The biological fertilities of planetary materials can be assessed using microcosms based on meteorites. This study applies microcosm tests to martian meteorites and analogues and to carbonaceous chondrites. The biological fertilities of these materials are rated based on the soluble electrolyte nutrients, the growth of mesophile and cold-tolerant algae, and plant tissue cultures. The results show that the meteorites, in particular the Murchison CM2 carbonaceous chondrite and DaG 476 martian shergottite, contain high levels of water-extractable Ca, Mg, and SO4‐S. The martian meteorites DaG 476 and EETA 79001 also contain higher levels of extractable essential nutrients NO3‐N (0.013‐0.017 g kg −1 ) and PO4‐P (0.019‐ 0.046 g kg −1 ) than the terrestrial analogues. The yields of most of the water-extractable electrolytes vary only by factors of 2‐3 under a wide range of planetary conditions. However, the longterm extractable phosphate increases significantly under a CO2 atmosphere. The biological yields of algae and plant tissue cultures correlate with extractable NO3‐N and PO4‐P, identifying these as the limiting nutrients. Mesophilic algae and Asparagus officinalis cultures are identified as useful bioassay agents. A fertility rating system based on microcosm tests is proposed. The results rate the fertilities in the order martian basalts > terrestrial basalt, agricultural soil > carbonaceous chondrites, lava ash > cumulate igneous rock. The results demonstrate the application of planetary microcosms in experimental astroecology to rate planetary materials as targets for astrobiology exploration and as potential space bioresources. For example, the extractable materials in Murchison suggest that concentrated internal solutions in carbonaceous asteroids (3.8 mol L −1 electrolytes and 10 g L −1 organics) can support and disperse microorganisms introduced by natural or directed panspermia in early solar systems. The results also suggest that carbonaceous asteroids and martian basalts can serve as potential future resources for substantial biological populations in the Solar System. c � 2002 Elsevier Science (USA)