system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] An Inquiry into the effects of a Nova Cannon on a planetary target.

So, as a Captain of the Imperial Navy, I have a certain obligation to uphold my reputation. Thus, the comments made by a Certain Water Caste degenerate at a negotiation with the Tau xenos cannot be allowed to stand. While the reprobate in question has been redistributed across her continent of origin in accordance with Tau principles, her remarks have been spread across the Tau empire, and thus something more dramatic seems required to balance the scales.

As I am the commander of an Invincible-Class Fast Battleship modified to carry a Nova Cannon, I believe use of this weapon may represent my best course of action. What effects could I expect to see if a shell impact the surface of a Tau Sept World?

Also, I have contemplated moving my vessel to some distance well outside the stellar system in question, plot out the entirely predicable location of the planet, and begin firing the Nova Cannon to intersect with the planet. Then, as even an Imperial battleship is some seven times faster than a Tau Interstellar craft, I would proceed to make good my escape.

Is this course of action likely to be successful?
gpt
Nova cannons are one of Humanity's greatest weapons against the xeno-hordes. The impact of a single warhead of a Nova cannon is the equivalent of a K-T extinction event on ancient Earth. 

As for your plan to bombard the Tau Sept World, our current level of tech leaves the accuracy of the Nova Cannon much to be desired. Therefore, you'll need to be relatively much closer to your target.