Hundreds of millions of miles away from Earth, the landscape of Titan, Saturn's largest moon, bears a striking resemblance to our own planet - but with dunes of hydrocarbon sands rather than silica sands, and rain, rivers, lakes and seas of liquid methane and ethane rather than liquid water.
The NASA Dragonfly mission is set to explore this world in unprecedented detail with a rotorcraft lander that will collect samples of the surface material for characterization and analysis. Bringing the project one step closer to fruition, Lawrence Livermore National Laboratory (LLNL) has delivered an advanced gamma-ray spectrometer to its partners at the Johns Hopkins Applied Physics Laboratory (APL) in Maryland. This spectrometer will be part of the Dragonfly Gamma-ray and Neutron Spectrometer (DraGNS) that is being built by APL and is currently undergoing integration and testing in preparation for launch.
The Dragonfly mission, led by APL for NASA, is scheduled to launch in 2028. Dragonfly will be first mission to land on the surface of Titan since NASA's Cassini spacecraft delivered the European Space Agency's Huygens lander in 2005. Dragonfly is set arrive at Titan in 2034 and will fly between multiple sites to explore the sandy Shangri-La region and the nearby Selk impact crater.
Titan is the only moon in our solar system with a dense atmosphere and stable surface liquids, making it a compelling target for astrobiology research into prebiotic chemistry. The extremely cold surface temperature makes it an unlikely place to host water-based life; however, its complex organic chemistry and the opportunity in the past for carbon-rich molecules to have mixed with liquid water, such as at impact crater sites, could help scientists understand the early (pre-biotic) chemical processes like those that ultimately led to the development of life on the early Earth.
DraGNS will play an important role in the mission by performing on-the-ground measurements that provide analysis to guide sample selection. The instrument will identify and characterize the chemical composition of surface materials to help the scientists determine which targets are most promising for further analysis.
"We expect the surface of Titan to be comprised mainly of mixtures of water-ice with hydrocarbons and ammonia," said LLNL physicist Morgan Burks. "But it may contain many surprises as well. In particular, we're interested in whether chemical processes in Titan's past could have formed molecules like amino acids or proteins."
The heart of the detector is a germanium crystal, which measures the energy of gamma rays that interact in the detector with a resolution 10-20 times higher than competing technologies. The gamma-ray energy acts like a fingerprint for determining the elemental composition of planetary bodies such as moons, asteroids or the surface of planets.
With decades of experience, LLNL is a world leader in developing high-resolution gamma-ray spectroscopy for planetary-science exploration. In collaboration with APL, the Laboratory built the first gamma-ray spectrometer to orbit the planet Mercury onboard NASA's MESSENGER mission, a spectrometer currently on its way to the asteroid belt for NASA's Psyche mission and a spectrometer for JAXA's upcoming Martian Moons eXploration mission.
Nevertheless, the Dragonfly mission presented unique challenges compared to previous missions. Over the six-year journey to Titan, the instrument will be exposed to radiation from galactic cosmic rays and solar storms. Once on the surface, it must survive the cold environment, including ambient temperatures as low as -180 degrees Celsius. DraGNS must also endure the shaking and rumbling of launch on a SpaceX Falcon Heavy rocket, as well as the shock and vibration of entry into Titan's atmosphere.
To address these challenges, LLNL spent two years testing the gamma-ray spectrometer across a range of anticipated conditions. The instrument was subjected to vibration tests that mimic rocket launch and entry into Titan's atmosphere; it was operated in temperatures ranging from -200 to +115 degrees Celsius; and it was subjected to high-energy protons to simulated 10 years' worth of radiation exposure in space.
"The Dragonfly mission to Titan will explore an alien world and is one of the most ambitious NASA missions ever attempted," said Burks. "This project is fantastically interesting, and we are excited to make a contribution."
As the project has transitioned from development to integration and testing, anticipation for Dragonfly grows. The gamma-ray spectrometer data will deepen our knowledge of Titan and possibly transform our understanding of planetary formation and how far prebiotic chemistry could have progressed on a world in the outer solar system.
