Abstract
ABSTRACT The past year has seen numerous publications underlining the importance of a space mission to the ice giants in the upcoming decade. Proposed mission plans involve a ∼10 yr cruise time to the ice giants. This cruise time can be utilized to search for low-frequency gravitational waves (GWs) by observing the Doppler shift caused by them in the Earth–spacecraft radio link. We calculate the sensitivity of prospective ice giant missions to GWs. Then, adopting a steady-state black hole binary population, we derive a conservative estimate for the detection rate of extreme mass ratio inspirals (EMRIs), supermassive black hole (SMBH), and stellar mass binary black hole (sBBH) mergers. We link the SMBH population to the fraction of quasars fbin resulting from Galaxy mergers that pair SMBHs to a binary. For a total of 10 40-d observations during the cruise of a single spacecraft, $\mathcal {O}(f_\mathrm{bin})\sim 0.5$ detections of SMBH mergers are likely, if Allan deviation of Cassini-era noise is improved by ∼102 in the 10−5 − 10−3 Hz range. For EMRIs the number of detections lies between $\mathcal {O}(0.1) \ \mathrm{ and} \ \mathcal {O}(100)$. Furthermore, ice giant missions combined with the Laser Interferometer Space Antenna (LISA) would improve the localization by an order of magnitude compared to LISA by itself.
Highlights
Uranus and Neptune are the outermost planets in our solar system, orbiting at roughly 20 and 30 AU from the Sun, respectively
Adopting a steady-state black hole binary population, we derive a conservative estimate for the detection rate of extreme mass ratio inspirals (EMRIs), supermassive– (SMBH) and stellar mass binary black hole mergers
We focus on three cases, where the total Allan deviation is improved by a factor of 3, 30 and 100 with respect to Cassini-era values
Summary
Uranus and Neptune are the outermost planets in our solar system, orbiting at roughly 20 and 30 AU from the Sun, respectively. The time frame is reported to be around 2029-2030 for Neptune and early 2030s for Uranus, especially if a Jupiter Gravity Assist (JGA) will be used to reach the ice giants (Hofstadter et al 2019) Considering that they will spend most of their time in interplanetary space (rather than orbiting the planets they are destined for), the science potential of such mission configurations is limited to a. We expand on the details later and note that this process is elegantly described in Armstrong (2006) and the references therein This use of Doppler tracking with interplanetary spacecraft was previously suggested for many space missions; most notably in the Pioneer 11 data analysis Armstrong et al (1987), the Galileo– Ulysses–Mars Observer coincidence experiment (Anderson et al 1992; Bertotti et al 1992), and the Cassini (Comoretto et al 1992; Bertotti et al 1999) mission. With increasing capabilities to combat detection noise, we suggest Doppler tracking could be a cheap and efficient way to do science during the cruise phase of prospective ice giant missions
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