Extrasolar planets and their moons

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Pishkapa, Feb 3, 2005.

  1. Pishkapa Registered Member

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    5
    So a thought just occured to me... whenever I read something or see something on television about extrasolar planets and they usually being gas giants, typically the point of view taken by the writer/reporter is that life cannot exist on these planets unlike 'terrestrial' ones which would indicate more of a hope for extraterrestrial life. However, looking at the Titan pictures (although I do know that those are methane seas I'm seeing) I was thinking - Has anyone taken into account the moons that typically surround these gas giants and the potential for life on them?

    Like if we take the two big gas giants in our own solar system Jupitar and Saturn and put them in the position of the Earth in relation to the sun, wouldn't at least one of those moons have optimum conditions for supporting life? Wouldn't Europa and Ganymede have at least some kind of life with their water/atmosphere?

    Is there any research going on into this? I've been looking on the net but haven't come up with too much. What kind of factors would rule out life on these moons? Would constantly going around to the dark side of the planet diminish the chances of sunlight kick-starting life? I know these planets give off their own heat so wouldn't that heat compensate for the loss of sunlight?

    Sorry for the barrage of questions but I'm having a 'bout of insomnia and the question kept me up all last night wondering.
     
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  3. invert_nexus Ze do caixao Valued Senior Member

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    Don't understand what you mean by research. Gas giants are the only planets easily found because they're massive enough to cause a wobble in the star. I think that they've also begun looking for planets by the dimming and brightening of stars due to planets passing in front of them relative to us. And I think that this method is able to find smaller planets although I'm not sure how many have been discovered this way.

    Anyway, considering the fact that an Earth-size planet is almost imperceptible, a moon orbiting a planet would be even more so.

    I don't think there's any doubt that life can exist on a moon given the proper conditions. The question is what are the proper conditions. What are the boundaries within which life can exist? It's possible that life may exist in our own frozen moons. We don't know. Life may exist practically everywhere, you may not be able to keep life down.

    But, there can be no research into life on moons surrounding extrasolar gas giants as we have no means of examining them. We can barely examine the moons surrounding our own gas giants. Europa and Titan being prime examples of this.

    I imagine that there might be simulations that might track weather and climate on a moon orbitting a gas giant that is relatively close to it's star. It would be a more complex climate than a planet, I think I'm safe in saying that. But, in the absence of far more sensitive equipment all that we can do is conjecture. Not research.

    By the way, never apologize. It turns people off.
     
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  5. Maddad Time is a Weighty Problem Registered Senior Member

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    The only extrasolar planets we've seen so far have been the hot Jupiters because that's what we capable of seeing. It doesn't matter if terrestrial-sized objects are out there or not; we can't see them if they are.
     
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  7. blobrana Registered Senior Member

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    2,214
    Hum,
    You may be intrested to know that the search for double transit planetary systems, (by looking at the light curves of stars with confirmed planetary companions), has recently found one around OGLE-TR-111.

    Photometric measurements and radial velocities were consistent with the presence of a second planet. That would make it, if confirmed, the first extrasolar planetary system detected by transits.

    The parameters of the possible new planet OGLE-TR-111c are:
    period P= 16.0644 days
    semimajor axis a = 0.12 AU
    orbital inclination i = 88-89 deg
    mass M = 0.7 M_Jup
    radius R = 0.85 R_Jup
    density \rho = 1.4 g/cm<sup>3</sup>.

    OGLE-TR-111c would be the smallest and densest extrasolar planet measured todate, a hot shorter period Jovian planet, with properties intermediate between Jupiter and Saturn.

    So still a way to go...
     
  8. Ophiolite Valued Senior Member

    Messages:
    9,232
    Interesting questions pishkapa. Some thoughts off the top of my head.

    Since most of the planets discovered so far have been substantially larger than Jupiter we might expect one of two things:
    a) Either the moons are going to be substantially larger, because the large gravity well is pulling more material into the planet's range,
    or
    b)The moons are going to be smaller and less numerous, because the planets attracts planetesimals to itself rather than to its orbit.
    [The former seems to me more likely, but this is based on supposition, not evidence.]

