Editing Openai/6946e998-79f0-8007-9a65-19828450838d (section)

===== For what you really care about: =====

: 

you want to integrate over all stellar generations:
* First-generation (Population II → then enriched Pop I)
* All Sun-like stars that already passed through main sequence and are now white dwarfs
* All stars currently on the main sequence
* Future low-mass stars that will live far longer than the current age of the universe are extra, but you’re focusing on “up to now.”

A back-of-the-envelope way to think about it:
* The Milky Way has formed a few × 10¹¹ stars total over its history (similar to, but somewhat larger than, the present-day count because many massive stars have died).
* If you apply your very conservative η⊕ ≈ 0.01 not just to surviving stars, but to all stars that have ever formed that were capable of having long-lived habitable zones (roughly F, G, K, M stars, not O/B’s), then you’d multiply by something like: (total suitable stars ever formed)∼(a few)×1011\text{(total suitable stars ever formed)} \sim \text{(a few)} \times 10^{11}(total suitable stars ever formed)∼(a few)×1011

Even if you:
* Restrict to “Sun-like enough + long-lived enough” stars, and
* Knock that down by another factor of a few to stay pessimistic,

you’re still plausibly in the regime:

NEarth-ish HZ planets ever∼109−1010N_{\text{Earth-ish HZ planets ever}} \sim 10^9 - 10^{10}NEarth-ish HZ planets ever∼109−1010
under your η⊕ = 0.01 pessimistic assumption.

So:
* Earlier: ~10⁹ candidate Earth-ish planets now.
* Over the entire history of the Galaxy: likely a few times larger, on the order of billions to tens of billions even with that harsh η⊕.

If you relax η⊕ back up toward more standard values (0.1–0.3 for Sun-like stars), the cumulative historical number easily pushes toward 10¹⁰–10¹¹ Earth-ish-HZ planets that have ever existed.