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“This,” he said, gesturing at the air above their heads, “is an object called 1I/2017 U1. Also known as ‘Oumuamua, which is a Hawaiian word meaning ‘first messenger.’

In this process, scientists refer to a “first messenger,” which arrives at the cell from outside, often as a hormone.

The first messenger’s arrival at the outer wall of the cell eventually causes production within the cell of a “second messenger,” which prompts the cell to act.

Activated by the arrival of the first messenger, it goes on to activate the production of the second.

A first messenger of storm passed darkly over the sky, leaving the way clear again.