Question

What sort of exoplanets are the easiest target for direct imaging, and why?

Answer 1

let's understand the meaning of direct imaging first. it means that we observe the planet through telescope in various wavelengths of light or in other words different spectrum.

now the star is a black body which means that it emit radiation in all the spectrums. so, to distinguish the planet, it must be relatively far.secondly, lets think what spectrum could we possibly see a planet?

visible- difficult to see

uv and beyond- planet doesn't emit that radiation

infrared- heat of planet radiates spectrum in IR spectrum

below IR - difficult to see planets

hence, the planet must emit substantial amount of IR waves which means that the planet must be hot. the hotter planets are generally young ones. i.e recently formed.

so, the direct imaging work bests on

1. younger planets

2. planets far away from stars

several planets have been discovered through this technique like Beta pictoris B, Formalhaut B etc.