water beneath their surface, owing to the tidal frictions driven by the varying distance to the host planet. “Since Cassini we have known that this is happening. At Enceladus, a Saturnian moon, the presence of an internal water ocean was confirmed, and even hydrothermal activity at the interface ocean-silicate core was inferred. This is a tantalising prospect for astrobiology and such moons could be a common habitat in the galaxy for life as we know it.”

NASA’s reasoning is similar. Europa is the most likely place to look for life according to Dr Curt Niebur, programme scientist for the Europa Mission at NASA. But that’s not all. “Europa is only one of the fascinating members of the Jupiter system. There is Io, the most volcanically active body in the solar system, far more active than Earth. This is a moon turning itself inside out. Ganymede, a moon as large as a planet, has its own deep buried ocean, a magnetosphere, and evidence of complex tectonic activity. There is also Callisto, possessing an extremely old surface that has captured the record of the very earliest time in our solar system.”

Jupiter possesses the largest magnetosphere in the Solar System, due to its quick rotation around its core and interactions in its liquid metallic hydrogen outer core

[caption id="attachment_57946" align="alignnone" width="620"] The strength of Jupiter's magnetosphere means that any spacecraft sent there either has to spend short periods of time in proximity to the planet or have some sort of radiation shielding to not be affected by it.[/caption]

Ambitious missions then, and the teams involved are deeply aware of the difficulties of operating in the Jovian environment. Jupiter possesses the largest magnetosphere in the Solar System, due to its quick rotation around its core and interactions in its liquid metallic hydrogen outer core. Because of this, one of the main challenges for any spacecraft in its vicinity is avoiding any analytical equipment being severely damaged by electromagnetic radiation. NASA will attempt to counter this by making their orbiter radiation-tolerant – aided by 150kg of titanium shielding. In addition, to avoid spending too much time being bombarded with radiation, the spacecraft will undergo long, looping orbits around Jupiter. This will also have the added benefit of assisting data transfer back to Earth over a period of seven to 10 days as well as enabling close, brief flybys around Europa.

ESA’s mission involves exploring the whole Jovian system to compare different moons and how they interact with the magnetosphere. Dr Altobelli says: “JUICE will carry out two flybys of Europa, specially designed over geologically interesting locations ensuring the total radiation dose also allows flyby of Ganymede, Callisto, and close approaches of Jupiter for atmospheric studies, before studying Ganymede in depth from an elliptical and circular orbit at low altitude.” Ganymede is of particular interest to researchers as it is thought to be at an intermediate evolutionary stage between Europa and Callista. Although similar to Titan, another Jovian moon, it does not share its thick atmosphere. The JUICE mission will spend more time observing Ganymede and Callisto than Europa so researchers can better understand the evolution of icy worlds as well as understanding their habitability.

Europa - Jupiter’s icy enigma

[caption id="attachment_57850" align="alignnone" width="620"]
First discovered in 1610 by Simon Marius, not Galileo as commonly thought – and later confirmed by a court three centuries later¹ – it is the same age as Jupiter, four and a half billion years old. What we know currently about Europa is the result of data from the Galileo mission as well as pictures taken by the Hubble Space Telescope – which is how water vapour plumes were discovered.[/caption]

First discovered in 1610 by Simon Marius, not Galileo as commonly thought – and later confirmed by a court three centuries later1 – it is the same age as Jupiter, four and a half billion years old. What we know currently about Europa is the result of data from the Galileo mission as well as pictures taken by the Hubble Space Telescope – which is how water vapour plumes were discovered.

Back to Europa – and the NASA mission. Firstly, NASA want to determine if Europa is habitable. “As part of this we hope to resolve many of the long-standing mysteries that Europa presented from the Galileo mission,” explains Dr Niebur. “Questions such as how thick the ice crust is on top of the ocean, and does it drag material from the ocean to the surface? Chaos regions, where the terrain is ridged, cracked and appears jumbled; suggest that this activity is occurring. We also see brownish-red areas on the surface that look like they may come from underground.” Secondly, if life cannot be found – astrobiologists will want to understand why. “Life is ubiquitous on Earth, where water, energy and the necessary chemical compounds are common,” says Dr Niebur. “Perhaps we won’t find life on Europa simply because those three ingredients are not present. And if Europa is habitable but not inhabited, if those three necessary ingredients are present but no life has arisen, then that tells us that Earth and its life are even more precious and rare than we ever dreamt. I would hope that would have a tangible impact on how we treat our home and one another.”

