Europa, an intriguing moon of Jupiter, could be key in the mystery of the origins of life, said William B. McKinnon, Ph.D., professor of earth and planetary sciences in Arts & Sciences.
McKinnon’s address on the subject was standing-room only at the American Association for the Advancement of Science Annual Meeting Feb. 20 in San Francisco.
McKinnon, among the planetary scientists studying the rich data set from NASA’s Galileo mission to the outer solar system, is making a push for the planetary community to go to Europa.
“Of the four Galilean moons, Europa is the one that has the best chance to reveal the most about the origin of life, which is the biggest unanswered scientific question we have, bar none,” he said. “With its massive body of liquid water, multiple energy sources proposed and different ways to provide carbon and other biogenic elements, the central question must be Europa’s potential for life. What greater question can you ask of a planet?”
There are four large moons of Jupiter that in their character and behavior are more like planets than Earth’s moon: Io, Europa, Ganymede and Callisto. The last three are icy. All are named after Greek mythological characters.
Each of the moons differs in the way it can reveal more about planets and how they behave. And though unanswered questions revolve around them all, McKinnon thinks Europa commands the most attention.
Io’s volcanic hyperactivity is well known, but there are mysteries about the temperature of its magmas and its spectacular mountains and what they might reveal about the satellite’s interior processes.
As for the exterior moon Callisto, how did it acquire an ocean yet not be deeply differentiated? Ganymede’s liquid iron core still is generating a magnetic field, an unpredicted situation that has much to teach about how magnetic fields are generated in the solar system.
Then, there is Europa.
“Europa has been recently geologically active, but because Galileo’s main antenna did not unfurl, we did not take enough images to catch any active geysering, such as seen on Saturn’s itsy-bitsy, icy moon, Enceladus,” McKinnon said. “Europa’s surface appears very young and there are lots of interesting ice tectonics and surface eruptions with weird colors and spectral signatures whose compositional implications everyone just loves to argue about.”
Galileo — first to measure Jupiter’s atmosphere with a descent probe — plunged into Jupiter’s atmosphere in 2003 and found evidence of subsurface saltwater on Europa, according to NASA.
The accumulated evidence points to an ocean lying no more than 10 kilometers to 20 kilometers below Europa’s icy, airless surface, McKinnon said.
“That sounds really deep to a person with a pick ax or even a drilling rig, but in geologic terms, it’s really pretty close,” he said. “It’s basically a capped ocean.”
The existence of the ocean is related to the great amount of heat rising from Europa’s interior.
“If you look at the surface and how deformed it is, you can tell the ice shell is relatively thin and really has been active in recent geological time, indeed is probably active today,” McKinnon said.
Europa has a few, but not many, impact craters, also indicating its relative youth. Europa’s ocean begs to be studied, McKinnon said, as do the strikingly colored surface materials that Galileo images captured.
“To go into orbit around Europa with high-resolution cameras, spectral imagers and sophisticated ice-penetrating radars of the sort mapping Mars right now would allow us to really characterize that ocean and give us clues about the biogenic potential of the surface materials,” McKinnon said. “We’d see to the bottom of the ice shell, I predict. It would be a fantastic proof of concept.”
A mission to Europa is feasible, McKinnon said. It would take about 10 years if started today — with six of those years being spent to reach the satellite — and would cost about $2 billion, McKinnon estimated.
“It would also have to compete for funds with NASA’s plans to establish a moon base,” he said. “The Europeans are interested as well, so maybe we could cooperate and share the cost.”
NASA has committees exploring a number of options, McKinnon said, including returning to Europa or Enceladus.
“It’s a tiny moon, but it has an active plume that, because of that moon’s very low gravity, extends well out into space, so you can just fly right through it,” McKinnon said of Enceladus. “That’s a nifty way to go sampling.”
But Europa is a much bigger target to explore.
“It has 40 times the surface area of Enceladus,” McKinnon said. “There’s a lot more ‘there’ there.”