Titan, Saturn’s largest moon, is unique in many ways. It is the only moon in our Solar System known to have a thick atmosphere. Other than Earth, is the only celestial object known to have stable bodies of surface liquid. For these reasons and more, Titan sparks the imaginations and curiosity of planetary scientists around the world. NASA’s Cassini spacecraft, launched in 1997, sent the ESA’s Huygens probe to penetrate Titan’s thick atmosphere. It revealed Titan to us for the first time. We talked to Dr. Ralph Lorenz, a planetary scientist at the Johns Hopkins Applied Physics Laboratory, who worked on the Huygens probe, to find out more.
What are the main obstacles we face in conducting science from probes and landers at other worlds?
There are really only a few things that are technologically beyond our present capabilities. For example, a long-lived Venus lander with sophisticated instruments would need perhaps decades of development simply because it is so hard to stay cool in a hot, corrosive, high-pressure atmosphere. There are also some missions where it would be beneficial to have more scientific data from preceding missions – to be sure we’re asking the right scientific questions, and to be sure we send the right systems and instruments to the right place.
But, technologically, we could do a lot more planetary exploration with our capabilities today than we can afford. The main obstacle is money. Indeed, the technical readiness of planetary exploration is evidenced by the number of other countries (and non-state-actors) starting to reach out to the planets. When NASA called for Discovery mission ideas, costing roughly $500 million, it received 28 or so “ready to go” proposals, covering perhaps a dozen mission types. But the budget will only allow one or two of those proposals to go forward. They will be chosen from some balance of scientific merit and low technical risk. Meanwhile, the rest will get back in line for the next opportunity a year or two later.
For me, the interesting part of designing probes and landers is figuring out how the systems and scientific instruments will interact with these alien environments. There are a lot of “boogeyman” possibilities that you can never say are never going to happen – the challenge is to sit down and evaluate them rationally. You do this by using basic physical principles and perhaps experience in extreme environments on Earth. You evaluate quantitatively how likely it is something will occur, how bad might it be, and whether there is something that can or should be done about it.
Why is there a fascination amongst scientists with studying Titan?
Titan is a unique world – a moon with a thick atmosphere. It has a strikingly diverse landscape, shaped by the same processes that shape our own planet. The materials are exotic, though – organics and super-cold ice are “rocks”, and liquid methane forms rain and lakes and seas. The phenomena and landforms we see there are remarkably familiar. Titan has tides and winds, river deltas, many flavors of clouds, and so on. It’s a rich world with a lot to study physically and chemically. Reactions there may inform us about the first steps toward chemical complexity that ultimately can lead to life.
During your career, what achievement are you most proud of?
I’ve been fortunate to work on many exciting projects and ideas, but for now my proudest moment was seeing the data from the penetrometer instrument on the Huygens probe. Having spent three years designing and building the hardware as a PhD student, then waiting another seven years as Cassini-Huygens sailed through space, seeing that the instrument worked for that climactic one-twentieth of a second as intended when Huygens hit the ground on Titan was amazing.
I’ve been able to communicate my work and experiences in a number of books, such as Exploring Planetary Climate, Space Systems Failures, Dune Worlds, and Titan Unveiled. It’s always nicely fulfilling when people tell me they’ve enjoyed these books.
I am hoping that 15 years from now, towards the end of my career, my Huygens work will be eclipsed by the many successful landings of the recently-selected Dragonfly mission, which I played a central role in putting together. If you’re an aerospace-engineer-turned-planetary-scientist who’s devoted their career to Titan, things don’t get much more exciting than a nuclear-powered octocopter with drills and a neutron gun!