Saturn’s giant moon, Titan, has been a source of speculation of decades. Shrouded in a dense, methane-nitrogen rich atmosphere, potentially harbouring a liquid water ocean beneath its crust, the moon has long be thought to have the conditions in which basic life might arise.
The joint NASA-ESA Cassini-Huygens mission has, over the span of thirteen years, added immeasurably to our understanding of Titan – and to the mysteries of its potential. In doing so, it has also provided us with evidence of processes taking place which are the precursors to the development of life. For example, we know that within Titan’s ionosphere, nitrogen, carbon and hydrogen are exposed to sunlight and energetic particles from Saturn’s magnetosphere. This exposure drives a process wherein these elements are transformed into more complex prebiotic compounds, which then drift down towards the lower atmosphere and form a thick haze of organic aerosols that are thought to eventually reach the surface.
However, while the drivers of the process are known, the nature of the process itself has been something of a mystery – one which an international team of scientists led by the University College London (UCL) think they now understand. In Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere the team identify Titan’s upper atmosphere contains a negatively charged species of linear molecule in Titan’s atmosphere called “carbon chain anions” – which, it has in the past been theorised, may have acted as the basis for the earliest forms of life on Earth.
The molecules were detected by CAPS, the Cassini Plasma Spectrometer, as the vehicle passed through the upper reaches of Titan’s atmosphere on a final flyby before commencing its “Grand Finale” of flights between Saturn and its rings. The discovery came as a surprise, as carbon chain anions are highly reactive, and should not survive long in Titan’s atmosphere. However, what particularly caught the attention of the science team was that the data show that the carbon chains become depleted closer to the moon, while precursors to larger aerosol molecules undergo rapid growth. This suggests a close relationship between the two, with the carbon chains ‘seeding’ the larger molecules – those prebiotics mentioned above – which then fall to the surface.
“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,” said Ravi Desai, the lead author for the study in a press release from UCL.
He continued, “This is a known process in the interstellar medium – the large molecular clouds from which stars themselves form – but now we’ve seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules. The question is, could it also be happening at other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties?”
With its rich mix of complex chemistry coupled with its basic composition, Titan is something of a planetary laboratory; one which probably mirrors the very early atmosphere surrounding Earth before the emergence of oxygen-producing micro-organisms which started the transformation of our atmosphere into something far more amenable for the advance of life. As such, the discovery of carbon chain anions in Titan’s atmosphere potentially confirms that long-held theory that they help kick-start the life creating processes here on Earth, and suggest conditions on Titan might allow the same to happen there. It also offers insight into how life might start elsewhere in the galaxy.
“These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere,” Dr Nicolas Altobelli, ESA’s Cassini project scientist, said in the same press release. “While we haven’t detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors.”
Dream Chaser ISS Flights target 2020 Commencement
Sierra Nevada Corporation (SNC) has confirmed than United Launch Alliance (ULA) will provide the veritable Atlas V booster as the launch vehicle for the Dream Chaser Cargo mini-shuttle, which will be joining fleet of uncrewed vehicles from America, Russia and Japan keeping the International Space Station (ISS) supplied with consumables, equipment and science experiments. The company also indicate that launches of the vehicle could start in 2020.
Dream Chaser was originally conceived to fly crews to and from the ISS as part of NASA’s commercial crew transportation joint venture with the private sector. Four companies vied for contracts to supply NASA with vehicles capable of shuttling up to six personnel to and from the space station. Despite being one of the most advanced of the designs in terms of feasibility and development, the Dream Chaser was not selected for that work, with NASA opting for the SpaceX Dragon 2 vehicle and Boeing’s CST-100 Starliner capsule.
However, support within the US space agency for the Dream Chaser continued, allowing SNC to propose the development of Dream Chaser Cargo, a revised version of the original concept, capable of supplying up to 5.5 tonnes of cargo to the ISS. In January 2016, in renewing its contract with SpaceX (Dragon) and Orbital ATK (Cygnus) for such resupply missions, NASA extended it to include SNC. This was followed a year ago by formal approval being given for Dream Chaser missions to the ISS, which allowed SNC to push ahead with testing of the revised vehicle.
Dream Chaser will launch atop the commercial Atlas V in its most powerful configuration, dubbed Atlas V 552, with five strap on solid rocket motors and a dual engine Centaur upper stage. The cargo vehicle will be held inside a five metre diameter payload fairing with its wings folded. Cargo will be carried both within the vehicle itself and in a support module mounted on the rear of the spacecraft, which will also house a docking adaptor for connecting with the space station. The latter will be supplied to SNC by the European Space Agency, which is also supplying NASA with the Service Module for the Orion multi-Purpose Crew Vehicle.
In addition to flying up to 5.5 tonnes to the ISS, Dream Chaser Cargo will be able to return some 2 tonnes of equipment, experiments and other items from the space station to Earth, where it will make a conventional runway landing using the former space shuttle runway at Kennedy Space Centre – or any other suitable landing facility in the United States.
It is expected that Dream Chaser cargo will fly a total of six missions to the ISS between 2020 and 2024, when it is currently anticipated the space station will be decommissioned.