Britney Schmidt grabs the worn-out silver skull atop the stick shift of her 1977 Datsun 280Z and speeds south onto I-35 out of Austin, Texas. The roaring engine momentarily drowns out the heavy metal cranking through the stereo, but Schmidt eagerly talks over them both. The 30-year-old planetary scientist has many passions, from the social commentary of Dostoyevsky to the lyrics of Metallica, but none measure up to her obsession with alien life. Although the kind of aliens she seeks are rather unsexy—perhaps nothing more than floating microbes—their discovery would be staggering. If life can arise independently on two worlds, she knows, it is likely to be ubiquitous through the universe.
To harbor life, an extraterrestrial world must satisfy three basic requirements. First, it must have a consistent source of sufficient energy. Second, it needs the right ingredients: a substantial collection of molecules such as hydrogen peroxide or sulfur dioxide, which play vital roles in the chemical reactions that form the foundation of life. Finally, it must have water. So where can you find all three?
As Schmidt’s electric-blue Datsun, nicknamed Zorro, settles into the highway’s middle lane, she quickly dismisses a few popular suggestions. Many scientists favor Saturn’s moon Titan, which has lakes of methane, an organic molecule that can give rise to life’s building blocks. “Maybe,” Schmidt says. “Compelling chemistry. But where’s the energy?” It is not clear whether Titan has enough heat to support life. Mars is only marginally better. “It probably had life at one time, but again, where’s the energy?” she asks.
Then Schmidt turns to her favorite: Jupiter’s moon Europa. Slightly smaller than Earth’s moon, Europa might not seem like an ideal nursery at first. The surface temperature rarely exceeds –260 degrees Fahrenheit, and it is entirely covered by an ice shell up to 10 miles thick. Still, Schmidt says Europa is the only location in the solar system that clearly meets all three of life’s requirements. Although located a half-billion miles away from the sun, it receives a strong tug from the gravity of mighty Jupiter that warms the moon’s insides. Europa’s landscape is littered with molecules like sulfur dioxide and peroxide that are required for life. And best of all, beneath the ice shell resides an ocean of liquid water some 50 miles deep.
Astronomers have known about Europa’s biological trifecta for almost two decades, yet there have always been doubts: For Europa to support life, the vital molecules on the surface need to mix with the water and energy below, and there is a giant slab of ice lying in between. Late last year in a paper in Nature, Schmidt and University of Texas at Austin geophysicist Don Blankenship solved that problem. They demonstrated that the icy shell is most likely not a rigid barrier but rather a churning conveyor belt capable of shuttling life-friendly molecules from the frigid surface to the more inviting conditions far beneath.
