CR flux can vary widely and the erosion time for a given icy ISO can vary according to the cosmic ray strength.
The authors point out that we need to know more about the varying strength of cosmic rays in the Milky Way to make more progress.
"It is also clear from this example that a more detailed study of the spatial profile of Galactic CRs might help to shed light on the origin of ISOs passing through the Solar System," they write.The study of ISOs is in its infancy.
With only two ISOs known so far, there's not many hard data to go on.
The researchers end their letter with the following: "It would be interesting to incorporate a detailed modelling of the CR distribution in the Galactic disk to set more rigorous constraints on the birth site of known ISOs and this might help to better clarify their origin.".