[meteorite-list] OT: New Smallest, Possibly Earth-like, Extra-Solar Plane...

[Sterling K. Webb]

Hi,

    My example of a SuperEarth was based on taking the same materials (bulk
composition) as the Earth is made from and just piling more of them together.  We have
no idea (and no way of knowing, for now) if the planetesimals of the Gliese 876 system
were the same mix as the Sol planetesimals, but we think the raw materials of solar
systems are generally similar.
    When I started suggesting the loss of some water so we could have continents and a
higher albedo so it would be cooler and so forth, you were being treated to an ugly
display of a rational mind crumbling under the pressures of "interstellar optimism,"
the desire to improve things just a touch.
    After all, planetary systems have unique histories.  The Earth picked up this
whonking huge Moon to stabilize its axis and its climate though blind luck at
incredible odds.  Mars got all these volariles (we think) but then got its atmosphere
stripped off and died.  Venus really got a dirty deal; don't know what it was, but it
was nasty.  Them's the breaks.
    It does make it look like there's more planetary bad luck than good luck, doesn't
it?  I'm sure we all wish Europa well!  And I have a soft spot in my head for Titan.
Always have had...
    The interstellar "optimists" tend to think of extra-solar worlds as similar to what
we know, but 50-60 years ago the interplanetary "optimists" tended to think of solar
worlds as more Earth-like than they turned out to be.
    As a teenager in the early Fifties, I devoured every scientific book on other
planets that there was, and the picture they presented was rosy compared to reality,
The very best book on Mars, "The Physics of the Planet Mars," by the great Gerald de
Vaucouleurs, was translated in English in 1953, a substantial tome filled with
equations, graphs, and tables.  I special ordered it, and it was damned expensive.
    It presented a Mars with an atmospheric pressure of 100 to 200 millibars and 85
degree F. noonday temperatures.  All the astronaut would have to do was slip on flight
mask with a 10 pound oxygen tank on his back and go for a stroll.  He could leave his
leather jacket and white scarf back in the rocket because it's comfortable weather out
there, at least in the daytime.
    The notions of Venus were rosier still.  It seems that the less you know, the
happier the picture you get.
    Here's the kind of paradox that arises from "happy" thinking.  Venus gets twice as
much solar energy as the Earth.  But the albedo (reflectivity for those of you
listening in) of Venus is more than twice that of the Earth (as we estimated the
Earth's albedo in those days), so Venus shouldn't be any warmer than the Earth (and a
few brave souls even suggested it was cooler, with big polar ice caps)
    In the 1940's, Rupert Wildt measured huge fat CO2 absorption features in the Venus
spectrum and concluded that Venus was a waterless inferno as hot as hell's hinges.
What he got for his suggestion was a lot of scowls and being ignored for a decade or
so.  Other scientists (big names and I ain't saying who) measured H2O bands,  They were
dead wrong about the water, because the water they were measuring was in the atmosphere
of Earth, not Venus!  Who knew?
    So, Venus was maybe a little warm, very wet, always cloudy but bright, kind of like
the Permian had been on Earth.  Venus was so remarkably like the Earth on paper that
everyone figured it was the twin it appeared to be.  Probably had oxygen under those
clouds,  Get out of the spaceship, wear good boots (it was bound to be muddy), and keep
an eye out for Venusian dinosaurs.
    I'm not talking about science fiction writers here; I'm talking about real
honest-to-gosh scientists.  We had gotten over Lowell and his canals on Mars, but not
by much.  Pickering was still talking about life on the Moon, for heaven's sake.
