What is Habitable zone: Definition and 21 Discussions

In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. The bounds of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the CHZ and the objects within it may be instrumental in determining the scope and distribution of planets capable of supporting Earth-like extraterrestrial life and intelligence.
The habitable zone is also called the Goldilocks zone, a metaphor, allusion and antonomasia of the children's fairy tale of "Goldilocks and the Three Bears", in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is "just right".
Since the concept was first presented in 1953, many stars have been confirmed to possess a CHZ planet, including some systems that consist of multiple CHZ planets. Most such planets, being either super-Earths or gas giants, are more massive than Earth, because such planets are easier to detect. On November 4, 2013, astronomers reported, based on Kepler data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way. About 11 billion of these may be orbiting Sun-like stars. Proxima Centauri b, located about 4.2 light-years (1.3 parsecs) from Earth in the constellation of Centaurus, is the nearest known exoplanet, and is orbiting in the habitable zone of its star. The CHZ is also of particular interest to the emerging field of habitability of natural satellites, because planetary-mass moons in the CHZ might outnumber planets.In subsequent decades, the CHZ concept began to be challenged as a primary criterion for life, so the concept is still evolving. Since the discovery of evidence for extraterrestrial liquid water, substantial quantities of it are now thought to occur outside the circumstellar habitable zone. The concept of deep biospheres, like Earth's, that exist independently of stellar energy, are now generally accepted in astrobiology given the large amount of liquid water known to exist within in lithospheres and asthenospheres of the Solar System. Sustained by other energy sources, such as tidal heating or radioactive decay or pressurized by non-atmospheric means, liquid water may be found even on rogue planets, or their moons. Liquid water can also exist at a wider range of temperatures and pressures as a solution, for example with sodium chlorides in seawater on Earth, chlorides and sulphates on equatorial Mars, or ammoniates, due to its different colligative properties.Thus, the term Goldilocks Edge has also been suggested. In addition, other circumstellar zones, where non-water solvents favorable to hypothetical life based on alternative biochemistries could exist in liquid form at the surface, have been proposed.

View More On Wikipedia.org
  1. Nik_2213

    Oxygenating a 'primordial' atmosphere...

    Imagine a generic terrestrial planet in potentially hab zone around a generic mid-K star. No life as yet, carbon dioxide about 15% of atmosphere and nitrogen 75%, so significant 'greenhouse' effect. Mild tectonic cycle. Cool enough for hydrological cycle: Clouds, rain, rivers, seas, lakes etc...
  2. xpell

    B At what distance would a Venus-like planet have a HZ temperature?

    Well... that: Please, could you please assist me in obtaining a rough estimate of the distance from the Sun at which a planet resembling Venus or a hypothetical Venus-like planet (for the sake of simplicity) would have a habitable-zone surface temperature? A "back-of-the-envelope" educated...
  3. S

    Stargazing Impact of Kepler Telescope Findings on the Drake Equation

    How much more refined are the various variables of the Drake Equation in view of the recent findings by the Kepler Telescope? I imagine fp and ne would surely be better estimates. Is there a study on this anywhere?
  4. S

    B Should we search for non-biological "life"?

    I am very interested in Astrobiology and just came across this 7-year old abstract by Seth Shostak (of SETI): http://www.sciencedirect.com/science/article/pii/S0094576510002195 There is a lot of emphasis on searching for biological life outside of our solar system, especially with the...
  5. P

    I The Sun's habitable zone and orbital resonaces/stability

    Let's say there's five Mars/Earth massed planets orbiting a star like the sun between 0.6 AU and 2 AU, what orbital resonance configuration can they be into ensure maximum stability? Would adding gas giants to the system enhance stability?
  6. C

    B Super-Earth Found in Habitable Zone of Nearby Red Dwarf

    The interview: John Batchelor Show The scientific paper: https://www.nature.com/nature/journal/v544/n7650/full/nature22055.html[/PLAIN] ]Nature and ArXiv The basic facts: Star Name: LHS 1140 Constellation: Cetus the Whale Distance from Sun: 41 light-years Star type: Red dwarf (much...
  7. Q

    I Planetary Orbits in AU - Stability & Mass Limits

    All of the planets should have individual orbits, and should be between the mass of Mercury and Mars. What can their orbits be in AU's? Is there a way to find out how close they can be without destabilizing each other? If we assume the star is about the same size as Sol.
  8. GW150914

    I Why do we need "planetary equilibrium temperature"?

