Final answer:
Planets that will be difficult to detect in other solar systems are dim, far away, and lost in the glare of their parent stars. The small amount of light reflected by these planets and their distance from us make them hard to observe.
Step-by-step explanation:
Planets that will be very difficult to detect in other solar systems are those that are dim, far away, and lost in the glare of their parent stars. We can only see planets in our own solar system because they reflect sunlight and are close by. When we look at other stars, the amount of light a planet reflects is a tiny fraction of the light its star gives off, making it hard to detect. Furthermore, these distant planets are often overshadowed by the brightness of their parent stars.