Finding exoplanets in the habitable zone with light echoes

In practice, technologies attempting to recover direct images of extra-solar planets run into noise floors governed by systematics (most notably, quasi-static speckles) before reaching fundamental limits (such as photon noise). To enhance detection reach to higher contrasts, discrimination by exploiting distinctive planetary signatures have been proposed. Here we explore a novel possibility: detecting exoplanets around bright variable stars based on the variability-phase difference between the speckles and the reflected light from the planet. Hot variable stars (the kind most favorable to this idea) host relatively distant Habitable Zones, which will allow a considerable phase delay to be displayed by planet in reflection. We have carried out a systematic series of simulations and analysis to explore the potential for this method. We show that this technique could improve contrast reach of an extreme-AO imagery by a factor of 5-10 against speckle noise.