Debris discs are dusty belts of planetesimals around main-sequence stars,
similar to comets and asteroids in the solar system. The planetesimals
themselves cannot be observed directly, yet they produce detectable dust in
mutual collisions. Observing this debris 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 and extent of outer planetesimal belts, i.e.,
"Kuiper belts" that encompass extrasolar planetary systems. A standard method
is using resolved images at millimetre wavelengths, which reveal dust grains of
comparable sizes. This is because smaller dust particles seen in the infrared
or optical are subject to a large array of non-gravitational forces that drag
them away from their birth places, and so may not closely trace the parent
bodies. In this study, we examine whether imaging of debris discs at shorter,
far- or even mid-infrared, wavelengths with future facilities such as the James
Webb Space Telescope, which offer high resolution, would allow one to determine
the spatial location of the exo-Kuiper belts with sufficient accuracy. We find
that around A-type stars, where the majority of debris discs is found, and even
around G-type stars discs are brightest at the location of the birth ring in
both the millimetre and the mid-infrared wavelength bands. Thus, we are able to
trace planetesimal belts even at shorter wavelengths.
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