    I mean, currently it seems that scientists are using equilibrium temperature of exoplanets (calculated assuming an Earth-like albedo) to determine whether a planet is habitable or not. But aren't there other more accurate ways to determine surface temperatures of exoplanets? I learned Wien's...
  9. L

    Range of Earth's year within habitable zone?

    Hi all, So the (hypothetical) question I have is about the range of the Earth's length of orbit (number of days) within the Sun's habitable zone which could sustain human life. I.e. what would the length of the shortest 'habitable' year be, and the longest (in days)? What would our living...
  10. RooksAndBooks

    New Closest Earth-like Planet (20/12/15)

    Welcome to my thread. As you have seen from the title, scientists have just discovered a new potentially earth-like planet; it's the closest to us. It's four times the mass of the Earth and it's only 14 light years away. The planet is called Wolf 1060c. Read more about it here. What do you...
  11. JohnPrior3

    Death of Sun: Habitable Zone & Timeline

    So I am working on making a simulation that shows the habitable zone of our solar system from now until our sun reaches the end of it's red giant phase. The sun will die when it is 10 billion years old and will reach the end of the red giant stage at 5 billion years. I know the habitable zone...
  12. C

    Galactic Habitable Zone Theory: A Physiologist's Inquiry

    I'm a physiologist, not in anyway well-versed in physics beyond what I took as a pre-medical student. Forgive any lapses in proper vocabulary or wording of my inquiries. I have a question about the habitable zone theory. Not so much this...
  13. reenmachine

    Earth-sized exoplanet spotted in star’s habitable zone

    http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/index.html#.U1BUR1csSuQ Don't know if this is the right section to post this , but I'm a sucker for any news on exoplanets so here goes.
  14. D

    Habitable zone for binary star systems

    Does anyone know which type of orbit is most likely to result in habitable worlds in a binary star system -- a planet orbiting one of the two stars, or orbiting both of the stars, or are they both very likely/unlikely? Wikipedia quotes a paper that simulated binary stars and found that 50-60%...
  15. W

    Exploring the Habitable Zone: Limits and Possibilities for Detecting Alien Life

    What are the inner and outer limits of the habitable zone in distance for the sun?
  16. mrspeedybob

    How to keep the earth in the habitable zone

    This article speaks of the Earth leaving our solar systems habitable zone in a billion years or so. I would like to propose a serious discussion of what we, as a species, can do about it. A billion years is a large amount of time, but the scope of the problem is also very large. One...
  17. H

    AU and the Circumstellar Habitable Zone

    Hi, I'm an IB math student trying to begin my mathematics project and I just have a really basic question: I'm trying to simulate some orbits within the Circumstellar Habitable Zone (the zone in which a planet can sustain liquid water) and I know that this zone exists from .725 AU to 3.0 AU...
  18. Orion1

    Habitable zone planet discovered

    http://fastcache.gawkerassets.com/assets/images/8/2011/09/xlarge_hd85512btop.jpg HD 85512 b Reference: [PLAIN]http://en.wikipedia.org/wiki/HD_85512_b"
  19. R

    Least massive earth like planet possible in the habitable zone?

    I mean the smallest, lowest mass, and/or lowest g terrestrial planet that can hold onto and support a favorable atmosphere for potential life, and is in the zone where water can exist as a liquid. I'm really asking: what's the smallest "Earth" possible? I heard that the upper limit for...
  20. F

    Exploring the Habitable Zone and Tidal Lock in Exoplanet Systems

    I am new and would like some help. I have two questions for a shout out. 1) I need some info to help detirmine the Habitable Zone of a paticular star. I think that JF Kasting propsed some kind of equation but I can't find anymore info on it. I don't really need the equation per say just data...
  21. marcus

    How much of the Milky Way is within the Galactic Habitable Zone?

    A recent paper by three Australian astronomers http://arxiv.org./abs/astro-ph/0401024 It has a bearing on Fermi's Question "Where are they" -----quote from the abstract------- "We modeled the evolution of the Milky Way to trace the distribution in space and time of four prerequisites...