Top 3 candidates in our solar system to host microbial life from Earth

[lifeonmercury]

Assume that you are commissioned to select three solar system bodies (planets or moons) to deposit a colony of bacteria or microbes of your choice outside (i.e. either on the surface or underground, but not in any man-made enclosure). No resources from Earth (such as food, water, organic material) may be deposited.

The aim is for the bacterial populations to flourish (or at least maintain their population size in a non-dormant state) indefinitely without any further assistance from humans. Also assume there is an enormous budget for this, so the cost and resources that would need to be devoted to getting the microbes there is not a factor.

Based on your current knowledge and assumptions, which planets/moons would be best suited to sustain microbial life from Earth if you were forced to pick three? (To those who would rather criticize or ridicule the question instead of answering it, please don't feel obligated to respond, thanks!)

 

[Ernest S Walton]

1. Enceladus
2. Sub-surface Europa
3. Sub-surface Mars

 

[Bandersnatch]

It's essentially the same question as where can we hope to find microbial life.

1. Enceladus
2. Sub-surface Europa
3. Sub-surface Mars

Surely, 1 is also sub-surface?
And why Mars? You'd need liquid water.

 

[lifeonmercury]

There is water vapor in Mars' atmosphere. Not much, but maybe sufficient for some extremophile microorganisms to survive on.

 

[Ernest S Walton]

Surely, 1 is also sub-surface?

Technically sub-surface yes but possibly no more than tens of metres compared to kilometres in the case of e.g. Europa

And why Mars? You'd need liquid water.

Liquid water is still a live possibility on Mars but essentially this third-place pick illustrates the largely inhospitable reality that is the Solar System.

 

[newjerseyrunner]

Wait, are you talking about transplanting Earth life or which places are best to find native life? Stop thinking about contaminating the solar system. We crash our probes specifically to avoid contamination. You want to see how tough Earth-life is, fine, replicate environments in a lab, don't destroy potential habitats for non-Earth life. The idea that Earth life is special is a religious idea, not a scientific one.

Also, Mars is wet inside. Don't expect life to exist anywhere near the surface of any place in the solar system other than Earth.Titan is also a possibility for some more exotic forms of life.

 

[lifeonmercury]

This is about where Earth-based life could best survive elsewhere (and not about where it most likely might already exist). Thinking about it won't contaminate anything.
I'd prefer not to have this discussion devolve into an argument about the merits (or lack thereof) of planetary protection laws.