Although he had a great explanation for Martian canals: they were the migratory routes
of Martian herbivores, fertilized by their droppings.
    Tommy Gold had his own special heresy for Venus (doesn't he always?), an ocean of
hydrocarbons, an idea that would get picked up from Venus and moved to Titan for 30 or
40 years.  Ain't there.
    You don't suppose wishful thinking has anything to do with the notion of a
planetary body with oceans of gasoline, do you?  Nah...  Sorry, no oceans of free
gasoline.  You can leave the SUV at home, buddy.
    In some ways, science fiction writers could be more realistic than scientists in
those days.  Hal Clement (Harry Stubbs) wrote two novels about life on a SuperJupiter
around 61 Cyngi which are better pieces of rigorous thinking about these really alien
worlds than any scientific work that had been done on the question.  He made me think
about eutectic melts of ammonia and water in all its complexity until my head really
hurt. Of course, in those days, no one was doing scientific work on the question.
    Turns out the SuperJupiter around 61 Cyngi is really there!  Along with scores of
other SuperJupiters around other stars.
    Even more fascinating is the possibility of other kinds of stars.  We have always
assumed that the tiniest faint dink of an M9 star is as small as "stars" get.  Less
mass and you get essentially non-luminous bodies:  brown dwarves, very brown dwarves,
and black dwarves.
    But 2MASS (the Two Micron All Sky Survey) turned up huge numbers of very, very
faint stars never seen before, too faint to be seen in visible light.  About twenty of
them have been assigned on their spectral characteristics to a new class of stars: the
Class L main sequence stars. About six are brown dwarves.  Since 2MASS only sampled a
very small patch of sky chosen at random and since their low emission sets a limit to
how far away we could detect these faintest of all stellar objects, we can calculate
their abundance.
    The astounding answer is that they are more abundant than the M Class stars that we
used to think were the most abundant, so much so that the likelihood is that there are
about 2000 L Class main sequence stars within 50 light years of the Sun.  Yes, that's
2000 neighboring stars to our Sun that we can't even see in visible light!
<http://astron.berkeley.edu/~basri/bdwarfs/sec4.htm>
<http://astron.berkeley.edu/~basri/bdwarfs/sec6.htm>
    That's an average of about one such star per 260 cubic light years.  Hmmm... What's
the radius of a sphere with a volume of 260 cubic lightyears centered on our Sun?  It's
a shade less than the distance to the "nearest star," good old alpha Centauri.  I put
quotes around that phrase "nearest star" because, if 2MASS is right (and it seems to
be), there is a good chance there's an "invisible" star just as close or closer to the
Sun than that star we can see!
    Really big bright stars don't seem to have planets.  They gobble up all the planet
food and blow off the rest; it too energetic an environment for a solar system to form
in.  We used to think low-mass stars, like M class, wouldn't have planets because there
wasn't enough mass around, but the detections of extra-solar planets seem to indicate
that the formation of a less energetic star leaves plenty of material left over for
planets.  Little Gliese 876 has two SuperJupiters!
    So, following that line of reasoning, why wouldn't the new L Class stars have lots
of planets too?  Despite the fact that "happy" thinking would like alpha Centauri to
have planets because it's the closest, hence easiest, star to get to, no detection
attempt has ever found any hint of planets.  A closer L Class main sequence star with
planets would genuinely be worth looking for!
    But trying to find a nearby "invisible" star is a truly daunting technical problem
concerning which no light bulbs have turned on in my brain...  It's as dim in there as
the L dwarves themselves!


