Status of NASA’s stellar astrometry testbeds for exoplanet detection: Science and technology overview

Accurate measurement of exoplanetary masses is a critical step in addressing key aspects of NASA’s science vision. Measuring masses of Earth-analogs around FGK stars out to 10 pc requires sub-microarcsecond astrometric accuracy, which is not within the capabilities of current instrumentation. Thus, new technology will be required to build an astrometric instrument capable of achieving such performance. This will immediately empower the possibility for dedicated astrometric missions, and perhaps most enticingly, it will enable astrometric observing modes to be added to any mission boasting a sufficiently stable direct imaging platform. In this paper, we provide an overview of the scientific goals and technology utilized on NASA’s testbeds dedicated to advancing stellar astrometry for exoplanet detection. The first one, located at the Jet Propulsion Laboratory (JPL), is dedicated to imaging stellar astrometry on sparse fields. The goal of this testbed is to mature the Diffractive Pupil technology to TRL-5, demonstrating high-fidelity performance in a relevant environment. This testbed operates in a vacuum tank at the High Contrast Imaging Testbed (HCIT) at JPL, and has demonstrated detection of signals of 1.58e-5 λ/D which is equivalent to 0.75 µas on Hubble. The second testbed, Is also located at JPL, but it is dedicated to advancing narrow angle relative astrometry to detect exoplanets around nearby binary stars. The key technology in this testbed is a diffractive pupil specially designed to measure the angle between two sources on the sky. This testbed operates in air now, but we are designing a new version of this testbed that will operate in vacuum with the goal of demonstrating sub-microarcsecond accuracy astrometric measurements between binary stars.