Discs around young planets , so-called circumplanetary discs ( CPDs ) , are essential for planet growth , satellite formation , and planet detection .
We study the millimetre and centimetre emission from accreting CPDs by using the simple \alpha disc model .
We find that it is easier to detect CPDs at shorter radio wavelengths ( e.g . \lambda \lesssim 1 mm ) .
For example , if the system is 140 pc away from us , deep observations ( e.g .
5 hours ) at ALMA Band 7 ( 0.87 mm ) are sensitive to as small as 0.03 lunar mass of dust in CPDs .
If the CPD is around a Jupiter mass planet 20 AU away from the host star and has \alpha \lesssim 0.001 , ALMA can detect this disc when it accretes faster than 10 ^ { -10 } M _ { \odot } / yr .
ALMA can also detect the ‘ ‘ minimum mass sub-nebulae ’ ’ disc if such a disc exists around a young planet in YSOs .
However , to distinguish the embedded compact CPD from the circumstellar disc material , we should observe circumstellar discs with large gaps/cavities using the highest resolution possible .
We also calculate the CPD fluxes at VLA bands , and discuss the possibility of detecting radio emission from jets/winds launched in CPDs .
Finally we argue that , if the radial drift of dust particles is considered , the drifting timescale for millimetre dust in CPDs can be extremely short .
It only takes 10 ^ { 2 } -10 ^ { 3 } years for CPDs to lose millimetre dust .
Thus , for CPDs to be detectable at radio wavelengths , mm-sized dust in CPDs needs to be replenished continuously , or the disc has a significant fraction of micron-sized dust or a high gas surface density so that the particle drifting timescale is long , or the radial drift is prevented by other means ( e.g .
pressure traps ) .