Astrobotany

Astrobotany is an applied sub-discipline of botany that is the study of plants in space environments. It is a branch of astrobiology and botany.

A zucchini being grown on the International Space Station

It has been a subject of study that plants may be grown in outer space typically in a weightless but pressurized controlled environment in specific space gardens.[1] In the context of human spaceflight, they can be consumed as food and/or provide a refreshing atmosphere.[2] Plants can metabolize carbon dioxide in the air to produce valuable oxygen, and can help control cabin humidity.[3] Growing plants in space may provide a psychological benefit to human spaceflight crews.[3]

The first challenge in growing plants in space is how to get plants to grow without gravity.[4] This runs into difficulties regarding the effects of gravity on root development, providing appropriate types of lighting, and other challenges. In particular, the nutrient supply to root as well as the nutrient biogeochemical cycles, and the microbiological interactions in soil-based substrates are particularly complex, but have been shown to make possible space farming in hypo- and micro-gravity.[5][6]

NASA plans to grow plants in space to help feed astronauts, and to provide psychological benefits for long-term space flight.[7]

Extraterrestrial vegetation
Astrobotany has been the investigation of the idea that alien plant life may exist on other planets. Here an artist has envisioned alien plants on shores of an exomoon exosea.[8]

The search for vegetation on other planets began with Gavriil Tikhov, who attempted to detect extraterrestrial vegetation via analyzing the wavelengths of a planet's reflected light, or planetshine. Photosynthetic pigments, like chlorophylls on Earth, reflect light spectra that spike in the range of 700–750 nm. This pronounced spike is referred to as "vegetation's red edge."[9] It was thought that observing this spike in a reading of planetshine would signal a surface covered in green vegetation. Searching for extraterrestrial vegetation has been outcompeted by the search for microbial life on other planets[10] or mathematical models to predict the viability of life on exoplanets.[11]

Growing plants in space

The study of plant response in space environments is another subject of astrobotany research. In space, plants encounter unique environmental stressors not found on Earth including microgravity, ionizing radiation, and oxidative stress.[12] Experiments have shown that these stressors cause genetic alterations in plant metabolism pathways. Changes in genetic expression have shown that plants respond on a molecular level to a space environment.[13] Astrobotanical research has been applied to the challenges of creating life support systems both in space and on other planets, primarily Mars.

History

Russian scientist Konstantin Tsiolkovsky was one of the first people to discuss using photosynthetic life as a resource in space agricultural systems. Speculation about plant cultivation in space has been around since the early 20th century.[14] The term astrobotany was first used in 1945 by Russian astronomer and astrobiology pioneer Gavriil Adrianovich Tikhov.[15] Tikhov is considered to be the father of astrobotany. Research in the field has been conducted both with growing Earth plants in space environments and searching for botanical life on other planets.

Seeds

The first organisms in space were "specially developed strains of seeds" launched to 134 km (83 mi) on 9 July 1946 on a U.S. launched V-2 rocket. These samples were not recovered. The first seeds launched into space and successfully recovered were maize seeds launched on 30 July 1946, which were soon followed rye and cotton. These early suborbital biological experiments were handled by Harvard University and the Naval Research Laboratory and were concerned with radiation exposure on living tissue.[16] In 1971, 500 tree seeds (Loblolly pine, Sycamore, Sweetgum, Redwood, and Douglas fir) were flown around the Moon on Apollo 14. These Moon trees were planted and grown with controls back on Earth where no changes were detected.

Plants
The arugula-like lettuce Mizuna growing for Veg-03

In 1982, the crew of the Soviet Salyut 7 space station conducted an experiment, prepared by Lithuanian scientists (Alfonsas Merkys and others), and grew some Arabidopsis using Fiton-3 experimental micro-greenhouse apparatus, thus becoming the first plants to flower and produce seeds in space.[17][18] A Skylab experiment studied the effects of gravity and light on rice plants.[19][20] The SVET-2 Space Greenhouse successfully achieved seed to seed plant growth in 1997 aboard space station Mir.[3] Bion 5 carried Daucus carota and Bion 7 carried maize (aka corn).

Plant research continued on the International Space Station. Biomass Production System was used on the ISS Expedition 4. The Vegetable Production System (Veggie) system was later used aboard ISS.[21] Plants tested in Veggie before going into space included lettuce, Swiss chard, radishes, Chinese cabbage and peas.[22] Red Romaine lettuce was grown in space on Expedition 40 which were harvested when mature, frozen and tested back on Earth. Expedition 44 members became the first American astronauts to eat plants grown in space on 10 August 2015, when their crop of Red Romaine was harvested.[23] Since 2003 Russian cosmonauts have been eating half of their crop while the other half goes towards further research.[24] In 2012, a sunflower bloomed aboard the ISS under the care of NASA astronaut Donald Pettit.[25] In January 2016, US astronauts announced that a zinnia had blossomed aboard the ISS.[26]

in 2018 the Veggie-3 experiment was tested with plant pillows and root mats.[27] One of the goals is to grow food for crew consumption.[28] Crops tested at this time include cabbage, lettuce, and mizuna.[29]

Known terrestrial plants grown in space
Main article: Plants in space
'Outredgeous' red lettuce cultivar grown aboard the International Space Station.

Plants that have been grown in space include:

Some plants, like tobacco and morning glory, have not been directly grown in space but have been subjected to space environments and then germinated and grown on Earth.[40]

Plants for life support in space
Lettuce being grown and harvested in the International Space Station before being frozen and returned to Earth.

