Asteroids for µ Hz gravitational-wave detection

Abstract

A major challenge for gravitational-wave (GW) detection in the μ Hz band is engineering a test mass (TM) with sufficiently low acceleration noise. We propose a GW detection concept using asteroids located in the inner Solar System as TMs. Our main purpose is to evaluate the acceleration noise of asteroids in the μ Hz band. We show that a wide variety of environmental perturbations are small enough to enable an appropriate class of ∼10 km -diameter asteroids to be employed as TMs. This would allow a sensitive GW detector in the band (few ) ×10^-7 Hz ≲f_GW≲(few ) ×10^-5 Hz , reaching strain h_c∼10^-19 around f_GW∼10 μ Hz , sufficient to detect a wide variety of sources. To exploit these asteroid TMs, human-engineered base stations could be deployed on multiple asteroids, each equipped with an electromagnetic transmitter/receiver to permit measurement of variations in the distance between them. We discuss a potential conceptual design with two base stations, each with a space-qualified optical atomic clock measuring the round-trip electromagnetic pulse travel time via laser ranging. Trade space exists to optimize multiple aspects of this mission: for example, using a radio-ranging or interferometric link system instead of laser ranging. This motivates future dedicated technical design study. This mission concept holds exceptional promise for accessing this GW frequency band.