Asteroids for $\mu$Hz gravitational-wave detection

TL;DR

This paper proposes using asteroids as test masses for gravitational-wave detection in the microhertz band, evaluating their environmental noise levels and outlining a conceptual mission design with asteroid-based stations.

Contribution

It introduces a novel concept of asteroid-based test masses for low-frequency gravitational-wave detection and assesses their environmental noise suitability.

Findings

Asteroids of about 10 km diameter have sufficiently low acceleration noise.

A GW detector in the microhertz band could reach strain sensitivities of around 10^{-19}.

A conceptual design with asteroid-based stations and laser ranging is discussed.

Abstract

A major challenge for gravitational-wave (GW) detection in the $\mu$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 $\mu$Hz band. We show that a wide variety of environmental perturbations are small enough to enable an appropriate class of $\sim 10$ km-diameter asteroids to be employed as TMs. This would allow a sensitive GW detector in the band $\text{(few)} \times 10^{-7} \text{Hz} \lesssim f_{\text{GW}} \lesssim \text{(few)} \times 10^{-5} \text{Hz}$, reaching strain $h_c \sim 10^{-19}$ around $f_{\text{GW}} \sim 10 \mu$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. Tradespace 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.