Microbes carried by laser-powered sails could serve as interstellar probes that can build communication stations to call home from Alpha Centauri, suggests a scientist known for wanting to resurrect extinct woolly mammoths and use DNA to detect dark matter.
This concept by George Church, a geneticist at Harvard University, is based on efforts to greatly accelerate space flight. Current spacecraft typically take years to travel within the solar system; for example, NASA’s New Horizons probe took nearly 10 years to reach Pluto.
Theoretically, a spacecraft using conventional rockets would take thousands of years to complete an interstellar journey. For example, Alpha Centauri, the closest star system to Earth, is located at a distance of about 4.37 light-years – more than 25.6 trillion miles (41.2 trillion kilometers), or more than 276,000 times the distance from Earth to the Sun. NASA’s Voyager 1 spacecraft, launched in 1977 and reaching interstellar space in 2012, will take about 75,000 years to reach Alpha Centauri, even if the probe is heading in the right direction, which it isn’t.
The problem that all rocket engines face is that the propellant they carry has mass. Long flights require a lot of fuel, which makes the spacecraft heavy. This, in turn, requires more fuel, makes them heavier, and so on.
Previous research has shown that “easy sailing” may be one of the only possible ways to get a spacecraft to another star within a person’s lifetime. While light doesn’t exert much pressure, scientists have long suggested that the slight pressure it exerts can have a big effect. Indeed, many experiments have shown that “solar sails” can rely on sunlight for propulsion if the spacecraft is light enough and has a large enough sail.
Indeed, the $100 million Breakthrough Starshot initiative, announced in 2016, plans to launch a swarm of microchip-sized spacecraft to Alpha Centauri, each equipped with extraordinarily thin, incredibly reflective sails powered by the most powerful lasers ever or created. According to the plan, they travel at up to 20% the speed of light and reach Alpha Centauri in about 20 years.
However, Starshot faces many technical challenges. These include creating lasers powerful enough to propel, and creating sails that can withstand extreme forces and stay on track for their targets.
George Church, PhD, professor of genetics at Harvard Medical School and founder of the main faculty, and head of synthetic biology at the Wyss Institute at Harvard University. He is also a professor of health sciences and technology at Harvard and the Massachusetts Institute of Technology and is director of the Energy Technology Center of the US Department of Energy and the Center of Excellence in Genomic Sciences at the National Institutes of Health.
Also, even if Starshot were to successfully launch “space chips” at Alpha Centauri without another laser in that location, they would not be able to slow down. This likely limits Starshot missions to overflights rather than landings.
Any attempt by the Starshot probe to land could lead to disaster. Although spacecraft are designed to be extraordinarily light—each only 0.035 ounces (1 gram) or so—when traveling at 20% the speed of light, each would have as much energy as one-eighth of the atomic bomb dropped on Hiroshima. in the world. The second war, Church noted.
Instead, Church suggests using probes a billion times lighter. He noted that if they really had an impact, then the energy in them would be no more than half a food calorie.
“A probe that lands is much more valuable than one that flies a long distance and for a very short time,” Church told Space.com.
Interstellar picogram probes
(Image credit: Breakthrough Prize Foundation (via livestream))
How can such an incredibly light probe be useful? Church theorized that if they were carrying genetically engineered microbes, they could create equipment for themselves after landing.
Church has previously made a number of radical proposals that sound like science fiction. For example, he suggested that DNA could help detect dark matter, an invisible and largely intangible substance that researchers believe makes up about five-sixths of all matter in the universe. He also wants to resurrect extinct animals like the woolly mammoth.
However, Church is also a pioneering biologist. In 1984, he developed the first direct genome sequencing method, which resulted in the first genome sequencing of Helicobacter pylori, a bacterium commonly found in the human stomach. He also helped initiate the Human Genome Project in 1984 to fully map the approximately 3 billion letters contained in human DNA.
Church noted that he was interested in this new idea because he grew up in Florida in the shadow of the rocket launches at Cape Canaveral, and also because he teaches a course at the Massachusetts Institute of Technology called “How to grow almost everything.” . As such, he was “looking for projects that went beyond that,” he said.
