But regarding your last sentence: I'm not very fond of that risk analysis. Potentially introducing an alien aquatic micro-organism (that's what we hope to bring back, remember) into earth's system... No competition, paradise compared to its hostile home. No meteorite has ever been shown to carry life, but into this case we intend to deliberately introduce it, either controlled or uncontrolled.
NASA can bill me for the extra cost for taking it to ISS instead of earth's surface.