The Atacama Cosmology Telescope: A Search for Planet 9

Abstract

We use Atacama Cosmology Telescope (ACT) observations at 98 GHz (2015–2019), 150 GHz (2013–2019), and 229 GHz (2017–2019) to perform a blind shift-and-stack search for Planet 9. The search explores distances from 300 au to 2000 au and velocities up to 6.′3 per year, depending on the distance (r). For a 5 Earth-mass Planet 9 the detection limit varies from 325 au to 625 au, depending on the sky location. For a 10 Earth-mass planet the corresponding range is 425 au to 775 au. The predicted aphelion and most likely location of the planet corresponds to the shallower end of these ranges. The search covers the whole 18,000 square degrees of the ACT survey. No significant detections are found, which is used to place limits on the millimeter-wave flux density of Planet 9 over much of its orbit. Overall we eliminate roughly 17% and 9% of the parameter space for a 5 and 10 Earth-mass Planet 9, respectively. These bounds approach those of a recent INPOP19a ephemeris-based analysis, but do not exceed it. We also provide a list of the 10 strongest candidates from the search for possible follow-up. More generally, we exclude (at 95% confidence) the presence of an unknown solar system object within our survey area brighter than 4–12 mJy (depending on position) at 150 GHz with current distance 300 au < r < 600 au and heliocentric angular velocity 1 .′ 5 yr − 1 < v · 500 au r < 2 .″ 3 yr − 1 , corresponding to low-to-moderate eccentricities. These limits worsen gradually beyond 600 au, reaching 5–15 mJy by 1500 au.

The Simons Observatory: Galactic Science Goals and Forecasts

“…While faint at optical wavelengths, the putative Planet 9 could be detected from its thermal emission in the far-infrared and microwave. Although Naess et al (2021a) reported no significant detection, they were able to shrink the allowed parameter space by 17% and 9% for 5 and 10 M ⊕ planets, respectively. With increased sensitivity and longer time baselines, SO data can complement and extend this analysis.…”

“…A recent study employing ACT data has demonstrated the utility of CMB telescopes for studying the solar system (Naess et al 2021a). Based on the clustering of Kuiper Belt objects, it has been proposed that a 5-10 M ⊕ Planet 9 may be orbiting the Sun at 400-800 au (Batygin & Brown 2016;Batygin et al 2019).…”

Including Planet 9 in the Solar System Increases the Coherence between the Sunspot Number Record and Solar Inertial Motion

“…Clearly, in the continuing absence of direct observation, e.g. [4]; other supporting evidence would be welcome.…”

Asteroid Measurements at Millimeter Wavelengths with the South Pole Telescope

“…Although the Planck Collaboration has previously published detections of asteroids in their analysis connecting dust observations to asteroid families (Cremonese et al 2002;Planck Collaboration et al 2014) and the Atacama Cosmology Telescope (ACT) collaboration masked asteroids in their search for Planet 9 (Naess et al 2021), this work represents the first focused analysis of asteroid flux in data from an experiment designed to measure the CMB. With continued analysis, historic and future data measuring the CMB can provide more observations of asteroids at submillimeter and millimeter wavelengths.…”