Mars is inhospitable. I understand that we have plans to terraform the place with the next (mumbles) centuries, but anyone we send there is as expendable as a red shirt on Star Trek. Space itself is dangerous and once you land, so is Mars itself. And while the Moon is a smart first step, Mars is an order of magnitude distant from there.
Science suggested that there would be many (define ‘many’) planets that would be hospitable for life as we know it. The reality is very different. There are planets such as K2-18b that are a big reach in terms of being “near earth conditions”, but they’re about as close as we’ve come, and they’re a long way from here. Sure, a million monkeys pounding on a million typewriters will some day write the Gettysburg Address… but it looks as though we’re going to have to make it work here. There don’t seem to be many places to go even if we could travel really fast or utilize some sort of wormhole technology.
In order to have life as we know it – based on what we now (think that we) know, you need a large moon that can keep the interior of the planet churned up, hot and liquid so that it will generate protective radiation belts. The distance from the star needs to be within tolerances. The star needs to be stable over a long period of time. It helps to have one or more really big “Jupiters and Saturns” out there sweeping space of comets and debris. The star should be metal rich (third generation or later), but it doesn’t have to be. The planet needs to have large water seas.
15,000 years ago, much of the planet could be considered to be a ‘giant snowball’ with ice sheets extending far down toward the equator. Many people think that the ‘global warming’ that is discussed is noting more than an end to the ice age. Which is to say that even a planet as hospitable to life as ours goes through growing pains.