“[On early Earth] you need to have gone from simple to complex chemistry before jumping to biology, but we don’t know all the steps. Titan allows us to uncover some of them.”
— Zibi Turtle, Dragonfly principal investigator
“A bizarre Earth” is how one investigator describes icy Titan, Saturn’s largest moon, and the target of NASA’s most ambitious robotic mission to date. Titan has long been the darling of exobiologists (biologists whose interest is extraterrestrial life) who, I’m told, are practically salivating in anticipation of Dragonfly — essentially a large drone — slated to arrive at Titan in 2034.
Titan, more than any other body in our solar system, bears a strong resemblance to early Earth, with the three essentials for life as we know it: an energy source (the Sun), organics (carbon-based molecules, building blocks for amino acids and proteins) and liquid water (solvent). Some 4 billion years ago, scientists believe organic compounds here on Earth enriched themselves in a “primeval soup,” becoming more and more complex until — after perhaps several millions of years — nature stumbled upon a self-replicating molecule, aka “life.”
That “prebiotic” process, from simple to complex chemistry, has all but been obliterated here by the very life it spawned. Titan, however, holds the promise of a virgin laboratory, where it might be possible to view the complexification as it happens. Like early Earth, Titan’s hazy skies are mostly composed of methane that, when bombarded with UV rays from the sun, forms organic molecules that fall as rain onto the moon’s surface. And it’s Titan’s surface, comprised of deep-frozen water ice and longitudinal dunes similar to those seen in Namibia’s ancient coastal desert (with hydrocarbons instead of silica sand) that’s the main target of NASA’s Dragonfly mission.
In astronomical terms, Titan is an “ocean world,” the term given to a planet or satellite that, scientists suspect, contain a substantial amount of oceanic water. Earth, of course, is an ocean world, as are Jupiter’s moons Europa and Ganymede and Saturn’s Titan and Enceladus, although the others are subsurface. In Titan’s case, we’re pretty sure that some 100 miles below the frozen surface, there’s a vast water ocean, kept liquid by both heat from the moon’s core and salt and/or ammonia dissolved in the water. No conceivable future mission will be able to directly sample Titan’s ocean, which, with all sorts of caveats, may harbor primitive life. However, the Dragonfly mission is designed to sample sites where liquid water may have once existed on the surface. Which is why Dragonfly will be landing in, or close to, Selk impact crater, where liquid water may once have mixed with surface organics, since an impact from a comet or meteorite may have melted otherwise deep-frozen ice, perhaps briefly creating conditions similar to those on early Earth.
Dragonfly will be landing near the equator, nowhere near another area of interest to exobiologists, Titan’s polar methane lakes. The moon’s frigid temperature, about 90 degrees Kelvin (minus 300 Fahrenheit), precludes any liquid water currently, but that’s just fine for liquid methane and ethane. NASA’s Cassini mission, in orbit around Saturn from 2004 to 2017, discovered these lakes from radar reflections. They are huge, one comparable in size to the Caspian Sea, although they were probably once much larger, perhaps covering the entire surface.
Dragonfly won’t be the first craft to land on Titan. That honor goes to a remarkable little probe named Huygens (after the discoverer of Titan in 1655) that hitchhiked on Cassini. Built by the European Space Agency, Huygens was deployed from Cassini in January of 2005. It operated for four hours, including 90 minutes on the surface following it’s descent by parachute, before its batteries died. Most of what we currently know about Titan comes from the 100 MB of data transmitted back to Earth (via Cassini) from that vanguard mission.
Next week, we’ll look at what makes NASA’s Dragonfly mission so innovative and exciting.
Barry Evans (he/him, barryevans9@yahoo.com) notes that Mars’ 72-flight Ingenuity was first drone-type craft to fly on another world.
This article appears in 731 Dogs.