As far as we 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. Eleven of these are multiple star systems, of which our nearest neighbour — a triple star system called Alpha Centauri A and B and Proxima Centauri — is a mere 4.3 to 4.22 light years away (basically a stone's throw away, although in space a stone's throw can get you a long way if you have enough time). There may be a few more very faint stars (and those so-called brown dwarfs, which are close to initiating their thermonuclear reactions in the cores but remain mostly very hot gaseous planets) within this 12 light-years range, but our instruments are not yet sensitive enough to detect them.
A brief analysis of all the known stars within this specified range shows that red dwarfs are well represented throughout the Milky Way, and our neck of the cosmic woods is no exception. These are small stars that are thought to have the absolute minimum mass required to initiate thermonuclear reactions needed to describe these objects as true stars. Because of their low mass compared to other stars, red dwarfs glow a dim red and burn their hydrogen fuel very slowly, giving them the longest lifespan of any star. For example, Barnard's Star is a red dwarf 6 light years from Earth; its estimated age of 11 to 12 billion years (or more likely much older) is very old by red dwarf standards. In fact, 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?
Aside from the age of the universe controversy, red dwarfs are not considered ideal places to find alien life, at least not of the native technologically advanced variety. This is mainly because a planet has to huddle close to the star to receive reasonable warmth (orbiting the star every month or two), and hope that there are no major flare-ups from these stellar objects to significantly affect the temperatures on the surface of the life-bearing alien planet. On the other hand, 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 that life could survive in a cave, or deep beneath an ocean, as long as the temperatures are not too high from the flare-ups to cause planet-wide evaporation of most of the water. In which case, might as well get excited by the prospect of finding alien bacteria or other forms of primitive life on a planet near a red dwarf.
According to a study published in the 10 July 2013 issue of The Astrophysical Journal Letters, scientists have raised the prospect of finding life in a red dwarf system in a very significant way by suggesting that thick clouds in the atmosphere of an alien planet (made up mostly of water vapour) could stabilise and, to some extent, regulate the temperature on the planet's surface as they do here on Earth, making it potentially hospitable for the establishment of alien life. If this is true according to complex 3D computer simulations carried out by researchers at the University of Chicago and Northwestern University in Illinois, astronomers claim that as many as 60 billion planets could be circling these dimly glowing red balls of light in our galaxy at distances considered suitable for life — far more than previously thought. 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 likely that at least one Earth-sized planet will be found that could support life.
Yet all this discussion somehow conveniently excludes the more sun-like stars and the likelihood of finding more complex and, given the age of the stars, more technologically-advanced alien life in those places. One could almost say that someone in these U.S. government-funded organisations, such as NASA, do not want to give the public too high an expectation of finding really advanced aliens, and instead hope they will settle for mediocre alien bacteria.
Yet even if life could eke out an existence on the surface of a planet orbiting one of these red dwarf systems, we should not get our hopes up too high about 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 successfully evolved to a reasonable size. And if not, the clouds and the dim red glow of the parent star would keep the surface of the planet exceedingly dark. It will probably be nothing more than what you might find on a full Moon here on Earth in the late evening after the Sun has set over the horizon (but everything will look red to our eyes), or even darker with clouds thick enough to make you feel like you are sitting inside a cave — the creatures in such a darkened environment will almost certainly be blind and crawling around on the surface looking for their next meal (sounds like a good place to start the next alien sci-fi movie 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 that 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 no life is found, the idea of living on an Earth-sized planet around a red dwarf is still excites some scientists (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 point out the positive aspects for life on Earth with the potential to find alien life. Avi Loeb from the Harvard-Smithsonian Center for Astrophysics and an advisor to the Breakthrough Starshot project, has suggested that we could live on this planet when 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 that these scientists will not do to show the positives of these red dwarfs in the search for extraterrestrial life, if not to colonise for the sake of human survival in this universe.
Well, whether it is to find alien bacteria or a new place for humans to live (1), if the real aim is to find aliens capable of communicating with humans and even possessing a technology, there is only one place in the universe we should go: the more yellow and bright sun-like stars. In fact, if enough members of the public could have their say on the matter, many would support the search for life there. Forget the red dwarfs, just go for the sun-like stars. Simple and sweet. As people would say, "Go for gold!"
Speaking of sun-like stars, of all the stars within 12 light years of Earth that could support the kind of alien life the public is looking for, Tau Ceti is sufficiently similar to our Sun, and has been around long enough, to be an excellent candidate.
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 about the idea of little green men coming from Alpha Centauri, the separation distance of the two sun-like stars in the Alpha Centauri system is sufficient to allow at least one, and potentiually two Earth-like planets, at the right distance to keep water in the liquid state for billions of years, and thus host a variety of exquisite 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. So we should expect some of this alien life to be extremely intelligent. And with the amount of metals found in the stars composition, the planets will have enough metals to support a technology. This means that if scientists find land masses on at least one Earth-like world orbiting one of these 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 find that Alpha Centauri A and/or B would be the classic first port-of-call for humanity to find out whether ETs exist. Well, think about it. Alpha Centauri is not that far away. We can get there in the shortest amount of time compared to other sun-like stars. And if scientists still want to go for a second-rate red dwarf and watch a bit of alien bacteria grow on a nearby alien planet, Proxima Centauri just so happens to be even closer and part of the Alpha Centauri system.
Alpha Centauri really is the perfect trifecta for satisfying not only the scientific desire for alien bacteria (fine, if that tickles their fancy), but also the public desire for more advanced alien life and all the other things we might want to see. Just imagine. Three independent planetary systems to explore, and with the likelihood of finding up to two highly advanced alien worlds around the sun-like stars, as well as different cultures, new technological solutions to world problems, and an understanding of new ways of solving social problems. And, even after all of that, if scientists still want to go to the red dwarf, then go for it. Let the scientists have all the alien bacteria they can handle. But if you had to choose, which would you prefer to visit? Proxima Centauri, or Alpha Centauri? The public definitely knows where they want to go. Just go for gold by going to the closest yellow sun-like stars after our Sun, and the answer should be clear and irrefutable.
What more do scientists want?
Well, perhaps we could try to throw in a fridge and a few drinks in there too once the spacecraft is built to take us to the stars. Might as well enjoy the trip while we are at it.