Transcript How to Build a Planet

How to Build
a Planet
Dr. Will Briggs
Computer Science
Lynchburg College
How to build a planet:
1.
2.
3.
4.
What are your goals?
What kind of star system?
What kind of planet?
What kind of beings?
Goals
Human life
Alien home world
• temperature ~70°F
• 1 atmosphere pressure
• liquid water
• free oxygen
• only small variations
...it may not be easy to convert an uninhabitable
planet; we don’t know
?
What your alien life will need
If it’s machine “life,” all bets are off; if not:
• Complex molecules
• A solvent
A good basis for complex molecules:
Anything in column 4.
A good basis for complex molecules:
Anything in column 4.
...but the lighter (upper) elements are more
common.
...along with this “backbone” you’ll need
other elements to make interesting
molecules
...when it makes a difference, we often find
that earth life took the easiest route
Solvents
Polar
• water
• alcohol (rarer)
• ammonia
Nonpolar
• methane
• nitrogen
• helium
Nonpolar liquids tend to require lower temperatures
To get the temperature ranges:
• pick a world you know allows it
(Earth; Titan)
• check the CRC Handbook of
Chemistry and Physics (too much work
I think)
“Oh, be a fine girl, kiss me right
now, sweetheart!”
O B A F G K M R N S
brightest
biggest
hottest
short-lived ()
RARE
the Sun
common
dim
small
cool
long-lived
common
“Oh, be a fine girl, kiss me right
now, sweetheart!”
O B A F G K M R N S
EXCEPTION: when a star is old, it expands and turns
red (“red giant” phase).
Only B-type??? or higher can go supernova
...and how many?
2 or 3 stars per system is common.
Maximum insolation =
sum over both stars
Minimum insolation
approximately = that
of brighter star
Tight binary
...and how many?
Minimum insolation = insolation from primary.
Maximum insolation = insolation from primary +
insolation from companion at closest approach.
Loose binary
Trojan relationship
Planet stays in an
equilateral triangle
with two stars, 60°
before or behind.
Drawback: it seems
unlikely this much
stuff could collect at a
"Trojan" point -- but
then we've never seen
a binary up close.
Making the solar system
In our solar system, the inner planets are
roughly evenly spaced; each outer planet is
about twice as far out as the previous.
Others --?
Three ways to set up geography
• Venus: Gaussian distribution of elevations
• Mars: A few really huge features dominate
the landscape
• Earth: Plate tectonics. Almost all the earth
is at ocean-bottom level or sea level. If you
draw a map, make the continents look like
they fit together!
Stability
If there’s no large moon, the axis will wobble
a lot
Is there a lot of junk in the system -- without a
Jupiter to vacuum it up? You’ll get a lot of
comet strikes
Some think comet strikes are needed for
evolution; I don’t
Climate
• If you don’t have oceans, CO2 won’t
dissolve, and you get runaway greenhouse.
• Planets where it doesn’t get colder as you
get higher are apt to lose water
Climate
• If you don’t have oceans, CO2 won’t
dissolve, and you get runaway greenhouse.
• Planets where it doesn’t get colder as you
get higher are apt to lose water
Weather
• East of cold currents in subtropical zone ->
desert
• Extreme inland -> desert (sometimes)
• Equator -> wet
• Ice ages may depend having an arctic ocean
surrounded by land:
Weather
Thing about aliens is, they’re alien
...and this one isn’t.
Similar functions can make for
similar bodies . . .
WALKERS:
... or not.
SWIMMERS:
Now, THIS is an alien.
ALIEN!
ALIENS
Your alien life will have no mammals, no
“avians,” no grass
It will instead have types unique to your world
Good luck naming them if you don’t know
Latin!
Earth life has common themes:
backbones, flowers, mitochondria
(There are relatively few because of
mass extinctions -- most body types
died out)
Now an example of mine ...
...and an example of yours!