In my search for a solution to the issue discussed in the title, I came across this question and also observed this intriguing demo. As a result, I have decided to utilize the ThREEx.atmospherematerial() from the THREEx.planets package.
The material consists of two parameters: power (denoted as p in the demo) and coefficient (c in the same demo). It is apparent that power controls the gradient steepness, while the coefficient determines its extent.
Upon examining the demo, it is clear that the outer edge of the atmosphere has a crisp appearance while the inner edge gradually fades into transparency towards the sphere. My goal, however, is to reverse this effect: with the inner edge having minimal transparency and the outer edge gently fading out.
My attempts to achieve this by using a negative power value have been unsuccessful thus far.
If anyone could offer assistance, I would greatly appreciate it!