Why colonize the planets of Alpha Centauri and Proxima Centauri
The proximity to us (four light years is really a trifle when compared to normal space distances)
played a fundamental role in making Alpha Centauri the subject of science fiction speculation
and that it was mentioned in literature and video games. The best-known example in the literary
field is that of Isaac Asimov: in his Cycle of the Foundation, in particular in the book
Foundation and Earth, Alpha Centauri is the last stage of the journey of Golan Trevize,
councilor of the Foundation, before reaching the planet Land; the star in the novel is called
by the diminutive "Alpha" and around the main component of the system orbits a planet, in fact,
covered by a single immense ocean in which there is a single inhabited land, whose inhabitants are
able to control the climate. From here Trevize sets off to reach the Sun, the closest star,
where it seems we can find planet Earth. In the cinematographic field, the name of this
star has been widely used, especially for science fiction travels concerning galactic exploration
or the immediate surroundings of the Sun. In fact, Alpha Centauri, even in reality, would be
one of the very first destinations of a possible future interstellar trip manned with a human crew.
In Babylon 5, a science fiction television series shot in the 1990s,
the system, simply called "Proxima", is one of the major colonies of the Earth Alliance;
in this planetary system, orbiting around Proxima Centauri, there are three planets,
the third of which is also the largest colony in the alliance. Over the course of the episodes,
the planet declares independence, causing an interplanetary civil war. In closing of
the Italian film 2019 - After the fall of New York, the protagonist Parsifal leaves for Alpha
Centauri. Among the films of the 2000s there is Avatar by James Cameron, mostly set on Pandora,
one of the many moons of Polyphemus, a gas giant the size of the planet Saturn,
revolving around the star. In the 1960s television series Lost in space, a family of space settlers
attempt to colonize an Alpha Centauri planet. In the DC Comics comic series, planet Rann
originated in the Alpha Centauri system, until it was teleported to Polaris; in the
Rann series it is important as the foster planet of explorer and hero Adam Strange.
In the world of video games, one of the most famous examples is that of
the Civilization series, which places as one of the victory conditions that of
sending an expedition of colonists to the Alpha Centauri system. In Sid Meier's Alpha Centauri,
victory is given by the outcome of a competition between different civilizations for the conquest
of the planet Chiron, orbiting the star. In the various Transformers series most of the
time the native planet of the alien robots, Cybertron, orbits the aforementioned star.
Science fiction and video games aside,
why colonize the planets of Alpha Centauri and Proxima Centauri?
First of all for its proximity: that of Alpha Centauri is the closest star system to ours,
just 4.3 light years from the Sun: one light year is the distance traveled by light in a year in a
vacuum, and is equivalent to about ten thousand billions of kilometers. This means that, traveling
at the speed of light, it would take us 4.3 years to reach Alpha Centauri. The Alpha Centauri system
is a triple system consisting of two stars similar to the Sun in mass and size quite
close to each other, known as Alpha Centauri A and B, and a more distant and faint red dwarf star,
known as Alpha Centauri C or Proxima Centauri. The name Proxima, from the Latin, means "closest":
and in fact, to be precise, Proxima Centauri is the closest star to the Sun, which is 4.22 light
years away, and not Alpha Centauri. The brightness of Proxima is only 0.0008 times that of the Sun,
while its mass is about one tenth of the solar mass and its dimensions are smaller than that
of Saturn. It is located approximately 15,000 astronomical units from components A and B.
Another reason concerns the planets discovered around two of the three components of the
Alpha Centauri system. We recall that, to date, two planets in orbit around Proxima,
known as Proxima Cen b and Proxima Cen c, are confirmed; some time ago the existence of a third
planet around Proxima (Proxima Cen d) and two planets orbiting Alpfa Cen B was hypothesized,
but subsequent observations have not yet been able to confirm them with certainty. As for
the two confirmed planets, Proxima Centauri b was discovered in 2016 by analyzing data
obtained through the HARPS spectrograph mounted on the European Southern Observatory 3.6 m telescope
in La Silla, Chile. Proxima Cen b orbits the star in just over 11 days:
a year on this planet lasts as little as a week and a half on Earth! The average distance of
Proxima Cen b from its star is equal to about 0.049 astronomical units, which is less than
5% of the average distance between Earth and Sun! Its mass is equal to 1.17 times the earth's mass,
and it receives only 65% ​​of the energy that the Earth receives from the Sun.
Proxima Centauri c is a super-Earth (i.e. a rocky planet like ours but a bit larger)
about 7 times more massive than Earth, which orbits around Proxima at an average distance
of about 1.5 astronomical units (more or less the same distance between Mars and the Sun),
taking just over 5 years. Its average temperature is about 39 K, equal to about -230 ° C.
It was discovered by the group of researchers led by Italian astrophysicist
Mario Damasso in April 2019, by studying the small oscillations in radial velocities
detected by the HARPS spectrograph. During 2020 the existence of the planet was confirmed through
observations from the Hubble Space Telescope. Due to the slight differences in brightness it
presents as it travels through its orbit, it is believed that it may have a ring system.
It is believed that only Proxima Cen b is located within the habitability range
of its star. Recall that the habitability belt is the area around a certain star where a planet
can have liquid water on its surface and a surface temperature that is neither too low nor too high,
making it potentially suitable for hosting life forms. And the search for extraterrestrial life is
undoubtedly one of the reasons for colonizing the Proxima Centauri system of planets.
