  We present a pre-discovery H-band image of the HR 8799 planetary system that
reveals all three planets in August 2007. The data were obtained with the Keck
adaptive optics system, using angular differential imaging and a coronagraph.
We confirm the physical association of all three planets, including HR 8799d,
which had only been detected in 2008 images taken two months apart, and whose
association with HR 8799 was least secure until now. We confirm that the
planets are 2-3 mag fainter than field brown dwarfs of comparable near-infrared
colors. We note that similar under-luminosity is characteristic of young
substellar objects at the L/T spectral type transition, and is likely due to
enhanced dust content and non-equilibrium CO/CH_4 chemistry in their
atmospheres. Finally, we place an upper limit of 18 mag per square arc second
on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The
upper limit on the integrated scattered light flux is 1e-4 times the
photospheric level, 24 times fainter than the debris ring around HR 4796A.
