Choosing Your Target Well

Project Daedalus

First steps in reaching for the stars. Published by the British Interplanetary Society 1978. Cover design by David Holmes.

It seems that Barnard’s Star may have at least one planet orbiting it after all.  This fact has a particular significance for the British Interplanetary Society because that star was the chosen target system for the unmanned interstellar spacecraft described in the Project Daedalus feasibility study, published in 1978.  The star is a red dwarf around six light years from Earth, and the nearest to us after the Alpha Centauri triple star system which is a little closer at four light years away.

Several of the papers in the study were devoted to analyzing why this specific system should be the goal of the mission.  In The Ranking of Nearby Stellar Systems for Exploration, Anthony R Martin commented that it was selected because of the possibility that it possessed planetary companions, which had indeed been suggested by observational data of the perturbation of the star.  And in The Evidence for Planetary Companions of Barnard’s Star, he concluded that, at the time, the case for such planets must be regarded as “not proven”, although there was sufficient to indicate that this would be well worth investigating further.  However, none were found until now.

Clearly, it would be more interesting to visit a star with planets than one without, and there was no evidence of planets orbiting any of the Alpha Centauri stars until just a few years ago.  The closest of all, a world a little larger than the Earth in orbit around Proxima Centauri, was found as recently as 2016.  But now, in A Candidate super-Earth planet orbiting near the snow line of Barnard’s Star (Nature, 14 November 2018), Ignasi Ribas of the Institute of Space Studies of Catalonia and his colleagues present evidence of a planet between three and four times the mass of the Earth orbiting Barnard’s Star, detected using analyses of the wobble of the star caused by the planet’s movement.

It’s satisfying to know that there are even more exoplanets orbiting nearby stars – they can provide realistic shorter-term targets to encourage potential human colonization of the Galaxy in the long term.  There is a well-known argument that interplanetary exploration would be severely hampered if the Earth didn’t have a convenient Moon which could be reached relatively easily, and which could act as a stepping stone to what is further away.  Similarly, science fiction has occasionally described intelligent alien races whose development of interstellar flight is restricted because they inhabit a solitary planet circling a star with no neighbouring worlds to be visited first, so they’re stuck there.

Likewise, unless some imaginary invention that enables instantaneous transport anywhere in the cosmos appears in due course, humanity will be limited to progressing from star to star in a gradual fashion.  Having worlds to visit, and possibly colonize, at each stage would be a strong advantage.

Isaac Asimov’s 1986 science fiction novel Foundation and Earth describes a search for Earth, the legendary home of humanity, at a time when the human race has spread throughout the Galaxy.  The quest focuses on those worlds which are understood to be the oldest colonies and, when the planet Alpha, orbiting Alpha Centauri, is eventually reached, it becomes clear that this may effectively be amongst the first colonies of the original homeworld.  The first was the closest.

But this new exoplanet orbiting Barnard’s Star is very cold, with a surface temperature of -150 degrees C – not at all like some of the more optimistic fictional representations of planets in that location.  Robert Forward’s 1984 novel The Flight of the Dragonfly depicts a forty-year journey to that system by a spacecraft propelled by a laser-driven light sail.  Unmanned probes have already discovered planets there, and human colonization can begin, though not without considerable obstacles to be overcome.  In reality, Barnard’s Star may not be the first choice for a colonization expedition, but it nevertheless appears to have a planetary system well worth investigating.

 

Richard Hayes, Assistant Editor (Odyssey)

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