    If it is the latter, this would be bad news for life. Unless the moon is approaching Earth sized it will be unable to hold an atmosphere. (The only reason Titan has one is that the temperatures out at Saturn are very low.)

    Jupiter and to a lesser extent Saturn, both have powerful magnetic fields. These trap severe radiation levels that would inhibit the development of life.

    The large gravity well would attract many comets and residual asteroids. (Think Shoemaker-Levy.) At least some of these would impact with the 'terrestrial' moon - and we know what happened to the dinosaurs. With a much higher frequency of such impacts life might never have enough time to recover.

    So, a first look at your scenario suggests it would not be a very promising one for either the origin or maintenance of life. (That said, I'm sure one could think up a dozen reasons why it would be beneficial!)
     
  9. eburacum45 Valued Senior Member

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    1,297
    A number of people have been looking into this question; here is an interesting summary of the work done so far.
    http://skyandtelescope.com/resources/seti/article_255_1.asp

    of course it is all speculation at the moment; but the examples in our own solar system are useful guides.

    The worst problem with an Earth-like moon of a large gas giant would be the extent of the giant's magnetic field, and the ionising radiation that gets trapped in it. Titan is largely outside of Saturn's relatively weak field; any moon with a biosphere similar to that on Earth would need to orbit well outside the gas giant's magnetic field.

    Oh and a bonus image from Orion's Arm; - Silence

    Please Register or Log in to view the hidden image!

     
  10. Starthane Xyzth returns occasionally... Valued Senior Member

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    1,465
    The prospect of Earth-sized moons around epistellar giant planets does vastly increase the potential number of biospheres in the galaxy. Consider: red dwarfs, with average luminosities only a few percent that of our Sun, are by far the most numerous type of star. A planet close enough to such a star for liquid water to exist on its surface would be subject to overwhelming tidal effect, which would synchronise its rotation: one hemisphere would be baked dry and the other permanently frozen, rendering the planet inhospitable (except for a narrow Twilight Zone...

    Please Register or Log in to view the hidden image!

    )

    BUT - if the planet were a giant, its satellites would be tidelocked to it, not to the star. Therefore, a moon of a warm red-dwarf jupiter could have day & night just like Earth does, and be suitable for life - with very little UV to worry about, either. Not to mention that, with the minimal stellar wind of a red dwarf sun, the primary planet's magnetosphere probably wouldn't accumulate such intense radiation belts as those of our familiar Jupiter & Saturn.

    Photosynthesis might be less efficient there, having only red wavelengths to work with... it could still manage, I'm sure :m: ; and not all Earthly ecosystems require photosynthesis.
     
  11. Ophiolite Valued Senior Member

    Messages:
    9,232
    Interesting point on the tidal lock. I hadn't thought about that.
    On the negative side, very few of the giant planets have low orbital eccentricity. There orbits are probably not stable in the order of billion of years. This instability would potentially throw the Earth like world out of orbit, or lead to routine movement into and out of the habitable zone, or lead to a permanent move out of the habitable zone.
    All of this will be much easier to assess once we have refined the planet detection methods to the point where we can pick up terrestrial sized worlds and can therefore get a better idea of the composition and geometry of stellar systems, not just be aware of a single planet.
    Again, I can envisage microbial life being common in this scenario, but I think advanced life might have a tough time of it.
     
  12. Starthane Xyzth returns occasionally... Valued Senior Member

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    Yes, it's been widely theorised that the hot-jupiter type planets must have migrated inward to their close orbits after forming much further from the star, where the primordial nebula would be cold enough to allow accretion of volatiles. During its inward spiral, a giant planet would almost certainly absorb or eject any smaller planets forming thereabouts (or it might just capture them as satellites).

    Any suitably-placed terrestrial planets orbiting further from their star than a hot jupiter would have to be formed AFTER it had migrated inwards, or move to their orbits from somewhere else.
     