Sterling K. Webb
------------------------------------------------------
MexicoDoug at aol.com wrote:

> Hola Sterling,
>
> Your Super-Earth got me  thinking about viable life forms though I'm not yet
> too adjusted.  There  certainly will be continents, though they will be
> floating quagmires of life and  useful excreta, and will probably get quite thick.
> Easily enough to walk  on, despite those who worry about finding a surface on
> such gas-liquid giant  planets.  Not that walking will be too easy, so I guess
> you would need  bigger muscles to deal with that.  The interesting thing with
> such a world  is there would be several interfaces - multilevel continents -
> especially  suitable as anchors (surfaces) for life depending on the vertical
> profile of  gases and liquids present.  Gravity might be similar to that on
> Earth  believe it or not, or even less in some of the upper level continents
> since the  rarification will reduce the gravitational acceleration by the height
> squared  (If you are on a planet 8 times the mass of earth but at 2.8X the
> radius,  "surface gravity" is the same as Earth.)
>
> But you're right it would get  stuffy, so life would probably be pretty
> acuatic-like and evolution driven by  the rise to an upper or lower continent in
> addition to competition for low  hanging fruit resources.  There would probably
> be heavy development using  bouyancy, and things would probably fly in that
> fashion.  So the mosquitos  you would swat would land on you by regulating their
> body densities with  intestinal waste gas.  Yuck.
>
> Dense Ice would be at least down where  pressures (and depths) were at 3000
> atm, and very unstable given the dynamics of  the situation, it would be more
> like a cloud formation, as probably not to  present much of an issue.  But the
> sort of magnetosphere this planet would  have...could metallic hydrogen make
> it Earth-like?  Probably too  small.  It would be a pretty boring place, though
> as meteorites would not  be much less likely  than on the surface of ...
> Venus... so I guess these  water breathing nitrogen-fixing creatures would do
> something else for kicks  (Starlight would not be very plentiful - and we need a
> renewable energy source  or biosphere equilibrium with net energy going into
> support the net entropy  production of the system).
>
> What I wonder is how the higher forms would  generate and harness electricity
> for progress, considering the whole planet is  sounding rather grounded in a
> lightening sauna?  It would make for a hell  of a set of oceanmill farms
> working off the sea currents for anyone who could  come up with a good insulator...
>
> Saludos, Doug
>
> Sterling W.  wrote:
> Hi,
>
> Is this an all time high or an all time  low?  I'm replying to
> my own post (see below)!
> While I don't have the most recent edition, I dug out my copy of
> "Planetary  Engineers' Handbook" (Dresden, 15th Ed., 2314 AD) to
> investiigate the  characteristics of a "SuperEarth."  Here's what
> I  found:
> So, what would a SuperEarth be like? If you start  with the
> same recipe mix of ingredients as the Earth and just made  a
> bigger batch of planet, is it just the same, only more so? Nope,
> more of  the same is not the same.
> If the Earth were bigger, it  would retain more volatiles to
> begin with.  But in addition, the volume  of water would
> increase faster than the increase in surface area, so  the
> oceans would be deeper. Because of the deeper oceans and the
> greater  gravity, the pressures at the bottoms of those oceans
> would be much  higher.
> Continents and their mountains would be much  lower, because
> the temperatures in the crust would increase faster with  depth,
> until the fluid point would be reached in the crust instead of
> the  mantle like it is on "our" Earth. Mountains can only pile
> up until the  pressures under them are about 3000 to 3500
> atmospheres, and that zone would  be reached at shallower and
> shallower depths on a bigger  Earth.
> The solid crust of a larger "Earth" would be much  thinner,
> heat transfer to the surface much faster, volcanism  much
> livelier, plate tectonics much zippier.
> Imagine an  "Earth" exactly twice the diameter of our Earth:
> 16,000 miles across. It  would have four times the surface,
> eight times the volume, and 12 times the  mass (compressibility
> squishes). It's surface gravity would be 3 times  greater. The
> escape velocity from the surface would 2.45 times  greater.
> Because it would have 12 times the water but only  four
> times the surface, the average ocean depth would be about  9000
> meters! The pressure at the depths of these oceans would be
> about  3000 atmospheres. The highest mountains possible would be
> about 4000 meters  (calculating from the median diameter), so if
> you were the greatest mountain  climber on the SuperEarth,
> standing on the top of SuperEarth's highest  mountain, you would
> have 5000 meters of water above  you!
> Whoops! No continents. The SuperEarth is a  WaterWorld.
> On our Earth, the crust is about 30 kilometers  thick, but
> the lithosphere (rocks that stay stiff and not slushy  and
> slippy) is about 75 kilometers, so the Earth's lithosphere
> contains  all the crust and the top part of the mantle.
> The crust of  the SuperEarth would be about 90 km thick, but
> the lithosphere would only be  about 30 kilometers thick. This
> means that it would be very difficult to sink  pieces of crust
> (subduction) and equally difficult to bring deep basalt  magmas
> to the surface.
> On the other hand, the  SuperEarth's silicate crust would be
> recylced very rapidly with lots of local  vulcanism and
> "hotspots" and have a very similar composition everywhere.  The
> only weathering that would be possible would be chemical,
> because all  the volitiles are released into the oceans rather
> than the  atmosphere.
> The only question we can't answer is how hot  or cold a
> SuperEarth would be, since that depends on the distunce to  its
> Sun. Too far away and the oceans turn to ice, even Ice III,
> which  sinks instead of rising.  Wow, did you know that?.
> Too close and the oceans boil away, creating a
> SuperVenus. But I discover  that making a Super Venus is
> not as easy as it sounds.  It's very hard  to strip all that
> atmosphere and immense oceans of volatiles away from  a
> planet that has an escape velocity of 27,400 meters  per
> second!
> And remember, a SuperEarth would  have
> proportionately more volatiles than a puny little Earth
> like ours. It  could even afford to lose some of those
> 9000 meters of ocean, don't you  think?  Maybe
> enough to have continents?
> Its  immense atmosphere would have a very high
> albedo from a water cloud deck  100's of kilometers
> deep, and the surface temperatures could well be  below
> 100 degrees C.  Hmm, starting to sound interesting.
> (Originally  posted to the List 08-31-2004 in anticipation
> of the discovery of a  "SuperEarth," and Heck! I didn't
> even have to wait a year... What  next?)
>
> Sterling K.  Webb
> ------------------------------------------