One of the biggest challenges of amateur astronomy is the effect called atmospheric seeing. It can be a problem with wide-frame deep sky shots, but it is especially a problem when using a high magnification to image a planet. The atmosphere is turbulent and can distort the light rays entering it, causing objects to undulate. When things are low, close to the horizon, this effect is amplified.
I typically choose targets that are as high above in the sky as I can, but planets arc relatively lowly in the night sky this time of year, so this seeing can be particularly detrimental. My last imaging of session of Saturn was a good example of this. The following clip shows the effects of seeing.
Stacking dozens or hundreds of images does help with the signal-to-noise ratio, but if the object is distorted in each image, the stacking can only do so much. Imaging planets has definitely been more challenging because of this.
