  A distinct population of planetary systems that contain dynamically isolated,
Earth-size planets with orbital periods $P_\mathrm{orb}\sim 1\,$day was
recently identified in an analysis of data from the Kepler planet candidate
catalog. We argue that these objects could represent the remnant rocky cores of
giant planets that arrived at the stellar vicinity on high-eccentricity orbits
and were rapidly stripped of their gaseous envelopes after crossing their
respective Roche limits (RLs) $a_\mathrm{R,p}$. In this picture, objects with
$P_\mathrm{orb}\gtrsim1\,$day are mostly "early" cores that originated in
planets with an initial periastron distance $a_\mathrm{per,0}\le
a_\mathrm{R,p}$; they had high initial eccentricities but their orbits
underwent fast tidal circularization after the cores were exposed. Objects with
$P_\mathrm{orb}\lesssim 1\,$day are, by contrast, mostly "late" cores that
originated in planets with $a_\mathrm{per,0}>a_\mathrm{R,p}$; these planets
underwent orbital circularization to a radius $>a_\mathrm{per,0}$ but
eventually reached $a_\mathrm{R,p}$ through tidal orbital decay. This picture
naturally accounts for the spatial distribution of hot Earths and for the
similarity of their inferred occurrence rate to that of hot Jupiters, and it
fits well with the interpretation of the so-called sub-Jovian desert in the
orbital-period--planetary-mass plane in terms of high-eccentricity planet
migration to the vicinity of the RL.
