Subject:
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Re: The "geography" of local space
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Newsgroups:
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lugnet.space
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Date:
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Tue, 23 Nov 1999 12:01:22 GMT
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Viewed:
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1033 times
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Greetings, Earthilings.
Mr L F Braun wrote:
> "John J. Ladasky Jr." wrote:
>
> > This thread just keeps going and going!
>
> Hey, it's a good thread.
>
> > > "John J. Ladasky Jr." wrote:
> > >
> > > > We don't know yet whether such planets actually exist! In recent years, you may
> > > > have been hearing in the news that planets have been discovered orbiting other
> > > > stars. ...
> > >
> > > Apparently they actually got occlusion readings from a near star in the
> > > last week--by "near" I'm talking ~40pc. I can find the article and the
> > > star name, but it's one of the HDs (that narrows it down to several hundred
> > > thousand objects....;) ).
> >
> > Right. Lindsay is referring to HD 209458. Catchy name, huh? 8^)
>
> Dangnab frickin' frackin' million-and-fifty-two catalogues...
At least there's a pretty well-done on-line cross reference to the common catalogs now. Paul Baulch was kind enough start me down the road to finding this. I know that I mentioned it before, but here's the URL again for good measure:
http://cdsweb.u-strasbg.fr/Simbad.html
[snip more discussion of HD 209458's possible planet]
> Nice incitation effect there. It does seem that an intensity change of over 1.5% ought to be detectable again! Given (as you said) that a perfect lineup of their ecliptic to us is a real needle-in-a-haystack sort of thing, I'd say that
> criticality is warranted.
It's not as rare an event as it might seem: NASA is considering a space astrometry mission that would survey thousands of stars for minute drops in light intensity, i.e., planetary transit events. Their web pages even discuss the statistical odds
of seeing transits, and the odds are suprisingly far from zero. Check out the Kepler mission:
http://www.kepler.arc.nasa.gov/
Still, it's disappointing that they weren't able to get that second transit. Follow that DejaNews link that I gave you, and you'll read a report from one of the astrometry team scientists. He reports that they went for the press release because
the constellation Pegasus, which contains HD 209458, was crossing into the daytime sky and they wouldn't have many opportunities to view it until next spring. The idea was to get someone with good seeing conditions to get a fix on it before
observations became impossible. It appears that only one transit event was able to be observed. Confirmation will need to wait until next year.
> Also, wouldn't you think that a planet of three Jupiter masses (almost certainly a gas giant) that circles a star in 3.5 days would be *very* malformed--vaguely teardrop-shaped if in tidal lock, perhaps even more flattened than Jupiter if not?
Actually, the predicted mass of HD 209458's companion is 0.63 Jupiter masses -- still pretty large. Yes, there has been a lot of discussion about the odd shape that this body must assume. They feel pretty confident, however, that all the mass of
the planet is inside the Roche limit, and so there's no mass siphoning off of the planet to the star.
> > [snip material on E Eridani's flareness/get to the companion stuff]
>
> It's something that I remember from a while back--might be from the heady days of raw hypothesis. I haven't studied in any systematic manner in many years, I'm afraid.
>
> > e Eri, a.k.a. HD 22049, a.k.a. HIP 16537, is on this list. They state confidently that
> > the stars listed have no bodies orbiting them that are larger than three Jupiter masses.
>
> Then I'll take that as definitive, but I wouldn't be surprised if something much less than 33.5 Jupiter masses is circling it.
Less than three Jupiters, you mean? Sure, I'll buy that. Oh, that Doppler report I quoted also said something about the upper limit of the period of that three-Jupiter mass body, too -- something like 12 years? So, if there's a three-Jupiter
mass orbiting with a period of, say, 50 years, it will have been missed.
> > Now, how about 61 Cygni? For starters, it's a double star system. The two stars are spectral types K5 and
> > K7. As I mentioned above, I placed my cutoff, somewhat arbitrarily perhaps, at spectral type K4. Synonyms
> > for 61 Cygni A include HD 201091 and HIP 104214. This star is listed as a "variable of BY Draconis type."
