By Dr Valerie Jeffries FLS
Language of Life
The term ‘Earthlife’ acknowledges that all life we know uses the same universal coding system to read its DNA. The way it translates DNA into bodies is amazingly neat, but uses a ‘language’ that’s arisen by chance. When humans first made words with meanings, two tribes on opposite continents would each develop a system that worked, but they’d hardly be likely to come up with the same words. Similarly another origin of Life would arrive at a different system from Earth’s. So all Earthlife originates from one beginning; we are all kin. Living samples from the Red Planet could show us a different coding system – meaning a separate origin of life. If microbes found on Mars were operating the same coding system as Earth’s, it would reveal contamination instead of demonstrating native Martian life. To know the truth, contamination of other planets and moons by microbes from Earth must be avoided. A large part of NASA’s budget for planetary missions goes into scrupulous sterilisation of every part of every space vehicle before it’s launched. On return, samples locked into containers are opened only in secure conditions, as for studying dangerous microbes. Returning vehicles are re-sterilised, astronauts quarantined, and their space suits stripped of any possible non-Earth life. This is important for research, and for human safety however tiny the risk that alien microbes could affect us.
Inner Solar System, worst and best : Tardigrades, tiny but tough.
One place we are confident has no current life is our Moon, and precautions were perhaps more lax for the Moon landings 52 years ago. Just possibly around 3.5 billion years back, when crater-forming meteor bombardment had slowed, Moon like Mars could have received space-travelling microbes from nearby Earth, but we don’t think they would have survived there. The Moon is dusty like a cold desert, it has no atmosphere, and receives intense deadly radiation. Surface temperatures are either too hot or too cold, and it’s been like that for 3.5 billion years. A dead world, apart from its extremely fleeting habitation by Homo sapiens. Except . . . . .
While modern precautionary rules should apply to the Moon, there has in fact been an accidental infringement. In April 2019, when the Israeli lunar lander Beresheet crashed onto the Moon’s surface, bringing its mission to an abrupt end, its cargo was spilt. Its cargo (alongside classic books, human blood samples and the entirety of Wikipedia) included some Tardigrades, the toughest animals known. They are the only species to stand comparison with the hardiest bacteria for endurance of hostile environments. Tardigrades, also affectionately know as ‘water bears’, were experimentally exposed on the outside of a Russian orbiter, suffering the vacuum, cold and radiation of space for 12 days. They survived, revived, then laid eggs that hatched! Just a couple of mm long or less, they can shrivel into a husk-like ‘tun’ form that survives freezing for decades, boiling, dessication, irradiation, starvation, pressure extremes, and poisonous gases. The dormant tun is almost indestructible, and revives within hours of immersion in water. Biologists believe the tiny Beresheet astronauts are extremely likely to have survived their impact. A lucky coincidence that the animal with best chance of survival on the Moon was the type accidentally ‘offered’ a chance to try ? There’s been no water to revive them, but who knows if any tiny tuns are still potentially viable on that dead world, long after the last Apollo astronaut departed ?
Microscopic but mighty:
Mercury is another small ‘dead world’, with its enigmatic history, its peculiar orbit, its terrifying temperature extremes up close to the Sun, and no real atmosphere. Whatever its past, it’s uninhabitable now.
The great hope for extra-terrestrial life remains Mars, ever since telescopes revealed its surface features resembling Earth.
Venus is another story, long written off as “Hell in the sky”. The surface temperature is about 460 degrees C all over, swathed in a thick heavy atmosphere of carbon dioxide and clouds of acid rain, suggesting a deadly endpoint of extreme greenhouse effect. No known Earthlife could survive that, and nor did the 1960’s Soviet Venera probes which ceased to function within two hours of landing. So when a Cardiff University team announced in 2020 that they had evidence of traces of phosphine gas in the atmosphere of Venus, there was great excitement. Phosphine is produced on Earth only by certain industrial processes, and by certain bacteria. Even the tiny amount detected would need to be forming currently, as the surrounding chemistry would eliminate it fast, so it was hailed as possible evidence of life – on what looks like a poisonous planet!
But high in the cooler clouds above Venus, could some hardy germ of life arise and persist?
That would be a transformative discovery. Could deadly Venus be offering hints of current living processes ahead of benevolent Mars? The controversy rages on as to whether phosphine could result from some unknown non-living chemistry, with agreement that more evidence is needed…
By Dr Valerie Jeffries FLS