Quote:
Originally Posted by ardeegee
No offense meant, but I would suggest that you learn some science before you start trying to write science fiction. Not knowing that the size of the planet doesn't determine the spin of it's axis and that a planet "three of four times the size of the Earth" would have "about the same gravity" means that you lack the knowledge to make an even remotely plausible science fiction world. Stick to calling it "magic." (I don't demand that Terry Pratchett explain how a flat world on top of a elephants on top of a turtle works.)
A friend of mine happened to have crunched the numbers for a terrestrial planet of 3 Earth-masses just a few months back after a press release about a possible exoplanet discovery (which may or may not have been an anomaly in the data.)
The relevant section:
" 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 as the Earth, only more so? Nope,
more of the same is definitely not the same.
If the Earth were bigger, 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 and
bigger Earth.
Since the solid crust of a larger "Earth" would be
much thinner, heat transfer to the surface much faster,
vulcanism much livelier, plate tectonics much zippier.
This "Earth" has a diameter 1.40 times that of our Earth:
11,200 miles across. It would have twice the surface area,
2.75 times the volume, and 3 times the mass (compressibility
squishes). It's surface gravity would be 51% greater. If the planet
is four Earth masses, its diameter would be 1.58 times the
Earth's without accounting for compressibility and about
1.50 to 1.53 Earth radii squished. Its surface gravity would
be 73% greater than the Earth's, in that case.
But I'll continue to calculate based on three E-masses...
Because it would have 3 times the water but only two
times the surface, the average ocean depth would be about
4500 meters! The pressure at the depths of these oceans
would be about 9000 atmospheres. The highest mountains
possible would be about 4000 meters (calculating from the
median diameter), so if you were the greatest mountain
climber on this Super Earth, standing on the top of Super
Earth's highest mountain, you would still have 500 meters
of water above you!
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 Super Earth would be about 60 km thick, but
the lithosphere would only be about 40 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 Super Earth's silicate crust would be
recylced very rapidly with lots of local vulcanism and lots of
"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.
So a bigger Earth is not just a bigger Earth. Knowing that
somebody will ask how much bigger a bigger Earth has to be
before there's no land at all, just oceans, the answer is:
somewhere between 2-1/2 and 3 Earth masses is the point
where the median ocean depths equal the height of the
highest possible mountain.
Whoops! No continents. This Super Earth is a WaterWorld!
Possibly very few islands. That's serious. It means "No Surfing,"
because there's no land for the waves to break on. It's almost
certain that it would have more water than our Earth, because
the star is metall-poor (see below)."
http://www.mail-archive.com/meteorit.../msg90546.html |
If every fiction writer and movie maker had to be a master of their project's genre we would have very few pieces of fiction entertainment. If facts are wanted then I would suggest documentaries.
We all have questions, even the experts.