The Appeal of ‘Mars’ Adds Some Glamour to Research

(December 3rd, 2014) A Research Letter by Jeremy Garwood from the corner of the planet Mars located in a greenhouse in the Netherlands.

Sometimes research seems to benefit from fashions. Media attention can generate superficial interest in long-term projects that can be phrased in simple terms. However, there are scientists who seem to be happy to use media fashion as a substitute for real scientific effort. Perhaps, they have noticed that it is easier to publish ‘sexy’ claims and that journalists rarely look too closely at the research details.

Consider the recent research report by Wieger Wamelink, from Wageningen University in the Netherlands, who asks a ‘sexy’ question - “Can Plants Grow on Mars and the Moon?”. Here, the fashionable goal is to go to the planet Mars. At the start of his abstract, Wamelink sets the scene: “When humans will settle on the moon or Mars they will have to eat there. Food may be flown in. An alternative could be to cultivate plants at the site itself, preferably in native soils.”

This recurring theme of exploring Outer Space has become a source of recent media excitement. The European Space Agency probe, Rosetta, landed on comet 67P this autumn after a 10-year flight. Meanwhile, tourist ‘hops’ up into Outer Space received a setback when Virgin Galactic’s manned ‘Spaceship Two’ crashed on earth re-entry.

There have also been several announcements of projects to colonise the Moon and Mars, including Mars One from the Netherlands, which intends to “establish a permanent human settlement on Mars.” It plans to launch its first unmanned mission to Mars in 2018, to be followed by spacecraft manned by “crews of four” that will “depart every two years, starting in 2024”.

This is all inspiring stuff. Mankind will ‘boldly go’ etc. etc. But what are these Dutch Mars-onauts going to eat when they finally get to the Red Planet? Wamelink suggests that they learn how to grow their own food.

Grow your own

Wamelink claims to have conducted the “first large-scale controlled experiment to investigate the possibility of growing plants in Mars and moon soil simulants.” For the sake of future colonists, one hopes other attempts will go further than this. For a start, note the use of the term “soil simulant” because, as explained below, the whole project looks a lot less interesting when you realise that Wamelink has been comparing plant growth on Earth soil that has a debatable resemblance to the surface of Mars.

But a research project with interplanetary interest would not be complete without a press release. Wamelink’s research report was published in PLoS ONE in August 2014. However, in a media move that truly resembles space programmes rather than biology, Wamelink issued his first press release before he had even started the experiment. This dates from March 2013, that’s to say, a whole 17 months before the research paper was published. Even better, in this press release Wamelink announces the day on which he will start the experiment: “The future will begin on 2 April” (2013) when the first trial crops “will be planted in greenhouses”!

The press release says the project was “initially prompted by Dutch plans to establish a colony on Mars” but Wamelink explained that, for him, the main objective was the Moon - “Mars is still a long way off, but the Moon is closer, so it would be more realistic to establish a colony there. What’s more, we already know the mineral composition of the soil on the Moon, and of Moon dust. So what I’m aiming to find out now is whether plants will grow in Moon substrate, or whether certain essential elements are lacking.” However, Wamelink did admit that “we are gradually discovering more about Mars,” and that this was why “the planet has been included in this research.” Nevertheless, in the subsequent press releases and final paper, Mars gains greater prominence over the Moon.

The experiment

In April 2013, Wamelink began the experiment. He planted seeds from different plant groups in three types of soils (named “Earth, Moon, Mars”) and waited 50 days to see if they would germinate and live long enough to go through the first stages of plant development on “Mars and Moon regolith simulant.” (‘regolith’ = a mixture of dust, soil, broken rock etc.).

Despite his interplanetary goals, Wamelink’s experimental conditions are decidedly ‘down to Earth’ and not at all like Mars or the Moon. The Moon is a particularly tough environment. Its gravity is 0.17 of Earth’s, but it has no atmosphere to speak of. The surface temperature at the equator varies from -173°C to 117°C (average -53°C).

By comparison, Mars may look better but not by much. It has 0.378 of Earth’s gravity, and its atmosphere, which only has an average pressure of 0.636 kPa (0.6% of Earth’s) is composed of 96% carbon dioxide, 1.9% argon, 1.9% nitrogen, 0.15% oxygen, and 210ppm water vapour. The surface temperature ranges from -143°C to 35°C (average -63°C).

In addition, lacking a protective atmosphere means the surfaces of both Mars and the Moon are exposed to lots of UV radiation.

Rather than even try to recreate such harsh conditions Wamelink has simply (but not unreasonably) decided that colonisers should be using “an artificial surrounding.” Hence, instead of worrying about inconvenient details like different gravities, atmosphere, temperatures or radiation, he has carried out his experiment in closed surroundings with Earth-like light and atmospheric conditions. Luckily for Wamelink, “Earth-like” conditions are a lot easier (and cheaper) to find on Earth!

Even better, by reasoning that someone else will create ‘Earth-like’ conditions on a future Mars/Moon colony, Wamelink can justify using a standard Dutch university greenhouse instead. Into his greenhouse, he placed 840 small flowerpots. Into these pots were placed one of three soils – Mars ‘simulant’, Moon ‘simulant’ and a ‘control’ Earth.

