1. What if......the earth were a moon? Pandora (earth-like) Polyphemus (gas giant)

2. Formation of Polyphemus Has to take place in „Goldilock's Zone“ > Problem? By now giants are discovered that are closer to their stars then Mercury is to the sun (<0.466 AU)!

3. Formation of Pandora Similar to our Moon > crash on Polyphemus and formation out of the debris Pandora Polyphemus Formation elsewhere and later capture. Parallel to Polyphemus's formation. > out of debris (ring) like Saturn's 4 largest moons

4. A life-bearing planet like Pandora can exist.

5. Where is Pandora? wrt. Polyphemus Outside the Roche Limit! d=R*(2*  M /  m ) 1 / 3 Inside, matter is torn apart by gravity of the host planet / star. > No substantial moon could form!

6. Where is Pandora? wrt. Polyphemus Outside (geo)synchronous orbit. Generation of Water-Tides on Polyphemus by its moon Pandora. Pandora spirals in- or outwards!

7. How fast does Pandora rotate? As fast as Pandora orbits Polyphemus! (just like the Moon) > Always the same side of Pandora faces Polyphemus Generation of Land-Tides by Polyphemus on Pandora!

8. Roche Limit for object Of Pandoras mass (inside Polyphemus) Synchronous Orbit 17 M e a r t h 4 R e a r t h 290000 km P o r b ~100h 1 M e a r t h 5.5 billion years after formation

9. „Dressing“ Pandora Water/Land-Tides Since Pandora is always facing Polyphemus with the same side it only has a constant tide. High Tide a few °

10. „Dressing“ Pandora @290k distance, Polyphemus spans 9° on the sky (Moon=0.5°)

11. „Dressing“ Pandora Phases of Polyphemus It takes our Moon from „Full“ to „New“ to „Full“ 29.5 days (period around earth). Pandora rotates once every 100h around itself and around Polyphemus (synchronous Rotation) > one day last 100 hours. On Pandora, Polyphemus passes this phases once a day!

12. „Dressing“ Pandora Seasons Earth spin axis tilted by 23,5° against ecliptic (due to impact?) If nothing similar happened on Pandora, only very little seasonal change due to the shape of Polyphemus orbit around the sun.

13. „Dressing“ Pandora Everyday eclipses Once every orbital period (i.e. once a day) Pandora will pass behind Polyphemus and experience a full eclipse covering Half the planets surface (the side facing Polyphemus). The other side will never experience an eclipse.

14. „Dressing“ Pandora Day and night Days and nights are equally long throughout the year. The sun rises and sets straight in the same places throughout the year.

15. „Dressing“ Pandora Brightness profiles 1 2 3 4 2 Eclipse 1 Sunrise 3 Sunset 4 Polyphemus in full phase brightness Far side heats up more > weather!

16. „Dressing“ Pandora Magnetic Field Van Allen's Belt Pandora is rotating slower (102h) > weaker magnetic-field > Aurora borealis

17. „Dressing“ Pandora Development of Life Do two different species develop on different sides of Pandora? Each adapted to the different cycles of daytime? Maybe...

18. based on... Prof. of Physics / Astronomy University of Maine

19. Further Chapters What if the earth had two moons? What if the earth were a moon? What if the moon orbited backwards? What if the earth crust were thicker? What if the earth formed fifteen billion years from now? What if there were a counter-earth on the other side of the sun? What if the earth had formed elsewhere in the Galaxy? What if the sun were less massive? What if the earth had two suns? What if another galaxy collided with the Milky Way? Thank you!