Love letters across time and space.
From the introduction:
The astrobots are a colony of self-replicating robots sent from a distant Earth to explore the planets near the Earth for suitability for exploitation and colonization. However, something has gone awry with these astrobots, they missed their target and have travelled further and longer than they were ever designed. Now they have manoeuvred into the Cluster, a collection of stars and planets. And during the long travel, the astrobots have become something more than servile minions of Earth, they have begun to think for themselves. As they explore these new worlds, and the wonders and dangers they present, the astrobots will discover signs of ancient beings who once walked these stars. And the astrobots will decide whether to learn who they will become from those ancients or forge a path of their own.