"This type of technology is exactly what we want to use in the future to look for signs of life on an Earth-like planet." - Dimitri Mawet, study author, Caltech and JPL.
Sources:
Press Release: Exoplanet stepping stones
Research Paper: Detecting Water in the Atmosphere of HR 8799 c with L-band High-dispersion Spectroscopy Aided by Adaptive Optics
Wikipedia Entry: HR 8799
Research Paper: Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Keck Observatory: Telescope Instrumentation