There are 4 books in the ESS Space Marines series.
The ESS Space Marines series does not have a new book coming out soon. The latest book, Nebula (Book 4), was published in October 2017.
The first book in the ESS Space Marines series, Zenith, was published in July 2017.
The ESS Space Marines series primarily falls into the Space Opera and Science Fiction genres. This young adult series was written for ages 12-17, but can be enjoyed by adults too.