I'm open to correction, but unfortunately, the formulae in your (I'm jealous,) book are expressed in the wrong domain for a renderer like Cycles. They're parametric surfaces.
That is to say, in the book, a surface is expressed as a function of parameters i,j in certain ranges. Given i and j, a point on the surface (X,Y,Z) is generated.
Cycles starts from the ...
You can do it with particles:
Create your meteor, give it a particle system, in the Field Weights switch off the Gravity, in the Velocity give a bit of Normal and Object Aligned X to give the particles a direction. Create a stretched sphere that will be your particle, in the particle system Render panel choose Render As > Object and under Object > ...
With current experimental build 2.91 you can base this on Volume Object.
create the shape from a Mesh Object.
add Volume Object and in modifiers choose Mesh to Volume, as source Object choose created shape one
add Point Light object in trail direction (close to a sphere)
With second modifier Volume Displace you can use texture to distort. Here is a few ...
Using another Shape is indeed not a bad idea. (@Jachym Michal)
But here is a node setup to give you pretty good controll of the density border.
For better visibility I haven't multiplied it with your current density setup yet, but the math node already is sitting in place as you can see.
user1853's comment in pictures :)
Change Transmission to 1
... or use Glass shader instead of Principled BSDF.
The only weird thing is when I replicate your node, result is totally white, not transparent as yours ... hm. Some changes happened from 2.81?
I'm no node wizard, so I'd recommend the Displacement node.
Then you can use UV maps for better control.
Add a Subdivision modifier set to Simple (4+ levels)
Use your hexagon texture to drive the Displacement node
Enable true Displacement in material properties
You can also drive the thickness using a BW texture