[{"id":159,"title":"Sulfur-Bearing Polycyclic Aromatic Hydrocarbons in Interstellar Environments","sha":"c910680b94a3558d7ca47a4fe2046c4a","user_id":555,"state":"published","body":"Polycyclic aromatic hydrocarbons (PAHs) are widely studied in an astrophysical context. Studies have also been performed on nitrogen-bearing PAH species ([Hudgins+2005](http://adsabs.harvard.edu/abs/2005ApJ...632..316H)) and unsuccessful searches have been performed for interstellar nitrogen-bearing PAHs ([Ali-Haïmoud+2015](http://adsabs.harvard.edu/abs/2015MNRAS.447..315A)). Laboratory irradiation of ices containing aromatic hydrocarbons has recently been found to produce oxygen and nitrogen heterocycles ([Materese+2015](http://adsabs.harvard.edu/abs/2015ApJ...800..116M)), though previous astronomical searches for such heterocycles have proven unsuccessful ([Charnley+2005](http://adsabs.harvard.edu/abs/2005AdSpR..36..137C); [Dezafra+1972](http://adsabs.harvard.edu/abs/1972ApL....10....1D); [Kutner+1980](http://adsabs.harvard.edu/abs/1980ApJ...242..541K)). \r\n\r\nHowever, astrochemical studies on interstellar sulfur are quite neglected. Sulfur heterocycles have received little astrochemical attention, despite having been detected inside meteorites ([Krishnamurthy+1992](http://www.sciencedirect.com/science/article/pii/001670379290015B); [Sephton+2002](http://rsta.royalsocietypublishing.org/content/363/1837/2729)). Thiophenes are expected to be stable at interstellar medium (ISM) temperatures ([Guillemin+2010](http://adsabs.harvard.edu/abs/2010cosp...38.3235G)). Observed sulfur depletion does not follow the same pattern as other elements in dust grains ([White+2011](http://adsabs.harvard.edu/abs/2011AAS...21812923W)), and small sulfur compounds like H₂CS are detected in outflows where they are expected to form into more complex species ([Minh+2011](http://adsabs.harvard.edu/abs/2011ApJ...737L..25M)).\r\n\r\nGiven that sulfur and carbon have similar electronegativities and both have extensive chemistries, it is logical to consider heterocyclic sulfur-bearing PAH molecules in astrochemical studies, both experimentally and observationally. Vibrational wavelengths are expected to fall in the 6-9 µm region and at longer wavelengths, where it is well known that many observed emission bands are still poorly understood, with several unidentified or tentatively assigned lines remaining.","created_at":"2015-05-01T10:08:28.636Z","updated_at":"2015-05-14T21:28:20.848Z","zenodo_id":28346,"doi":"http://dx.doi.org/10.5281/zenodo.17292","subject":null,"tags":["astronomy","astrochemistry","molecular astrophysics","sulfur","hydrocarbons","pahs","interstellar medium"],"vote_count":2,"view_count":1,"score":2.1,"deleted":false,"muted":false,"tweeted":true,"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}]