One subject that caught my eye several months ago seems like a natural follow up to the posting I wrote on September 17th about what the Monarch Butterfly could teach us about biological ways to succeed at interstellar travel. For humanity to send a reproducible population to a second Earth in a neighbouring solar system presents an enormous challenge for which we currently lack the knowledge and technology. Our imperfect understanding of population genetics and the dangers of interstellar space makes it highly improbable that we can pull this off without massive loss of life, and in the end without knowing if the people we send actually make it to their destination.

An astrophysicist at the University of Strasbourg, Frédéric Marin, has recently published a paper in which he works the success numbers for an interstellar crew complement taking a 6,300-year journey to Proxima Centauri-b, the planet  referenced in my previous Monarch Butterfly posting.

Why 6,300 years? Marin chooses an optimal speed for the spacecraft of better than 500,000 kilometers per hour, three times faster than the Juno spacecraft currently circling Jupiter. At that speed the 40-trillion-kilometer voyage would last more than 6 millennia.

Marin looks at parameters for survival including issues like sudden death, accidents, space rock collisions, cosmic rays, infertility, inbreeding, pandemics and unforeseen random events. Applying a Monte Carlo simulation, a program called Heritage, Marin recently ran several different population configurations to determine the optimal minimal number needed to survive a multi-generational voyage. If you are unfamiliar with Monte Carlo simulations, these were first conceived by scientists who were working on the Manhattan Project to help them use quantitative analysis to predict a range of possible and probable outcomes.

Marin, who normally simulates remote galaxies and black holes, used Heritage beginning with 50 humans made up of 25 breeding-aged pairs. At those numbers Heritage concluded a crew would not survive the voyage. He then raised the numbers incrementally testing each in the simulation. All scenarios up until the number 98 indicated failure with the human crew dying off before reaching Centauri-b. But at 98, Heritage predicted a 100% survival outcome.

With 98 healthy humans, the population would be self-perpetuating with enough diversity to make up for the lack of being able to remove old genes through emigration and introduce new ones by immigration. Marin’s spaceship simulation allows for the 98 to grow the population over the journey to 500 as the interstellar spaceship gets close to Centauri-b.

Even Elon Musk’s BFR, the largest passenger rocket ship being planned today wouldn’t be able to handle a crew of 98, 30 at best, according to those who have studied the specifications. So one can conclude that the infrastructure and self-sustaining, environmental requirements of an interstellar ship are well beyond our best technological skill sets today.

But the exercise regardless has merit Marin states: “The same elements are essential for any self-sustaining colony, so our code can easily compute the survival rate of a group of humans after a local or global catastrophe as well.” I guess one could call this good post-apocalyptic thinking.

But others tackling the same thought experiment have disputed the number. One of those is anthropologist Cameron Smith, of Portland State University in Oregon, who has come up with a minimum of 14,000 to a maximum of 44,000 as the right numbers for human survival through interstellar space.

In his study, Smith concludes that the unforeseen has to be accounted for such as sudden death by accident or disease involving a disproportionate number of either the female or the male population which would impact viable genetic diversity to ensure survival.

As an anthropologist, Smith uses Polynesian migration modeling which looks at the numbers needed for a small population to spread from one island to many throughout the Pacific Ocean. Smith states that Polynesian groups of up to 100 or fewer hunter-gatherers set out on long sea voyages to reach other islands. The Polynesians came in a series of waves. Many didn’t survive these journeys. Many died after arrival. But the total number of migrants amount to the tens of thousands. Otherwise colonization fails. The same can be said about the European colonization of the Americas, New Zealand, and Australia. Thousands died before sustainable populations were established.

Of course, neither Marin or Smith in their thought experiments considered altering the human genome of the crew to make the voyage survivable. In my Monarch Butterfly article, I theorized that advanced genetic engineering would allow us to alter the species and make us genetically flexible. We could even go through a metamorphosis turning into chrysalides to emerge before making landfall at a new planet. On a trip to Centauri-b we would thus minimize many of the risks that both Marin and Smith accept as necessary to human migration over the long distances and perils of interstellar space.

Getting our house in order here on Earth should be the first imperative. That means making sure the environment remains sustainable for our species and the remaining biodiversity that keeps the status quo. It means we must do better in balancing our technological civilization with the planet’s carrying capacity.

At the same time, the stars represent an opportunity too good to pass up. Spreading ourselves to other planets in our own local area, the Solar System, and then beyond to our nearest neighbouring stars would ensure the near immortality of humanity, an appropriate goal for the sole intelligence in the Universe as the Oxford researchers would have us believe.

