Results 1 to 17 of 17

Thread: Habitable zone

  1. #1
    Join Date
    Nov 2004
    Posts
    1,534

    Habitable zone

    The habitable zone around a star is defined by the range of orbital distance within which liquid water can exist on a planet.

    However, both Mars and Venus in our solar system exist roughly within the Suns habitable zone but neither has liquid water. We are told both had liquid water in the past.

    It would seem to me that both edges of the habitable zone experience runaway effects that get rid of any liquid water on the planet. Are the processes likely to occur on any planet? If so, the idea of a habitable zone might have to be rethought slightly.

    Another thing I'm wondering, is that Earths rotation rate is unusual for a planet in this position because of the presence of the moon. Would a normal planet sitting where we are suffer either of the fates of Mars or Venus?

  2. #2
    Join Date
    Sep 2005
    Posts
    96
    Dont' know about the last question your asking.

    But the processes one, maybe, but it will also largely depend on the planet's characteristics(mass, atmosphere, land/water ratio,etc...), also the surrounding area (density of the dust in space) may block some of the suns' rays.

    As a planet thats about same mass as Earth or most likey more massive than the Earth it will be able to retain its atmosphere in either the outer zone of the habitable area if its' active or has a higher water to land ratio. On the opposite side it will be able to retain the water vapor and produce a very humid, jungle type planet. We dont' know if Venus's atmosphere is caused by a runaway greenhouse effect or something happened to it in the early life of the solar system.

    But the closer a planet will get to these the harder it will be for life to start.

  3. #3
    Join Date
    Sep 2003
    Posts
    3,237
    We need details on quite a few solar systems before we'll know the answers for sure.

  4. #4
    Join Date
    Sep 2002
    Posts
    10,438
    I heard it once said that if Mars and Venus were to swap orbits, there would be three comfortably livable planets in this system. I think the term habitable zone is something of a logical fallacy, since the conditions for which liquid water would need to exist depend as much on the moake up of the planet as they do on the distance from the star.

    I also think the term's a little anthropogenic, since its also referenced from the point of view of habitability for human life (or Earth life, more generally). We're now seeing signs of liquid water in quite inhospitable locations for Earth life on Europa, Eceladus, and possibly Ganymeade, brought on by tidal forces resultant from the gravitational pull of the primary planet.

    So, to my eyes, the concept of a "habitable zone", per that definition, is a little dated.

  5. #5
    Join Date
    Apr 2005
    Posts
    1,553
    <<Another thing I'm wondering, is that Earths rotation rate is unusual for a planet in this position because of the presence of the moon. Would a normal planet sitting where we are suffer either of the fates of Mars or Venus? >>

    The moon has SLOWED DOWN the rotation of the earth. Without it, the day would be shorter and the day-night temperature fluctuation would presumably be less.

    In many ways that would make the planet MORE liveable, not less. I don't know what the effect of shorter days would be on the daily weather and overall climate, that's one for the experts.

  6. #6
    Join Date
    Jul 2005
    Location
    Pontoise France
    Posts
    1,936
    Quote Originally Posted by kzb
    <<Another thing I'm wondering, is that Earths rotation rate is unusual for a planet in this position because of the presence of the moon. Would a normal planet sitting where we are suffer either of the fates of Mars or Venus? >>

    The moon has SLOWED DOWN the rotation of the earth. Without it, the day would be shorter and the day-night temperature fluctuation would presumably be less.

    In many ways that would make the planet MORE liveable, not less. I don't know what the effect of shorter days would be on the daily weather and overall climate, that's one for the experts.
    Yes but without the moon the inclinaison of Earth would vary wildly and within rather short periods. Life would have to adapt to frequent drastic changes of climate.

  7. #7
    Join Date
    Apr 2005
    Posts
    1,553
    <<Yes but without the moon the inclinaison of Earth would vary wildly and within rather short periods>>

    I've seen this a lot recently, about the moon stabilising the earth's inclination, but no other planet has such a relatively large satellite (except pluto), and we don't see them tumbling out of control.

    Anyway, a bit of climatic instability isn't enough to wipe out life, in fact it would drive it on to evolve and advance. It may be the ice ages were crucial in driving early man to advance technology in order to survive the harsh conditions.

  8. #8
    Join Date
    Jul 2005
    Location
    Pontoise France
    Posts
    1,936
    Quote Originally Posted by kzb
    <<Yes but without the moon the inclinaison of Earth would vary wildly and within rather short periods>>

    I've seen this a lot recently, about the moon stabilising the earth's inclination, but no other planet has such a relatively large satellite (except pluto), and we don't see them tumbling out of control.

    Anyway, a bit of climatic instability isn't enough to wipe out life, in fact it would drive it on to evolve and advance. It may be the ice ages were crucial in driving early man to advance technology in order to survive the harsh conditions.
    Astronomers agree there is a lot of variation on Mars : The more common values for obliquity are : from 15 to 35.5 with a period of 1.2 x 1,000,000 years. Venus is a complete mystery. Mercury i dont know. Big planets have all a lot of big satellites. Uranus is also a mystery.

