NASA's Cassini spacecraft has sniffed out a particular type of negatively charged molecule on the hazy Saturnian moon of Titan. Some of these molecules, known as anions, were identified as carbon-chain anions, which are believed to be the building blocks for more complex organic molecules and may have been the basis for the earliest forms of life on Earth. The molecules could be a universal driver for prebiotic chemistry.
Cassini's plasma spectrometer instrument captured the particles as it flew through the upper atmosphere of Titan. The finding has been published in Astrophysical Journal Letters. Ravi Desai of University College London and lead author of the study says, "We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger and more complex organic molecules, such as the moon’s large haze particles. This is a known process in the interstellar medium, but now we’ve seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules."
The atmosphere on titan is rich with methane and nitrogen and has among the most complex chemistry seen in the solar system. The finding indicates the possibility that similar molecules may also be present on other planets which have methane and nitrogen in their atmospheres. Bodies within the solar system with such an atmosphere include Pluto and Triton, a satellite of Neptune. Titan is understood to be a planet-scale laboratory that can be used to study the emergence of life on Earth, or life on exoplanets in orbit around other stars.
Although Titan is a moon of a gas giant, for planetary scientists, it is convenient to consider any spherical celestial body that is not on fire as a planet. That would mean the solar system has 110 known planets. The last close flyby of Titan by Cassini was executed just before the spacecraft started its grand finale series of dives. Cassini has previously beamed back images of methane clouds streaking across Titan and the hydrocarbon lakes on the surface. The thick atmosphere makes it difficult for space probes to capture details of the surface of the moon.
On 15 September, Cassini will conclude its 20-year mission with a science-rich dive into Saturn. Till the very end, when it becomes a shooting star in the skies of Saturn, Cassini will continue to beam back images and observations to Earth. The decision to deorbit the spacecraft is being taken as there is not enough fuel on board to maintain control of Cassini. Without this control, Cassini may drift into one of the moons of Saturn and potentially contaminate it with molecules from Earth, which may be harmful to any life forms on the Saturnian moons.