First, we will explore Earth. Earth is a beautiful blue planet that is very rare in the Universe because there is life on it. Today, we will talk about why there are life on Earth.
1. The Universe must have the correct laws of physics to sustain life. e.g., gravity, heat, energy, etc.
2. The Universe must have already past one generation of stars to let neutron stars create heavier elements.
About the galaxy and the galactic neighbourhood
3. The galactic neighbourhood mustn’t consist of active galaxies to prevent high doses of powerful electromagnetic radiation, the galaxy itself too. The galaxy must be relatively quiet and dim to prevent emitting high doses of radiation or collision courses.
4. The galaxy must not be the source of frequent gamma-ray burst (a galaxy full of low mass stars will be better for life)
About the interstellar neighbourhood
5. The interstellar neighbourhood mustn’t be close to the galactic centre to prevent high doses of radiation (that’s why finding alien life is best to be near Earth). Also, it mustn’t be too far away to prevent failure of forming terrestrial planets.
6. The interstellar neighbourhood must have relatively little star (advantage of living in the habitable zone of the galaxy), and they are relatively stable, making life safe from nearby supernovas (like ours, which are entirely made of low-mass stars)
7. The interstellar neighbourhood mustn’t have sources of high doses of powerful electromagnetic radiation such as pulsars.
About the host star
8. The host star must be an early K-type star, G-type star, or a late F-type star to prevent high doses of radiation or being tidally locked (the planet)
9. The host star must not have stellar companions or have a faraway one to stabilise the habitable zone of the star.
10. The host star must not be a variable star that changes its luminosity or a variable star which slightly change its luminosity (like the Sun) to stabilise the habitable zone.
11. The host star must have higher metallicity, to indicate there are enough heavier elements to create terrestrial planets. (Or it has terrestrial planets)
12. The host star’s orbit must be nearly circular, avoiding dense clusters of stars, especailly globulars.
13. The host star must not be near the galactic centre to prevent high doses of radiations or collision courses.
About the planetary system
13. The planetary system must have balanced planets to keep each other in place.
14. The planetary system must form with rocky planets.
15. The planetary system must have some water reservoir e.g. comets and strike the habitable planet when it formed.
16. The asteroids must be concentrated in one region (especially in tight orbits around the star), to prevent hitting the habitable planet after its formation.
About the planet
17. The planet must be in the host star’s habitable zone to maintain temperatures for liquid water to exist on the surface.
18. The planet must be rocky.
19. The planet must have an atmosphere to breathe and regulate the planet’s temperature by greenhouse effect. Also, it regulates the climate and temperature fluctuations to prevent it from being too bad for life.
20. The planet must have a magnetosphere to prevent it from being hit by charged particles. Therefore, it needs the rotational difference between the inner core and the rest of the planet.
21. The planet must have a moon to produce tides and regulate the planet’s seasons and rotation.
22. The planet must be tectonically active to regulate itself.
23. The planet must be rotating in a period that maintains its temperature habitable.
24. The planet must have an appropriate mass, size, g-force to prevent the abesnce of an atmosphere or it being overdense.
25. The planet must have seasons (tilted axis in the correct angle) to make a right cycle for life. e.g. growing the right plants in the right seasons, more heat in high latitudes, preventing seasonal diseases
26. The planet must not be tidally locked to prevent one side being burnt while the other being frozen.
27. The planet must have something like hydrogen, oxygen, phosphorus, sulphur (sulfur), nitrogen and carbon to produce RNA.
28. The planet must have a layer of atmosphere to protect it from UV radiation.
These are the reasons there is life on Earth, and to explore deeper about the planet, it is in the next episode.