[{"id":73,"title":"Extragalactic radio sources as lighthouses for SETI","sha":"be48a68df1c2b616f413017a9138c386","user_id":62,"state":"published","body":"The search for extraterrestrial intelligence (SETI) is one of the most ambitious scientific endeavors. It aims at detecting signals produced intentionally or unintentionally by extraterrestrial civilizations ([Siemion et al., 2013](http://arxiv.org/abs/1412.4867)). The Galaxy, however, is vast and finding suitable telescope targets for SETI is a critical task ([Turnbull \u0026 Tarter, 2003](http://iopscience.iop.org/0067-0049/145/1/181)).\r\n\r\nWe examine a strategy for selecting target areas for (active and passive) SETI aimed at improving chances for success.  The aim is to search for and/or send electromagnetic signals towards and/or from notable extragalactic radio sources.  Assuming that astronomy-wise civilizations are also involved in frequent multi-wavelength monitoring of conspicuous radio sources, the probability for interstellar observers to detect each other when observing in the same direction is increased. A similar idea was proposed by [Lemarchand (1995)](http://link.springer.com/article/10.1007/BF00982337) using Supernova 1987A.  However, radio sources are constant \"lighthouses\" and exist all across the sky.\r\n\r\nFor illustration purposes, we calculate that a signal emitted in a ~1 degree beam in the opposite direction of Centaurus A, could reach ~200 stars, mostly M-dwarfs, at distances \u003c600pc (stellar density model by [Gould et al., 1996](http://iopscience.iop.org/0004-637X/482/2/913)). Conversely if we search for ETI signals around Centaurus A, using the Allen-array (PFOV ~3 degrees, [Deboer et al., 2006](http://link.springer.com/article/10.1007/s10686-005-4193-3)), ~200 stars at distances \u003c300pc will be included in the field and the chance of detecting a message from a civilization using this strategy, is large.","created_at":"2015-02-20T00:46:47.737Z","updated_at":"2018-02-18T07:02:57.524Z","zenodo_id":23173,"doi":"http://dx.doi.org/10.5281/zenodo.15539","subject":null,"tags":["seti","astronomy","astrobiology"],"vote_count":8,"view_count":1,"score":8.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null},{"id":622,"title":"Want to be a Martian? Be a photoautotrophic man","sha":"384a6f535bef3e390fc784a5da396acc","user_id":null,"state":"published","body":"Being a Martian is not too far impossible. Now, scientists are looking forward to changing the Martian environment into a favorable state with the current advancement of the technology. Producing O2and food are predominantly seen challenges at present. All the available hypotheses in this are about changing Mars environment to get earth-like conditions. But, it would take ages to do that, maybe hundreds of years. For example, cyanobacteria had taken 2.7billion years to naturally change O2 content to a habitable level on the Earth. Here, we argue that with the available advancements of science today and perhaps years to come, the maximum, the humans would be able to do on the Mars in the future is to live inside a chamber with controlled conditions. But, no one would be able to be a real Martian who can walk freely on the Mars soil. Thinking outside the box, there is a great possibility for us to do that by getting ourselves changed a little bit to be adaptable to Martian conditions, which is much more achievable than changing a whole planet. Here, we suggest that by being photoautotrophic men, like the spotted salamander, we would be able to be real Martians.","created_at":"2019-09-20T05:02:35.743Z","updated_at":"2019-11-20T05:50:08.130Z","zenodo_id":3451528,"doi":"https://doi.org/10.5281/zenodo.3451528","subject":null,"tags":["mars colonization","martian","astrobiology","microbial biotechnology","endosymbiosis"],"vote_count":3,"view_count":1,"score":3.1,"deleted":false,"muted":false,"tweeted":false,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null},{"id":187,"title":"Supercritical Exoplanetary Atmospheres as Potential Habitats for Extraterrestrial Aeroplankton","sha":"e464b97c0ead0438ccb94a7abe9dbc85","user_id":null,"state":"published","body":"An increasingly familiar class of exoplanets amongst those being continually discovered is the \"Super-Earth\" ([Valencia+2007](http://iopscience.iop.org/0004-637X/656/1/545/)), with a mass intermediate between Earth and Neptune. These have been found inside habitable zones ([Udry+2007](http://www.aanda.org/articles/aa/abs/2007/27/aa7612-07/aa7612-07.html)) and likely have dense atmospheres ([Lopez+2014](http://iopscience.iop.org/0004-637X/792/1/1), [Lammer+2012](http://mnras.oxfordjournals.org/content/430/2/1247)). With sufficient atmospheric pressure and temperature, these atmospheres are likely to enter a supercritical fluid phase with properties intermediate between gas and liquid. Supercritical fluid phases are typically considered for gas giant interiors ([Trachenko+2014](http://journals.aps.org/pre/abstract/10.1103/PhysRevE.89.032126)) or water oceans ([Elkins-Tanton+2008](http://iopscience.iop.org/0004-637X/685/2/1237)), though any gas or liquid can form such a phase. For example, an Earth-like atmospheric composition will enter a supercritical phase at T \u003e 132.6 K and p \u003e 37.21 atm. This pressure is significantly lower than the ≳300 atm ([Koschinsky+2008](http://geology.geoscienceworld.org/content/36/8/615)) experienced by life on the abyssal plain of Earth's oceans ([Rona+1986](http://www.nature.com/nature/journal/v321/n6065/abs/321033a0.html)). It is therefore possible for Earth-like life to tolerate the pressure-temperature conditions of a supercritical atmosphere. \r\n\r\nIn Earth's atmosphere, microbes have been found airborne as \"aeroplankton\" ([Sharma+2007](http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8817.2007.00373.x/abstract)) and living microbes have been found at high altitudes ([Sattler+2002](http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=894204)), prompting planetary atmospheres to be considered as astrobiological targets ([Smith2013](http://online.liebertpub.com/doi/abs/10.1089/ast.2013.1074)). A denser atmosphere can support a greater number density of suspended particles, raising the possibility of aeroplankton ecologies in the dense supercritical atmospheres of Super-Earths.","created_at":"2015-07-07T08:44:34.680Z","updated_at":"2015-07-09T06:00:38.431Z","zenodo_id":35174,"doi":"http://dx.doi.org/10.5281/zenodo.19667","subject":null,"tags":["astrobiology","exoplanets","microbiology","fluid dynamics","astronomy"],"vote_count":0,"view_count":1,"score":0.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null}]