>>11941692There are much more barriers at N° 1 alone.
It's not just "the right star system".
For the conditions on Earth you need:
1. A star that is stable on the main sequence for billions of years. Many stars do not fulfill this criteria, though billions of them do. K-type and G-type stars seem the most likely.
2. A star that is bright enough to avoid tidal locking on its Goldilocks Zone. This rules out most red dwarfs. It's very unlikely there is life on tidally-locked worlds like those of the Trappist system. The window for the evolution of life on such worlds would be very narrow and basically limited to the terminator zone (permanent twilight zone between the ultrahot day hemisphere and the ultracold night hemisphere).
3. A rocky or watery planet located on the Goldilocks Zone on such a system, able to support liquid water.
4. The planet in question needs to have liquid water.
5. If the planet in question is rocky, it definitively needs to have a breathable atmosphere of sorts to keep temperatures spread even and life possible.
6. The atmosphere must have a low content of greenhouse gases to avoid a runaway greenhouse effect as in Venus.
7. The planet in question needs to have the proper size, and thus the proper pressure to support liquid water. Too great pressure will only support ice. Too low pressure and it will only have vapour and ice.
8. The planet in question needs to have magnetic shield strong enough so that it doesn't lose its atmosphere over the years.
9. The planet in question needs to have an orbit with a very low eccentricity so as to not suffer from extreme "seasons", avoiding crust-melting summers and ice age winters.