> > Now, I don't know the details about this type of variable star. Do you? However, the visual magnitude of 61
> > Cyg A was observed to vary from +5.16 to +5.85 by Hipparcos. Other variable measurements are
> > references. This is nearly a two-fold variation in intensity. That didn't sound too hospitable to life to me.
>
> I think the designation "BY Draconis type" simply means that it's like BY Draconis because it's (they're?) roughly the same spectral type (K7e?) as BY Draconis. Burnham's says "Elliptical Variable" for BY but doesn't give detailed notes of it as
> a "type star."
>
> I guess your arbitrary cutoff isn't so odd here--but I wonder if, bearing in mind the stability of the variability cycle, life couldn't adapt to changes in energy output--it would be a weird system of living, but not an impossible one. Were the
> cycles variable, however, I'd be a lot less forgiving. :) The tidal-lock issue is harder to pass by, however. I think it could go either way--I've always been of the mind that planets' rotational motion will tend to decrease unless you whack it
> at an angle with another marble (asteroid or planetoid); there's more drag closer in towards a star so tidal locking happens sooner.
I want to say three things here.
First, I think that the whole point of these parameters -- star not too dim so that the planet is not tidally-locked, the output of the star is reasonably constant, and the planet's orbit is reasonably circular (we haven't talked about that one,
yet) -- is to maximize the odds for liquid water to exist on the surface of a planet, over a large area and over a long period of time. All of the chemistry of life, as we understand it, requires liquid water.
Second, on the basis of that, I guess I'll back away from my insistence that a TWO-fold variation in light intensity automatically discounts a system as habitable or capable of nurturing the formation of life. After all, Earth has day and night.
Even tidal locking doesn't necessarily rule out liquid water on the surface of an appropriately-located planet. Theoreticians are still working on this one. On a planet with little convection, all the water would freeze into a permanent ice cap on
the night-time side of the planet. If there was enough convection, there might be a narrow habitable zone with liquid water near the terminator, flanked by glaciers in the darkness, and deserts towards the permanent noon-time site located directly
under the planet's sun.
Third, I want to make a distinction between places that can harbor indigenous life, and those which technologically-minded humans might colonize. I think that, if we had the technology to send humans to the stars, we would also have the means to
turn any blasted rock we might encounter into a home. On a planet orbiting a M-class red dwarf flare star, we might be living underground in pressurized tunnels, but we would be able to do it. (Personally, I would need a darn good reason for
living that way!)
> > 61 Cygni B, a.k.a. HD 201092, a.k.a. HIP 104217, is much more stable in its output.
> > However, it has a spectral type of K7, as I mentioned, so it wasn't included on my list.
> > A K7 star is about 1/10 as bright as our own Sun, so a planet that would receive an
> > equivalent amount of light as Earth would have to be located about 100 times closer >than the Earth is to the Sun. That's tidal-locking distance, I would guess.
>
> Isn't there a bit of trivia (or urban legend?) that, devoid of environmental cues, the human body operates on a 25-26 hour cycle, hinting at a different speed of rotation at some seminal (pun perhaps intended) moment?
Have you seen the time stamps on my posts? Isn't it clear that I'm presently living my life completely devoid of environmental cues? 8^) Oh, yeah, for your information, I'd love a 28-hour day.
Seriously, there was a study where a fellow spent a few months in a cave, with only radio communication to a monitoring team on the surface. The cave-dweller had things to do, but no set schedule or clock. This was a deliberate part of the
experimental design. He was told to stay awake as long as he wished and sleep as long as he liked. His cycles definitely trended longer than 24 hours, though some "days" were as short as 18 hours and one went as long as 48, as I recall. The
research team was French, and the study was documented (and possibly sponsored in part) by National Geographic. I don't know if that's enough for you to track down the study.
'Till next time,
--
John J. Ladasky Jr., Ph.D.
Department of Structural Biology
Stanford University Medical Center
Stanford, CA 94305
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Message is in Reply To:
 | | Re: The "geography" of local space
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| (...) Hey, it's a good thread. (...) Dangnab frickin' frackin' million-and-fifty-two catalogues... (...) Nice incitation effect there. It does seem that an intensity change of over 1.5% ought to be detectable again! Given (as you said) that a (...) (25 years ago, 22-Nov-99, to lugnet.space)
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