[awalton]

It's not enough to make a difference either way around it. The sample return container could be filled to the brim with pure osmium or iridium and would make it through the atmosphere just fine.

The scientists are mostly worried because they want as much of the sample as they can possibly get, and they're a little worried about closing the sample container - if there's a rock that gets stuck somewhere, the container might not seal shut and then they've got a real bad problem they've gotta contend with.

It's 2020, they don't want to jinx it, just shut it up in the container and wait for the time capsule to arrive in 2023.