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

Tue Jun 14 03:45:17 EDT 2005

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
------------------------------------------
"Sterling K. Webb"  wrote:

> Hi, All,
>
>     The "Marcy  Team," with 106 detections of extra-solar planets to its
> credit,  announced today number 107, the discovery of the smallest yet
> detected  (by about half the previous detection),  It's only 7.5 (+/-
> 1.5)  Earth masses.  It orbits Gliese 876, an M-class dwarf about
>  one-third the mass of our Sun and only 15 light years away.  We're
>  practically neighbors...
>
>     The planet is  close enough to its star to be pretty warm (200 to 400
> degrees C).   In theory, it could be a hot mini-Uranus, but Marcy seems
> to think it's  a rocky terrestrial world since it would be hard to hang
> onto all that  gas at 200 degrees C or more.  If confirmed, it would be
> the first  detection of an Earth-like world outside the Solar  System.
>
>     Gliese 876 had already been  discovered to have, not one, but two
> Super Jupiters orbiting further out  than the new discovery.  If the new
> planet is a rocky terrestrial  world, it seems to me to be more likely to
> be a "Super Venus" than a  "Super Earth"!
>
>     The kind of star these  planets orbit, M-class, are the most abundant
> class of stars, far more  numerous than the larger K-class and the even
> larger G-class (that's  us!).  M class stars are all over the place.  We
> have more M  class neighboring stars (within 10-20 light years) than all
> the other  kinds put together.  If M class stars can have terrestrial
> planets  close enough to be warm, then we may be sailing along in a cloud
> of  Earths!
>
>     Here's the National Science  Foundation press release:
>  <http://www.nsf.gov/news/news_summ.jsp?cntn_id=104243&org=NSF&from=news>
>
>      And a somewhat less technical one:
>  <http://skyandtelescope.com/news/article_1530_1.asp>
>
>  Sterling K.  Webb

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