  Recent exoplanet observations reported a large number of multiple-planet
systems, in which some of the planets are in a chain of resonances. The
fraction of resonant systems to non-resonant systems provides clues about their
formation history. We investigated the orbital stability of planets in resonant
chains by considering the long-term evolution of planetary mass and stellar
mass and using orbital calculations. We found that while resonant chains were
stable, they can be destabilized by a change of $\sim$10% in planetary mass.
Such a mass evolution can occur by atmospheric escape due to photoevaporation.
We also found that resonant chains can be broken by a stellar mass loss of
$\lesssim1$%, which would be explained by stellar winds or coronal mass
ejections. The long-term mass change of planets and stars plays an important
role in the orbital evolutions of planetary systems including super-Earths.
