  Debris discs are dusty belts of planetesimals around main-sequence stars,
similar to the asteroid and Kuiper belts in our solar system. The planetesimals
cannot be observed directly, yet they produce detectable dust in mutual
collisions. Observing the dust, we can try to infer properties of invisible
planetesimals. Here we address the question of what is the best way to measure
the location of outer planetesimal belts that encompass extrasolar planetary
systems. A standard method is using resolved images at mm-wavelengths, which
reveal dust grains with sizes comparable to the observational wavelength.
Smaller grains seen in the infrared (IR) are subject to several
non-gravitational forces that drag them away from their birth rings, and so may
not closely trace the parent bodies. In this study, we examine whether imaging
of debris discs at shorter wavelengths might enable determining the spatial
location of the exo-Kuiper belts with sufficient accuracy. We find that around
M-type stars the dust best visible in the mid-IR is efficiently displaced
inward from their birth location by stellar winds, causing the discs to look
more compact in mid-IR images than they actually are. However, around
earlier-type stars where the majority of debris discs is found, discs are still
the brightest at the birth ring location in the mid-IR regime. Thus, sensitive
IR facilities with good angular resolution, such as MIRI on JWST, will enable
tracing exo-Kuiper belts in nearby debris disc systems.
