The small size of the reddwarfstars, typically with spectral types K and M, gives a greater relative drop in brightness when low-mass planets pass in front of them, making it easier to search for planets around them.
"To our complete surprise, we found several reddwarf binaries with orbital periods significantly shorter than the 5-hour cut-off found for sun-like stars, something previously thought to be impossible, " the study's lead author Bas Nefs, from Leiden Observatory in the Netherlands, said in a statement.