As far as our Earthly scientists can observe at the moment using our telescopes, there are at least thirty stars lying within a radius of approximately 12 light years from Earth. Seven of them are multiple star systems, of which our closest neighbour a triple star system called Alpha Centuari A and B, and Proxima Centauri is located a mere 4.3 to 4.22 light years away (basically a stone's throw away, although in space a stone's throw will definitely go a long way indeed if you give it enough time). Perhaps a few more very faint stars (and those so-called brown dwarfs, the ones that are very close to initiating their thermonuclear reactions at the core) may exist within this 12 light-years range, but our instruments are not quite sensitive enough to detect them at the present time.
A brief analysis of all the known stars within this specified range shows Red Dwarfs are the most common. These are small stars believed to possess the minimum mass required to initiate thermonuclear reactions for generating heat and light in their central core. Because red dwarfs have a low mass compared to other stars, they glow a dim red colour and burn their hydrogen fuel very slowly and so have the longest lifespan of any star. For example, Barnard's Star is a red dwarf lying at a distance of 6 light years from Earth; its estimated age of 11 to 12 billion years (or more likely much older) is considered very old by red dwarf standards. Indeed, almost as old as what some scientists think the age of the finite visible universe should be, which may sound a bit odd considering this star should not have been formed before the universe began. Does this mean the universe is much bigger and older than we think?
Leaving aside the age of the universe controversy, red dwarfs are not considered ideal places to find alien life native to a neighbouring planet. Well, certainly not of the native technologically advanced alien life variety. This is mainly because a planet has to be huddled close to the star to receive reasonable warmth (orbiting the star every month or two) and hope there are no major flare-ups from these stellar objects to significantly affect the temperatures on the surface of the planet. Then again, readers should never cease to be amazed at what scientists can discover if there is a chance of finding alien life in these star systems. For example, to survive these flare-ups, it is possible life could survive inside a cave. So why not get excited by the prospect of finding alien life at a red dwarf system, right? Nothing like supporting your local NASA scientist with more public funds to help find these mostly alien bacteria while somehow conveniently excluding the more sun-like stars and how likely we will find more complex and, given the age of the stars, technologically-advanced alien life in those places. You would almost have to say that someone in these U.S. government-funded scientific organisations designed to explore space do not want the public to reach too high a goal and instead we should settle and be motivated by a bit of alien bacteria from another planet around a red dwarf. Good luck with this approach!
Funny we should mention it, because the scientific boffins have well and truly made every effort to convince the public this is where we should go. A study published in the 10 July 2013 issue of The Astrophysical Journal Letters has raised this prospect of finding life in a red dwarf system significantly by suggesting thick clouds in the atmosphere of an alien planet (made mostly of water vapour) could stabilise and, up to a point, regulate the temperature on the surface of the planet as they do here on Earth, making it potentially hospitable in the establishment of alien life. If this is true according to complex 3D computer simulations conducted by researchers at the University of Chicago and Northwestern University in Illinois, the astronomers claim that as many as 60 billion planets may be circling these dimly glowing red balls of light in our galaxy at distances considered suitable for life far more than previously realised. If such water-based clouds exist, the habitable zone (the imaginary region where water exists in the three physical phases of solid, liquid and vapour) around the stars will increase in size, making it more probable that at least one earth-sized planet will be found and could sustain life.
However, even if life could be carving out an existence on the surface of a planet circling around one of these red dwarf systems, we should not get our hopes up too high in finding life that we can communicate with, let alone one that can apply a technology. Life will almost certainly be primitive indeed, perhaps nothing more than tiny bacteria or small worms wriggling on the surface assuming they have evolved successfully to a reasonable size. And if not, the clouds and the dim red glow of the parent star would make things dark on the surface of the planet. It will probably be nothing more than what you might find on a full moon at the late evening after the Sun has set over the horizon on Earth (but everything will look red to our eyes) or even darker still with thick enough clouds to the point where you might as well be sitting inside a cave the creatures inside such a darkened environment will almost certainly be blind and crawling on the surface to find its next meal (sounds like a good place to start the next alien sci-fi film with creatures keen to come after you for a feed).
