nomadski wrote:So it does look like no life on Mars. And Mars is so like Earth.
Lol far from it. Walter Sullivan noted that Viking's failure to find life on Mars was disappointing but not unexpected. With only a tenth of Earth's mass and a third of its surface gravity, Mars was unable to retain a substantial atmosphere "and its fate has little bearing on that of more Earthlike planets throughout the Universe."
As you said we need a giant planet like Jupiter to absorb the impacts. And some say we need a moon for tidal Oceans for life.
I don't think life needed either. Or, both can be liabilities as well as assets. Jovian planets may absorb oort junk but their gravity may be pulling it into the inner solar system in the first place. As for a moon for tides, if life originated in clay as Cairns Smith thought, ocean tides were irrelevant. Stable planetary obliquity, due to the gravity of a moon, is also thought vital but I don't think obliquity shifts would make a planet uninhabitable.
An almost identical solar system to our own.
I do believe planetary conditions must be quite earthlike but that might be possible in a much different planetary system. For example, a gas giant might exist close to a relatively dim star,, with an earthlike moon orbiting it. Ordinarily a planet close enough to a dim star to get adaquate energy would be tidally locked but potentially this is a way to get around that difficulty.
And we should not look at all with radio....
Agreed, given the likely brevity of that technological stage, on a cosmic timescale, SETI is probably a waste of time.