A beautifully told story with colorful characters out of epic tradition, a tight and complex plot, and solid pacing. -- Booklist, starred review of On the Razor's Edge

Great writing, vivid scenarios, and thoughtful commentary ... the stories will linger after the last page is turned. -- Publisher's Weekly, on Captive Dreams

Monday, April 16, 2012

For Some Values of "Unique"

The lead for an article on extrasolar planets runs:
HD 10180—a sunlike star in the southern constellation Hydrus—may have as many as nine orbiting planets. 
And concludes with the following quote from the study leader:
"So [our] solar system is only one example among a spectrum of different planetary systems we will find in the near future and [is] definitely not unique."
-- study leader Mikko Tuomi, astronomer at the University of Hertfordshire
Let us ponder this.

What is HD 10180 system like?  The star lies about 127 ly distant and cannot be seen north of the tropics.  It is a G1-V star, not unlike the Sun.  Its mass is about 1.06S, its diameter 1.20S, and its luminosity 1.49S.  Its elemental abundance (exc. H and He) is 1.20 times the Sun.  Its estimated age is 7.3 bya, making it 60% older than the Sun.  It is a stable star but with no significant magnetic activity.  So: older, fatter, brighter, but not putting out.

There were five planets identified previously, two additionals confirmed by the reanalysis, and two new possibles also identified in the reanalysis.  This makes a total of nine planets. 

  1. HD 10180 b.  Hot Super-Earth.  Mass: 1.4 Earths.  Distance: 0.02 AU (one-seventh the distance of Mercury, and from a hotter, bigger star).  Orbit: 1.1 days.
  2. HD 10180 c.  Hot Neptune. Mass: 13 Earths (comparable to Uranus), likely a gas giant. Distance:  0.06 AU (still closer than Mercury).  Orbit: 5.7 days
  3. HD 10180 i.  Possible Hot Super-Earth.  Mass: 1.9 Earths.  Distance:  0.09 AU (still closer than Mercury).  Orbit: 9.6 days
  4. HD 10180 d.  Hot Neptune.  Mass: 11.9 Earths (somewhat smaller than Uranus), likely a gas giant.  Distance: 0.13 AU (still closer than Mercury!).  Orbit: 16 days. 
  5. HD 10180 e.  Hot Neptune.   Mass:  25 Earths (ca. 1.5 Neptunes; 0.25 Saturn).  Distance: 0.27 AU (just a little closer than Mercury).  Orbit: 49.8 days.  
  6. HD 10180 j.  Possible Hot Super-Earth or gas dwarf.  Mass: 5.1 Earths.  Distance: 0.33 AU (about the distance of Mercury).  Orbit: 68 days.  
  7. HD 10180 f.  Hot Neptune.  Mass: 24 Earths (ca. 1.5 Neptunes; 0.25 Saturn).  Distance: 0.49AU (beyond Mercury, but not near Venus).  Orbit: 122 days. 
    "tight and wild orbit is analogous to that of Mercury, with a similar black body temperature range, though with its immense mass, any greenhouse effect caused by an atmosphere would give it searing Venus like or greater temperatures." 
  8. HD 10180 g.  Gas giant.  Mass: 21.4 Earths (ca. 1.25 Neptunes).  Distance: 1.4 AU (Just short of Mars).  Orbit: 596 days. 
    "fully within the system's predicted habitable zone, though it does not fit the current models for planet habitability.  Due to its large mass, it is likely to be a Sudarsky Class II gas giant. there is a possibility that a natural satellite with sufficient atmospheric pressure could have liquid water on its surface."
  9. HD 10180 h.  Saturn-size Gas Giant. The largest and outermost known planet in the sytem.  Mass: 65 Earths (2/3rd Saturn).  Distance: 3.4 AU (comparable to outer part of asteroid belt). 
That is, it packs into a space smaller than the solar distance to the outer asteroid belt no less than seven and possibly nine planets, five of which are between Neptune and Saturn in size.  No less than six of them -- incl. three "hot Neptunes" -- orbit within the orbit of Mercury.

So what are we to make of Prof. Tuomi's assertion that this shows that "[our] solar system ... [is] definitely not unique."  A fine example of the Copernican Syndrome.   He can only mean that it is not unique in being a solar system; but it certainly seems so far that it is unique in terms of its make up.  That is, it does not differ in matter, but surely does in form.  And as we all know, it is form that imparts powers to matter.

There have been 763 extrasolar planets discovered in 611 solar systems, 101 of which contain multiple planets.   Can anyone think of any manner in which our solar system remains unique among them?


  1. This stellar system contains temporarily ambulatory bags of chemical in an aqueous solution which vociferously assert that there is no objective value nor objective morality ... and that it is wrong (onjectively immoral) and stupid (objectively unworthy) to claim otherwise.

  2. Ah, but there's something more important here! The gentleman implies that our solar system contains nine planets, not eight!

    Mwahahah! Pluto Lives!

    PL PL PL

    (Yeah, I did a report on Pluto once. Not that I'm bitter about the reclassification or anything.)

    1. I am bitter. Henry Wentworth Akeley is bitter. Lensmen Nadreck of Palain VII.

    2. It was an IAU **rump** session [in Prague -- wasn't that a clue? Looking for astronomical solidarity in a country that couldn't even stick with Slovakia!], done without a proper quorum and the rest of the membership were too louche to rise against the infamy of the decision by repealing it.



  3. I remember reading (last year I think, maybe the year before) about a planet that had the media gushing about how they had discovered a planet about the size of earth within the "habital zone" of a star and how it may contain life etc. *gush* *gush* more etc.

    As an afterthought they mentioned that it was tidally locked!!!! (for those reading who don't know that means it doesn't rotate on its own axis...a minor problem if you're claiming it could sustain life)

    And then they decided it might not exist (despite a stunning artists impression) as it was still to be verified.

    1. [small correction: a tidally locked planet/moon does rotate on it's axis. Rotation period = revolution period, leading to one face always showing to primary.]

      I wonder if anyone has done a story of an actual non-rotating planet? Is such a planet even theoretically possible?

  4. The difference is: most of our hot balls of gas have academic degrees.

  5. We're not sure that they've invented solipsism in any of them?

  6. I noticed comments have been closed on a different thread. Was that deliberate? I wanted to ask you a few questions, but I don't want to be rude. Also, if you prefer to end a discussion with me, or have me stop posting in a thread, just say so. I won['t be offended, and this is your blog, so you make the rules.


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