Next-generation telescopes, such as the European Extremely Large Telescope, will be used to conduct
an intensive study of Proxima b in the hope of finding life forms other than terrestrial ones.
Proxima Cen c, due to the great distance from its star,
and the very low temperatures, is probably outside the habitability belt of its star.
Another reason for colonizing the Alpha Cen system is represented by the longevity of
red dwarf stars, which is identified with the duration of the main sequence phase.
The main sequence is a phase of stability in which the star, through the thermonuclear reactions that
take place in the core, produces helium from the combustion of hydrogen. In the case of red dwarfs,
having a mass much smaller than the solar one, the main sequence phase, and therefore of stability,
would last longer than the entire age of the universe! And this happens because,
as red dwarfs have a small mass, the rate at which they burn hydrogen to produce helium is lower than
for stars of greater mass. In comparison with what has happened on Earth, it is believed that life is
more likely to develop on planets orbiting stars with a very long main sequence phase duration.
On the other hand, however, there are some doubts that the planets orbiting the red dwarfs
may actually be suitable for hosting life forms: the red dwarfs are in fact much more active stars
than those similar to the Sun, and can therefore produce very intense flares, associated with a
conspicuous emission of ultraviolet radiation and X-rays, which can be harmful to living organisms
if absorbed in high doses. These high-energy radiations, investing the surface of the
planets near the red dwarfs, could sterilize their surface making them unsuitable for life.
It would therefore be necessary to understand if any life forms could survive in the subsoil of
these planets. Another reason why the planets around the red dwarfs may not be suitable for
life is the probable synchronous rotation due to the tidal star-planet interactions, which
would act for the planets closest to their star: this means that the planet takes the same time
to make a rotation on themselves and a revolution around the star: this would imply that one planet
would always show the same hemisphere to the star, while the other would always be in the dark.
Furthermore, the colonization of the Alpha Cen system would perhaps allow us to answer, citing
Douglas Adams' "Hitchhiker's Guide to the Galaxy", the "fundamental question about life, the Universe
and everything": are we alone? Are there other habitable worlds in our galactic neighborhood?
And then: after the Moon, could we make the great leap to the stars? And surely the answer
would not be 42, but a much more articulated answer depending on economic, political,
technological, scientific reasons. And the desire to go beyond the Moon is the basis
of a proposal to NASA by John Culberson, a member of the House of Representatives
for the state of Texas, to send a mission to Proxima Centauri by 2069:
the date is not accidental, but it would fall in the centenary of the conquest of the Moon.
It must be remembered that scientists continue to discover esoplanets using powerful orbiting
telescopes but we, physically, have moved very little from the Earth:
only the Voyager 1 and Voyager 2 missions, launched in 1977 and containing a disc
with the sounds of the Earth intended for any extraterrestrial listeners who might come across
the probe in a distant future, have recently crossed the boundaries of our solar system.
For this purpose, one cannot fail to mention the Breakthrough Initiatives:
announced in July 2015 by the Russian tycoon Yuri Milner, it is a scientific program aimed
at searching for signals coming from space and sent by any extraterrestrial civilizations.
It is divided into three projects: Breakthrough Listen, whose idea is to obtain the spectrum of
about a million stars, in search of possible non-terrestrial signals of artificial origin,
and Breakthrough Message, which will have as its purpose, in case the Listen phase
there allowed to discover extraterrestrial civilizations, to send them a message.
The third project, Breakthrough Initiative, is perhaps the most interesting. Announced
on April 12, 2016, it was born with the intention of developing a propotype of laser-powered light
spacecraft, called StarChip, capable of traveling up to the Alpha Centauri star system at a speed
between 15% and 20% of that of the light in the vacuum, thus taking 20 to 30 years to reach it
and about 4 years to notify it to planet Earth. In addition to Yuri Milner, the project initially
included Facebook founder Mark Zuckerberg and the late British astrophysicist Stephen Hawking.
It is believed that at least twenty years are required for the realization of the project.
The Starshot concept involves the launch of a "mother ship" that carries small spacecraft the
size of a few centimeters to the outside of Earth's orbit. From here a laser beam coming
from the ground will accelerate the 4 x 4 m sails connected to the microprobes up to 100 km / s2.
Thanks to these probes it will be possible to reach and visit the planet Proxima Centauri b
in about 30 years and capture an image of high quality
sufficient to fully understand the surface characteristics of the planet.
A swarm of about 1000 units is assumed to compensate for the losses
caused by interstellar dust collisions while navigating to the planet of interest. In a recent
detailed study, astrophysicist Chi-Thiem Hoang and his collaborators found that mitigating collisions
with dust, hydrogen and cosmic rays may not be as serious an engineering problem as one might think.
In conclusion, using our current technology, a trip to Alpha Centauri for a probe with the
same characteristics as the New Horizons, the probe that recently visited Pluto,
Ultima Thule and is now entering the Kuiper belt, would take approximately
78,000 years. But projects like Breakthrough Starshot or similar would give a big boost to the
development of new methods of space propulsion and new technologies for miniaturization of cameras
and other electronic components, because it is surely cool to travel "To infinity and beyond",
as Buzz Lightyear said in the Disney’s movie “Toy Story”, but it is equally cool to look
for applications that are unthinkable today, useful for improving daily life.