    About the consequences , you may be right

    http://www.nhm.ac.uk/research-curati...arameters.html

  9. #9
    Liquid water cannot exist in too thin or too thick of an atmosphere. The Habital Zone is a lie.

  10. #10
    Join Date
    Jan 2003
    Posts
    5,245
    Well, it should be noted that water isn't necessarily a requirement for life.

    Quote Originally Posted by William_Thompson
    The Habital Zone is a lie.
    Why?

  11. #11
    Join Date
    Jul 2004
    Location
    Phoenix, AZ
    Posts
    590

    A Myth?

    Quote Originally Posted by galacsi
    Yes but without the moon the inclinaison of Earth would vary wildly and within rather short periods. Life would have to adapt to frequent drastic changes of climate.
    How do we know this is so? Mars and Venus do not have any moons anywhere approaching the size of Luna but they do not seem to suffer any wild variations.

    I've seen this assertion numerous times, but have never seen an explanation that explained Earth, Venus and Mars.

    Maybe we should stop repeating this until the assertion is backed up with evidence, theory and includes an explanation of these apparent exceptions.

    Bob

  12. #12
    Join Date
    Jul 2005
    Location
    Pontoise France
    Posts
    1,936
    Quote Originally Posted by William_Thompson
    Liquid water cannot exist in too thin or too thick of an atmosphere. The Habital Zone is a lie.
    I agree with Wolverine : Why ? Do you think the limits are badly defined or do you challenge the idea itself ?

  13. #13
    Join Date
    May 2003
    Posts
    2,458

    Extra solar planets/systems

    Does anyone find it curious that all/most of the extra solar planets thus far discovered are "hot Jupiters"; ie. planets that orbit their parent stars at extremely close proximity. What of the systems where we don't detect anything at all? I'm betting that these systems are the real interesting ones because the systems with "nothing" detected so far are likely the ones that are more like our own. It's just a matter of time before an instrument that is sensitive enough with detect planets like our own.

  14. #14
    Join Date
    Jan 2005
    Posts
    2,819
    ^
    I'm willing to be that we could detect plenty of "regular Jupiters"; however, their long orbital periods mean that astronomers will have to wait a long time to get a solid, confirmable measurement. The time we've been studying various stars with high-accuracy radial velocity techniques hasn't been half a Saturnian year, for instance.

  15. #15
    Join Date
    Sep 2003
    Posts
    3,882
    Mars is small and relatively far from the Sun:

    => its inner core has solidified

    => its magnetic field has decayed

    => the solar wind has eroded its atmosphere

    => it surface atmospheric pressure has dropped

    => liquid water cannot exist on the surface of Mars.

    If Mars was bigger or closer to the sun its inner core might still be liquid and it could sustain liquid water....

  16. #16
    Join Date
    Dec 2002
    Location
    Nashville, TN
    Posts
    1,483
    Quote Originally Posted by Damburger
    The habitable zone around a star is defined by the range of orbital distance within which liquid water can exist on a planet.

    However, both Mars and Venus in our solar system exist roughly within the Suns habitable zone but neither has liquid water. We are told both had liquid water in the past...
    Both Mars and Venus are outside the CURRENT habitable zone (Mars just slightly), which is 0.95 AU to 1.37 AU for a roughly earth-like planet.

    Venus is at 0.72 to 0.73 AU and Mars is from 1.38 to 1.66 AU.

    Also there's a difference between the current momentary HZ and the long term or continuously HZ. Earth's long term HZ is considered 0.95 AU to 1.15 AU, at least according this research paper: http://tinyurl.com/bfaj6

    http://www.nasa.gov/111384main_BHabitableZone1.TIF
    http://www.solstation.com/habitable.htm

    Just because a planet is within the HZ doesn't mean it can support life. For example earth's moon is within the HZ and it's very hostile to life. Rather being within the HZ is only one enabling factor of many required to support life.

  17. #17

    Habitable zone is more narrow than once thought:

    Habitable zone is more narrow than once thought:

    http://www.bautforum.com/showpost.ph...&postcount=964

Similar Threads

  1. Is There a Methane Habitable Zone?
    By Fraser in forum Universe Today
    Replies: 0
    Last Post: 2011-Nov-15, 01:20 PM
  2. Habitable zone calculation
    By Extrasolar in forum Space/Astronomy Questions and Answers
    Replies: 8
    Last Post: 2011-Nov-02, 10:56 PM
  3. Habitable zone
    By patrick in forum Space/Astronomy Questions and Answers
    Replies: 3
    Last Post: 2009-Apr-10, 08:32 PM
  4. Wdith of the Sun's habitable zone?
    By Grashtel in forum Space/Astronomy Questions and Answers
    Replies: 5
    Last Post: 2008-Nov-04, 10:51 AM
  5. Martian habitable zone:
    By marsbug in forum Life in Space
    Replies: 14
    Last Post: 2008-Oct-02, 06:50 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
here
The forum is sponsored in-part by: