I came across the documentary http://watchdocumentary.com/watch/weirdest-planets-video_685ea1fd2.html "Weirdest planets". Fairly decent popular science about exoplanets. So, what about interesting features for exoplanets to make them truly unique? Here is one amusing idea I got from http://pipeline.corante.com/archives/2012/05/15/things_i_wont_work_with_... Stink Stink is simultaneously a treasure trove and deeply annoying. It is a terrestrial world, with a local ecosphere and transhuman-compatible atmosphere... almost. While Earth and most other terrestrial worlds have lost most of their surface selenium and tellurium early in their development Stink didn't. Instead these substances are part of the local biochemistry. For the most part they act as heavier analogues of sulphur, just like the rare selenium amino acids on Earth. Unfortunately many selenium and tellurium compounds *stink*. There are enough volatile compounds in the atmosphere to make it profoundly odorous - something between decayed leeks or garlic, burning rubber and sulphur. One explorer memorably described it as "like a robot farted". Getting any of the compounds into a biomorph body means that now that body will stink too. Synthmorphs do slightly better (and can turn off their sense of smell, if they have it) but tend to quickly pick up the odour from the environment anyway. In principle they can be cleaned when they return, but in practice it is easier to recycle them. Stink is still worth exploring thanks to the many intriguing biochemical pathways found in the biosphere. It is just that nobody will want to move material back from it into inhabited environments, just stacks and information.