There are currently two missions in development that will explore Jupiter and three of its moons to determine if they are capable of producing and sustaining life. Prior research has been mostly observation by flybys with the exception being Galileo that orbited Europa for observations. Since then, the National Aeronautics and Space Administrations (NASA) mission, Europa Clipper, and the European Space Agencies (ESA) mission Jupiter’s Icy Moons Explorer (JUICE) have been in development. The data provided by each agency was analyzed to compare and contrast the mission’s orbital plans, fuel source, science objectives and their overall missions. Both spacecraft have yet to be launched, but the outcomes from JUICE and Europa Clipper should be the same. If JUICE finds that any of the Jovian moons are habitable then Europa Clipper should as well, and vise versa.
Keywords: Europa Clipper, European Space Agency, Jupiter’s Icy Moons Explorer, National Aeronautics and Space Administration.
Analysis of Missions to Jupiter’s Moons
Many missions have set their sights on planets and moons to discover the possibility of life, but arguably none more than the European Space Agencies (ESA) JUICE mission and the National Aeronautics and Space Administrations (NASA) Europa Clipper mission. For both missions, the destination is Jupiter’s icy moons with the goal of orbiting the large planet and slowly analyzing the moons and their atmospheres. Europa Clipper focuses only on Europa, the moon that scientist predict is the most promising for life (NASA, 2019). JUICE focuses on Europa, Ganymede, and Callisto for their own unique characteristics that could produce life, like Ganymede’s magnetic field (NASA, 2019).
The Moons
There are currently has 53 confirmed moons in orbit around Jupiter and 26 conditional moons that are awaiting verification (NASA, 2019). Out of those, there are only three of interest to these missions, Europa, Ganymede, and Callisto. These are three of the four largest moons orbiting Jupiter known as the Galilean satellites (the excluded moon being IO) (NASA, 2019). These three are also thought to be the most likely places in the solar system to harbor life.
Europa
Of the Galilean satellites, Europa is the likeliest place to find life because of the potential for a vast ocean under its icy surface. In fact, scientists are almost certain that there is about twice as much saltwater on Europa than there is on Earth (Howell & Pappalardo, 2020). The outer layer of Europa is thought to be about 10 to 15 miles thick, with an ocean estimated between 40 and 100 miles deep and a rocky surface and iron core (NASA, 2019).
So far, five spacecraft have passed and observed Europa. Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 did flybys and gave the first observations up close, then Galileo was sent to conduct orbital observations of Europa (NASA, 2019). In the future, NASA plans the Europa Clipper mission, and the ESA plan the JUICE mission.
Ganymede
Ganymede is the largest moon in the solar system (about the size of Mercury), has its own magnetic field and potentially has an ocean under its icy crust (Jara-Orué & Vermeersen, 2016). Unlike Europa, the icy outer shell is estimated to be almost 500 miles thick and predicted to have rock mixed in the ice (NASA, 2019).
Callisto
Callisto is the second-largest Jovian moon and the third-largest in the solar system (ESA, 2019). Unlike the other Galilean satellites, its orbit is further from Jupiter and it is not as susceptible to its radiation, making it much more stable (ESA, 2019).
JUICE
JUICE is ESA’s first large mission in its Cosmic Vision program, planned for a 2022 launch and a 2029 Jupiter arrival (ESA, 2019). The mission will spend 7.6 years getting to Jupiter and 3.5 years orbiting to observe Jupiter, Ganymede, Callisto and Europa (ESA, 2019).
Science Objectives and Orbital Plans
The overall mission is to study the “emergence of habitable worlds around gas giants” with cosmic vision themes of finding out “What are the conditions for planet formation and the emergence of life?” and “How does the solar system work?” (ESA, 2019).
On the ESA’s website, a ten-phase baseline of the mission is provided that gives the mission and science priorities. Phase one is the 7.6-year cruise to get to Jupiter. Phase two is an eleven-month stint that will intercept Jupiter’s Equator and then transition to Callisto. The science priority is to observe the Jovian atmosphere, the Jovian magnetosphere, and remote observations of the inner system. Phase three is a 36-day Europa flyby with the priority of examining composition, geology, subsurface, and its plasma. Phase four is a 260-day transition to higher latitudes with Callisto and a reduction of velocity. In this phase, the science priority is to observe Jupiter’s atmosphere at higher latitudes, plasma and field out of the equatorial plane, Callisto’s internal structure, surface and exosphere and remote observations of more Jovian moons. Phase five is an eleven-month transition to Ganymede where the mission is to understand how Ganymede and Jupiter magnetic fields interact. Phase six is a 30-day stint that begins the Ganymede tour with the priority of geological mapping, search for past and present activity, composition mapping, and observing the plasma environment and magnetosphere. Phase seven, eight, and ten do not have a science priority. But, phase 9 is a 102-day medium-altitude circular orbit. The priority here is to observe the ratio of the ocean and the deep interior (ESA, 2019).
Spacecraft and Payload
The spacecraft is designed to have large solar sails because of its distance from the sun and the need to depend on solar energy (ESA, 2019). The mission calls for over 25 flybys, so over 3000 kg of propellant is also required on board (ESA, 2019). Also, the ship must be somewhat autonomous, due to the distance from Earth causing a signal to take 1 hour and 46 minutes to travel round trip (ESA, 2019). ESA claims that “the JUICE spacecraft will carry the most powerful remote sensing, geophysical, and in situ payload complement ever flown to the outer Solar System” (ESA, 2019).
