This is a fascinating article:
Excerpt of the start of the article:
Distinct days and nights have helped life flourish on Earth. But many alien worlds capable of supporting life may not have such clear delineations.
Do aliens sleep? You may take sleep for granted, but research suggests many planets that could evolve life don't have a day-night cycle. It's hard to imagine, but there are organisms living in Earth's lightless habitats, deep underground or at the bottom of the sea, that give us an idea what alien life without a circadian rhythm may be like.
There are billions of potentially habitable planets in our galaxy. How do we arrive at this number? The Milky Way has between 100 billion and 400 billion stars.
Alien worlds might not have a night and day. How would that change evolution?
Distinct days and nights have helped life flourish on Earth. But many alien worlds capable of supporting life may not have such clear delineations.
www.bbc.com