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.

 
 
 
 

Covid-19 is highlighting cities' unequal access to green space

In the UK, Londoners are most likely to rely on their local park for green space, and have the best access to parks. (Leon Neal/Getty Images)

As coronavirus lockdowns ease, people are flooding back to parks – but not everyone has easy access to green space in their city.

Statistics from Google show that park attendance in countries across the globe has shot up as people have been allowed to move around their cities again.

This is especially true in urban areas, where densely populated neighbourhoods limit the size of private green space – meaning residents have to go to the park to get in touch with nature. Readers from England can use our interactive tool below to find out how much green space people have access to in their area, and how it compares to the rest of the country.

 

Prime Minister Boris Johnson’s announcement Monday that people are allowed to mingle in parks and gardens with groups of up to six people was partially following what people were doing already.

Data from mobile phones show people have been returning to parks across the UK, and also across Europe, as weather improves and lockdown eases.

People have been returning to parks across the world

Stay-at-home requirements were eased in Italy on 4 May, which led to a flood of people returning to parks.

France eased restrictions on 1 May, and the UK eased up slightly on 13 May, allowing people to sit down in public places so long as they remain socially distanced.

Other countries have seen park attendance rise without major easing of lockdown – including Canada, Spain, and the US (although states there have individual rules and some have eased restrictions).

In some countries, people never really stopped going to parks.

Authorities in the Netherlands and Germany were not as strict as other countries about their citizens visiting local parks during lockdown, while Sweden has famously been avoiding placing many restrictions on people’s daily lives.


There is a growing body of evidence to suggest that access to green space has major benefits for public health.

A recent study by researchers at the University of Exeter found that spending time in the garden is linked to similar benefits for health and wellbeing as living in wealthy areas.

People with access to a private garden also had higher psychological wellbeing, and those with an outdoor space such as a yard were more likely to meet physical activity guidelines than those without access to outdoor space. 

Separate UK research has found that living with a regular view of a green space provides health benefits worth £300 per person per year.

Access is not shared equally, however, which has important implications for equality under lockdown, and the spread of disease.

Statistics from the UK show that one in eight households has no garden, making access to parks more important.

There is a geographic inequality here. Londoners, who have the least access to private gardens, are most likely to rely on their local park for green space, and have the best access to parks. 

However the high population in the capital means that on the whole, green space per person is lower – an issue for people living in densely populated cities everywhere.

There is also an occupational inequality.

Those on low pay – including in what are statistically classed as “semi-skilled” and “unskilled” manual occupations, casual workers and those who are unemployed – are almost three times as likely as those in managerial, administrative, professional occupations to be without a garden, meaning they rely more heavily on their local park.

Britain’s parks and fields are also at significant risk of development, according to new research by the Fields in Trust charity, which shows the number of people living further than a 10-minute walk from a public park rising by 5% over the next five years. That loss of green spaces is likely to impact disadvantaged communities the most, the researchers say.

This is borne out by looking at the parts of the country that have private gardens.

The least deprived areas have the largest gardens

Though the relationship is not crystal clear, it shows at the top end: Those living in the least deprived areas have the largest private green space.

Although the risk of catching coronavirus is lower outdoors, spending time in parks among other people is undoubtedly more risky when it comes to transmitting or catching the virus than spending time in your own outdoor space. 

Access to green space is therefore another example – along with the ability to work from home and death rates – of how the burden of the pandemic has not been equally shouldered by all.

Michael Goodier is a data reporter at New Statesman Media Group, and Josh Rayman is a graphics and data visualisation developer at New Statesman Media Group.