Is There Life on Europa?

Scientists at the University of Texas Institute for Geophysics are working to discover if Jupiter's icy moon could support life.

BY CONSTANTINO PANAGOPULOS

Ever since astronomers first peered through telescopes at the worlds of our solar system, people have looked to Mars for signs of life off Earth. But when scientists got a closer look at the red planet’s desolate landscape, many turned their search to the outer planets and the ice-covered moons of Jupiter and Saturn.

Unlike Mars, Jupiter’s moon Europa has all the requirements for life — energy, chemistry and an abundance of water in its interior ocean. But how do you spot signs of life through an ice shell that could be tens of miles thick?

That’s a question that scientists at the University of Texas Institute for Geophysics are working to answer using computer simulations, field studies and a spacecraft instrument they’ve developed, called REASON. If all goes to plan, on Oct. 10, 2024, they’ll watch REASON blast off for Jupiter aboard NASA’s Europa Clipper spacecraft.

The UTIG researchers want to know whether life could have evolved on Europa — and other icy ocean worlds — and if it did, where a future lander might go to find it.

To do that, they’re simulating ocean worlds to learn how warm water and nutrients circulate. And they’re investigating Earth’s polar ice sheets in search of exotic frozen environments and places to test their Europa prototype instrument.

The Earth-based tests are vital, but Europa is covered by an ice shell that’s thicker and much older than any on Earth.

That’s why UTIG researchers such as Cyril Grima and Krista Soderlund are using radar and computer simulations to probe the inner workings of icy ocean worlds and their prospects for harboring life.

Together with REASON’s principal investigator Senior Research Scientist Don Blankenship, Research Scientist Duncan Young and graduate students such as Kristian Chan and Natalie Wolfenbarger, UTIG researchers are delivering some of the most tangible clues about what lies above, below and inside Europa’s ice.

“Far from the sun’s warming rays and deep within Jupiter’s radiation belts, there are few less-hospitable places in the solar system than the surface of Europa,” said UTIG Director Demian Saffer. “But from the depths of the oceans to the coldest places on Earth, UTIG researchers have a reputation for making scientific discoveries in extreme environments.”

Ice-Penetrating Radar

On Earth, when scientists want to see what’s going on inside an ice sheet, they can scan it with ice-penetrating radar the way doctors use X-rays to look inside a human body.

The reflecting radar waves tell glaciologists how thick the ice is, what it’s made of, how it’s shaped by ice flow or ocean currents, and where water might work its way to the surface. It’s a quick way to get information about large regions of ice. It’s also possible to learn how cold the ice is, what minerals are dissolved in it, whether it melted and refroze, what direction it’s flowing, and so on. In short, radar can tell the story of the ice: where it’s been, where it’s going and how it’s changed.

It’s a story that UTIG researchers have studied with Earth’s ice sheets for decades. They’re good at it. That’s why NASA selected UTIG to design, test and operate the ice penetrating radar that will fly on Europa Clipper.

But there’s never been an ice-penetrating radar in the outer solar system.

That’s where Grima, a UTIG research scientist, comes in.

Grima’s background is in radar reflectometry on Mars. The European Space Agency built radar instruments for Mars 20 years ago, and they’ve been in orbit ever since. As a graduate student Grima came up with a statistical technique that greatly improved what the radars can reveal about the ground.

The technique was robust enough that in 2015 Grima used it to help NASA select a safe landing site for its InSight Mars lander. Later, he applied it to the radar altimeter on NASA’s Cassini spacecraft to measure inch-tall waves crossing Titan’s mirror-like hydrocarbon lakes.

For Europa Clipper, Grima is working on a technique that uses radar wobbles to illuminate Europa’s invisible ionosphere. It’s not the mission’s primary objective, but it could find important clues about plumes erupting on Europa’s surface (which are thought to fuel the ionosphere).

