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NASA is still on track to use its new Space Launch System (SLS) to launch its $2 billion-plus ‘Europa Clipper’* mission to Jupiter’s fabled, frozen moon. That might even happen as early as Spring of 2022 and would involve a direct two and a half year transfer to our solar system's largest planet. Over a three and a half year period, the spacecraft would use a long orbit around Jupiter to do 46 reconnaissance flybys of Europa at altitudes varying from 2700 to 25 kilometers above the moon’s surface.
The aim is to use this three and a half year reconnaissance phase of the mission to search Europa for signs of a subsurface liquid ocean and for habitability. Many astrobiologists still think that this beguiling moon offers the best chance of finding life elsewhere in our solar system.
And if NASA launches a follow-on Europa lander mission, astrobiologists may find biological treasure in one of its Europa samples long before a Mars sample-return mission could be attempted.
But Europa Clipper really isn’t designed to detect life.
“A definite detection with [Europa] Clipper’s instrument suite would require taking a picture of say, a breaching whale and, unfortunately, we just don’t think that’s very likely,” Kate Craft, a NASA Europa Clipper project staff scientist and a planetary scientist at Johns Hopkins University’s Applied Physics Lab in Maryland, told me.
To detect life, a mission to Europa would need several instruments looking for biosignatures in either a plume or subsurface sample, says Craft.
“To say Europa is or was habitable, we’d want to confirm there is an ocean; see evidence of chemistry in the ocean that can be a source of energy for life beneath the ice,” said Craft. “And see evidence of ice-ocean exchange processes that could enable chemical mixing.”
Europa is about the size of Earth’s moon yet has almost the same amount of water as all of earth’s surface water bodies. And as noted here in a previous post, Europa is gravitationally-locked with Jupiter and orbits our solar system’s largest planet every 3.5 days.
It’s thought to have a 100-kilometer-deep salty ocean, with an iron core surrounded by a rocky mantle. However, also as noted here previously, for life to evolve on Europa, it would need liquid water; a handful of essential elements such as carbon, hydrogen, oxygen, nitrogen, phosphorous, sulfur; and some sort of energy to harness. Don’t count on photosynthesis, which would be impossible under such a thick layer of ice.
Yet because Europa’s orbital distance from Jupiter creates gravitational tides, its seafloor may still be undergoing volcanic or hydrothermal activity that would, in theory, offer any burgeoning subsurface life a steady supply of nutrients via chemical synthesis. That is, energy derived from the interaction of Europa’s rocky seafloor and its ocean.
The Europa Clipper team hopes that the spacecraft may detect all or part of such activity.
Once Europa Clipper goes into its cadence of flybys every two weeks or so, Craft says all of its nine instruments --- which span the wavelength range from ultraviolet to radar as well as a magnetometer to measure magnetic fields --- will collect data at every pass by. And once its observations are complete, it will have made criss-cross measurements of much of Europa.
Yet Craft says the Europa Clipper’s biggest challenge will be the danger of faults and instrument noise when handling high-radiation once it arrives at Europa. The spacecraft will dip into Europa’s radiation with every close flyby.
“The team is reducing this risk tremendously by designing a radiation tolerant vault, testing parts and hardware to high radiation levels, and setting up data collection strategies that will be as robust to faults as possible,” said Craft.
Many American taxpayers may wonder why NASA didn’t simply design a mission that also includes a lander.
But the idea is that by sending the Europa Clipper first, researchers will be able to assess Europa’s habitability, possibly find indicators of life, determine the best places that life might have signatures waiting for discovery, and enable a more robust follow-on biosignature-finding mission.
NASA is doing a concept study for a future Europa lander, however.
If funded, the lander could see launch as early as the middle of the next decade. Meanwhile, there’s the Clipper mission.
As for the most exciting thing that Europa Clipper might detect?
“Plumes of icy material that would mean Europa is currently active,” said Craft.
The spacecraft might then be able to fly through the plume and analyze its particles’ grain sizes and their composition; particularly looking for salts, hydrogen and carbon concentrations. This would enable the team to determine if the plume had come directly from the ocean underneath the ice or from shallow water bodies within the ice.
This would be a fantastic discovery that would indicate the ocean’s habitability, says Craft. And assuming the plumes were determined to be long-lived, she says they could also provide locations to be sampled by a follow-on lander or plume collector.
And if life is there, says Craft, this follow-on lander mission would come equipped with instruments able to detect it.
*Correction: Please note that this story has been updated to reflect that the mission's full name is 'Europa Clipper.'
