As a child, I remember pouring a package of desiccated, powdery sea monkey eggs into water and, a few days later, getting full-developed sea monkeys. Well, technically I got brine shrimp, which was a bit of a let-down. But I never thought to ask how an aquatic animal could survive being totally dried up for so long. The surprising answer to how sea monkeys survive a trip across dry land to my mailbox is also the answer to how they could potentially survive a trip to another star system.
The tardigrade, also known as the water bear or the moss piglet, is a microscopic 8-legged animal no more than 1.5 mm long, which lives mainly in mosses and lichens. There are over 1000 species, and though they prefer wet, temperate habitats, they can be found everywhere from the North Pole to the Sahara Desert. The name for any organism that can survive that kind of temperature range is an extremophile. And the water bear’s extremophilism is the most extreme of all. It’s not only one of the cutest animals in the world, it’s the toughest animal in the world. Perhaps any world.
How tough is the water bear? Well, it can survive temperatures of -272 Celsius, which is 1 degree above absolute zero, and 151 Celsius (303 Fahrenheit), well past boiling. Although an aquatic animal, it can survive without water for over a decade. And three years ago, astronauts left some water bears outside their shuttle for ten days in the vacuum of space: no oxygen, no water, barely any heat, and a thousand times more radiation than would kill a human in minutes. The water bears came back to Earth, shook it off, and continued reproducing.
How is that possible? Without water, water bears (and sea monkeys) go into a state of cryptobiosis, a state of suspended animation. During cryptobiosis, all metabolic functions cease. The animal is essentially living dead, until it is rehydrated, and can survive indefinitely until then. This explains how the water bear can exist without water, but how it survives what should be a lethal flogging of cosmic radiation is still a mystery.
What is the origin of life on Earth? It may be that lightning struck a pool of primordial soup, non-living amino acids which suddenly were compelled to form a protein. Or those early prokaryotes might have been formed by the magnetism of a highly-pressurized slab of iron sulfide. Or maybe the Earth can’t take credit for inventing life; maybe it came to us. Maybe we’re all a colony of lost extraterrestrials.
Two separate experiments aim to measure the possibility that life on Earth is the result of transpermia, or interstellar life-sharing. One is the LIFE program (Living Interplanetary Flight Experiment), in which many types of bacteria will be shot into space in the crevices of an artificial meteor to see how long they survive. The other is the TARDIS program (Tardigrades In Space), which wants to see just how long those little moss piglets can go, if they were, say, blasted off the Earth by a larger asteroid. Keep in mind, space is huge and life-supporting worlds are so few we haven’t found another one yet, so the probability that two planets can share germs via an asteroid-induced cosmic sneeze is pretty slim. But the possibility exists. Perhaps planets can communicate with life, across the galaxy, with simple creatures hidden in space rocks. If Earth is an island, maybe we can still send out a message in a bottle. Or maybe, just maybe, we opened a message in a bottle sent by some other island… and we’re still reading it.