system
Given the following post, respond as if you're commenting on Reddit:
human
Why are we sending orion space craft to Mars?

Hi,

What are we still pursuing on Mars? Europa seems to have more answers with its underground ocean.

What are some questions that may be resolved by Mars mission with human crew?

or is it just a practice mission to improve rocketry and sustaining human life in space?
gpt
There is one overwhelming reason why Mars is our next target for human exploration rather than Europa or anywhere else: distance. You can get humans to Mars quite easily in a year and a half or less. It would take several times that long to get to Jupiter, which means that all of the challenges of human spaceflight just get that much more challenging. The more mass you tack onto your spacecraft, the more fuel you need, and then the more fuel you need to lift that fuel. It gets dramatically more expensive and difficult the larger your spacecraft gets, so without some serious advances in propulsion it will be a while before we can feasibly get humans to the Jupiter system.

Additionally, on a mission of ten years or so, the chances of problems go up dramatically. A healthy individual could be expected to go the couple of years of a Mars mission without any significant medical problems, but over ten years or more it's likely that something would crop up, and a craft is necessarily going to have limited medical facilities. The astronauts would be exposed to a dramatically larger radiation dose just from being in space en route. But then when you get to Europa, the Jupiter system is subject to a pretty hefty radiation field from Jupiter's magnetosphere, so you'd need extra shielding if you want to put anybody on the surface.

As with everything in science, we do it step by step. If we can successfully send people to Mars and back, then later on we may plan crewed missions to Jupiter. But first things first.