|Habitable Zone around a Red Dwarf star|
...the circumstellar distance at which surface temperatures allow liquid water to be present on the planet’s surface, assuming variable H2O/CO2/CH4 greenhouse forcings. The Habitable Zone has a minimum and maximum extent, forming inner (closer to the star) and outer boundaries that are set in part by biogeochemical climate feedback mechanisms and stellar luminosity.
If a planet has the right conditions and resides within the Habitable Zone, life still has to appear and evolve in some sort of sequence. Taking Earth as the only example we have,
... this stepwise progression began with the origin of life, continued through the transition from replicating molecules to RNA and then DNA [1B years after Earth formation], from prokaryotes to eukaryotes [1.5 to 2.5B yrs after Earth formation] and cell differentiation [3.5 to 4B yrs after Earth formation], and concluded with the ﬁnal step from primate to human societies [4.54B years after Earth formation].However, if just one of these steps takes a lot longer, there is a drastically lessen chance of having enough time to develop intelligent life similar to humans; assuming the march toward more intelligent creatures is inherent to the process of evolution on different planets. Different stars may also extend or reduce the time-frame within which life may appear and develop. Larger stars will have short Habitable Zone lifespans. Smaller stars, such as Red Dwarfs may have very long and stable Habitable Zone lifespans.
Of course, a lot of this is based on assumptions that life on other planets will resemble life that formed on Earth. Maybe life of different kinds exist in the Universe. The rules may be different for different kinds of life. Maybe Earth is extremely unusual. Worse, maybe we will not be able to immediately recognize other forms of life simply because it is so different from our experience. As more information is gathered, these issues will hopefully be addressed.
Andrew J. Rushby, Mark W. Claire, Hugh Osborn, and Andrew J. Watson. Astrobiology. September 2013, 13(9): 833-849. doi:10.1089/ast.2012.0938, Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars.
- Limited lifespan of Habitable Zones around other stars [and a loosely held secret finally revealed about me]
- Small stars may have stable Habitable Zones, but habitable planets might not be common there
- Habitable Planets around White Dwarfs
- Habitable Worlds Around Binary Star Systems might not match Sci-fi
- How many Earth-like planets are orbiting Sun-like stars?
- First round of life in the Universe might have been possible extremely early
- Factors a planet needs for suitability of life; perhaps
- "Goldilocks zone of metallicity" on a galactic scale
- Maybe we are the first