There are a number of places within our solar system where life may have come to pass – and indeed, may still exist – beyond the Earth. There’s Mars, Saturn’s massive moon Titan, and the so-called “icy world” moons, such as Neptune’s Triton, Saturn’s Enceladus, and Jupiter’s Europa, all of which may harbour sub-surface oceans between their icy crusts and solid interiors.
Of these moons, Enceladus has shown clear signs of activity relating to the existence of a sub-surface ocean: the ESA / NASA Cassini mission captured images of great plumes of water erupting from the moon’s south polar region, and the Cassini vehicle passed through this plumes towards the end of its mission to “taste” them, confirm they were predominantly water.
However, the icy world that has garnered the most interest in terms of detailed study remains Jupiter’s Europa. Currently, there are two missions being developed to probe Europa in greater detail than ever before: NASA’s Europa Clipper and ESA’s Jupiter Icy Moons Explorer (JUICE).
Europa Clipper has had something of an up-and-down ride. Originally, scientists wanted to send a vehicle to study all of the icy moons around Jupiter – Europa, Callisto and mighty Ganymede. However, the US $16 billion price tag for the mission (including vehicle development, launch and operation) was too high. It was scaled back to a more modest US $4.3 billion mission, the Europa Orbiter, which would have included a lander. Then it was scaled back again to a US $2 billion mission.
In 2014, the mission eventually morphed into the Europa Multiple Flyby mission: rather than placing a vehicle directly in orbit around Europa, this would put the vehicle in orbit around Jupiter from where it would be able to make multiple fly-bys of Europa. This then became Europa Clipper – which has still suffered from attempts to axe it, surviving only because it has very strong support within the US Congress.
This support has allowed the mission to both receive continued funding and proceed through various design and review activities. As a part of this, on Monday, August 19th, 2019, NASA announced that it had formally confirmed the mission can proceed to what is called Phase C, a process that will see the mission through the final spacecraft design and then on to assembly and testing.
We are all excited about the decision that moves the Europa Clipper mission one key step closer to unlocking the mysteries of this ocean world.
– Thomas Zurbuchen, NASA associate administrator for science
While Enceladus was the first moon where we positively witnessed plumes of water ice erupting from the surface (2005), evidence that similar outgassing may be occurring at Europa has been gathered by the Hubble Space Telescope. This information, gathered in the form of images, and data gathered by the magnetometer instrument carried by NASA’s Galileo space vehicle that surveyed Jupiter and his moons in the 1990s, offer the clearest indication that there is an ocean of water, possibly containing more than twice the volume of all the Earth’s oceans and sea combined, sitting beneath the surface ice on Europa.
The solar-powered craft – solar power being a lot cheaper than nuclear RTGs – will carry a total of nine primary science instruments, with eight confirmed as being:
- The Europa Thermal Emission Imaging System (E-Themis) will provide high spatial resolution, multi-spectral imaging of Europa in the mid and far infra-red bands to help detect active sites, such as potential vents erupting plumes of water into space.
- The Mapping Imaging Spectrometer for Europa (MIS), an imaging near infra-red spectrometer that will probe the surface composition of Europa, identifying and mapping the distributions of organics (including amino acids and tholins), salts, acid hydrates, water ice phases, and other materials. Scientists hope to be able to relate the moon’s surface composition to the habitability of its ocean.
- The Europa Imaging System (EIS), a visible-spectrum wide and narrow angle camera instrument that will map most of Europa at 50 m (160 ft) resolution, and will provide images of selected surface areas at up to 0.5 m resolution.
- The Europa Ultraviolet Spectrograph (Europa-UVS) instrument will be able to detect small plumes of material ejected by Europa, and will provide valuable data about the composition and dynamics of the moon’s exosphere.
- The Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON), a dual-frequency ice penetrating radar instrument designed to characterise and sound Europa’s ice crust from the near-surface to the ocean, revealing the hidden structure of Europa’s ice shell and potential water pockets within.
- The Plasma Instrument for Magnetic Sounding (PIMS) working in conjunction with a magnetometer, PIMS is key to determining Europa’s ice shell thickness, ocean depth, and salinity. PIMS will also probe the mechanisms responsible for weathering and releasing material from Europa’s surface into the atmosphere and ionosphere and understanding how Europa influences its local space environment and Jupiter’s magnetosphere.
- The Mass Spectrometer for Planetary Exploration (MASPEX) will determine the composition of the surface and subsurface ocean by measuring Europa’s extremely tenuous atmosphere and any surface materials ejected into space.
- The Surface Dust Mass Analyser (SUDA), a second mass spectrometer that will measure the composition of small solid particles ejected from Europa, providing the opportunity to directly sample the surface and potential plumes on low-altitude flybys. The instrument is capable of identifying traces of organic and inorganic compounds in the ice of ejecta.
The ninth instrument will be a magnetometer, although this has yet to be sourced – the dedicated instrument, called Interior Characterisation of Europa using Magnetometry (ICEMAG) was cancelled due to spiralling costs and development complications. It will be replaced by a more “off the shelf” system that will be less sensitive than ICEMAG, but the mission team are confident they can compensate for this be more frequent re-calibration operations during the mission.
Early concepts for a Europa mission – as noted above – included a lander – and possibly even a drilling mechanism and an automated submarine that could potentially be dropped under the ice and explore the ocean under it. These ideas were dropped – perhaps wisely – until more is known about the structure and thickness of the surface ice and exactly what lies beneath it. However, Europa Clipper has some additional payload capacity – around 250 kg – and NASA has been seeking ideas on what might be flown; some of the suggestions have included by a payload of supporting CubeSats or a small-scale lander.
