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Habitable Planets: Disaster Zones and Safe Havens

  1. Apr 6, 2005 #1

    Ivan Seeking

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    http://space.com/scienceastronomy/050405_earth_like.html
     
  2. jcsd
  3. Apr 6, 2005 #2
    They posted this article right after the "Five out five researchers agree solar system is special"...they changed their mind quick
     
  4. Apr 6, 2005 #3

    Chronos

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    It is also worth pointing out that most of the exosolar planets discovered to date are larger, much closer to the parent star, and have more eccentric orbits than jupiter. This should not be taken to suggest this is the norm for exosolar planetary systems, rather that these are the easiest to detect using current technology. It would be very reasonable to suspect many of the other ~1800 nearby sunlike stars could have jupiter sized planets in jupiter-like orbits. They have merely escaped detection because the wobble effect on the parent star is smaller and takes years to complete a cycle.
     
  5. Apr 6, 2005 #4

    turbo

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    Thank you for pointing this out, Chronos. Our detection technology is new and not very sensitive, so we will preferentially find the oddballs. It's the same with our detections of high-redshift objects. The brightest, most active objects will be preferentially seen at high redshifts, leading us to believe that objects at these redshifts are fundamentally different from objects in our own neighborhood. Selection effects are insiduous.
     
  6. Apr 6, 2005 #5
    So it is just detection bias.
     
  7. Apr 6, 2005 #6

    marcus

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    On the face of it I can see no contradiction

    the solar system can be considered special because it has a giant at distance 5 AU and nothing (except little stuff like earth etc) closer
    and it is stable with mostly circular orbits. This is unusual.

    most other systems found so far have giants much closer in, or giants in eccentric (oval) orbits, and we dont know they are even stable-----they may be in process of self-destruction from badly synchronized orbits.


    I am not talking Life/No Life probabilities. I think that is jumping off with premature excitement. Let's get interested in how planetary systems form and what the various abundances of the various types are, just like we study chemical elements and compounds, or other stuff scientists study


    For sure, if you have a system with a giant Jupiter planet as close in as Mercury, you can still SPECULATE there might be an earth size planet further out from the giant, at 1 AU. Might be or might not, who is to say at this point when we dont SEE earthsize planets? I think speculation like that is boring and it looks all to much like a way of keeping the pubic excited, The public seems only able to imagine alien life so you have to talk about earthlike planets to get their attention.

    [EDIT] the detection is adequate to pick up Jupiters at 5 AU. the distribution of what has been found does not simply reflect technical limitations. That is why Marcy shows the statistical distribution curve up front on his site. He is interested in it from way back.[/EDIT]
     
    Last edited: Apr 6, 2005
  8. Apr 6, 2005 #7
    But thats the whole point of Chronos and turbo-1's post, that we detect these Hot Jupiters with eccentric orbits because the method we use could only detect those kinds of planets (detection bias), a Jupiter/gas giant with its distance 5 AU or further might take longer to wobble its sun.

    EDIT: Who is Marcy?
     
  9. Apr 6, 2005 #8
  10. Apr 6, 2005 #9

    marcus

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    the eccentricity doesnt help, believe it makes it slightly harder, but circular orbits CLOSE IN are easiest because of short time

    however Marcy's site shows that a giant planet HAS BEEN DETECTED AT 5.6 AU

    this is part of a multiple system at the star 55 Cancer
    there is one giant at about 0.1 AU and another at about 0.2 AU and still another at 5.6 AU

    that also is weird by solar system standards, but also kind of normal looking becaus it has hot giants.

    Marcy and Butler have been the world leaders in this search since about 1996 when they verified a french team that was using the signal from a pulsar and then Marcy and Butler came out with a bunch of finds using the optical doppler wobble method they developed

    it has been become the main way exoplanets are found

    check out the website of marcy's organization. there are other good people but I heard him talk about this in 1996 and I'm a fan

    http://exoplanets.org/
     
  11. Apr 6, 2005 #10

    marcus

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    good article

    as I've said I don't doubt there are lots and lots of earthlike planets in the milkyway. but it is more interesting to look at the actual data than to speculate.

    here is what your article says:

    "...The solar systems that have been found so far, the ones that contain hot Jupiters or eccentric Jupiters, probably don't contain habitable Earth-like planets.

    The motions of these closer-in giants prevent terrestrial planets from forming stable orbits in the habitable zone. But a solar system with a large planet in a circular orbit at 5 AU - even a Neptune-sized planet - is a solar system in which a habitable Earth-like planet could exist quite comfortably..."

    Present technology can see a giant at 5 AU (eg 55 Cancer d)

    tho it is easier to detect ones closer in

    however the statistics are skewed towards giants very close in ("hot jupiters") above and beyond observational bias

    you can see this in the statistics on giants that have been found at 1-3 AU (as several have!)
     
  12. Apr 6, 2005 #11
    Well just because they found 3 or 4 gas giants at 5 or more AU doesnt mean they can detect it easily, doesnt it tell you something that they have only found one 5 AU (5.9) and four 4 AU's (4.5, 4.403, 4.26, 4.15) and the rest are below 4 AU. I got a feeling that there will be gas giants galore to discover that will be 5+ AU.
     
  13. Apr 6, 2005 #12

    Chronos

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    We can detect jupiters at 5 AU in circular orbits, it is just more difficult and takes longer. The bias in distribution that marcus has noted is entirely valid and strongly suggests hot jupiter configurations are common, and very likely prevalent. I only wished to add that jupiter configurations similar to this solar system can be expected to be under represented at present. And, as also noted by marcus, there is more popular interest in finding earth like planets. It's a good marketing tool come grant time.
     
  14. Apr 6, 2005 #13

    marcus

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    wait and see :smile:
    I think Chronos sounded the right note.
    BTW as someone who's speculated about exoplanets for a long time and is fascinated by the prospect of extrasolar life, I would be as delighted as anyone (as you I expect) were the search to come up with a lot of systems with one giant at 5 AU and none closer (tending to disrupt the habitable zone). If only further search does find Sol-like systems galore, to use your word.

    but the distributions curve that is taking shape already shows stuff that is not just observational bias, I would argue, and shows stuff people did not expect back prior 1996. we can learn from it, I think.

    So I do not now expect systems like the Sol planetary system to predominate, as a larger database accumulates. prior to 1996 I would have guessed, based on a kind of Copernican principle, that Sol system would turn out kind of typical or ordinary in certain ways. I dont expect that anymore.
     
    Last edited: Apr 6, 2005
  15. Apr 6, 2005 #14
    But do Hot Jupiters mean no habitable planet in that solar system?
     
  16. Apr 6, 2005 #15

    SpaceTiger

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    This question of the uniqueness of our solar sytem (and even more specifically, our planet) is very unanswerable right now, as was already mentioned. We're a long way from searching enough of parameter space to even define what "normal" is. Let's just settle on saying that the observations allow for both possibilities (normal and not). Any speculation about one or the other seems counter-productive.
     
  17. Apr 6, 2005 #16
    But dont you agree that the method we use right now to find planets is biased towards Hot Jupiters and eccentric orbits?
     
  18. Apr 6, 2005 #17

    SpaceTiger

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    Of course.
     
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