Prospects for Panspermia via Interstellar Objects like 3I/ATLAS

We study the feasibility of natural and directed panspermia via interstellar objects (ISOs) like 3I/ATLAS. The paper is organized around two questions. First, could natural panspermia occur if microbes or biomolecules survived inside shielded ice and were later exposed during perihelion and outbound activity? Second, could directed panspermia occur if a technological civilization planted life-bearing material inside or onto an icy ISO so that it later transported life through the Milky Way? We combine data on 3I/ATLAS with order-of-magnitude thermal, biological, and mission constraints. SPHEREx provides the volatile and organic context through CO 2, H 2 O, CO, dust, and a broad C--H feature, while JWST/MIRI provides the first direct CH 4 detection in an interstellar object and confirms an unusual volatile inventory, including enhanced CO 2:H 2 O and CH 4:H 2 O ratios. We distinguish dormant interstellar cruise from active perihelion. Natural panspermia is plausible as microbes can survive or repair damage in ice films, veins, or frozen matrices at very low metabolic rates. Methane production is more nuanced. Frozen survival metabolism would require about10 14 -- 10 15 kg of biomass to match the JWST CH 4 rates, but active methanogenic archaea in warm, liquid, substrate-rich settings can produce methane many orders of magnitude faster, reducing the required biomass in optimistic laboratory-rate comparisons. Directed panspermia faces a different challenge: a direct 60 km s-1 impact releases 1.8 times10 9 J kg-1, hundreds of times the specific energy of TNT, and would destroy a biological capsule. 3I/ATLAS-like objects are therefore best treated as test cases for panspermia diagnostics rather than as evidence for life. Natural panspermia requires preservation plus a credible liquid-water or near-surface activation pathway.