Rosetta spacecraft: "Comets could have played a crucial role in the emergence of life on Earth"by Rebecca Priestley
A spacecraft has found new clues that suggest life may have been bombed into existence by comets.
The European Space Agency’s Rosetta spacecraft, which has been orbiting comet 67P/Churyumov-Gerasimenko since 2014, has detected fundamental building blocks of life in the body’s surrounding gas cloud.
Although this isn’t evidence that we have company in the solar system, the discovery of glycine and phosphorus “demonstrates that comets could have played a crucial role in the emergence of life on Earth”, scientists said.
Along with oxygen, alcohols and simple sugars already detected around the comet, the amino acid glycine and the element phosphorus support the idea that comets hitting Earth may have delivered all the essential ingredients for life, says Professor Kathy Campbell, a geoscientist and astrobiologist at the University of Auckland.
If a comet carrying this sort of “cocktail of chemicals” landed in the early Earth’s ocean and then received energy from the Sun, “you could start seeing other molecular combinations”, and perhaps the first life forms, she says.
On Earth, the oldest signs of life – fossilised single-celled organisms – are found preserved in rocks up to 3.5 billion years old. Scientists have long believed that these simple life forms emerged in shallow marine environments, but a recent collaboration between Campbell and Australian geologists has found they may have been extremophile micro-organisms that thrived in hot springs such as Rotorua’s.
But all possibilities – that life emerged in shallow marine environments, hot springs or came from comets – could be correct (see “Origins of life”, below). “There’s more than one way that life could have taken hold on Earth. It could even have done so more than once,” says Campbell.
When comets and asteroids hit the Earth – occurrences that were more frequent in the early history of the solar system – “they can destroy what’s already there but they can also deliver essential nutrients or molecules. So you could have had life starting out hot or you could have had life starting out in cooler pockets on early Earth, or life taking hold a few times and being wiped out during these bombardments.”
Understanding the conditions under which life emerged on Earth is helping scientists to know where to look for life elsewhere in the solar system and beyond. Nasa’s Mars rovers have found “what appears to be fossil hot springs” on the red planet, says Campbell. “There are hopes these Martian deposits could be home to fossilised primitive life forms.”
On Mars today, UV radiation levels are too high to sustain life at the surface, but one possible landing site for Nasa’s planned Mars 2020 mission is around the ancient hot-spring deposits, where it’s hoped samples containing fossils might be found. Campbell also has hopes for what lies beneath the planet’s surface. “Let’s drill down and get beneath the irradiated surface layer and see what’s under there, because we have plenty of life in our subsurface.”
Another candidate for life in our solar system is Europa, one of the moons of Jupiter, which was surveyed when Nasa’s Galileo spacecraft was in the Jupiter system from 1995-2003. In a 2014 statement, Nasa described the cycling of materials between Europa’s saltwater ocean and its ice shell as having the potential to “provide sources of chemical energy that could sustain simple life forms”.
As the field moves from a theoretical to an exploration phase, this is an exciting time to be an astrobiologist. Campbell would like to be alive to “see us drill through the ice on Europa and find out what’s in the oceans underneath. I’d like us to bring back samples from Mars – from places that the engineers don’t want to go to.” Engineers prefer flat, accessible landing surfaces, but Campbell would like to see a search for hot springs on the flanks of Mt Olympus or other Martian volcanoes.
Other projects, such as the ambitious Breakthrough Initiatives (see below), are searching for life beyond our solar system. In the Breakthrough Starshot programme, thousands of nanocraft – chip-sized probes with light sails – will be sent to explore the nearest star system, Alpha Centauri.
A massive Earth-based laser array would blast the probes into space, where they are expected to travel at up to 160 million kilometres an hour and reach the system in 20 years, from where they will beam home images of planets and other data. First launch is planned “within a generation”. “I’m very optimistic for the future,” says Campbell. “It would change everything if we knew we weren’t alone.”
Origins of life
Scientists have many theories about where and how life on earth originated.
Comet seeding: the building blocks of life arrived on Earth on comets and asteroids.
Hot springs: earliest life evolved either in terrestrial hot springs or in deep- or shallow-sea hydrothermal vents.
A spark in the primordial soup: sunlight acting on inorganic compounds created the first organic compounds, creating a “primordial soup” (our early oceans) in which ever-more-complex organic molecules, and eventually life, were created.
Clay mineral templating: self-replicating organic molecules first emerged on inorganic repeating structures such as silicate crystals.
The Breakthrough Initiatives – which boast Stephen Hawking and Mark Zuckerburg as board members – were founded in 2015 by Russian physicist and billionaire Yuri Milner and his wife, Julia, to “explore the universe, seek scientific evidence of life beyond Earth and encourage public debate from a planetary perspective”.
Breakthrough Listen is a $100 million programme of astronomical observations in search of evidence of intelligent life involving a survey of the million nearest stars and hundred nearest galaxies.
Breakthrough Message is a $1 million competition to design a message representing Earth, life and humanity that could potentially be understood by another civilisation.
Breakthrough Starshot is a $100 million research and engineering programme aiming to demonstrate proof of concept for a new technology to enable ultralight unmanned space flight at 20% of the speed of light and lay the foundations for a fly-by mission to Alpha Centauri within a generation.
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