A Pan-STARRS1 Search for Planet Nine

Abstract: We present a search for Planet Nine using the second data release of the Pan-STARRS1survey. We rule out the existence of a Planet Nine with the characteristics of that predicted in Brown & Batygin (2021) to a 50% completion depth of $V=21.5$. This survey, along with previous analyses of the Zwicky Transient Facility (ZTF) and Dark EnergySurvey (DES) data, rules out 78% of the Brown & Batygin parameter space. Much of the remaining parameter space is at $V>21$ in regions near and in the area where the northern galactic plane crosses the ecliptic.

• The paper introduces a refined transient detection and orbit-linking algorithm to robustly search for Planet Nine using PS1 data.
• It processed over 244 million detections to rule out 78% of the Brown and Batygin parameter space with a 50% detection depth at V=21.5.
• The study’s combined analysis with ZTF and DES refines Planet Nine’s potential characteristics and guides future surveys like the Vera Rubin Observatory.

An Analysis of the Pan-STARRS1 Search for Planet Nine

This paper presents a comprehensive search for the hypothetical Planet Nine using data from the Pan-STARRS1 (PS1) survey. Building on previous investigations utilizing data from the Zwicky Transient Facility (ZTF) and the Dark Energy Survey (DES), the authors aim to constrain the existence of Planet Nine by analyzing PS1's deeper but less frequent sky observations conducted between 2009 and 2015.

Methodology

The study employs a robust method of detecting transient objects consistent with Planet Nine's characteristics as suggested by the Brown and Batygin (BB21) model. This involves identifying single-night transients within the PS1 data, filtering out systematic noise, and calibrating the data using known asteroid tracks as a reference. The challenge lies in linking transient detections across five years of data to approximate Keplerian orbits. This is managed by adapting an orbit-linking algorithm that accounts for heliocentric distance assumptions, while seeking to minimize false positives by increasing the detection threshold to nine registered detections.

The search was augmented by a synthetic reference population tuning based on BB21's predictions, tailored conformations of mass and orbit distributions to which the synthetic Planet Nine candidates were subjected to the PS1 detection capabilities. This framework facilitates a full calibration, allowing a detailed quantification of the observational limits of the PS1 survey.

Results and Numerical Findings

The survey processed over 244 million transient detections, successfully ruling out the presence of a Planet Nine with the predicted parameters to a 50% detection depth of $V=21.5$. Cumulatively, when combined with ZTF and DES, the search negates 78% of the potential parameter space suggested by BB21. Notable limitations include deep coverage inefficiencies in the northern galactic plane due to inherent survey constraints.

The overlapping methodology revealed that 69082 synthetic reference candidates aligned with the survey's observations, wherein 99.2% were accurately linked – demonstrating the algorithm's efficacy. With a combined survey analysis, any Planet Nine candidate brighter than $V \sim 20.5$ is almost assuredly non-existent as it would have been detected by the collective efforts of these comprehensive surveys.

Implications and Future Work

The expansive dismissal of the allotted phase space significantly tightens the constraints on Planet Nine's physical properties and potential location. The recalibrated estimates of its semimajor axis, mass, aphelion distance, current distance, and V magnitude underscore a more refined understanding albeit on a premise contingent on a planet hypothesis rather than more exotic alternatives (e.g., primordial black holes).

While the remaining parameter space is limited, particularly in under-observed southerly and galactic regions, upcoming surveys such as the Vera Rubin Observatory promise to probe these niches with unprecedented depth and coverage, potentially closing gaps left by the present conglomeration of efforts.

The impact of any non-detection continues to hinge on the persistence of observational oddities in the distant solar system and the theoretical models that suggest the existence of a massive perturbing body. Thus, alternate hypotheses must be continuously scrutinized to resolve discrepancies in the absence of Planet Nine's empirical discovery.

In conclusion, while a majority of the theoretical phase space for Planet Nine is negated through this study and previous efforts, remaining uncertainties call for continued observational advancements and theoretical development. The fidelity of tracking Planet Nine's elusive signature presses on the limits of astronomical survey capabilities and serves as a testament to the intricate challenges faced in contemporary planetary science.