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outer space seeds

Moon Trees: The Story of the Seeds That Went to Outer Space

These seeds became a living legacy of the U.S. space program.

  • Columbia University Graduate School of Journalism
  • University of California, Santa Cruz
  • Western New Mexico University

NASA HQ PHOTO / Flickr / CC BY-NC-ND 2.0

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NASA, the U.S. space agency, has learned a lot since the 1940s about the effects of extreme conditions during space travel on the human body, from bone density loss to changes in the immune system to effects of radiation. But what do we know about how space travel affects plants? One of the early attempts to find out came in 1971 when the Apollo 14 mission carried hundreds of tree seeds to the moon.

After studying the seeds back on Earth, the “moon trees” were planted across the United States for the nation’s bicentennial, and for years after they were largely forgotten about. But the experiment endures as a notable early step in understanding how space affects plants.

How Seeds Survived Space

When astronaut Stuart Roosa blasted off on the Apollo 14 moon mission in 1971, he carried the moon tree seeds sealed in tiny plastic bags. The idea originated with U.S. Forest Service chief Ed Cliff, who knew Roosa back when he was a USFS smokejumper. Cliff contacted Roosa and initiated a joint effort with NASA that garnered publicity for the Forest Service but also had a real scientific purpose: to further understand the effects of deep space on seeds.

It wasn’t the first time seeds had traveled to space. In 1946, a NASA V-2 rocket mission carried maize seeds to observe the effects of cosmic and ultraviolet (UV) radiation. Seeds in space are exposed to powerful radiation, low pressure, and microgravity.

But they also have unique defenses. Many seeds carry duplicate genes that can step in when genes are damaged. The outer coating of seeds contains chemicals that protect their DNA from UV radiation. Such early experiments helped lay the groundwork for much more advanced research into how these processes aid seeds’ survival in space.

Roosa, the command module pilot for the Apollo 14 mission, carried his sealed bags of tree seeds inside a metal canister. They came from five species: loblolly pine, sycamore, sweetgum, redwood, and Douglas fir. The seeds orbited with Roosa while commander Alan Shephard and lunar module pilot Edgar Mitchell set foot on the moon.

Upon returning to Earth, both astronauts and seeds underwent a decontamination process to ensure they weren’t inadvertently bringing back dangerous substances. During decontamination, the canister popped open and the seeds scattered. Exposed to the vacuum inside the decontamination chamber, the seeds were feared dead. But hundreds survived to become saplings.

Where Are Moon Trees Today?

The saplings were planted at schools, government properties, parks, and historic sites around the country—many in conjunction with the 1976 bicentennial celebrations. Some were planted next to their control counterparts, which had remained behind on Earth. NASA reported that scientists found no discernable differences between the earthly and “lunar” trees.

Some moon trees found homes in sites of special historical significance. A loblolly pine was planted at the White House while others went to Washington Square in Philadelphia, Valley Forge, the International Forest of Friendship, the Alabama birthplace of Helen Keller, and various NASA centers. A few trees even traveled to Brazil and Switzerland, and one was presented to the Emperor of Japan.

Many of the original moon trees have now died, though at about the same rate as the control trees. Some died of disease, others of infestations. A moon tree in New Orleans perished after Hurricane Katrina in 2005. Fifty years later, the surviving trees have reached an impressive size.

The moon trees might have been largely lost to history if it weren’t for Indiana teacher Joan Goble. In 1995, Goble and her third-grade class came across a tree at a local Girl Scouts camp with a modest plaque that said “moon tree.” After some poking around on the then-rudimentary internet, she found a NASA web page with the email address of an agency archivist, Dave Williams, and contacted him.

Williams, a planetary scientist based at the Goddard Space Flight Center, had never heard of the moon trees—and soon discovered he wasn’t alone. NASA hadn’t even maintained records of where the trees were planted. But eventually, Williams tracked down newspaper coverage of the bicentennial moon tree ceremonies. He created a web page to document the surviving trees and invited people to contact him about moon trees in their community. So far, about 100 original moon trees are listed on the site.

Today, the second generation of moon trees, sometimes referred to as “half-moon trees,” have been grown using cuttings or seeds from the originals. One of these, a sycamore, is planted at Arlington National Cemetery in tribute to Roosa, who died in 1994.

The "Roots" of Plant Research in Space

NASA Kennedy / Flickr / CC BY-NC-ND 2.0

The original moon trees may not have led to big breakthroughs, but they serve as tangible reminders of how far plant science in space has come. One area of plant research on the International Space Station today explores how astronauts can be healthier and more self-sufficient on long missions by growing their own food.

The space station garden grows a variety of leafy greens, which may help protect against bone density loss, among other ailments associated with space travel. Some plants already provide fresh produce for crew members. In the future, scientists hope to grow berries and beans high in antioxidants, which may help protect astronauts against radiation.

Scientists on the International Space Station are also observing how space affects plant genes, and how plants might be genetically modified to enhance nutrition. In addition, studying plants may help scientists better understand the effects of space travel on humans, including clues to how being in space causes bone and muscle loss. All of this data will support long-term space expeditions.

The moon trees were a modest but memorable step, and they endure as living links to those early moon missions. They serve not only as a reminder of the distance traveled by humans beyond Earth but how precious and unique is the planet we come from.

