S-type is the name for the orbit of a planet that revolves around just one of the two stars within a binary system. P-type is the name for the orbit of a planet that revolves around both stars within a binary system, having a common barycenter (or center of mass) with the suns as the suns orbit around each other.
S-type orbits are interesting, but for this article, I'll cover P-type because this is more interesting to me when talking about Habitable Zones, particularly where the suns have similar masses. Of course, even with p-type orbits, there exist many possible varieties for how the suns can orbit each other.
The ability of a planet to maintain liquid water depends on the interaction between stellar radiation and the top of its atmosphere. Also, that interaction is complicated in a binary system. There can be substantial difference in energy received by the dual suns. Sometimes both suns appear side by side in the sky, providing maximum energy. However, when one sun is eclipsed by the other, the amount of energy is lessened due to the closer sun blocking the stellar radiation from its partner.
In either case, this variation in stellar radiation can limit how small a planet's orbit can be around the dual suns and still be capable of harboring life. As stated in Calculating the Habitable Zone of Binary Start Systems II: P-Type Binaries:
This interaction strongly depends on the stellar spectral energy distributions implying that stars with different energy distributions will contribute differently to the absolute incident flux at the top of the planet’s atmosphere.Even with all of these factors, planet formation within the Habitable Zone of a binary system would be similar to that of a singular star system.
|Two suns of similar mass with elliptical orbits around a common barycenter|
| Two suns of similar mass in the same orbit around a common barycenter |
N. Haghighipour, L. Kaltenegger, The Astrophysical Journal, 777 (Nov., 2013) 166, arXiv:1306.2890 [astro-ph.EP], Calculating the Habitable Zone of Binary Star Systems II: P-Type Binaries
- 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