A Conversation with the Robert Pappalardo, Europa Clipper’s Lead Scientist

For the last thirty years, Dr. Robert Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory, has dedicated his life to studying the icy moons of the solar system. For the last twenty, he has worked tirelessly to build a mission to Europa, the ocean moon of Jupiter, considered the place most likely in the solar system to harbor extant life forms. 

Early next week, Pappalardo will at last succeed in his efforts. 

Europa Clipper is NASA’s first outer planets flagship to launch since Cassini-Huygens left Earth in 1997. It will ride atop a Falcon Heavy rocket before beginning a six-year voyage to Jupiter. About the size of a professional basketball court, Europa Clipper is the largest planetary spacecraft ever flown. After being protected by NASA's ride out teams during Hurricane Milton, SpaceX and the mission's team are tentatively planning for launch on Sunday.

Once it arrives at the Jovian system, the spacecraft will enter orbit around Jupiter, and across four years, encounter Europa forty-nine times at various angles and approaches, flying as close as sixteen miles to its surface, capturing the moon in swaths. A powerful, onboard radar will map Europa’s ice shell in three dimensions, while its cameras and spectrometers build a high resolution map of its geology and composition. Its magnetometer and plasma instrument will characterize the ocean’s depth and salinity. By the end of its prime mission, Europa Clipper will have captured over 90 percent of Europa, and allow scientist to say for certain whether the moon’s ocean is habitable for life. 

It is the culmination of the life’s work of Pappalardo, who leads the mission as its project scientist.

Before launch, I caught up with him to get some answers to some of the burning questions the public has about such a bold mission. This is a lightly-edited transcript of our chat.

Despite NASA's best efforts to explain this, I think the biggest misconception about Europa Clipper is that it's a life detection mission. Rather, it's a habitability mission. Perhaps you could describe why that is a necessary step in a campaign of exploration?

We need to do the initial survey of Europa to understand how it works as a world before we’re ready to go for the brass ring of searching for life. Arguably, we don't even yet know how to do that search. 

I wouldn't turn down a lander if we had the option, but a global reconnaissance of Europa will help us understand first where we should even look for life, and whether the necessary ingredients—the water, the chemistry, and the chemical energy—are actually present. And then we can go in and say, ‘Ah, there’s the place: a warm spot with liquid water in the subsurface, signs of organics, and maybe there's a plume source.’ That's where we’ll go and search for life.

What does a habitable Europa even look like? Habitable means a lot of things to different creatures.

Another way of framing that question is: Could we find a Europa that is not habitable? 

We can certainly find a Europa that is less habitable: a Europa that has a sulfuric acid ocean instead of a magnesium sulfate ocean, or a Europa that doesn't have an ocean after all, and we are being fooled by the magnetometry results from Galileo. We have to be careful in not taking our current best picture of how a world works, based on limited data, and assuming that we know all. 

We want to understand if there is liquid water, where that liquid water exists, and whether the chemistry seem conducive to life. Do we expect redox potential in the ocean—oxidants and reductants—and where might we go to search? How might we do that search in the future, with what techniques?

Scientists have been debating how Europa works for centuries. I recall a Victorian-era hypothesis Europa might be a swarm of icy comets—

Oh, man, I like that.

So can you give me a sample of some of the key disputed scientific debates today that Europa Clipper is going to settle?

Plumes, first and foremost. Are there plumes there? Are they real? The initial plume results from Hubble have a signal-to-noise of one-to-two. That's really tough. It’s a very hard observation from Earth. So we're going to be able to observe over the course of four years whether there are plumes, and where are they? Are they sporadic? Are they consistent? Do they not exist? What are their characteristics? Do they tap an ocean? If they're real, we’ll fly through them.

So that's one. Chaos: How did chaos form? Is there really liquid water under there? There's a model that, right now, is only out in the ‘gray literature’—conference abstract form—that says instead of water being below the chaos surface, there is simply dry-but-warm material beneath. So maybe there's no water associated with chaos. Maybe we need to seek other oases at Europa. So if we send a lander to Thera Macula now, thinking, ‘Oh boy, there could be water there!’ It could be that that was the wrong place to go. 

Another is how do ridges form? Do they involve water? Did material spew up from the subsurface, or is it just contraction of the surface that forms ridges. You know, it’s kind of esoteric—how do ridges form—but what comes into play is where is there liquid water and how is that involved, and that starts getting into issues of habitability and the exchange of materials from the surface to the subsurface.

Aside from sort of those big questions about habitability, what's an abstruse, weird question that you personally look forward to having answered after almost thirty years of studying Europa?

Is the ice shell convecting? It’s like a lava lamp. Are there blobs of warm ice that rise up through the ice shell and create pits and spots and domes—or not? 

So convection goes on in the Earth's mantle, where warm rock rises up, and denser, colder rock sinks. It's a fundamental process that affects rocky world interiors. But we don't have an ice shell thick enough on planet Earth that would convect and bring up blobs from below toward the surface. It's relevant to habitability and the exchange of materials. So we want to understand whether Europa's ice is convecting.

And my final question: You've been trying to get this mission launched for more than twenty years. It's finally going to leave planet Earth. How does your job change now?

Oh, how does my job change? 

I already know you're going to feel good!

Yeah, yeah. I will feel good. 

Keeping a team together for another five-and-a-half years through cruise is the challenge that lies ahead. To keep people engaged and working together and not drifting off, while at the same time letting the team evolve as it will during cruise —that's an important part of my job. But I'll continue to be the science voice during cruise as operations-specifics are developed, and as we plan for tour, and as calibrations are done—including during the Mars flyby and the Earth flyby. That key role will continue. And I hope to take a sabbatical in there at some point.

As always, thank you for your time today. I’m looking forward to seeing you at the launch.

Thank you so much. It’s been a lot of fun.

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David W. Brown is the author of THE MISSION, or: How a Disciple of Carl Sagan, an Ex-Motocross Racer, a Texas Tea Party Congressman, the World's Worst Typewriter Saleswoman, California Mountain People, and an Anonymous NASA Functionary Went to War with Mars, Survived an Insurgency at Saturn, Traded Blows with Washington, and Stole a Ride on an Alabama Moon Rocket to Send a Space Robot to Jupiter in Search of the Second Garden of Eden at the Bottom of an Alien Ocean Inside of an Ice World Called Europa (A True Story). He lives in New Orleans.

Editor's Note: David Brown, Dr. Pappalardo, and Supercluster team members Robin Seemangal and Jenny Hautmann will be on-site at Kennedy Space Center for the historic launch of Europa Clipper.