Finding planets that lie within the Habitable Zone (HZ) around other stars is hot in the list of Exoplaneteers. The growing list of habitable planets at the Planetary Habitability Lab's Habitable Exoplanets Catalog (HEC) and at The Habitable Zone Gallery is testament to the fervor at which scientists are focusing on finding that sweet spot.
All these are excellent! And now somehow i think that there should be an additional field of Thought to consider when trying to find life in other places.
How about the idea of Habitable Bubbles? It's very simple. Habitable Bubbles are tiny packets, or "bubbles" of environment where life can thrive. In contrast with the Habitable Zone, which is often represented as a disc around stars where liquid water can exist, Habitable Bubbles can simply be represented as tiny bubbles scattered throughout a planet--on the surface and underneath.
The idea of habitable bubbles can complement the Habitable Zone, and their relationship can be explored in this way: a planet that orbits within the habitable zone may probably have more habitable bubbles than a planet that lies outside the Habitable Zone.
In essence, Earth is a habitable bubble in and of itself. And it is ...