The Volatile Budget of 2I/Borisov: Gas Production, Erosion and Nucleus Survival

This paper addresses a single quantitative question about interstellar objects and interstellar traversal: How much of Borisov's nucleus was lost during its Solar System passage, and how deeply was its surface eroded? Working from published survey values for the known interstellar objects and for the local interstellar medium, the paper computes gas mass-loss rate, total mass lost, lost fraction and mean erosion depth. The headline values obtained are mdot = 29.9; frac = 0.77; erosion = 1.03. Each number is produced by the deposited computation script from inputs that are stated in full, so the result can be reproduced, checked and updated as survey measurements improve. The study is a computation from stated assumptions and published data; it presents no new observations. Its contribution is a transparent budget: a set of numbers, the relations that produce them, and an explicit account of how sensitively each number depends on the assumptions behind it.