Creating a Cosmic Inventory of Rocky Planets

This is an excerpt from my post on Astrobites:

Title: Terrestrial planets across space and time
Authors: Erik Zackrisson, Per Calissendorff, Juan González, Andrew Benson, Anders Johansen, and Markus Janson
First Author’s Affiliation: Uppsala University, Sweden
Paper status: Submitted for review

When I was born in 1989, there were just nine planets known throughout the entire universe (poor Pluto).  Now there are between 1600 and 2100 confirmed exoplanets (depending on whom you ask).  All these planets are located in a small region of our home galaxy (the Milky Way). However, there are billions of other galaxies. Therefore, you might ask just how many do we expect throughout the entire universe?  This paper attempts to create a “cosmic inventory” of terrestrial (rocky) planets by combining the fields of cosmology, galaxy formation, and exoplanet science to estimate the number of planets around FGKM stars.  (To distinguish stars of different masses, astronomers give them different letters.  The pneumonic, from most massive stars to least massive, is “Oh Be A Fine Girl/Guy, Kiss Me”.  For reference, the Sun is a G-dwarf star.)