Should we seed life through the cosmos using laser-driven ships?
来源：未知 作者：芮鹏猱 时间：2017-04-03 03:01:18
Richard Bizley/Science Photo Library By James Romero Our galaxy may contain billions of habitable worlds that don’t host any life. Should we attempt to change that? Claudius Gros at the Goethe University Frankfurt, Germany, thinks we should. He believes in directed panspermia: deliberately seeding life throughout the cosmos. And to do that, he proposes we use a laser propulsion system that may not be technically out of reach. Breakthrough Starshot is a project with ambitious aims to use such systems to send tiny, lightweight probes to Alpha Centauri. The goal is to take pictures of our nearest star, but these systems could also deliver much larger payloads into orbit around nearby stars, says Gros. Potential targets include the planetary system around TRAPPIST-1, a red dwarf star just 40 light years away. Earlier this year, astronomers revealed it was home to seven rocky planets, three of which orbit within the star’s habitable zone. Starshot’s proposed 20-year mission to our nearest star after the sun would rely on ultralight craft propelled up to 20 per cent of the speed of light by giant, Earth-based lasers pointed at a light sail – essentially a mirrored surface. While there are unprecedented challenges, particularly in laser design and the reflectivity of the light sail, the team remains confident of the mission’s feasibility. “It is just a matter of the will to make it happen,” says Chi Thiem Hoang at the Korea Astronomy and Space Science Institute. However, with no way to stop, Starshot’s single gram craft would zoom past its target star system just hours after arrival. Could the laser propulsion instead deliver a heavier, slower moving payload with an onboard braking system into orbit? Gros says it could – and it should. His interest in interstellar travel is not exploratory, or even scientific. He is focused on spreading life. “These kind of projects are useless for humanity, but life is something valuable and should have the possibility to develop on other planets,” he says. Gros feels emboldened in his quest by emerging theories that planets orbiting the most common type of stars in our galaxy, red dwarfs like TRAPPIST-1, may have ancient, oxygen-rich atmospheres. Although these would make them habitable today, they could have prevented life forming initially due to the oxidation of prebiotic organic chemistry. “Our galaxy may contain billions of sterile but habitable worlds,” says Gros. Under his proposed Genesis project, Gros is looking at the possibility of launching into space autonomous toolkits for life: miniaturised versions of the gene laboratories envisaged by researchers here on Earth. These would grow genes and cells from chemical ingredients and disseminate them across habitable planets. But how would these heavier payloads be slowed down upon arrival? Sails again have been suggested, but instead of acting as mirrors, they would be magnetic fields that stretch for kilometres and transfer the probe’s momentum to the interstellar particles hitting them. Once the lasers used for launch are no longer propelling them, they would use space dust to slow down. Deep space can be near empty, perhaps containing just one atom per cubic centimetre, so sails with a large surface area would be needed to make this work. Gros says that with the latest high-temperature superconducting wires – those that can transfer energy with barely any loss at temperatures above absolute zero – possible to produce magnetised sails large enough to slow down a heavier craft. Gros simulated interstellar particles hitting a magnetic sail and found four parameters determined a successful deceleration: the spacecraft mass, its velocity and therefore mission duration, the sail radius and the current flowing through the loop of superconducting wire within the main craft that would power the magnetic sails. “A superconducting current could be created just once prior to launch and run for eternity,” Gros says. The technology could certainly operate long enough for a mission to a relatively nearby star system like TRAPPIST-1. Gros estimates that a 1.5-tonne craft carrying the superconductor infrastructure for sails 50-kilometres wide could reach TRAPPIST-1 in 12,000 years if propelled by Breakthrough’s lasers. Jeff Kuhn, a Starshot adviser and physicist at the University of Hawaii, likes the paper, but worries that gaining support and funding for a mission that takes 12,000 years might be harder than actually building and launching one. “This doesn’t necessarily mean we shouldn’t be doing this, but the timescales are so long that it’s hard to imagine human organisations with this attention span,” Kuhn says. Hoang instead worries whether the superconducting ring itself could survive collisions with interstellar dust, though he agrees with Gros that the Starshot system could technically launch such a mission. “The project did not discuss the potential implication of a long-term mission for panspermia,” he says. “I think that it would be interesting to use the proposed system to spread some form of life to the interstellar space.” Journal reference: Journal of Physics Communications, DOI: 10.1088/2399-6528/aa927e Chi Thiem Hoang’s affiliation was corrected More on these topics: