Organic matter in the Titan lakes, and comparison with primitive Earth

Abstract

Titan is the only world in the solar system besides the Earth that has liquid on its surface. The liquid in the lakes is thought to be composed primarily of ethane with methane and nitrogen in solution. The clouds are thought to be composed of liquid methane drops. Surface liquid is present in polar lakes and in surface materials at equatorial sites. Studying the chemical processing that potentially results from organic material interacting with this liquid is one of the main goals of proposed missions to Titan. We have been engaged in producing tholin under Titan-like conditions for more than three decades, first at the Laboratory for Planetary Studies at Cornell University in collaboration with Late Dr. Carl Sagan and for over a decade at Laboratory for Planetary Studies at NASA Ames Research Center and Carl Sagan Center for the Study of Life in the Universe, SETI Institute. Our focus is to understand the capabilities for analysis of tholin solubility in liquid methane and ethane for flight instruments. Our results are expected to contribute to an understanding of the organic chemistry on Titan and to the development of an explicit and targeted scientific strategy for near term analysis of the products of organic-liquid interactions on Titan. Organics are produced as a haze in Titan’s high atmosphere due to photolysis of methane with the Sun’s extreme ultraviolet light and subsequent reaction with N. Also tholins are formed at a much higher level on Titan by charged particles of Saturn magnetosphere. However, the presence of organics is not the sole feature, which makes Titan significant to astrobiology; organics are widely present in the outer solar system. The reason Titan is a prime target for future outer solar system missions is the combination of organic material and liquid on the surface; liquid that could over a medium for further organic synthesis. NASA recently selected for further study a Discovery proposal TiME to investigate the chemistry of the lakes on Titan. As described by the team’s press release: “The TiME capsule would launch in 2016 and reach Titan in 2023, parachuting onto the moon’s second-largest northern sea, the Ligeia Mare. For 96 days the capsule would study the composition and behavior of the sea and its interaction with Titan’s weather and climate. TiME would also seek evidence of the complex organic chemistry that may be active on Titan today, and that may be similar to processes that led to the development of life on the early Earth”. The results of our on going research on how tholins interact with the liquid ethane and methane in the lakes on Titan will improve our chances of detecting any possible biology on this cold and distant world.