The possibility of interstellar travel is no longer confined to science fiction but has appeared tantalizingly on the horizon. Although we may not see it in our lifetimes – at least not a real-life version of the fictional warp-speeding, hyper driving, space-folding kind – we are having early discussions about how life could escape the tether of our solar system using technology that is currently available.
It’s an exciting time to be alive, according to UC Santa Barbara professors Philip Lubin and Joel Rothman. They carry the unbridled optimism and creative spark of the early Space Age when humans first discovered they could leave the Earth, as they are the product of a generation that witnessed breathtaking advances in space exploration.
“The Apollo moon missions were among the most momentous events in my life, and thinking about them still blows my mind,” said Rothman, a distinguished professor in the Department of Molecular, Cellular, and Developmental Biology and self-described “space geek.”
Only 50 years have passed since that watershed moment, but humanity’s understanding of space and the technology to explore it has advanced dramatically, prompting Rothman to join experimental cosmologist Lubin in pondering what it would take for living beings to embark on a journey across the vast distance separating us from our nearest neighbor in the galaxy. Their collaboration resulted in a paper published in the journal Acta Astronautica.
“I believe it is our destiny to continue exploring,” Rothman said. “Consider the evolution of the human species. We investigate at ever-smaller scales, all the way down to subatomic levels, as well as at ever-larger scales. Such a desire for never-ending exploration is at the heart of who we are as a species.”
Thinking Big, Starting Small
The biggest challenge to human-scale interstellar travel is the enormous distance between Earth and the nearest stars. The Voyager missions have proven that we can send objects across the 12 billion miles it takes to exit the bubble surrounding our solar system, the heliosphere. But the car-sized probes, traveling at speeds of more than 35,000 miles per hour, took 40 years to reach there and their distance from Earth is only a tiny fraction of that to the next star. If they were headed to the closest star, it would take them over 80,000 years to reach it.
This is a major theme in Lubin’s work, in which he reimagines the technology required to reach the next solar system in human terms. Traditional onboard chemical propulsion (also known as rocket fuel) is out; it can’t provide enough energy to move the craft quickly enough, and the weight and current systems required to propel it aren’t viable for the relativistic speeds the craft requires. New propulsion technologies are required, which is where the UCSB directed energy research program that uses light as a “propellant” comes in.
I believe it is our destiny to continue exploring. Consider the evolution of the human species. We investigate at ever-smaller scales, all the way down to subatomic levels, as well as at ever-larger scales. Such a desire for never-ending exploration is at the heart of who we are as a species.Professor Joel Rothman
“This has never been done before, pushing macroscopic objects at speeds approaching the speed of light,” said Lubin, a physics professor. In fact, mass is such a huge barrier that it precludes any human missions for the foreseeable future.
As a result, his team shifted its focus to robots and photonics. Small probes with onboard instrumentation that senses, collects, and transmits data back to Earth will be propelled up to 20-30% the speed of light by a laser array stationed on Earth or possibly the moon. “We don’t leave home with it,” Lubin explained, referring to the fact that the primary propulsion system remains “at home” while spacecraft are “shot out” at relativistic speeds. The main propulsion laser is activated for a brief period of time before the next probe is prepared for launch.
“It would probably resemble a semiconductor wafer with an edge to protect it from radiation and dust bombardment as it travels through the interstellar medium,” Lubin said. “It’d probably start out the size of your hand.” As the program progresses, the spacecraft become larger and more capable. The core technology can also be used in a modified mode to propel much larger spacecraft at slower speeds within our solar system, potentially allowing human missions to Mars in as little as one month, including stops. This is another method of spreading life, but this time in our solar system.
At relativistic speeds of around 100 million miles per hour, the watercraft would arrive at the next solar system, Proxima Centauri, in about 20 years. Getting to that level of technology will necessitate continuous innovation and improvement in both the spacing wafer and photonics, a field in which Lubin sees “exponential growth.” NASA and private foundations such as the Starlight program, as well as Breakthrough Initiatives such as the Starshot program, are supporting the basic project to develop a roadmap to achieve relativistic flight via directed energy propulsion.
