Is There Enough Light on Mars to power solar cells?

Written by letstalkscience.ca on November 16, 2021. Posted in Current News

Astronauts traveling to Mars will need to grow some of their own food in order to survive and stay healthy. To successfully grow plants on Mars, greenhouse structures will be necessary to provide similar growing conditions to those on Earth.

Greenhouses on Earth are structures with transparent glass or plastic walls and roofs that allow as much of the available sunlight as possible to reach the plants inside. But on Mars will there be enough light to meet the needs of growing plants? Several factors influence the amount of light that would be available on Mars for growing plants.

Distance from the Sun

Mars’ greater distance from the Sun means that the maximum intensity (brightness) of sunlight on Mars is much less (about 44 percent) than that on Earth. This means that the greatest light intensity that Mars ever experiences is about the same as the light intensity Canada experiences in the middle of the winter, when the northern hemisphere is tilted away from the Sun (See Figure 1).

Figure 1: Mars-Earth Sun intensity comparison. The maximum solar insolation on Mars is only about 590 W/m² compared to about 1370 W/m² at the Earth’s surface.

Martian Seasons

The seasons a planet experiences are determined by the tilt of the planet on its axis and the shape of its orbit around the Sun. Like Earth, Mars is tilted away from the Sun on its axis, so as it travels around the Sun there are times during the Martian year (days) that a part of the planet does not receive direct sunlight. This axial tilt causes four seasons on Mars, which is similar to Earth. Since Mars is twice as far from the Sun, each year on Mars is longer (1.88 Earth years), and the seasons are each twice as long as on Earth.

In addition, the shape of Mars’ orbit, which is very elliptical (an eccentric orbit) compared to Earth’s orbit, results in seasons that are of different lengths. For example, in the northern hemisphere on Mars, spring is 7 months, summer is 6 months, fall is 5.3 months and winter is a little over 4 months long. This means that the number of daylight hours and light intensity at different times of the year may not always be enough to meet the needs of plants.

The Impact of Weather

The amount of light reaching the surface of Mars can also be dramatically affected by weather. Due to its distance from the Sun and thin atmosphere, the surface of Mars is very cold, about six degrees Celsius. The most significant weather phenomena on Mars are dust storms and winds.

These dust storms can block out direct solar radiation from the Sun for very long periods of time, sometimes for up to several weeks or even months! (See The Weather of Mars video) Without enough light for that length of time, plants would not be able to produce enough food through photosynthesis and they would slowly die.

It appears that, depending on the location of habitation on Mars, the time of year and the weather conditions, artificial light sources will be needed to provide a reliable and adequate amount of light to grow plants on Mars. At the same time, scientists are also conducting research with plants to find ways to lower their requirements for light.

Mars Plant Research On Earth

Will there be enough natural sunlight on Mars to grow crops such as tomatoes? Will greenhouses with artificial light be required? Plant scientists have been working on finding answers to these key questions through studies conducted right here on Earth.

Devon Island in Nunavut, Canada, is the largest uninhabited island on Earth. It has surface characteristics that strongly resemble those of the surface of Mars, with a barren, rocky landscape and temperatures that often dip as low as –50°C and rarely go higher than 5°C (See Figure 2).

Figure 2: Map of Devon Island showing location of the Haughton Impact Crater.

Located at latitude of slightly more than 75°N, Devon Island has a solar insolation similar to the solar insolation at the Martian equator. Scientists are assuming that the location of the first Mars habitation by humans will occur near the Martian equator where seasonal changes that can affect light intensity are less noticeable. Except for a brief period in June, the intensity of the Sun on Devon Island never gets higher than the solar intensity on Mars.

This means Devon Island provides an excellent environment to do plant research with light conditions that resemble those on Mars. In 2002, the Arthur C. Clarke Mars Analogue Greenhouse was installed near the rim of the Haughton Impact Crater, on Devon Island near the Flashline Mars Arctic Research Station (FMARS). Researchers here are learning how to operate a greenhouse in this very extreme climate.

Plant scientists have been conducting experiments and testing sensor technologies (webcams and environment monitoring sensors) that can monitor the growing conditions inside the greenhouse and the condition of the plants (See Figure 5). Several crops, including radishes, beets, lettuce, and tomatoes have been grown in this greenhouse on Devon Island.

Figure 5: University of Guelph researcher Thomas Graham sets up the fall season autonomous growth trial experiment in 2008. Several cameras, as well as environmental monitoring sensors (light, temperature, humidity, etc.) are used to monitor and control the greenhouse after the research team leaves the field camp, returning 11 months later.

Source: Dr. Thomas Graham, University of Guelph

Devon Island research is also helping scientists to learn about how to keep a greenhouse operating and providing for the needs of the plants without actually having humans there to care for the plants.

For 11 months of the year the growing environment is maintained with remotely-controlled (satellite) and automated irrigation systems, solar panels, heating systems to support growth, and a webcam network to track the progress of the plants (See Figure 6). These automated gardening techniques could come in handy in preparing for the arrival of humans (to have food and air ready for crew when they arrive) on Mars, or for keeping plants growing between missions.

The success of this greenhouse in the extreme environment of Devon Island is a good indication of whether or not people will be able to grow crops on Mars.

Figure 6: Satellite telemetry of an autonomous, multi-crop growth trial (2006) at the Arthur C. Clarke Mars Greenhouse. Plants shown had been growing without direct human contact for two weeks, and continued to grow independently for another 8 weeks. The greenhouse was then put into ‘hibernation mode’ until favourable conditions returned after the long Arctic winter.

Source: Canadian Space Agency

References

• The Great Red North: Nunavut’s ‘Martian colony’ has become go-to spot to field-test extra-planetary tech (Retrieved April 21, 2016). This article, from National Post, discusses the research that is being done on Devon Island in the hopes of mimicking conditions on Mars.
• Arctic greenhouse may lead to farms on Mars (Retrieved July 25, 2016).This article from CBC features Canadian research efforts at growing crops remotely in the Arthur C. Clarke greenhouse on Devon Island, Nunavut.
• Green plants, red planet (Retrieved May 2, 2016). This article from Greenhouse Canada discusses greenhouse research that is being conducted on Devon Island, Nunavut, to support the future exploration of Mars.
• Solar Radiation in Space (Retrieved April 21, 2016). This website, from Photovoltaic Education Network, describes how to calculate solar radiation for different planets.
• Does Mars Have Seasons? (Retrieved February 27, 2017). This webpage from Universe Today explains the causes of the seasons on Mars.

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Header image: Dr. Thomas Graham, University of Guelph

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