So what would it take for us to become a multi-stellar species? Well, it means getting, first, to the nearest star with an exoplanet that is potentially inhabitable. That could be Proxima Centauri-b, 4.2 light-years away. Camille Beluffi and Frederic Marin, two French researchers, decided to take on a thought experiment, accompanied by a few algorithms, in which they imagined a spacecraft traveling from Earth to Proxima Centauri at the fastest speed we currently can produce with existing technology. At Apollo program top speed, 40,000 kilometers (25,000 miles) per hour, a trip to Proxima Centauri would take 100,000 years. But at robot spacecraft speed based on an upcoming launch of the Parker Solar Probe in August of this year, our current technology will attain speeds of more than 700,000 kilometers (420,000 miles) per hour. At that speed, a trip to Proxima Centauri-b would take 6,300 years.

What Beluffi and Marin wanted to understand was how we could sustain a human population in a spacecraft for a voyage of that duration using the technology on hand. How many could be sent on such a voyage knowing that survival will mean multi-generational breeding to complete the task? What would be the right ratio of men to women to ensure survival? What contingencies would be needed to deal with potential disasters like an accident, or disease outbreak? How could we avoid inbreeding?

The researchers looked at what successfully sustains a breeding population of animals here on Earth to ensure enough genetic diversity to thrive indefinitely without inbreeding. The number turns out to be 25 breeding pairs.

Applying their algorithms to the number led to the conclusion that 25 pairs would be too small and likely produce a 50% chance of population die-off before reaching Proxima Centauri-b. Instead, it was concluded that an ideal minimal breeding population would be 49 pairs to give us the best shot in making the 6,300-year voyage.

Nowhere in their evaluation did the authors of this thought experiment look beyond current technology as the means of getting from Earth to Proxima Centauri-b. There is no mention of humans traveling in a cryopreserved state for much of the trip as is often depicted in science fiction novels and films. Nor did they consider the possibility of assembling humans from detailed DNA specifications in databanks with robots making the voyage and printing out a human population along with a biodiverse supporting cast of other animals and plants upon arrival. In such a scenario, the robots would retain human knowledge and tend to the population of living things created until they could be self-sustaining in their new home.

Of course, all of this effort would go for naught if it turns out that the planets orbiting Proxima Centauri are not suitable Earth substitutes. We know very little about Proxima Centauri-b, other than it is a rocky planet with a mass slightly larger than Earth. It orbits its star at about half the distance from Earth’s orbit around the Sun. Proxima Centauri, being a red dwarf star, is less luminous than the Sun approximating 15% of the energy produced by our star. Taking these two aforementioned factors into consideration, exoplanet researchers hypothesize that water may exist in all three states on the planet’s surface as it does here on Earth. But before we start sending our seeds out to plant on Proxima Centauri-b, it behooves us to know more.

Beluffi and Marin’s thought experiment limited itself to what we have on hand now. So they didn’t consider Philip Lubin’s proposed faster method of propulsive technology using a photon beam to drive a spacecraft to speeds approaching one-quarter the speed of light. You can read more about this technology in a posting I wrote back in February of 2016.

Is what Lubin is proposing pure fantasy? Hardly, and he has suggested a test of the technology can easily be done in close proximity to Earth. Once proven he has proposed we do an interstellar voyage of discovery by sending send a small fleet of nano-spacecraft to Alpha Centauri, the binary star system which neighbours Proxima Centauri. That voyage would take 15 years.

Lubin acknowledges the limitation of his method of propulsion, noting it would have no braking mechanism, so couldn’t slow down. We would monitor the voyage throughout the 15 years, however, using laser communication technology which would send a continuous stream of data and images back to Earth. At the end of the fly by we would briefly glimpse the Alpha Centauri system before heading beyond.

But what if we used Lubin’s idea and made Proxima Centauri our target? And what if we devised a much larger spacecraft to be driven by this method of propulsion? Within it, we could include a payload to be ejected upon approaching Proxima Centauri. The payload would include its own onboard propulsion system to steer it to Proxima Centauri-b where it would have the capability to soft land.

And what could that payload contain? I would suggest robots capable of self-assembly and able to manufacture other robots and an infrastructure from the materials at hand on the planet’s surface. Once the infrastructure was built the DNA instructions kept on board would be the blueprint for the robots to manufacture our human presence along with companion biodiversity.