Is there life on Titan? Saturn’s moon may reveal how life first formed on Earth

Titan. Image: NASA/Getty.

How chemical reactions on a lifeless planet floating around in the cold darkness of space can suddenly give rise to living organisms is one of the biggest questions in science. We don’t even know whether the molecular building blocks of life on Earth were created here or whether they were brought here by comets and meteorites.

Using data from the NASA/ESA Cassini mission, we have now discovered molecules on Saturn’s largest moon Titan which we think drive the production of complex organic compounds. These are molecules that have never been seen in our solar system before. The discovery of such fascinating chemistry not only makes Titan a great contender for hosting some sort of primitive life, it also makes it the ideal place to study how life may have arisen from chemical reactions on our own planet.

The molecular building blocks of life are organic compounds including amino acids that can be assembled into proteins, RNA and DNA in living cells. To date, scientists have found these compounds in meteorites, comets and interstellar dust. But the problem is that these materials formed millions of years ago, which means we have no way of knowing how they were created.

Excitingly, it seems these compounds are being created on Titan today. Sunlight and energetic particles from Saturn’s magnetosphere drive reactions in the moon’s upper atmosphere, which is dominated by nitrogen, methane and hydrogen. These lead to larger organic compounds which drift downwards to form the moon’s characteristic “haze” and the extensive dunes – eventually reaching the surface.

The chemical reactions in Titan’s atmosphere. The carbon chain anions are in the green box. Image: ESA.

To make these surprising discoveries, published in the Astrophysical Journal Letters, the Cassini spacecraft dipped through Titan’s upper atmosphere. Using data beamed back to Earth, we identified the presence of negatively charged molecules called “carbon chain anions”. These appear to “seed” the larger organic compounds observed at the moon – such as polyaromatic hydrocarbons and cyanopolynnes – which could serve as key ingredients for early forms of life. Laboratory experiments have also shown that amino acids could exist there, but the instruments on Cassini are not equipped to detect them.

Negatively charged molecules like these are rare in space environments as they want to react and combine with other molecules – meaning they can be quickly lost. When present, however, they appear to be a crucial “missing link” between simple molecules and complex organic compounds.

So could life currently exist on Titan? It’s not impossible. Water plumes erupting from another of Saturn’s moons, Enceladus, provides a key source of oxygen, which rains down onto Titan’s upper atmosphere. Titan has even been judged the most likely place beyond the Earth to host life by the Planetary habitability index. But life there would likely be quite primitive due to the cold conditions. The presence of liquid methane and ethane seas also means potential organisms would have to function quite differently to those on Earth.

Tracing life on Earth

Remarkably, similar processes are observed in vast molecular clouds beyond our solar system, where stars are born. After the first stars in the universe entered their death throes and fused together heavier elements, rich organic chemistry took place. In these environments, negatively charged molecules have been shown to act as a catalyst for the formation of larger organics, which could then be transferred to solar systems and comets forming from the cloud.

Complex interstellar chemistry has led to the theory that the building blocks of life could have been delivered to Earth from comets which once formed in these molecular clouds. ESA’s Rosetta mission detected the amino acid glycine when visiting Comet 67P/Churymov-Gerasimenko. However, the new discovery makes it entirely possible that similar processes of creating complex organics, and thus life, took place on Earth instead.

Haze in Titan’s atmosphere. Image: Wikimedia commons.

Titan’s dense nitrogen and methane atmosphere is similar to the early Earth’s, some 2.5-4bn years ago. At this time, before the build-up of oxygen occurred, large quantities of methane resulted in organic chemistry similar to that observed at Titan today. The moon is therefore a high priority target in the search for the beginnings of life.

By making long-term, detailed observations of Titan, we may one day be able to trace the journey from small to large chemical species in order to understand how complex organic molecules are produced. Perhaps we may even be able catch the sudden change from complex organic molecules to living organisms. Follow-up observations of Titan’s atmosphere are already underway using powerful ground-based telescopes such as ALMA. Further missions to explore Titan are also in the works – it is crucial that these are equipped to detect the signatures of life.

Universal driver

The fact that we now see the same chemistry occurring at Titan as in molecular clouds is fascinating, as it indicates the universal nature of these processes. The question now is, could this also be happening within other atmospheres rich in nitrogen and methane, such as at Pluto or Neptune’s moon Triton? What about the thousands of exoplanets discovered in recent years, circling nearby stars?