“When I learned that the mass of these crafts could reach gram levels or larger, it became clear that they could accommodate living animals,” said Rothman, who realized that the creatures he’d been studying for decades, known as C. elegans, could be the first humans to travel between the stars. These intensively studied roundworms may be small and uninteresting, but they are experimentally accomplished creatures, according to Rothman.
“So far, research on this little animal has resulted in Nobel prizes for six researchers,” he noted.
C. elegans is already a veteran of space travel, has been the subject of experiments on the International Space Station and aboard the space shuttle, even surviving the tragic Columbia shuttle disintegration. Tardigrades (or, more affectionately, water bears) can be placed in suspended animation, which stops virtually all metabolic functions, which they share with other potential interstellar travelers studied by Rothman. Thousands of these tiny creatures could be placed on a wafer, suspended in time, and flown until they reached their destination. They could then be awoken in their tiny StarChip and precisely monitored for any detectable effects of interstellar travel on their biology, with the findings relayed to Earth via photonic communication.
“We can ask how well they remember trained behavior when they’re flying away from their earthly origin at near the speed of light,” Rothman added. “We can also examine their metabolism, physiology, neurological function, reproduction, and aging.” “The majority of experiments that can be done on these animals in a lab can be done onboard the StarChips as they whiz through the cosmos.” The effects of such long journeys on animal biology may allow scientists to extrapolate to potential human effects.
“We could begin thinking about the design of interstellar transporters, whatever they may be,” Rothman said, “in a way that could alleviate the issues that have been detected in these diminutive animals.”
Of course, being able to send humans into interstellar space is fantastic for movies, but it remains a distant dream in reality. By that time, we may have developed more suitable life forms or hybrid human-machine hybrids that are more resilient.
“This is a program for the next generation,” Lubin said. Scientists of future generations will ideally contribute to our understanding of interstellar space and its challenges, as well as improve the design of the craft as technology advances. Because the primary propulsion system is lightweight, the underlying technology is on an exponential growth curve, similar to electronics, with “Moore’s Law”-like expanding capability.
Planetary Protection and Extraterrestrial Propagation
We’re tethered to our solar system for the foreseeable future; humans are fragile and delicate when they’re not on their home planet. But that hasn’t stopped Lubin, Rothman, their research teams, and their diverse collaborators, which include a radiation specialist and a science-trained theologian, from thinking about the physiological and ethical aspects of sending life to space – and possibly even propagating life in space.
“There are the ethics of planetary protection,” Lubin explained, “in which serious consideration is given to the possibility of contamination, either from our planet to others or vice versa.” “I think if you started talking about directed propagation of life, which is sometimes called panspermia — this idea that life came from somewhere else and ended up on the earth through comets and other debris, or even intentionally from another civilization — the idea that we would purposefully send out life raises a lot of questions.”
According to the authors, there is no risk of forwarding contamination so far because probes approaching any other planet would either burn up in their atmosphere or be obliterated in a collision with the surface. There is no risk of extraterrestrial microbes returning to Earth because the watercraft are on a one-way trip.
While still on the fringe, the theory of panspermia appears to be receiving some serious, if limited, attention, given how easy it is to propagate life when conditions are favorable and the discovery of several exoplanets and other celestial bodies that may have been, or could be, supportive of life as we know it.
“Some people have pondered and published on ideas like, ‘Is the universe a lab experiment from some advanced civilization?'” Lubin said. “As a result, people are certainly willing to consider advanced civilizations. Questions are useful, but answers are preferable. We are simply pondering these questions right now because we do not yet have answers.”
Another issue being debated in the broader space exploration community is the ethics of sending humans to Mars and other distant places knowing they may never return. What about releasing microorganisms or human DNA? These existential questions are as old as the first human migrations and seafaring voyages, and the answers will most likely come when we are ready to embark on these journeys.
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