Free Astronomy Magazine March-April 2023

38 up our radio and television transmissions. The few signals intentionally sent to other stars (often twisted like the minds of those who thought them) had no chance of being intercepted along the way. Therefore, those who hope to receive signals from space, in response to any transmission coming from our atmosphere, appear very opti- mistic: such signals would need to come from more advanced technological civilizations than ours, located on planets less than 50 light-years away from the Earth. Within that distance, there are about 1,300 star sys- tems, containing 1,800 stars, and this already tells us that many of them are double or multiple systems, not particu- larly ideal environments for life as we know it. The same is true for more than half of the single stars, those belonging to spec- tral classes other than G and K. Around thirty planets have so far been discovered around all these stars, and only a dozen of them are in habitable zones (where liquid water can exist in the surface), orbiting stars that cannot guarantee stability for the long evolution of life. The true number of Earth-sized plan- ets in habitable zones within 50 light-years is estimated to be a few hundred, but the vast ma- jority of those are hosted by red dwarfs, thus uninhabitable by our standards. However unlikely as only few other things could possibly be, let’s assume that there is at least one other civilization in the Earth’s radiosphere capable of receiving and interpreting our broadcasts; it is probable that it has formed an awful opin- ion of humans. Why would it ever want to come into contact Life in the cosmos — From biosignatures to technosignatures Life in the Cosmos offers a thorough overview of the burgeon- ing field of astrobiology, including the salient methods and paradigms involved in the search for extraterrestrial life and in- telligence. Manasvi Lingam and Avi Loeb tackle three areas of interest in hunting for life “out there”: first, the pathways by which life originates and evolves; second, planetary and stellar factors that affect the habitability of worlds, with an eye on the biomarkers that may reveal the presence of microbial life; and finally, the detection of technological signals that could be indicative of intelligence. Aliens — Science asks: Is there anyone out there? Do Aliens Exist? And if they do — what would they look like? Where would they live? Would they be conscious beings? And what would happen if they found us? These are the biggest ques- tions we’ve ever asked - and here, Professor Jim Al-Khalili, theo- retical physicis, blasts off in search of answers. Coming with him are Martin Rees, Ian Stewart, Louisa Preston, Monica Grady, Sara Seager, Paul Davies and a crack team of scientists and experts who’ve made it their life’s work to discover the truth. Lively, curi- ous and filled with scientific insights fresh from the cutting edge of the Galaxy, Aliens is the perfect book for anyone who has ever looked up into the starry sky and wondered: are we alone? Strange new worlds Renowned astronomer Ray Jayawardhana brings news from the front lines of the epic quest to find planets —and alien life— beyond our solar system. In this book, Jayawardhana describes the latest findings —including his own— that are challenging our view of the cosmos and casting new light on the origins and evolution of planets and planetary systems. He reveals how technology is rapidly advancing to support direct observations of Jupiter-like gas giants and super-Earths —rocky planets with several times the mass of our own planet— and how as- tronomers use biomarkers to seek possible life on other worlds. Communication with extraterrestrial intelligence This book highlights the most recent developments in SETI discussed at that conference, emphasizing the ways that SETI has grown since its inception. The volume covers three broad themes: First, leading researchers examine the latest develop- ments in observational SETI programs. Second, both proponents and opponents of “Active SETI” debate whether humankind should be transmitting intentional signals to other possible civi- lizations, rather than only listening. Third, constructive proposals for interstellar messages are juxtaposed with critiques that ask whether any meaningful exchange is possible with an independ- ently evolved civilization.