“One of the exciting parts of Europa exploration for Clipper is that we know it’s going to be full of surprises,” Grima said. “Every time we get a new picture of Europa, we see something we weren’t expecting. It’s just a really weird, wonderful world.”

Nothing aboard Europa Clipper is designed to directly detect traces of life in or around Europa. The spacecraft’s primary mission is reconnaissance: map Europa inside and out and learn whether life could have evolved there.

With Grima’s help, REASON is expected to excel at reconnaissance. The next step will be to send a lander. That could be decades away, but Grima is already co-leading a group of scientists and engineers who want to make sure future spacecraft will know where to land on Europa and where to look for traces of life.

“When you choose a landing site, you don’t want it to be too rough or too soft, but you also want to land in a place where you can do science,” he said. “It’s no good landing on a solid block of ice that hasn’t changed for a billion years.”

That means knowing what’s going on in the top few feet of ice nearest the surface, where life, or its remains, might be found. Even with Grima’s statistical techniques, that’s a challenge. But it’s one that Jackson School grad student Kristian Chan thinks he’s found an answer to.

Mapping Europa’s Top Ice

Radar sounders for the subsurface work by shooting pulses of radio waves and measuring the time it takes for echoes to bounce back to the radar. Shorter radio waves react to rock and ice differently than longer ones do. By comparing different radio wavelengths, radars can calculate what reflected the wave and what the wave traveled through. Echoes that span a range of different radio wavelengths (the bandwidth) give even more detailed information about the material’s properties.

Chan works with Grima and Blankenship at UTIG as a graduate research assistant. In 2023, he published research that demonstrated how different radar wavelengths and bandwidths could be analyzed together to find objects that would usually be too small to resolve with a single bandwidth.

His technique measures differences in distortion between bandwidths. To test it in the real world, Chan analyzed past radar surveys of Devon Island in the Canadian Arctic from two ice-penetrating radar instruments, each with a different single bandwidth.

Individually, neither deep-penetrating instrument could see the upper few feet of the glacier. But by measuring differences between instruments, Chan extracted information that let him map the location and thickness of ice slabs lurking within the snow atop the ice cap.

Chan’s research raised eyebrows, not because of its findings, which confirmed that the ice cap is in an advanced state of melting, but because of how well it worked.

“When I presented this to the planetary science community, they asked ‘Does this actually work? Have you actually shown this?’” Chan said. “Then I pulled up Devon, and that’s when it clicked. Their reaction was like, ‘Oh wow.’”

For Devon Island, Chan combined two separate instruments. REASON, however, is equipped to emit radar waves across multiple wavelengths and bandwidths. In other words, the technology is already baked in.

Chan’s technique means that Europa Clipper can quickly map out interesting features hiding in the upper few feet of the ice shell — features that a future lander might reach.

For Chan, the Devon Island research is a twofer: It’s a new way to quickly survey Earth’s fading ice sheet, and it’s a robust proof of concept that REASON can look for features in Europa’s shallowest surface layers.

Underwater Snow

Europa’s ice sheet stretches on without end, but under the surface, the water isn’t that cold. It’s not all that different from the coast of Greenland where herring spawn, or the Antarctic Ocean where humpback whales forage.

“When you look at Europa’s global ice shell, it looks like a very alien environment. You’ve got these incredible features, almost like an egg cracking,” said former Jackson School student Natalie Wolfenbarger, now a postdoctoral scholar at Stanford University. “But when you go deeper and you realize that it’s overlying an ocean, there are certain conditions like the temperature and the pressure and potentially even the composition that are actually not so different from Earth.”

As a UTIG graduate research assistant with Blankenship, Wolfenbarger spent her time studying exotic forms of ice on Earth. Her work took her into the weird world of frazil ice — exceptionally pure ice flakes that form out of nowhere in turbulent, supercooled seawater.

On Earth, this underwater snow rises through the water to settle on the bottom of floating ice shelves, where it traps microorganisms and even fish into the ice. Wolfenbarger’s calculations suggest that this underwater snow is even more common among the inverted ice peaks and submerged ravines on the underside of Europa’s ice shell.