Substitute Soils

The Mars and Moon soil simulants were purchased from a US company, Orbitec. Wamelink says both regoliths were ‘manufactured by NASA’. In fact, they were simply dug out of the ground then milled and sieved to produce a fine dust (less than or equal to a 1mm particle size). NASA produced these ‘simulant’ dusts for materials experiments, prototype testing and dust mitigation of transportation equipment, advanced life support systems and in situ resource processing.

In choosing the Moon JSC1-1A simulant, comparisons could be made with some of the 382kg of Moon rocks and soil that NASA’s manned Apollo missions had brought back to Earth between 1969 and 1972. Based on physical analysis of this material, a substitute soil was found in a volcanic ash deposit of basaltic composition located in a volcano field near Flagstaff, Arizona (1kg costs $30).

However, it should be noted that no sample of real Mars soil has ever been returned to Earth. Instead, various spectral analyses and tests have been made on Mars by unmanned probes like the Viking lander 1. Based on this data, the Mars JSC-1A simulant soil was taken from the slopes of the Pu’u Nene cinder cone on the Island of Hawaii (910g costs $25).

Finally, the ‘control Earth’ soil Wamelink used was a low-quality sandy soil from 10 m deep layers at a site near the Rhine River.

Interplanetary Plant Growth

Into each of his 840 pots, he planted 5 seeds from one of 14 different plant species, giving a total of 60 pots per plant species, 20 on each of the 3 soils. The plants chosen were four crops, four nitrogen fixers and six wild plants “which occur naturally in the Netherlands” (a model for New Mars?). Furthermore, “only species with relatively small seeds were chosen so that the nutrient stock in the seeds would be quickly depleted and the plant becomes totally dependent on what is available in the soils for its growth.”

After 50 days in the greenhouse (average temperature 21.2°C), with lots of water (apparently water is not in short supply on Mars) and 16 hours light (supplemented by lamps on darker days), Wamelink measured his plant growth.

He found that all the plants were able to germinate and grow on both Martian and Moon soil simulant for a period of 50 days “without any addition of nutrients” (except Common vetch which did not germinate on Moon soil). Overall, plant growth and flowering “was much better” on Mars simulant than on either the Moon simulant or the control nutrient-poor river soil. “Reflexed stonecrop (a wild plant); the crops tomato, wheat, and cress; and the green manure species, field mustard, performed particularly well. The latter three flowered, and cress and field mustard also produced seeds.” Similarly, the plant biomass at the end of the experiment was significantly higher on Martian soil simulant for eleven out of the fourteen species, while the biomass for Earth and Moon soil simulant was “often quite similar.”

The experiment finished, Wamelink wrote his research report. Another press article appeared in January 2014, coinciding with the submission of his manuscript to PLOS ONE. Why wait for its publication when you can have more publicity? On 14th January 2014, The Amsterdam Herald wrote that “A Dutch scientist has managed to germinate seeds in conditions replicating the climate on Mars, suggesting the Red Planet is capable of sustaining plant life.”

“Wieger Wamelink planted a variety of species last year in soil created by NASA to mimic the environment on Mars, to see if they would grow.” Tomatoes, carrots, rye, garden cress and stinging nettles “all took hold in the ground”, but there was “one setback: the high levels of dense metal in Martian soil meant they were inedible”! (Not that since the biggest plant after 50 days only weighed one gram, there wasn’t much to eat anyway). However, Wamelink doesn’t say how he proposes to deal with this heavy metal contamination. Instead he ignores the question and proclaims success because, thanks to his experiment, we now know that “if we ever want to grow crops on Mars, we at least don’t need to take soil with us.”

The newspaper article enthusiastically asserted that Wamelink’s “discovery is the latest evidence that life could be revived on the Red Planet.” However, no evidence was presented to prove that life had ever existed on Mars, nor quite how it was going to be “revived” by Wamelink’s efforts at resuscitation.

Further press release – article still under review

During the next few months, Wamelink’s manuscript was being reviewed for publication by PLOS ONE. It was not finally accepted until the end of June, 2014 (and then published on 21st August), but this did not prevent another press release from being issued in April 2014: “Vegetables on Mars within ten years?” It again reported Wamelink’s “unique pilot experiment” testing the growth of 14 plant varieties on artificial Mars soil over 50 days, and noted his “surprise” when the plants “grew well.” He explained: “I had expected the germination process to work, but I thought the plants would die due to a lack of nutrients.”

However, the soil analysis showed that “Mars soil” contains more nutrients than expected. In fact, Wamelink said that his research into the cultivation of plants in difficult conditions is “not only relevant to future inhabitants of Mars”, but also on Earth: “Mars soil consists of volcanic rock. If we learn to bring it into cultivation, we can use the knowledge to cultivate crops on difficult soils here on earth.”

Wamelink concluded that his university had the expertise to solve Mars’ food problem: “Wageningen UR can develop a complete food cultivation system for Mars within ten years”!!