While the Europa Clipper mission won’t actually orbit Europa, the multiple fly-bys will enable it to achieve almost global coverage of the moon, allowing for the widest amount of data to be gathered. This will be transmitted back to Earth in the 7-day periods between each close fly-by.
Currently, the mission launch date has yet to be finalised, and this in part depends on the selected launch vehicle. The preferred launcher is NASA’s upcoming Space Launch System (SLS). If used, this would see the mission launched in 2023, with the booster powerful enough to put Europa Clipper on a 3-year direct flight to Jupiter. However, there is no guarantee that SLS will be available in the proposed time frame, so NASA is also looking to use a commercial vehicle such as the SpaceX Falcon Heavy or the ULA Delta IV Heavy. Either of these would allow the mission to launch in 2022, but as they are less powerful than SLS, they would require Europa Clipper use 3 gravity assist manoeuvres, two at Earth and one at Venus, in order to send it on its way, increasing the transit time to Jupiter to 6 years.
ESA’s JUICE mission is seen as something of a “companion” to Europa Clipper, although overall, it has a broader mission profile. Overall, the focus of the mission is Ganymede, the largest and most massive moon in the solar system. However, JUICE will also study Europa, Callisto and Jupiter.
Like the Europa Clipper mission, JUICE will be solar-powered, and will carry a suite of 11 instruments designed to probe Jupiter’s icy moons, comprising:
- The Jovis, Amorum ac Natorum Undique Scrutator (JANUS) camera system will image Ganymede and interesting parts of the surface of Callisto at better than 400 m/pixel (resolution limited by mission data volume).
- The Moons And Jupiter Imaging Spectrometer (MAJIS) a visible and infra-red imaging spectrograph that will observe tropospheric cloud features and minor gas species on Jupiter, and will investigate the composition of ices and minerals on the surfaces of the icy moons.
- UV imaging Spectrograph (UVS), a spectrograph that will characterise exospheres and aurorae of the icy moons, including plume searches on Europa, and study the Jovian upper atmosphere and aurorae.
- The Sub-millimetre Wave Instrument (SWI), a spectrometer that will study Jupiter’s stratosphere and troposphere, and the exospheres and surfaces of the icy moons.
- The Ganymede Laser Altimeter (GALA), a laser altimeter intended for studying topography of icy moons and tidal deformations of Ganymede.
- The Radar for Icy Moons Exploration (RIME), an ice-penetrating radar that will be used to study the subsurface structure of Jovian moons down to 9 km (5.6 mi) depth.
- The JUICE Magnetometer (J-MAG) experiment will study the subsurface oceans of the three moons and the interaction between Jupiter’s and Ganymede’s magnetic fields.
- The Particle Environment Package (PEP), a suite of six sensors to study the magnetosphere of Jupiter and its interactions with the Jovian moons.
- The Radio & Plasma Wave Investigation (RPWI) will characterise the plasma environment and radio emissions around the spacecraft using four sub-experiments: GANDALF, MIME, FRODO and JENRAGE.
- The Gravity & Geophysics of Jupiter and Galilean Moons (3GM) will be used to study the gravity field at Ganymede and the extent of internal oceans on the icy moons, and to investigate the structure of the neutral atmospheres and ionospheres of Jupiter and its moons.
- The Planetary Radio Interferometer & Doppler Experiment (PRIDE) experiment will generate specific signals transmitted by JUICE antenna and received by Very Long Baseline Interferometry to perform precision measurements of the gravity fields and of Jupiter and the icy moons.
JUICE is scheduled for launch in 2022 atop either an Ariane 5 or (preferably, and if available) an Ariane 64 rocket. However, it will take 88 months to reach Jupiter, requiring multiple fly-bys of Earth, together with fly-bys of Venus and Mars. These will occur in the following order: Earth (May 2023), Venus (October 2023), Earth (September 2024), Mars (February 2025) and Earth again (November 2026).
These flybys will allow the vehicle to gather the velocity needed to reach Jupiter and on a course to perform its initial fly-by of Ganymede in October 2029. That first Ganymede fly-by will swing JUICE into position to perform an orbital insertion around Jupiter. Once in orbit, it will perform a study of Jupiter’s upper atmosphere as well as performing two fly-bys of Europa and one of Callisto and multiple high-inclination orbits of Jupiter. Then, in 2032, it will enter into orbit around Ganymede, becoming the first spacecraft to orbit a moon other than Earth’s. From here, it will carry out an intensive two-year study of Ganymede and its environment, this phase of the mission being limited by the amount of manoeuvring propellants JUICE can carry.
Together, JUICE and Europa Clipper promise to completely revolutionise our understanding of the icy worlds orbiting Jupiter, and will hopefully reveal enough about any oceans that exist within Europa and / or Ganymede to enable scientists to make a fair determination of their potential habitability by microbial or simple life forms.
The Meteor that Lit Up Southern Australian Skies
I’ve written a lot of late about near-Earth objects (NEO) and the risk they can pose, and Australia had a further reminder that NEOs of various sizes do routinely hit the Earth’s atmosphere and burn-up on Tuesday, August 20th.
That was when the skies above Victoria and South Australia were lit up by an object estimated to be around the size of a car, and believed to have been a Near-Earth Object that entered the Earth’s atmosphere somewhat slower that most such objects. The object was filmed by cameras across south Australia, including security cameras in both Victoria and Adelaide, car dashcams and by people using their mobile devices.
As the object descend, the glow got brighter until, under the force of increasing air pressure before it, it broke up in a massive orange flashes, with the remnants thought to have struck the waters of the Great Australian Bight.