What happens if life is found? Currently both missions do not have instrumentation capable of searching for life, and due to the lengthy process of arranging space missions, it is unlikely the focus of JUICE or Europa missions will be changed. “JUICE will follow its science plan as defined upon mission adoption in 2014,” said Dr Altobelli. “There is currently no plan to change the mission profile toward more focus on Europa due to the Hubble observations.” So any kind of direct life-hunt will have to take place on a separate mission.

Dr Niebur says that if life was discovered at a later date, “the next step would be to step back and reassess our place in the universe! Then we would work to increase our understanding of that and how it arose and evolved.” Outside of any existential eureka moments, the potential discovery of lifeforms on other planets gives scientists plenty of practical problems to think about – least of which is the best way to transport samples back to Earth for further research. All space missions must abide by guidelines laid out by the Committee on Space Research (COSPAR) established in 1958. One of these is planetary protection, which covers both forward (from earth to another celestial body) and backwards (from space to Earth’s atmosphere) contamination with viable organisms. These rules would have to be adhered to if carrying samples back to Earth for further examination.

Earth is 588 million kilometres away from Jupiter so it takes at least seven years for any satellite to get there

And, of course, there is the sheer distance to consider. Earth is 588 million kilometres away from Jupiter so it takes at least seven years for any satellite to get there. As Dr Niebur puts it, “Every mission we fly affects the next mission, but given the cruise time needed to reach Jupiter, the timescales for feeding forward to the next mission can sometimes be fairly long. But there are ways we can shorten this. Sample return is challenging from any planet or moon in the solar system, but especially from Europa given its distance.” Now the missions have been agreed, it’s up to the researchers and engineers to make sure the final preparations and calculations are made so the missions can both launch successfully in six years’ time. Dr Altobelli puts it best. “I see both missions as complementary – taking the two missions together will result in a comprehensive data set on all icy moons and their interaction with their environment.”

These missions to Jupiter are two of many expected over the next few decades. These will be from both established space agencies – NASA, ESA and Roscosmos – and those less established such as the CNAS, JAXA and the Iranian Space Agency. These missions all have a shared goal, greater exploration of the incredible Jovian system. As such, a large amount of new information will hopefully be uncovered in less than 20 years. This should provide scientists and the public alike with a greater understanding of the most enigmatic of planets.

[box type="shadow" ]NASA and ESA will be taking a wide variety of instruments to Jupiter and its moons. Here’s how they compare:

NASA Europa mission instruments

• Plasma Instrument for Magnetic Sounding (PIMS)
• Interior Characterisation of Europa using MAGnetometry (ICEMAG)
• Mapping Imaging Spectrometer for Europa (MISE)
• Europa Imaging System (EIS)
• Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON)
• Europa THermal Emission Imaging System (E-THEMIS)
• MAss SPectrometer for Planetary EXploration/Europa (MASPEX)
• Ultraviolet Spectrograph/Europa (UVS)
• SUrface Dust Mass Analyzer (SUDA)

JUICE mission instruments

• JANUS - Camera system
• MAJIS - Moons and Jupiter Imaging Spectrometer
• UVS - UV imaging Spectrograph
• SWI - Sub-millimeter Wave Instrument
• GALA - GAnymede Laser Altimeter
• RIME - Radar for Icy Moons Exploration
• J-MAG - A magnetometer for JUICE
• PEP - Particle Environment Package
• RPWI - Radio & Plasma Wave Investigation
• 3GM - Gravity & Geophysics of Jupiter and Galilean Moons
• PRIDE - Planetary Radio Interferometer & Doppler Experiment

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Author: Carlisle Baker-Jackson, Web Editor

References 1. http://journals.sagepub.com/doi/abs/10.1177/0021828615585493 2. http://iopscience.iop.org/article/10.3847/0004-637X/829/2/121/meta 3. http://astro.cornell.edu/academics/courses/astro2202/lp1_europa.pdf