  TRAPPIST-1 is a nearby ultra-cool dwarf that is host to a remarkable
planetary system consisting of seven transiting planets. The orbital properties
and radii of the planets have been well-constrained, and recently the masses of
the inner six planets have been measured with additional ground and space-based
photometric observations. Large uncertainties in these mass measurements have
prevented a robust analysis of the planetary compositions. Here we perform many
thousands of N-body dynamical simulations with planet properties perturbed from
the observed values and identify those that are stable for millions of years.
This allows us to identify self-consistent orbital solutions that can be used
in future studies. From our range of dynamical masses, we find that most of the
planets are consistent with an Earth-like composition, where TRAPPIST-1f is
likely to have a volatile-rich envelope.

Earth and Planetary Astrophysics