Has Cassini found a universal driver for prebiotic chemistry at Titan?

July 27, 2017, University College London
Credit: University College London

An important type of molecule that helps produce complex organic material has been detected within Titan's hazy upper atmosphere by a UCL-led team as part of the international Cassini-Huygens mission.

In the study, published in Astrophysical Journal Letters, scientists identified negatively charged called 'carbon chain anions' in the of Titan, Saturn's largest moon. These linear molecules are understood to be building blocks towards more , and may have acted as the basis for the earliest forms of life on Earth.

The team say the discovery of the negatively charged carbon chain anions is surprising because they are highly reactive and should not last long in Titan's atmosphere before combining with other materials. Their discovery there is completely reshaping current understanding of the hazy moon's atmosphere.

The detections were made using Cassini's plasma spectrometer, called CAPS, as Cassini flew through Titan's , 950–1300 km above the surface.

Interestingly, 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 that are thought to fall down to, and deposit on, 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, study lead author and PhD student at UCL.

Credit: University College London

"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?"

Titan boasts a thick nitrogen and methane atmosphere with some of the most complex chemistry seen in the Solar System. It is even thought to mimic the atmosphere of early Earth, before the build-up of oxygen. As such, Titan can be seen as a planet-scale laboratory that can be studied to understand the chemical reactions that may have led to life on Earth, and that could be occurring on planets around other stars.

"The prospect of a universal pathway towards the ingredients for life has implications for what we should look for in the search for life in the Universe," said co-author Professor Andrew Coates, also from UCL and co-investigator of CAPS. "Titan presents a local example of exciting and exotic chemistry, from which we have much to learn."

In Titan's upper atmosphere, nitrogen and methane are exposed to energy from sunlight and energetic particles in Saturn's magnetosphere. These energy sources drive reactions involving nitrogen, hydrogen and carbon, which lead to more complicated prebiotic compounds.

These large molecules drift down towards the lower atmosphere, forming a thick haze of organic aerosols, and are thought to eventually reach the surface. But the process by which simple molecules in the upper atmosphere are transformed into the complex organic haze at lower altitudes is complicated and difficult to determine. This discovery adds vital information that will help scientists understand the chemical process.

"These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how are produced in an early Earth-like atmosphere," added Dr Nicolas Altobelli, ESA's Cassini project scientist. "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."

Cassini's 13-year odyssey in the Saturnian system will soon draw to a close, but future missions, such as the international James Webb Space Telescope and ESA's exoplanet mission Plato are equipped to look for this process not only in our own Solar System but elsewhere. Advanced ground-based facilities such as ALMA could also enable follow-up observations of this process at work in Titan's atmosphere, from Earth.

Explore further: Organic Materials Spotted in Titan's Atmosphere

More information: R. T. Desai et al. Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan's Ionosphere, The Astrophysical Journal (2017). DOI: 10.3847/2041-8213/aa7851

Related Stories

Organic Materials Spotted in Titan's Atmosphere

April 26, 2005

During its closest flyby of Saturn's moon Titan on April 16, the Cassini spacecraft came within 1,027 kilometers (638 miles) of the moon's surface and found that the outer layer of the thick, hazy atmosphere is brimming ...

Does Pluto have the ingredients for life?

February 23, 2017

Pluto has long been viewed as a distant, cold and mostly dead world, but the first spacecraft to pass by it last year revealed many surprises about this distant dwarf planet.

Cassini sees Titan cooking up smog

February 5, 2013

(Phys.org)—A paper published this week using data from NASA's Cassini mission describes in more detail than ever before how aerosols in the highest part of the atmosphere are kick-started at Saturn's moon Titan. Scientists ...

Image: Titan flyby 22 April 2017

April 25, 2017

In the early hours of Saturday morning, the international Cassini–Huygens mission made its final close flyby of Saturn's largest moon, Titan, coming within 1000 km of the atmosphere-clad world.

NASA team investigates complex chemistry at Titan

April 3, 2013

(Phys.org) —A laboratory experiment at NASA's Jet Propulsion Laboratory, Pasadena, Calif., simulating the atmosphere of Saturn's moon Titan suggests complex organic chemistry that could eventually lead to the building blocks ...

Recommended for you

Did a rogue star change the makeup of our solar system?

July 20, 2018

A team of researchers from the Max-Planck Institute and Queen's University has used new information to test a theory that suggests a rogue star passed close enough to our solar system millions of years ago to change its configuration. ...

Where to search for signs of life on Titan

July 20, 2018

New findings, published in the journal Astrobiology, suggest that large craters are the prime locations in which to find the building blocks of life on Saturn's largest moon, Titan.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

wduckss
not rated yet Jul 28, 2017
"This is a known process in the interstellar medium - the large molecular clouds from which stars form themselves - but now we have seen it in a completely different environment .." from article

These are two different processes for the formation of more complex atoms (the second is due to the constant radiation attack that is not in the molecular cloud).
Always observe the "working" temperature of the atom or compound and the environment (https://www.acade...Universe and https://www.acade...system).

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.