Extreme survival of seeds on Earth and in space

Anne Visscher from Kew’s Comparative Plant and Fungal Biology department discusses extreme survival of seeds on Earth and a research proposal to send seeds to the International Space Station to test their survival in outer space.

Extreme survival of dry seeds

Dry seeds can be exposed to extreme environmental conditions on Earth and in space, and their survival is known to vary between species. For example, dry seeds may survive an extreme range of temperatures (from ‑196°C during cryopreservation up to ≤+1000°C in wildfires); ultra-drying conditions associated with the vacuum of space or imposed during seed storage on Earth; and, ultraviolet radiation reaching the surface of the Earth (UV-A, UV-B) or present in space environments (UV-A, UV-B and UV-C) (1).

It is known, for instance, that seeds from many Aizoaceae species, including Mesembryanthemum crystallinum (common iceplant), are able to germinate successfully following extended heat treatments of 103°C, despite the absence of a thick seed coat (2). In addition, research on seven Brassicaceae (cabbage family) species, which were stored for five years under ultra-dry conditions, showed that seeds from Sisymbrium runcinatum benefitted from such storing conditions whilst the other species did not (3).

Little is known about the variation in dry seed survival between different species following exposure to ultraviolet radiation. When seeds from Arabidopsis thaliana (thale cress) and Nicotianum tabacum (cultivated tobacco) were exposed to UV on the outside of the International Space Station for 1.5 years, 23% produced viable plants upon return to Earth (4).

Below I will explain why we are interested in discovering more about the variation in resilience between dry seeds from different species to extreme conditions present in outer space.

Plants and human spaceflight

In the near future, astronauts may be able to spend longer periods of time on the Moon or Mars (for example in a lunar outpost or a Mars base) to improve our understanding of the geology and biology of these different environments.

For human missions that are longer than one or two years, it is expensive and challenging to launch and transport food, water, and atmospheric gases required for survival (5).

Instead of transporting all the necessary food from Earth, photosynthetic plants could be grown in closed life support systems to provide a healthy and varied diet during missions. Plants and microorganisms could also help to recycle waste, water and atmospheric gases, which would further save materials and associated launch costs. For example, photosynthetic higher plants would be able to provide a team of astronauts with a healthy and varied diet in the form of cereals, legumes, oilseeds, fruit and vegetables. In addition, plants could help to revitalise the atmosphere (by liberating oxygen and fixing carbon dioxide) and purify water (via transpiration) (6).

For even larger and longer-term habitats on the Moon or Mars, other benefits from plants could include construction materials, fabrics, medicines, dyes, lubricants, biofuels, and aesthetics.

Storing seeds for growth in space

Since plants have the potential to play several important roles in long-term life support systems on other planets, it is crucial to know how seeds should be stored and transported across space before being germinated and grown in such systems.

On Earth, seeds of many species can be stored for decades under standard seed bank conditions (drying to around 5% moisture content and storage at sub-zero temperatures) (7). But, over time, all seeds lose quality and will eventually die.

In space, seeds could be stored under similar conditions inside a space station or spacecraft, but this may not be necessary for all species. For example, some seeds are known to benefit from ultra-drying and anoxia, both of which are extreme conditions associated with the vacuum of outer space. Seeds that benefit from, or are tolerant of extreme space conditions (for example ultraviolet and ionising radiation, as well as temperature fluctuations) could be transported on the outside of a spacecraft in order to save space for more sensitive materials on the inside.

Comparative seed biology on the ISS

The aim of our proposed project with the European Space Agency is to research how and why seeds from a diverse set of 24 plant species differ in their responses to the outer space environment. As we cannot exactly reproduce the combination of extreme conditions found in outer space in our laboratory on Earth, we are planning to use a seed exposure facility on the outside of the International Space Station (ISS) for our experiments.

For the first time in the history of research on seeds exposed to outer space, we are also planning to monitor changes that are happening to seeds during their stay outside the ISS: for example, we would like to identify the molecules that are outgassed from the seeds in the vacuum of space by using miniature mass spectrometers.

Impact for seed storage on Earth and in space

Results from our research could lead to recommendations for seed transport through space, and improvements to protocols for the long-term storage of seeds on Earth. In addition, our findings may influence the potential design of orbiting seed banks, or even deep space seed banks, with the goal to preserve human life and ecosystems in the event of disaster.

Try this at home part 1: Grow your own space seeds

Though the center is temporarily closed, we are still passionate about sharing science and space! In this series, get hands-on with some fun and educational activities to do at home with the kiddos.

Grow your own space seeds

Objective

Explore plant-growing experiments on board the International Space Station and create your own space station “rooting pillow” containing a seed.

Materials

  • 1 Tbsp. potting soil
  • 1 seven-inch square of newspaper
  • 1 seed
  • Optional: flower pot

Creating your “rooting pillow”

Planting instructions

  1. Add one tablespoon of soil to your rooting pillow.
  2. Choose one seed, and it push lightly into the soil.
  3. Staple shut the top of rooting pillow.
  4. After a few days, dig a one-inch well in soil in a clay pot or in your backyard, tear off a little of the bottom of the rooting pillow, place rooting pillow in the soil, and open the top of the rooting pillow. Make sure the seed is covered by 1” of soil. Water lightly and place in a sunny spot where the seed should germinate.

Plan your stay

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