Radar images reveal lakes on Titan’s surface. Image: NASA/JPL-Caltech/ASI/USGS.

The concept of a universal pathway towards the building blocks of life has implications for what we need to look for in the onward search for life in the universe. If we detect the molecules just seen on Titan in another environment, we would know that much larger organics and therefore amino acids could possibly exist there.

Future missions, such as NASA’s James Webb Space Telescope and ESA’s exoplanet mission Plato, are set to further study these processes within our solar system and at planets orbiting nearby stars. The UK is even planning its own exoplanet mission, Twinkle, which will also search for signatures of organic molecules.

The ConversationAlthough we haven’t detected life itself, the presence of complex organic molecules at Titan, comets and within the interstellar medium means we are certainly coming close to finding its beginnings. And it’s all thanks to Cassini’s near 20-year exploratory journey. So spare a thought for this magnificent spacecraft as it ends its mission in September with a final death-plunge into Saturn’s atmosphere.

Ravi Desai is a PhD candidate in physics at UCL.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

A growing number of voters will never own their own home. Why is the government ignoring them?

A lettings agent window. Image: Getty.

The dream of a property-owning democracy continues to define British housing policy. From Right-to-Buy to Help-to-Buy, policies are framed around the model of the ‘first-time buyer’ and her quest for property acquisition. The goal of Philip Hammond’s upcoming budget is hailed as a major “intervention” in the “broken” housing market – is to ensure that “the next generation will have the same opportunities as their parents to own a home.”

These policies are designed for an alternative reality. Over the last two decades, the dream of the property-owning democracy has come completely undone. While government schemes used to churn out more home owners, today it moves in reverse.

Generation Rent’s new report, “Life in the Rental Sector”, suggests that more Britons are living longer in the private rental sector. We predict the number of ‘silver renters’ – pensioners in the private rental sector – will rise to one million by 2035, a three-fold increase from today.

These renters have drifted way beyond the dream of home ownership: only 11 per cent of renters over 65 expect to own a home. Our survey results show that these renters are twice as likely than renters in their 20s to prefer affordable rental tenure over homeownership.

Lowering stamp duty or providing mortgage relief completely miss the point. These are renters – life-long renters – and they want rental relief: guaranteed tenancies, protection from eviction, rent inflation regulation.

The assumption of a British ‘obsession’ with homeownership – which has informed so much housing policy over the years – stands on flimsy ground. Most of the time, it is based on a single survey question: Would you like to rent a home or own a home? It’s a preposterous question, of course, because, well, who wouldn’t like to own a home at a time when the chief economist of the Bank of England has made the case for homes as a ‘better bet’ for retirement than pensions?


Here we arrive at the real toxicity of the property-owning dream. It promotes a vicious cycle: support for first-time buyers increases demand for home ownership, fresh demand raises house prices, house price inflation turns housing into a profitable investment, and investment incentives stoke preferences for home ownership all over again.

The cycle is now, finally, breaking. Not without pain, Britons are waking up to the madness of a housing policy organised around home ownership. And they are demanding reforms that respect renting as a life-time tenure.

At the 1946 Conservative Party conference, Anthony Eden extolled the virtues of a property-owning democracy as a defence against socialist appeal. “The ownership of property is not a crime or a sin,” he said, “but a reward, a right and responsibility that must be shared as equitable as possible among all our citizens.”

The Tories are now sleeping in the bed they have made. Left out to dry, renters are beginning to turn against the Conservative vision. The election numbers tell the story of this left-ward drift of the rental sector: 29 per cent of private renters voted Labour in 2010, 39 in 2015, and 54 in June.

Philip Hammond’s budget – which, despite its radicalism, continues to ignore the welfare of this rental population – is unlikely to reverse this trend. Generation Rent is no longer simply a class in itself — it is becoming a class for itself, as well.

We appear, then, on the verge of a paradigm shift in housing policy. As the demographics of the housing market change, so must its politics. Wednesday’s budget signals that even the Conservatives – the “party of homeownership” – recognise the need for change. But it only goes halfway.

The gains for any political party willing to truly seize the day – to ditch the property-owning dream once and for all, to champion a property-renting one instead – are there for the taking. 

David Adler is a research association at the campaign group Generation Rent.

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