  13. blobrana Registered Senior Member

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    2,214
    Hum,
    Yeah, there is speculation that a nearby supernova caused the `peculiar` orbits of Jupiter and Saturn, and planetoids like Sedna....
    The evidence comes from recent discovers in meteorites of patterns of isotopes that can only have been caused by the radioactive decay of iron-60, an unstable isotope that has a half life of only a million and a half years.
    Iron-60 can only be formed in the heart of a massive star and thus the presence of live iron-60 in the young Solar System provides strong evidence that when the Sun formed a massive star was nearby...

    So 4.5 billion years ago the early Solar System would have been located in something similar to the present-day Eagle or Trifid nebulas.
    There is no doubt that the shockwave and the amount of radioactive material injected into the young solar system by the nearby supernova might have profoundly influenced the formation of the solar system and ultimately the habitability of the Earth...
     
  14. Ophiolite Valued Senior Member

    Messages:
    9,232
    blobrana I am unfamiliar with this work. Do you have any references? It sounds interesting and if valid points up again the very slim odds that were met to establish viable life on our planet.
     
  15. eburacum45 Valued Senior Member

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    Don't forget that practically every star is thought to be formed in a nebula of this sort, and most remain in a cluster for hundreds of millions of years; during that time the largest stars explode within the cluster, so it would be commonplace for young stars and planetary systems to be exposed to supernovae. After forty or fifty million years there would be no more big stars to explode, so the incidence of nearby supernovae would rapidly fall off.
     
  16. Maddad Time is a Weighty Problem Registered Senior Member

    Messages:
    251
    Remember that life fills the box you give it. If you're around a red dwarf, the life that evolves thrives on infrared and would be more vulnurable to ultraviolet. If it evolves in the vicinity of a more massive star then live comes to depend on that ultraviolet.
     
  17. Starthane Xyzth returns occasionally... Valued Senior Member

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    Who knows... perhaps the Sun was originally the smaller member of a wide binary system, with the larger star going supernova within its first 100 million years? There might now be an ancient neutron star just a few light-weeks away, long cooled to the point of invisibility, sharing a multi-million year mutual orbit with the Sun. It might be this dark counter-Sun which periodically disrupts the Oort Cloud and causes mass extinctions here on Earth; and it may still be attended by the frozen cinders of its own planets.
     
  18. Communist Hamster Cricetulus griseus leninus Valued Senior Member

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    3,026
  19. Starthane Xyzth returns occasionally... Valued Senior Member

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    1,465
    From the article you link, none of the 5 new discoveries involves satellites of an exoplanet. Details as follows -

    These planets were discovered by Doppler spectroscopy, measuring the periodic red & blue shifts in the spectra of their parent stars. That method can, by defintion, only provide the orbital period, eccentricity, and minimum possible mass of the planet. Any moons it will have can can only contribute their own gravity to the overall effect of the planet, and their presence cannot be inferred directly.

    However - the last planet on the list, HD 99492 B, is a particularly exciting find simply for its low minimum mass. If its orbit is at a low inclination relative to our line of sight (which could be confirmed if the planet actually transits its star), it is small enough to be more like Uranus or Neptune than Jupiter. This is a whole new class of extrasolar planet!
     
  20. blobrana Registered Senior Member

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    2,214
    HUM,
    no i haven`t....(i forgot where i put them)...

    <a href="http://mysite.wanadoo-members.co.uk/blobrana/news/explosion.html"> see!</a>
     
  21. Starthane Xyzth returns occasionally... Valued Senior Member

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    Nice link, Blobrana - did you write it yourself, or part of it?

    I was wondering about the iron-60 isotope that article refers to. What is its half-life? All the Earth's iron would have been released by supernovae originally, of course, though probably formed in the massive, ancient stars as a final phase of core burning BEFORE detonation. Are there theoretical reasons for assuming that iron-60 can only be formed in an actual supernova explosion, along with all the elements heavier than iron?
     
  22. Communist Hamster Cricetulus griseus leninus Valued Senior Member

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    3,026
    Actually I just linked the Planetquest site, not an article. The article is just on the main page. Try looking around.
     
  23. eburacum45 Valued Senior Member

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    I think Communist Hamster is referring to the recent discovery of a singleton brown dwarf with satellites/planets;

    a brown dwarf can sometimes occupy an orbit around a larger star and resemble a planet, so if they are by themselves in deep space are they planets or stars?
     

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