What makes Earth so gosh darn livable? How is it different from the other planets in our solar system, or viewable planets in our galaxy?
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There are a number of factors like the presence of water and being the right distance from the sun so that the water is actually mostly liquid, but those factors don’t tell the whole story.
Venus for example is almost Earth’s twin and technically in same “Goldilocks” range as Earth where it is not too close and not too far away from the sun and it really is not habitable for life as we know.
Meanwhile places like Jupiters moon Europa are far outside the zone, but still thought to have oceans of liquid ice under its surface.
Places like Mars are thought to have been much more like Earth in the distant past.
On the other hand our own planet Earth has in the distant past been completely hostile to our type of life. Being at points completely frozen over and having started out with an atmosphere toxic to us.
It might be argue that Earth today is so suitable to our own form of life because it evolved here.
Life as we know it depends on liquid water because our type of life started out in liquid water. It depends on a certain range of temperatures and the presence of certain chemicals because that is what we have to work with.
Life is so well adapted to the condition on this planet because this is where it evolved.
Life also shaped how the planet itself is, keeping it at the right temperature and keeping the atmosphere as it is. We basically “terrafromed” the planet by existing on it.
Life on other worlds may or may not thrive under completely different conditions.
We don’t know what range conditions life may evolve and exist under.
We only really have a single example of life to work with.
The only clues we have to work with are our own planet, the few other worlds we have checked and found empty and the notion that intelligent life must be extremely rare for us to not see the signs of any other civilizations out there.
We have only so little data available.
It doesn’t help that planets like Earth are rather harder to detect from a distance than others, We can see bigger planets and planets close to their sun easier.
A planet that is about the size of Earth and about the right distance from a sun like our own, is much harder to see. So mostly we have found planets that are not much like our own.
Maybe planets like Earth are extremely common out there. Maybe they are rare.
Maybe Earth like planets are all teeming with life. Maybe they are all barren.
Maybe life is common on planets completely unlike our own and we are a fluke. Maybe life is common on all sorts of planets. Maybe life is extremely rare. Maybe we are on the only place with life at all in this galaxy.
We need to do gather more data to check.
Since we can’t even know what forms life may possibly take and how to check for it, we are mostly looking for life like ours on places like ours.
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