Astrometric detection of rocky exoplanets from inexpensive space platforms

Abstract

The detection of orbiting exoplanets by way of astrometric monitoring of the host star to reveal gravitationally induced reflex motion requires extreme precision and measurement stability when targeting Earth-mass objects. Despite this, astrometry is widely regarded as the most promising avenue for the most desired of all targets: true Earth analogue systems in the solar neighbourhood. Formerly thought to require flagship class investment, recently several smaller concepts such as the TOLIMAN and SHERA missions have shown that detections are possible, at least in principle, from more modest space platforms. A key enabling feature is that these missions exploit narrow-angle astrometry. Observing only multiple star systems where the target provides its own astrometric reference greatly alleviates the challenges confronted by traditional astrometry with its reliance on distant, faint field stars. This principle underlies the TOLIMAN mission, for which progress and status is reported. However, only a tiny handful of nearby star systems are suited to such a TOLIMAN-like architecture. This paper discusses speculative optical concepts featuring ultra-stable telescopes of modest (<0.5m) aperture designed for astrometric monitoring of isolated single stars at the micro-arcsecond scales required for the discovery of Earth mass objects orbiting sun-like stars in temperate orbits. In simulation, highly sought-after neighbourhood systems such as Epsilon Eridani and Tau Ceti can be exhaustively searched for rocky planets with dedicated observing campaigns spanning several years, all from relatively inexpensive orbital platforms.