It feels like we're constantly searching for a friend out there in the cosmos, only to be repeatedly disappointed. But what if, in our quest to discover life beyond Earth, we've overlooking a more important question? What if the question we should really be asking is: How do we ensure life spreads beyond Earth?
Seeds from the humble morning glory flower could hold clues to making sure life goes on, somewhere, even if we humans self-destruct. In results published recently in the journal Astrobiology, biologists David Tepfer and Sydney Leach demonstrate that these hardy plant embryos can withstand incredibly high doses of ultraviolet radiation — up to six million times the amount used to sterilise drinking water. Given that outer space, and the surface of nearby planets like Mars, are awash in DNA-damaging UV light, the discovery bodes well for those hoping life might be able to hitchhike between worlds on asteroids, an age-old idea better known as panspermia.
"We cannot say that we have evidence for the panspermia hypothesis, but we can say that showing the resistance of plant seeds to conditions in space makes the hypothesis more plausible," Tepfer told Gizmodo.
Since the early 2000s, scientists have been testing the idea that life could survive an interstellar voyage, by strapping hapless microorganisms, seeds and even insect larvae to the outside of the International Space Station for weeks to months, exposing them to damaging solar radiation and cosmic rays, not to mention wild temperature swings and vacuum conditions.
As you might imagine, most of the subjects in these experiments have died. But in a test in 2009, roughly 20 per cent of seeds from tobacco plants and the flowering plant Arabidopsis thaliana were germinated back on Earth after 558 days in space. In the new study, Tepfer and Leach decided to see exactly how much radiation these seeds could handle, by blasting them in the laboratory with even higher doses of UV light, at the exact wavelength that does the most damage to DNA. They also performed the diabolical experiment on morning glory seeds, which are larger, have thick seed coats, and are known to survive decades in the soil before germinating.
Adding morning glory to the mix was a good call. In experiments lasting up to 300 days, when the radiation was cranked all the way up, these were the only seeds that didn't burn to a crisp. "This [highest] dose killed the Arabidopsis and tobacco seeds, but the morning glory seeds germinated normally and produced plants," Tepfer said.
It's a promising sign that certain seeds might have what it takes for an interstellar journey, although the results now ought to be replicated in space. Aside from their armoured coats, Tepfer speculates morning glory seeds might have "mechanisms to repair essential cellular components, e.g. DNA, RNA, ribosomes, membranes, etc," but further work is needed to confirm that hypothesis. Flavanoids, compounds also found in green tea and wine, might also be boosting the seeds' natural UV protection.
My first thought when I read Tepfer's study was that this is good news for humans looking to colonise places like Mars — after all, if we want to survive there long term, we'll need plants to furnish us with food and oxygen. Tepfer did not agree, calling the race to Mars "a publicity stunt". Rather, he suggests that seeds could provide a protective house and food for bacteria and fungi on an interstellar voyage, allowing us to disseminate (non-human) life to non-living worlds. Especially if we used lessons from nature to engineer seeds to become even better protectors of life.
"Imagine dormant seeds being sent to exoplanets to release microbial life or the building blocks of life, even if the seeds themselves might not germinate and form plants," he said. "We humans should stay on Earth and clean up our mess, but during the years our species is alive and technologically competent, we should embrace our role as disseminators of life — perhaps using plant seeds loaded with microorganisms."
"But," he added, "we need get started soon, given our propensity for self-destruction."