How to Build a Planet

1. How to Build a Planet Dr. Will Briggs Computer Science Lynchburg College

2. How to build a planet: 1. What are your goals? 2. What kind of star system? 3. What kind of planet? 4. What kind of beings?

3. Human life 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 Alien home world Goals ?

4. What your alien life will need If it’s machine “life,” all bets are off; if not: • Complex molecules • A solvent

5. A good basis for complex molecules: Anything in column 4.

6. 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

7. Polar water alcohol (rarer) ammonia Nonpolar methane nitrogen helium Solvents Nonpolar liquids tend to require lower temperatures

8. 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)

9. O B A FGK M R N S brightest biggest hottest short-lived () RARE “Oh, be a fine girl, kiss me right now, sweetheart!” the Sun common dim small cool long-lived common

10. O B A FGK 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 “Oh, be a fine girl, kiss me right now, sweetheart!”

11. Maximum insolation = sum over both stars Minimum insolation approximately = that of brighter star ...and how many? 2 or 3 stars per system is common. Tight binary

12. Loose binary Minimum insolation = insolation from primary. Maximum insolation = insolation from primary + insolation from companion at closest approach. ...and how many?

13. 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. Trojan relationship

14. 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 --?

15. 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!

16. 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

17. 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

18. 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

22. 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:

23. Weather

24. ...and this one isn’t. Thing about aliens is, they’re alien

25. Similar functions can make for similar bodies . . . WALKERS:

26. ... or not. SWIMMERS:

27. ALIEN! Now, THIS is an alien.

28. 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!

29. Earth life has common themes: backbones, flowers, mitochondria (There are relatively few because of mass extinctions -- most body types died out)

30. Now an example of mine ......and an example of yours!