Several moons of the giant planets that are substantially of ice possess probable internal oceans if they have internal heating sources (Kevin Hand; 7a-1). Concerned to argue their biology would be independent and therefore novel, he dismissed panspermia from Earth. I questioned his use of Gladman’s calculations of transfer of ejected rocks from Earth to dismiss contamination by terrestrial DNA, in particular of Europa (for which a mission proposal recently lost out).
Times longer than 5 Myr, including numerous smaller debris, and taking into account gravitational capture within the Jovian and Saturnian systems substantially raise probabilities. This gives many impacts at lower speed, some ~10km/s or less, while survivability is higher for impacts into ice compared with rock.
Kevin’s reply was that the probability of contamination would not be zero but orders of magnitude smaller than for Mars. Another example of someone concerned to deny panspermia by not considering realistic numbers and scenarios.