Besides from being a series of popular first-person shooter video games, half-life is an important factor to consider in any applications of radioactivity. It seems quite a weird quantity at first glance; we usually talk about the lifespan of things, rather than half a lifespan. But as you will see, the ‘half-life’ is far more logical, because the lifespan of a radioactive substance is… well, infinite (theoretically).
As a civilisation that rarely vacates the safety of the Earth’s atmosphere, we know an awful lot about the billions of kilometres of space around us. Of course, we don’t send human reconnaissance units on suicidal missions to scout the Solar System, because we have already have machines that can do that for us. We call them space probes.