Direct imaging of a planet around another star is exceedingly challenging. For even the closest stars observed with the largest ground-based telescopes, the angular separation between star and planet will be near the classical diffraction limit. Moreover, a typical star will be about a billion times brighter than the planet to be imaged, a challenge even for the most stable telescope in space. The planetary image is also buried in “speckle noise,” which is the result of uncorrected wavefront errors that propagate through the atmosphere and even the most accurately polished optical system. This speckle noise has complex properties which are different from planetary signals. While algorithms now exist that exploit some differences between the signal and noise characteristics, there has been little effort to address the full problem in a rigorous and comprehensive way. Our focus on speckle discrimination and control is motivated by key scientific measurements of exoplanetary systems:
- Pure detection: Is there a planet present in the image(s)?
- Astrometry: Where precisely is the planet located?
- Photometry: How bright is the planet, and does its brightness vary with time?
- Estimation of orbital parameters: How does it move relative to other bodies in the system?
- Spectrometry: What are the spectral characteristics of the light from the planet?
- Detection of life: Does the spectrum contain components consistent with living organisms?
Given the advent of high-precision focal plane wavefront control and low-noise fast-frame-rate detectors as well as the ongoing development of new facilities for exoplanet study, our proposed KISS workshop seeks to address several questions related to the development of statistically grounded strategies for detecting faint signals in the presence of both coherent and incoherent backgrounds:
- What are the fundamental limits to focal-plane wavefront sensing and coherent differential imaging?
- How is modulation best used in source-speckle discrimination and in speckle control?
- How do ground-based focal-plane wavefront sensing and control differ from the space-based case?
- What is the potential impact of new post-processing techniques, and rigorous statistical analyses on the next-generation instruments for extremely large ground- and space-based telescopes?