Europa Clipper
Europa Clipper is NASA’s mission to orbit Jupiter and investigate the moon Europa, specifically to determine if it is capable of harboring life. The mission is planned for a 2020s launch, and with a seven-year cruise period (like JUICE’s), NASA could expect to arrive at Jupiter between 2028 and 2037 (NASA, 2019). NASA does not provide a detailed timeline for the mission like ESA did for JUICE.
Science Objectives
The main scientific goal in the mission is to determine Europa’s habitability by conducting over 45 flybys with instruments that don’t detect life itself (NASA, 2019). The way that the mission will determine it is by verifying that water does exist beneath the crust, detecting life-forming chemicals, and determining if there are energy sources available to produce life (NASA, 2019). Some other objectives are to determine the thickness of Europa’s icy surface, determine the composition and geology as well (NASA, 2019).
Orbital Plans
The orbital pattern around Jupiter will cause the spacecraft to fly passed Europa between 16 and 1,675 miles with most being below 60 miles (NASA, 2019). The International Journal of Aerospace Engineering has posed another challenge and solution. It may be necessary to slow a probe from the elliptic Jupiter orbit and convert it to a circular orbit around Europa without using too much chemical propellant and wasting flight time (Federici, Zavoli & Colasurdo, 2018). It seems that there is a lot more work to be done by NASA to fine-tune the mission details.
Spacecraft and Payload
The spacecraft is around 20 feet tall with solar sails that are 72 feet wide and will weight over 13 thousand pounds at liftoff (NASA, 2019). The weight is because of the spacecraft’s need for a lot of fuel and its requirement for a thick barrier between the instruments and the radiation that Jupiter produces (NASA, 2019).
NASA claims that the Europa Clippers payload is “cameras and spectrometers to produce high-resolution images and compositional maps of Europa's surface and thin atmosphere, an ice-penetrating radar to search for subsurface water, and a magnetometer and gravity measurements to measure the moon's magnetic field and unlock clues about its ocean and deep interior” (NASA, 2019).
Comparing JUICE and Europa Clipper
The JUICE mission seems further along and closer to launch the Europa Clipper mission. It may be that NASA does not publish their research and timeline for the mission until it is finalized, and ESA does. Either way, it does seem that most of the JUICE mission is planned out and fine-tuning is taking place prior to launch in about one year.
Significance
Historically, humans have thought that the universe revolved around them. Not only did the sun orbit humans, but everything did because humans were the center of everything. Most would like to deviate from this idea, but it is impossible without knowing that some other form of life exists outside of Earth. The significance of these two missions is the potential impact dependent on the results. Some science fiction movies would convince viewers that Europa, and other Jovian moons, have underwater civilizations under them. This is not necessarily what is needed to make an impact, even a tardigrade on Europa would suffice.
Future Actions
JUICE launches in 2022 and should arrive at Jupiter in 2029. In phase three of the mission (11 months after arrival), the spacecraft is expected to do a 36-day reconnaissance mission around Europa (ESA, 2019). If ESA could gather the data and give it to NASA, it would make more sense for Europa Clipper to launch around 2030 or 2031 with the details that ESA gathers. This would be a significant delay to the mission, but it could allow time for NASA to adjust for variables that will be realized with JUICE.
The future of exploring Jovian Moons is dependent on the outcome of these two missions. If any of the moons appear to be habitable, there will definitely be more missions to them. On the other hand, if something like Jupiter’s radiation would prohibit life, then the next missions could explore moons like Callisto that are further from Jupiter’s radiation.
Conclusion
Both missions are planned for the near future, with the potential for Europa to extend launch to the end of the 2020s. They are the same in that they travel to Jupiter, orbit Jupiter, and analyze celestial bodies to provide composition reports of them and their atmospheres. The difference in the two missions is that JUICE conducts basic analysis of Jupiter and three of its Galilean Satellites and Europa Clipper has gone all-in on just Europa. In the end, both scientific objectives are the same, find out if the celestial bodies at question are capable of producing and sustaining life.
References
European Space Agency. (2019, September 1). JUICE. Retrieved September 23, 2020, from https://sci.esa.int/web/juice/
Federici, L., Zavoli, A., & Colasurdo, G. (2018). Preliminary Capture Trajectory Design for Europa Tomography Probe. International Journal of Aerospace Engineering, 2018, 1–12. https://doi.org/10.1155/2018/6890173
Greicius, T. (2015, April 27). Europa Clipper. Retrieved September 23, 2020, from https://www.nasa.gov/europa
Howell, S., & Pappalardo, R. (2020). NASA’s Europa Clipper-a mission to a potentially habitable ocean world. Nature Communications, 11(1), 1311–1314. https://doi.org/10.1038/s41467-020-15160-9
Jara-Orué, H., & Vermeersen, B. (2016). Tides on Jupiter’s moon Ganymede and their relation to its internal structure. Geologie En Mijnbouw, 95(2), 191–201. https://doi.org/10.1017/njg.2015.23
NASA. (2019, December 19). Jupiter Moons in Depth. Retrieved September 23, 2020, from https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/
