  TThe detection of gravitational waves from merging binary black holes has led
to a bound on the mass of a hypothetical massive carrier of the gravitational
interaction predicted by some modified gravity theories (a massive graviton,
for short), corresponding to a bound on the Compton wavelength $\lambda_g > 1.6
\times 10^{13}$ km. This bound is six times more stringent than a 1988 bound
inferred from solar-system dynamics. Using 30 years of improvements in solar
system data, chiefly from missions involving orbiters and probes of planets
from Mercury to Saturn, we revisit this bound. We show that data on the
perihelion advance of Mars obtained from the Mars Reconnaissance Orbiter leads
to a credible lower bound on $\lambda_g$ between $1.2$ and $2.2 \times 10^{14}$
km, surpassing the gravitational-wave bound by an order of magnitude. We
discuss ways in which each of these competing bounds may improve in the future.