Previously, scientists have proposed creating “von Neumann” interstellar probes capable of reproducing themselves and equipment. The concept is named after mathematician John von Neumann, who proposed the idea of self-replicating machines in 1948, Church noted.
Church based his new proposal on both his background in biology and the groundbreaking research he had done for Starshot. Since his probes are only one billionth the mass of the Starshot ship, he suggested that a billion of his probes could be launched for a similar cost to a single Starshot mission.
Starshot also calls for a 100 gigawatt laser array, which will be the most powerful laser ever built by mankind to date. Because Church offers unusually small probes, a relatively modest laser might suffice, he says. For example, a base ship weighing about 0.0014 ounces (40 mg) with a sail 1.3 feet (0.4 meters) in diameter, which carries many tiny probes, may require a laser system with a power of only 2 gigawatts.
Starshot probes often require a sail that is about 108 square feet (10 square meters) and weighs less than 0.035 ounces (1 gram). By comparison, given that a typical bacterium has a mass of about 1 picogram or one trillion gram, it would only need a sail of about 15 millionths of an inch (0.0001 square centimeter) with a mass of about 7.6. picograms, Church said. He added that light sails weighing about 8.8 million ounces (0.25 milligrams) have already been tested in vacuum and microgravity.
“Deceleration is difficult even on the picogram scale, but not even considered on the gram scale,” Church said.
Interstellar probes are likely to experience impacts that can disable or destroy them – from dust particles or even hydrogen atoms. However, the fact that it is possible to launch a billion or so microbial probes for the price of a single Starshot means that the loss of probes may not be a major setback.
Living probe with “biolaser”
A probe that lands is much more valuable than one that flies a long distance and for a very short time.
George Church, Ph.D.
After the probes reached their destination, Church theorized that genetically engineered microbes could build communication modules themselves. One communication strategy could be bioluminescence, by which microbes can emit light using the kinds of molecules found in fireflies or other naturally bioluminescent organisms. While this light can be relatively dim, Church noted that in the absence of predators and ideal growth conditions, microbes could cover the entire planetary surface in as little as 124 hours.
For a more compact approach, Church suggests that a living probe could create a “biolaser” capable of converting starlight into a communication beam. He noted that the gold beetle (Aspidimorpha tecta) could create reflective surfaces potentially useful for making such an organic device, though Church acknowledged that making one “would be an interesting lab challenge.”
Church suggested that the communications array built by these probes could transmit flares back to Earth. These beams can encode destination data such as temperature, pressure, and pH.
On the subject: The idea of a wild mission “Interstellar probe” is gaining momentum
It can be difficult to find places for these interstellar seeds to grow. “That’s why we need millions of shots on millions of targets,” Church said. Scientists can also rely on so-called extremophile microbes, which are known to survive extreme temperatures, pH, pressure and other conditions on Earth, Church said.
Church noted that one potential target could be the nearest known exoplanet, Proxima Centauri b, a rocky world in the Alpha Centauri system. However, it receives only 3% of the light needed for photosynthesis, which can make it difficult for any microbial probes to thrive. It could also potentially experience another 10,000 flares from its star, capable of stripping any atmosphere, making it a hostile place to live.
Other potential targets include worlds that may exist around the sun-like stars Alpha Centauri A and B in the Alpha Centauri system. These may not be rocky planets – instead, they may be more like Uranus and Neptune and are covered in water and ammonia. However, there are microbes on Earth that can survive in such places, such as bacteria found in deep ocean hydrothermal vents.
One of the main issues will be planetary defense issues – in this case, you need to make sure that the microbes on Earth do not harm any alien life that may exist at the destinations. Probes could be designed to “tend for severely limited growth,” Church suggested. He added that it would be “absolutely high priority” to test any potential interstellar probes on targets within the solar system to see how well they perform.
Church detailed his idea (will open in a new tab) December 6 in the journal Astrobiology.
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