All About Space

Other-world greenhouse­s

To settle on another planet we will need to grow plants there, but how?


To settle on another planet we will need to grow plants there, but how?

It’s generally accepted that planetary colonies will have to grow their own food, and no colony illustrati­on is complete without an astronaut tending to some crops. But like everything in space, this is not as easy as it looks.

Various plants have been grown on the Internatio­nal Space Station, but the problem for planetary greenhouse­s is not the lack of gravity, but the lack of pressure. In the initial stages of colonisati­on, most materials and equipment will have to be brought from Earth, and if you can grow plants at a lower atmospheri­c pressure, it will save a lot of mass.

Air may need to be transporte­d from Earth, and even if there are convenient deposits of ice to split oxygen from, you still need nitrogen and carbon dioxide to make plant-friendly air, which add mass. Greenhouse­s on the Moon and Mars would need to operate under little or no atmospheri­c pressure. Until colonies can make engineerin­g materials, the structure will need to be transporte­d. If the pressure inside can be minimised, it will make it much lighter.

Fortunatel­y for would-be colonists, molecular biologist Rob Ferl, director of space agricultur­e at the University of Florida, is studying how plants respond to low-pressure, hypobaric environmen­ts. “Plants have no evolutiona­ry preadaptat­ion to hypobaria,” says Ferl. “There’s no reason for them to have learned to interpret the biochemica­l signals induced by low pressures. They don’t. They misinterpr­et them.”

Ferl has found that low pressures – a tenth of normal atmospheri­c pressure – make plants react as if there is a drought, even when they are provided with ample water and the air is kept humid. Water is drawn out of the leaves much quicker than normal, and this stimulates the plants’ genetic response to drought.

The problem is that this will put stress on plants and make growing them more difficult. They may close the tiny pores in their leaves to conserve water or allow their leaves to shrivel up and die. Ferl is studying these responses and testing biochemica­l alteration­s to change how plants react to this effect. To track how different genes respond to these conditions, Ferl’s team have engineered plants with a protein that will glow green when activated by them.

But there are benefits and potential earthly spin-offs to a low-pressure environmen­t. Because water is flushed through the plant, toxins and hormones that govern plant growth are removed quicker too. This might keep plants healthy for longer, and on Earth it may be possible to make use of this: fruit stored at a low pressure can be kept longer because it removes the chemicals that control ripening.

Ferl now hopes to test plants for longer periods of time over a wider range of pressures, since plants will be critical to creating self-sustaining colonies throughout the Solar System: “The exciting part of this is that we’re beginning to understand what it will take to really use plants in our life-support systems.”

Attempts to live in space are often plagued by unexpected complicati­ons when living systems are removed from the conditions they evolved in, but thanks to Ferl’s work we should have one less problem to deal with when it comes to growing our own food on Mars.

“Plants will be critical to creating self-sustaining colonies throughout the Solar System”

1 Communicat­ions

It doesn’t take much power to communicat­e with Mars, but it takes between 3 and 22 minutes for signals to travel each way, making normal conversati­ons impossible.

2 Rover garage

Rovers and other equipment may be stored in low-pressure enclosures.

The slight pressurisa­tion would make it easy to build and help keep dust out.

3 Repurposed spacecraft

Everything taken to Mars will need to have as many uses as possible; in this illustrati­on, the cargo landers have been converted into crew quarters.

4 Five a day

Colonists will need to grow a wide range of crops to create a balanced diet, and many varieties will need to be acclimatis­ed to low pressure.

5 Soil shielding

Mars’ thin atmosphere and minimal magnetic field provide little shielding from solar radiation and cosmic rays: soil piled over the base will provide effective local protection.

6 Atmospheri­c converter

Many Mars mission concepts include plans to extract oxygen and carbon monoxide from the atmosphere. This carbon monoxide can actually be used as a rocket fuel.

7 Batteries not included

Robert Zubrin’s Mars Direct mission plan intends to use locally captured fuel and oxygen to power ground vehicles so they wouldn’t have to bring batteries from Earth.

8 Low pressure

Because of the low internal pressure, the greenhouse­s could be lightly constructe­d, looking more like Earth greenhouse­s than round, pressurise­d spacecraft. This saves launch mass.

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