Asteroids: The Interstellar Food Source for Future Astronauts?

Asteroids: The Interstellar Food Source for Future Astronauts?Long-duration space travel remains a significant challenge despite rapid technological advancements. Beyond the psychological impact of confinement on astronauts, the limited payload capacity of spacecraft restricts the provision of personnel, water, air, and food

Asteroids: The Interstellar Food Source for Future Astronauts?

Long-duration space travel remains a significant challenge despite rapid technological advancements. Beyond the psychological impact of confinement on astronauts, the limited payload capacity of spacecraft restricts the provision of personnel, water, air, and food. Relying solely on Earth for all essential supplies is not only incredibly expensive but also severely limits the scope of space exploration. For instance, one scientific study indicates that a six-person Mars mission requires 12 tons of food (excluding packaging), and even with relatively low-cost providers like SpaceX, the cost per kilogram of payload is a staggering $2720. The expense for missions to Jupiter, Saturn, or the outer solar system would be prohibitively high, with resupply times becoming extremely impractical. Therefore, research into space food continues unabated.

Currently, a viable approach involves space farming cultivating plants within space stations or spacecraft. Both the Chinese and American space stations have conducted multiple experiments successfully cultivating various vegetables; American astronauts have even consumed lettuce, carrots, and peppers grown in space. Beyond vegetables, experiments are underway with algae, mushrooms, and insects. However, these cultivation systems require complex designs and extensive maintenance to simulate Earth's ecosystem, ensuring the plants and animals thrive. Currently, the self-sufficiency of food production in space is far from adequate, necessitating increased equipment volume and quantity, which consumes considerable spacecraft space.

To find a simpler, more space- and cost-efficient method, scientists have turned their attention to asteroids: extracting organic matter from asteroids, processing it minimally, and feeding it to bacteria, which then digest it to create human-edible organic matter.

Humanity's study of asteroids spans centuries. While direct access to asteroid samples was previously impossible, a significant number of asteroid fragments, known as meteorites, fall to Earth annuallyan estimated 17,000 per year. Scientists categorize meteorites into three main types: stony, stony-iron, and iron meteorites, further subdividing them based on structure and composition. Approximately 86% of stony meteorites are chondrites, whose chondrules are believed to have formed directly from cooling nebular material in the early solar system. Chondrules combined to form asteroids, which grew through collisions, eventually leading to the formation of rocky planets. Asteroids that failed to form planets are concentrated in the asteroid belt.

The high proportion of chondrites on Earth suggests that most asteroids in the asteroid belt have a similar composition. As chondrules are among the oldest solid materials in the solar system, they are crucial for studying its early history. Scientists have analyzed chondrites in detail, classifying them into 15 distinct meteorite groups (CI, CM, CO, CV, CK, CR, CH, CB, H, L, LL, EH, EL, R, and K). Carbonaceous chondrites (those beginning with "C") contain high concentrations of organic compounds; some contain up to 5% organic matter.

The Murchison and Tagish Lake meteorites are extensively studied carbonaceous chondrites. Scientists have identified various small organic molecules, including ketones, alkanes, carboxylic acids, amino acids, methane, and polycyclic aromatic hydrocarbons, but mostly large organic molecules. These findings caused a sensation, fueling beliefs in extraterrestrial life and even the extraterrestrial origin of life on Earth. However, further research showed that natural chemical reactions can also form organic molecules; for example, the formation of amino acids requires only simple inorganic substances.

Meteorite organic molecules differ from their terrestrial counterparts in molecular structuremany are isomers (same molecular formula, different structure); their chirality also differs, with meteorite organic molecules exhibiting both left-handed and right-handed forms, whereas organic molecules in terrestrial life are exclusively left-handed. Advances in technology have also revealed organic molecule signatures in distant nebulae, indicating their widespread presence in the universe.

How to "eat" an asteroid? The most abundant organic matter in meteorites is large-molecule organic matter similar to plastics, making direct consumption infeasible. Scientists draw on recent experiments in plastic microbial processing. This involves the pyrolysis of plastic (400-900), breaking down large-molecule organic chains into a series of low-molecular-weight hydrocarbons, then utilizing bacteria to process these compounds. The results showed that bacteria could digest these compounds and multiply extensively. Scientists believe that future astronauts could also use pyrolysis to process asteroid minerals rich in carbonaceous chondrites, then use bacteria to digest these materials. Because bacteria grow rapidly, they would provide a continuous supply of food for astronauts. Furthermore, some scientists have discovered that under anaerobic conditions, certain bacteria in the Pseudomonadaceae family can even directly utilize meteorite powder for survival and reproduction. These experiments demonstrate that using bacteria to "eat" asteroids, and then humans "eating" the resulting biomass produced by bacteria, may be a promising space food solution.

To understand the potential organic matter yield from asteroids, scientists used asteroid (101955) Bennu as an example. Bennu, less than 500 meters in diameter and with a mass of 77.6 million tons, has a composition similar to carbonaceous chondrites. Calculations show that the biomass produced from Bennu, even under the lowest efficiency scenarios, would suffice for the annual food consumption of 631 astronauts, and under the highest efficiency scenarios, for 17,000 astronauts. This translates to processing approximately 160,000 tons of asteroid minerals to feed one astronaut annually at minimum efficiency, and only 5,000 tons at maximum efficiency.

While this research is promising, the prospect of future astronauts subsisting on bacteria is somewhat concerning. Further exploration is needed to fully uncover the potential of asteroids as a food source for future astronauts. The potential value of asteroids as a future food source for astronauts is not only a revolution in traditional space food supply systems but also a crucial step in humanity's adaptation to extreme environments and the realization of interstellar travel. Of course, transforming asteroids into a food source still faces many technological and ethical challenges.

Reference: Pilles E, Nicklin RI, Pearce JM. How we can mine asteroids for space food[J]. International Journal of Astrobiology, 2024, 23:e16.

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