In additional experiments, the researchers injected a drug into the brains of older mice to counter the drop in acetyl tag attachment, or acetylation.

Here's why: the next time you drop off a prescription order, you might see a robot behind the counter.

Without its six fly-bys—which used the gravitational fields of the planets involved to counter that effect—Messenger could not have slowed sufficiently to allow it to drop into its intended orbit.