Algae was the first candidate for human-plant life support systems. Initial research in the 1950s and 1960s used Chlorella, Anacystis, Synechocystis, Scenedesmus, Synechococcus, and Spirulina species to study how photosynthetic organisms could be used for O2 and CO2 cycling in closed systems.[41] Later research through Russia's BIOS program and the US's CELSS program investigated the use of higher plants to fulfill the roles of atmospheric regulators, waste recyclers, and food for sustained missions. The crops most commonly studied include starch crops such as wheat, potato, and rice; protein-rich crops such as soy, peanut, and common bean; and a host of other nutrition-enhancing crops like lettuce, strawberry, and kale.[42] Tests for optimal growth conditions in closed systems have required research both into environmental parameters necessary for particular crops (such as differing light periods for short-day versus long-day crops) and cultivars that are a best-fit for life support system growth.

Tests of human-plant life support systems in space are relatively few compared to similar testing performed on Earth and micro-gravity testing on plant growth in space. The first life support systems testing performed in space included gas exchange experiments with wheat, potato, and giant duckweed (Spyrodela polyrhiza). Smaller scale projects, sometimes referred to as "salad machines", have been used to provide fresh produce to astronauts as a dietary supplement.[41] Future studies have been planned to investigate the effects of keeping plants on the mental well-being of humans in confined environments.[43]

More recent research has been focused on extrapolating these life support systems to other planets, primarily Martian bases. Interlocking closed systems called "modular biospheres" have been prototyped to support four- to five-person crews on the Martian surface.[44] These encampments are designed as inflatable greenhouses and bases.[45] They are anticipated to use Martian soils for growth substrate and wastewater treatment, and crop cultivars developed specifically for extraplanetary life.[46] There has also been discussion of using the Martian moon Phobos as a resources base, potentially mining frozen water and carbon dioxide from the surface and eventually using hollowed craters for autonomous growth chambers that can be harvested during mining missions.[45]

Plant research

The study of plant research has yielded information useful to other areas of botany and horticulture. Extensive research into hydroponics systems was fielded successfully by NASA in both the CELSS and ALS programs, as well as the effects of increased photoperiod and light intensity for various crop species.[41] Research also led to optimization of yields beyond what had been previously achieved by indoor cropping systems. Intensive studying of gas exchange and plant volatile concentrations in closed systems led to increased understanding of plant response to extreme levels of gases such as carbon dioxide and ethylene. Usage of LEDs in closed life support systems research also prompted the increased use of LEDs in indoor growing operations.[47]

Experiments
Illustration of plants growing in a hypothetical Mars base.

Some experiments to do with plants include:

Results of experiments
A young sunflower plant aboard the ISS[55]

Several experiments have been focused on how plant growth and distribution compares in micro-gravity, space conditions versus Earth conditions. This enables scientists to explore whether certain plant growth patterns are innate or environmentally driven. For instance, Allan H. Brown tested seedling movements aboard the Space Shuttle Columbia in 1983. Sunflower seedling movements were recorded while in orbit. They observed that the seedlings still experienced rotational growth and circumnation despite lack of gravity, showing these behaviors are built-in.[56]

Other experiments have found that plants have the ability exhibit gravitropism, even in low-gravity conditions. For instance, the ESA's European Modular Cultivation System[57] enables experimentation with plant growth; acting as a miniature greenhouse, scientists aboard the International Space Station can investigate how plants react in variable-gravity conditions. The Gravi-1 experiment (2008) utilized the EMCS to study lentil seedling growth and amyloplast movement on the calcium-dependent pathways.[58] The results of this experiment found that the plants were able to sense the direction of gravity even at very low levels.[59] A later experiment with the EMCS placed 768 lentil seedlings in a centrifuge to stimulate various gravitational changes; this experiment, Gravi-2 (2014), displayed that plants change calcium signalling towards root growth while being grown in several gravity levels.[60]

Many experiments have a more generalized approach in observing overall plant growth patterns as opposed to one specific growth behavior. One such experiment from the Canadian Space Agency, for example, found that white spruce seedlings grew differently in the anti-gravity space environment compared with Earth-bound seedlings;[61] the space seedlings exhibited enhanced growth from the shoots and needles, and also had randomized amyloplast distribution compared with the Earth-bound control group.[62]

Astrobotany has had several acknowledgements in science fiction literature and film.

  • The book and film The Martian by Andy Weir highlights the heroic survival of botanist Mark Watney, who uses his horticultural background to grow potatoes for food while trapped on Mars.[63]
  • The film Avatar features an exobiologist, Dr. Grace Augustine, who wrote the first astrobotanical text on the flora of Pandora.[64]
  • Charles Sheffield's Proteus Unbound mentions the use of algae suspended in a giant hollow "planet" as a biofuel, creating a closed energy system.[65]
  • In the film Silent Running it is implied that, in the future, all plant life on Earth has become extinct. As many specimens as possible have been preserved in a series of enormous, greenhouse-like geodesic domes, attached to a large spaceship named "Valley Forge", forming part of a fleet of American Airlines space freighters, currently just outside the orbit of Saturn.
gollark: Unless you want some accursed DRM-type scheme.
gollark: That... is not meaningful?
gollark: Either your thing just uses the fingerprint to authenticate that you are X person (horrible privacy issue), or I can generate fake fingerprints rapidly.
gollark: No, I mean unless their system would allow that.
gollark: Unless I can just randomly generate "human" fingerprints.

See also
Interior view the hypothetical O'Neill cylinder space habitat, showing alternating land and window stripes.

References
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  4. NASA – Getting to The Root of Plant Growth Aboard The Space Station
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