Dorian S. Abbot, assistant professor in geophysical sciences at the University of Chicago and co-author of the report for this study, said:
"Clouds cause warming and they cause cooling on Earth. They reflect sunlight to cool things off and they absorb infrared radiation from the surface to make a greenhouse effect. That's part of what keeps the planet warm enough to sustain life."
The other person to author the report (together with Jun Yang) is Nicolas B. Cowan of Northwestern University. She summarised the results in the following way:
"Most of the planets in the Milky Way orbit red dwarfs. A thermostat [through the presence of clouds] that makes such planets more clement means we don't have to look as far [from the star] to find a habitable planet."
Nice to see the scientists are keen to increase the chances of finding alien life by including red dwarfs in the "extraterrestrial life" equation. Further details of the study can be found here (PDF).
Even if there is no life to be found, the idea of living on an Earth-sized planet around a red dwarf is still giving some scientists enormous excitement (and many wet dreams if there is an ocean of water to be had there). For example, the planet found orbiting Proxima Centauri has inspired one scientist to show the positives of it for life on Earth. Avi Loeb of the Harvard-Smithsonian Center for Astrophysics and an adviser to the Breakthrough Starshot project, has suggested that we could live on this planet if the Earth disappears. As he said:
"A habitable, rocky planet around Proxima would be the most natural location to where our civilization could aspire to move after the sun will die, five billion years from now."(Quote from here)
There is clearly nothing these scientists will not do to show the positives of these red dwarfs in finding alien life, if not to colonise for the sake of humans surviving in this universe.
Well, whether it is to find alien bacteria or a new place to live for humans (1), if the real aim is to find aliens capable of communicating with humans and even possess a technology, there is only one place in the universe we should go: the more sun-like stars. In fact, if enough members of the public could have their say on this matter, this is where many would support the search for life. Forget red dwarfs, just go for the sun-like stars. Simple and sweet.
Speaking of sun-like stars, of all the stars lying within 12 light years of Earth capable of supporting the kind of alien life the public is looking to find, Tau Ceti and Epsilon Eridani are sufficiently similar to our Sun to be excellent candidates.
Two other stars also worth noting in this regard are Alpha Centauri A and B, and Epsilon Indi. As much as some people may like to joke around about the idea of little green men coming from Alpha Centauri, the separating distance of both sun-like stars in the Alpha Centauri system are sufficient to permit one or two planets at the right distance to maintain water in the liquid state for billions of years and hence harbour alien life, and very complex life too given the age of the stars in question. In fact, these two sun-like stars are older than our Sun. It means that should scientists find land masses on at least one Earth-like world orbiting one or the other stars (or it is totally feasible to find two Earth-like worlds in the star system), we should expect to find highly complex and technologically-advanced alien life. Anyone from Earth who decides to venture out to this star system with the right electromagnetic technology will realise Alpha Centauri A and/or B would be the classic first port-of-call destination point for humankind to find out whether ETs exist and in the shortest amount of time required given the relative distance of these stars from our Sun. And if scientists still want to go for a second-rate red dwarf and watch a bit of bacteria grow on an alien planet nearby, Proxima Centauri just so happens to be even closer and part of the Alpha Centauri system.
If you had a choice, which would you prefer to visit? Proxima Centauri, or Alpha Centauri? The public definitely knows where it wants to go. Just go for gold by following the closest yellow sun-like stars after our Sun, and the answer will be clear and irrefutable.
Alpha Centauri is truly the perfect trifecta for satisfying not only the scientists desire for alien bacteria (fine, if that is what tickles their fancy), but also the public quest for more advanced alien life, and all the other things we may wish to see. Just imagine it. Three independent planetary systems to investigate, the likelihood of up to two highly advanced alien worlds around the sun-like stars, as well as different cultures, new technological solutions to world problems, and understanding new ways of solving social problems. Who knows? Perhaps these alien societies could teach us a thing or two about where we should be heading and developing on Earth.
What more could you possibly want?
Well, we will try to throw in a fridge and a few drinks in there too once the spacecraft is built to take us to the stars.