Meanwhile, patient scientific researchers still had to wait another 4 months to obtain the details of Wamelink’s plant experiments. It might almost seem an anti-climax after all the previous press releases, but the publication of his PLOS ONE paper was accompanied by yet more publicity. On 11th September, 2014, Patricia Waldron from Inside Science reported that: “Astronauts May Grow Better Salads On Mars Than On The Moon”.

She noted that no one has ever grown plants in Martian or moon soils but a Russian group showed that marigolds could grow and flower in simulated moon soil. Wamelink told her: “I didn't expect many plants to germinate because I know there are a lot of heavy metals in the soils. On the Martian soil it went very well - much better than we thought. It was really a surprise to us.”

But then Waldron spoke of some aspects of the experiment that are not at all mentioned in the PLOS ONE paper: “The researchers observed the plants for 50 days. Wamelink and his colleagues had originally overlooked an important aspect of plant growth on untested celestial bodies: pollinators. Because there are neither insects nor wind in the greenhouse, the researchers themselves played the role of bees. They moved pollen between the individual plants with a paintbrush, which was both time-consuming and difficult. Only field mustard (Mars soil) and garden cress (Mars and Earth) produced seeds. He suspects that astronauts would need to bring insects with them to pollinate the crops.”

“You need to set up a small ecosystem,” said Wamelink. “It's much more complicated than we first thought.”

Unexpected nutrient content

Bizarrely, the Mars simulant turns out to be more nutrient-rich than the Earth control. As such, it is not such a big surprise that it proved to be a better substrate for plant growth.

Wamelink made a new analysis of the Mars and Moon simulants since NASA, who had developed them for machine tests, had only looked at them for mineral content and particle size. He duly looked at potential plant nutrients, pH, organic matter content, total nitrogen and phosphorus content, ammonia, nitrates, iron, etc.

Both the Earth and Moon simulant were “truly nutrient poor”, which was not the case for the Mars simulant. Table 2 of Wamelink’s paper indicates that the Mars simulant contained more total nitrogen (0.26%) and total phosphorus (0.25%) than the Moon simulant (0% and 0.1% respectively) or Earth soil (0% and 0.006%). It also contained nitrates of ammonium, and a “significant amount of carbon.”

The pH of all three soils was basic - 7.3 for Mars, 8.3 earth, 9.6 moon. In general, the optimum plant pH is around 5.5 to 7, so the Mars simulant again appears better for plant growth.

Another big factor was water retention. The Mars simulant stayed wet when watered. As Wamelink noted, even in his Dutch greenhouse “it was difficult to keep the water content in the pots high enough, despite spraying twice a day. The Mars soil simulant resembles loess-like soils from Europe and holds water better than the other two soils. Moon soil simulant dried out fastest. The larger water holding capacity of Martian soil simulant may explain its better performance and, partly, the underperformance of moon soil simulant.”

Wamelink might just as well have said they were testing volcanic dust and sand to see if Earth’s poorer soils (e.g. in deserts) could support plant growth. After all, they have done nothing to test for the kind of radiation/gravity/etc. that is found on Mars and the Moon.

In fact, he could do better by giving data from previous plant growth studies of Earth soils. Not that you would know it from Wamelink’s paper, but there is, believe or not, an extensive history of botanic, agricultural, and geological research into the myriad soil types to be found on Earth (e.g. there are an estimated 70,000 different soil types in the US alone) and the requirements for plant fertility. Even a cursory look at the literature reveals classic textbooks such as Edward Russell’s ‘Soil conditions and plant growth’ (first published in 1912 and still in print). And there is abundant advice to farmers about soil fertility (e.g. this Australian guide on ‘How do the properties of soils affect plant growth’) that has become even more specialised for keen amateur gardeners whose houses are not always build on ideal soils.

Furthermore, a careful inspection of the origins of the Mars simulant used by Wamelink shows that it comes from ground between two volcanoes on the Island of Hawaii. As it happens, the island of Hawaii is quite fertile and there is agriculture on soils in this area as described in a 2011 paper.

Even better, the original paper describing NASA’s JSC-1A Mars soil simulant specifically says that it was a layer underneath surface soil: “An overlying soil horizon 30 to 40 cm in thickness was first removed from a 180 m2 area” before they dug out the 40-60 cm “altered ash” layer that became the Mars simulant. It is not hard to imagine how organic matter and nutrients washed down to ‘Mars’ from this overlying ‘soil horizon.’

Conclusion? Name Change and New Title

Wamelink reckons that his results show that it is “in principle” possible to grow plants in Mars and Moon soil simulants, but says: “Whether this extends to growing plants on Mars or the moon in full soils themselves remains an open question.”

But what has his whole study to do with the real planet Mars? In the final analysis, not much beyond the use of the term ‘Mars’. In fact, Wamelink might more accurately have titled his article ‘Can Plants grow on Hawaii and in Arizona: A growth experiment on volcanic soils from Hawaii and Arizona.’!


In 2011, the German space agency, DLR, reported that it had tried to grow microorganisms in conditions that resemble the exposed surface of Mars. They found that lichen could survive for at least 34 days but did not describe its edibility.

Jeremy Garwood

Images: Hudson (Planet), Sue (astronaut), NASA/JPL-Calech/University of Arizona (mars lander)

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