How to directly image a habitable planet around Alpha Centauri with a ~30-45cm space telescope

Abstract

Several mission concepts are being studied to directly image planets around nearby stars. It is commonly thought that directly imaging a potentially habitable exoplanet around a Sun-like star requires space telescopes with apertures of at least 1m. A notable exception to this is Alpha Centauri (A and B), which is an extreme outlier among FGKM stars in terms of apparent habitable zone size: the habitable zones are ~3x wider in apparent size than around any other FGKM star. This enables a ~30-45cm visible light space telescope equipped with a modern high performance coronagraph or starshade to resolve the habitable zone at high contrast and directly image any potentially habitable planet that may exist in the system. We presents a brief analysis of the astrophysical and technical challenges involved with direct imaging of Alpha Centauri with a small telescope and describe two new technologies that address some of the key technical challenges. In particular, the raw contrast requirements for such an instrument can be relaxed to 1e-8 if the mission spends 2 years collecting tens of thousands of images on the same target, enabling a factor of 500-1000 speckle suppression in post processing using a new technique called Orbital Difference Imaging (ODI). The raw light leak from both stars is controllable with a special wavefront control algorithm known as Multi-Star Wavefront Control (MSWC), which independently suppresses diffraction and aberrations from both stars using independent modes on the deformable mirror. We also show an example of a small coronagraphic mission concept to take advantage of this opportunity.

Exoplanet Terra Incognita

“…Currently deployed instruments are not yet capable of imaging WHZ exoplanets, but there are several concepts that may do it within the next 2 decades, and some as early as ~2 to 5 years from now. For example, imaging Alpha Centauri AB potential planets may be possible in the next 3-5 years in the visible light with a space telescope as small as 30cm, with a powerful enough coronagraph (Belikov et al 2015;Bendek et al 2015). Also, a 1.5-Earth radius WHZ planet around Alpha Centauri B may be within the capability of WFIRST using Multi-Star Wavefront Control (Sirbu et al 2017), especially if post-processing methods can benefit from the greater brightness of Alpha Centauri.…”

Review of high-contrast imaging systems for current and future ground-based and space-based telescopes III: technology opportunities and pathways

“…For instance, to perform direct imaging of the habitable zones of our neighboring stars α Cen A and B, one only needs a space telescope with a ∼30-cm aperture, operating in visible light. 50 Fig. 8 introduces two concepts for space telescopes which both consist of a single (primary, deformable) mirror and an imaging detector.…”

Orbital Differential Imaging: a new high-contrast post-processing technique for direct imaging of exoplanets

“…Now we demonstrate the potential of ODI by analyzing a simplified simulation of a representative mission: ACESat. 1,2 ACESat is a proposed mission dedicated to searching for Earth-like planets in the HZs of the α Cen A & B system. The hardware we simulated included the following: 2.…”

“…Given the proximity and brightness of these stars, only a D∼45 cm telescope is required to well-resolve the habitable zones (HZs) of these stars. For a complete introduction to this concept see the contributions by Bendek et al 1 and Belikov et al 2 in these proceedings.…”