Europa, an ice world that orbits Jupiter, is one of the most promising candidates for life in our solar system. Scientists believe this moon harbors a subsurface ocean that may contain twice as much water as all of Earth’s seas, raising the exciting prospect that aliens may lurk under its icy crust.
A team led by Marie Běhounková, a geophysicist at Charles University in the Czech Republic, has now demonstrated that Europa’s seafloor may be volcanically active, boosting its odds of habitability by providing chemical energy to speculative lifeforms in its oceans.
The researchers modeled the moon’s magmatic activity over billions of years and concluded that “future missions could confirm ongoing largescale seafloor activity,” according to a study published in Geophysical Research Letters, which NASA’s Jet Propulsion Laboratory shared on Tuesday.
Běhounková and her colleagues were initially inspired to produce their detailed 3D model of Europa’s interior after considering its lava-drenched neighboring moon, Io, which is the most geologically active world in the solar system. Io’s super-charged volcanism is generated by the enormous planet it orbits, Jupiter, which exerts immense gravitational pressure on its moons that causes tidal friction and heating.
“For Io and some other bodies in and beyond the solar system, tidal heating is known as a possibly strong energy source due to theoretical and numerical considerations and in the solar system, also, due to observations,” Běhounková said in an email. “It was only natural to check whether there is a potential of volcanic activity hidden in Europa's interior fed by a combination of radiogenic and tidal heating.”
The recent study provides the most comprehensive model of interior heating on Europa published yet, though Běhounková noted that her team built upon “the long-time effort of many authors for many decades.”
Io orbits closer to Jupiter, and so is subjected to stronger tidal forces, but the new 3D model suggests that volcanism could well be occurring to some extent on Europa’s seafloor too, though it is blocked from view by the moon’s ice crust and ocean.
Understanding the extent, intensity, and duration of any magmatic activity within Europa is vitally important for assessing its habitability, especially because seafloor volcanism nourishes hydrothermal ecosystems right here on our planet. Some scientists think organisms that live around deep-sea vents may have been the progenitors of all life on Earth.
As Europa has made its circuits around Jupiter over the past few billion years, its interior has been flexed and squeezed by the planet’s gravitational pull, which causes heat and energy to be released inside the world as part of a process known as tidal dissipation. The model produced by Běhounková and her colleagues shows that this heating may have stimulated volcanic activity over eons, and is likely to be especially evident at Europa’s poles.
Moreover, the team found that the evolution of Europa’s orbit around Jupiter over time has probably influenced geological activity on the moon’s seafloor, with more volcanism occurring during periods when Europa followed a more eccentric (or elongated) path around the planet.
“The magnitude of tidal dissipation is controlled by the shape of the orbit,” Běhounková explained. “Increased eccentricity (orbit's flattening) augments the tidal dissipation, which feeds the volcanic production.”
“The eccentricity may change in a complex manner as a result of the gravitational interaction with its neighbors Io and Ganymede,” she added, noting that this phenomenon is called Laplace resonance.
The upshot of all these findings is that Europa’s seafloor may have experienced sustained volcanism over billion-year periods, especially at its poles, providing a long-term source of heat and chemical energy to any speculative life-forms that might inhabit it now, or in the past.
The team’s conclusions also provide a handy roadmap for future missions to Europa, including NASA’s Europa Clipper mission, which is currently scheduled for launch in 2024.
“All the Europa Clipper's results will be exciting,” Běhounková said. She noted that further studies of Europa’s orbital changes, along with the detection of “gravity anomalies at high latitudes” (meaning the poles) and “hydrothermally-derived elements,” could “confirm a seafloor activity.”
The Clipper mission will not reach Europa until the 2030s, at the earliest, and other future missions will be needed to confirm or rule out the existence of life on this world.
But let’s say, for kicks, that aliens were discovered on Europa at some point in the coming decades or centuries. Such a breakthrough would change the human perspective on ourselves and our universe in myriad ways, which is reason enough to explore this enchanting moon, both from Earth and with space missions.
“From a scientific point of view (though I'm certainly not an expert in this field), we can learn from comparing the biology of alien life and life as we know it,” Běhounková said. “It would also raise important questions of the planetary protection and strategy of exploration.”
“From a broader perspective, finding life beyond the Earth would raise new scientific and ethical questions,” she concluded.