The first colonists on Mars probably won't be humans. More likely, they'll be plants. And the prototypes of these leafy pioneers are under development right now.
As part of a proposed mission that could put plants on Mars as soon as 2007, University of Florida professor Rob Ferl is bioengineering tiny mustard plants. He's not altering these plants so that they can adapt more easily to Martian conditions. Instead, he's adding reporter genes: part plant, part glowing jellyfish -- so that these diminutive explorers can send messages back to Earth about how they are faring on another planet.
The plants can be genetically wired to glow with a soft green aura when they encounter problems. Within a garden grouping, some plants could report (by glowing) low oxygen levels, while others might signal low water or, say, the wrong mix of nutrients in the soil.
"Just like humans, plants must learn how to adapt to any new environment," Ferl says. On Mars they would encounter extreme temperatures, low air pressure, exposure to harsh ultraviolet light, and generally inadequate soil. "We are using genetics to create plants that can give us data we can use to help them survive."
Learning to grow plants on Mars will be an important precursor to humans living there. Future explorers will need oxygen, food, and purified water -- items too costly to ferry from Earth to Mars on a regular basis. But plants can help provide those essentials inexpensively and locally as part of a self-contained "bioregenerative" life support system.
Bioregenerative life support means humans, plants, and microbes working together in a renewable system. Humans consume oxygen and produce carbon dioxide. Plants take carbon dioxide and turn it back into breathable air. Human waste (after processing by suitable microbes in bioreactor tanks) can provide nutrients for growing plants, which will, in turn, produce food for people.
Such life support systems on Mars will probably involve growing crop plants in Martian soil within specially designed greenhouses, says Andrew Schuerger, a manager of Mars projects with Dynamac Corporation at the NASA's Kennedy Space Center.
Ferl, Schuerger, and Chris McKay of NASA's Ames Research Center want to test the greenhouse concept by sending bioengineered plants to Mars on board a small NASA spacecraft -- a "Mars Scout." They envision a seed-bearing lander that would scoop up a portion of Martian soil, add buffers and nutrients, then germinate the seeds to grow within a miniature greenhouse.
Thriving plants won't glow at all. They'll look like normal mustard. But plants struggling to survive will emit a soft green light, a signal to researchers that something is amiss. A camera onboard the lander would record the telltale glows and then relay the signal back to Earth. No humans are required on the scene -- a big advantage for such a far away experiment.
The plants' designer genes consist of two parts: a sensor side to detect stress and a reporter side to trigger the glow.
The sensor side of the gene comes from the plant itself -- Arabidopsis thaliana, a member of the mustard family also known as thale cress. Ferl and his colleagues picked Arabidopsis because three attributes suit it well for a Mars mission: Its maximum height is about 6 inches, so it can fit inside a small greenhouse, its life cycle is only six weeks, and its entire genome has been mapped. (For these same reasons Arabidopsis plants are already orbiting Earth on board the International Space Station as part of an independent experiment to learn how plants react to free fall.)
The reporter side of the gene comes from Aequorea victoria, a jellyfish common along the Pacific coast of North America. Aequorea live about six months, grow to 5 or 10 cm, and can glow soft-green along the rim of their bell-shaped bodies. Scientists aren't sure why they glow -- Aequorea victoria do not flash at each other in the dark, nor do they glow continuously. But the touch of a human hand, for example, can stimulate the jellyfish to "light up."
Right above: An overhead flash reveals the outlines of Aequorea victoria. The blue glow is reflected light, not bioluminescence. Credit: C.E. Mills. Right below: True bioluminescence around at the rim of the jellyfish. The light produced by Aequorea is actually bluish in color, but in a living jellyfish it is emitted via a coupled molecule known as GFP, or green fluorescent protein, which causes the emitted light to appear green to us.
Once the sensor and the reporter gene fragments are stitched together, Ferl uses a bacteria to move the newly-constructed gene into the plant.
Because plants are sessile -- that is, they can't get up and walk away from stressful situations -- they can survive only by adapting to whatever their environment offers. So, they've developed an exquisite variety of sensing mechanisms to monitor their surroundings and trigger appropriate responses to stressors. By adding phosphorescent reporters to those sensors, Ferl says, "we can learn not just whether the plant is surviving, but whether it's struggling to survive, and whether it's surviving because it's mounting specific responses to the Mars environment."
Ferl offers this example of an adaptive response to hard times: Here on Earth when plants are flooded by water, they have access to less oxygen. The plants respond by changing their metabolism to generate energy anaerobically (without oxygen) -- a less efficient pathway, but one that is available to them. On Mars plants might adopt the same response to survive in the thin oxygen-poor atmosphere.
Water on Mars will also be very scarce, and plants will need to conserve every bit. The leaves of all plants contain stomata, little holes that let gas molecules in and out. Plants have the ability to open and close stomata as conditions demand. "One can imagine plants [living on the surface of Mars in the distant future] that might adapt by means of fewer stomata in their leaves: that means fewer opportunities for water vapor to leave, and maybe that would be a positive adaptation," says Ferl.
The first wave of Martian plants envisioned by Ferl and his colleagues would sprout inside a very small and protected greenhouse. We don't know exactly how big it's going to be," says Schuerger, "but we're shooting to fit a foot print of about 10 inches by 10 inches, and weighing about 15 to 20 pounds." The greenhouse, he expects, could hold as many as 20 to 30 plants. "We can grow a single plant," he says, "in one or two grams of soil, in a tiny glass or steel or Teflon container."
The plants might also be exposed to Martian light, which could be piped into the greenhouse (inside the lander) through fiber optics, and to a moisture-added, oxygen-enhanced version of the Martian atmosphere. But the project's primary goal is determining whether plants can thrive in Martian soil -- an experiment best done on Mars itself!
As important as it is to know whether plants can actually grow on the Red Planet, this project also has a philosophical purpose, says Chris McKay, the principal investigator of the proposed Scout mission. "It will be a symbolic step," he says, "of life from Earth, leaving Earth, and growing somewhere else." And when this little plant grows on Mars, he believes, it's going to be a major awakening of our interest in our future in space.