The Problem with Direct Sensing

  Could detect planetary light directly by integrating a long time,
  BUT noise from primary star makes it much harder...

  L	stellar luminosity
  d	distance to star
  a	planet orbital semimajor axis
  R	planet radius R
  A	planet albedo
  t	integration time * quantum efficiency

  stellar flux at Earth	L / (4*pi*d^2)
  planetary flux	L / (4*pi*a^2) * pi*R^2*A / (4*pi*d^2)
     "			LA * (R/ad)^2 / (16*pi)
  ratio			4*a^2 / (R^2*A) = 4/A * (a/R)^2

  NOTE: L and d both drop out of the flux ratio.

  S/N			sqrt(Lt/pi) * (A/8d) * (R/a)^2
...assuming zero read noise, zero sky background,
and NO SYSTEMATIC ERROR!