That means Europa’s shell might be purer than expected. If it is, that’s important because the ice will be much more transparent to radar, and it could be a clue for whether the environment can support life.

“The salinity and composition of the ocean is one of the things that will govern its potential habitability or even the type of life that might live there,” Wolfenbarger said.

Modeling Ocean Worlds

Earth’s ice sheets are an excellent stand-in for Europa. But Earth is a terrestrial planet and in fundamental ways very different from an ocean world. If Europa is a snow globe with a core, Earth is a big wet rock.

Simulating the parts of worlds that are totally unlike our own is where scientists such as Soderlund, a UTIG research scientist, come in. While her research is certainly informed by observations, the worlds she recreates inside computers are largely stripped down to just fluid dynamics.

In 2014, Soderlund published one of the first global ocean circulation models for Europa. The work was based on a doctoral thesis she’d written on planetary dynamos — interior mechanisms that generate a self-sustaining magnetic field — inside Earth, Uranus and Neptune.

“These are basically really similar systems,” she said. “One is a molten core, the other a global ocean. I can apply the same physics and the same numerical code.”

Soderlund demonstrated that Europa’s rotation directs interior heat out through the equator. The uneven warming drives complex and dynamic ocean currents.

Her results showed a world with thinner ice at the equator, where swings in pressure and temperature serve to pump plumes of purer, buoyant ice in the shell that rises and falls like a lava lamp. The predicted ice plumes matched the locations of rough “chaos terrain” — fractured topography that scientists think are created when the ice plumes push their way to the surface.

The story doesn’t quite end there. Soderlund is working with Daphné Lemasquerier, a former UTIG postdoctoral researcher and now a lecturer at the University of St. Andrews, to update her computer model using a different idea about how the icy moon’s interior is heated.

“Until now, we’d assumed heating is driven by radiogenic decay in the rocky mantle,” she said. “But if it’s also being heated by tidal dissipation in the rocks, the heat flux is going to be less uniform and much stronger at the poles.”

In the new model, the ocean at the poles is warmer than it is at the equator. With so little direct evidence of what’s really going on inside Europa, Soderlund knows that she’ll have to wait for Clipper to get there to learn which model is right. Until then, Soderlund will continue testing different scenarios using physics, new observations and what she calls “a little wild speculation.”

The Best Place to Look for Life

Assuming the 2024 launch is successful, it will be more than five years before Clipper closes the 380-million-mile gap to Jupiter and sends back its first radargram.

Young already has the date marked on his calendar: March 27, 2031.

The wait will have been worth it. Mars may have its attractions as our beststudied neighbor, but researchers know that the search for extraterrestrial life has to include a different, icier kind of world.

“Europa has always been special,” said Blankenship, who leads REASON’s development both at UTIG and Caltech’s Jet Propulsion Laboratory. “If you’re looking for a habitat where life may have evolved, then Europa is the place you go.”

Ice is the most common environment in our solar system. On ocean worlds like Europa, it’s all encompassing, while on rocky ones like Earth, the ice sheets cover only certain regions. But in every case the ice is a mirror that tells a story of the geology and, at least for Earth, the biology within.

“Earth is profoundly shaped by life. It seeps into every facet in every scale of how this planet works,” Young said. “If Europa has had life at similar timescales, I wouldn’t be surprised at all if we find it’s had profound influences on the ice shell.”

Whatever REASON sees when it first looks down on Europa’s icy surface, it will mark a massive achievement for everyone involved.

But the scientific discoveries the UTIG researchers have already made about radar, ice sheets and ocean worlds will leave a legacy of their own. It’s a legacy that Blankenship, Young, Grima, Chan, Wolfenbarger, Soderlund and their fellow UTIG researchers will build on as they continue to explore ice sheets on Earth and other worlds.