On the detectability of Planet X with LSST (1804.07713v2)

Abstract: Two planetary mass objects in the far outer Solar System --- collectively referred to here as Planet X --- have recently been hypothesized to explain the orbital distribution of distant Kuiper Belt Objects. Neither planet is thought to be exceptionally faint, but the sky locations of these putative planets are poorly constrained. Therefore, a wide area survey is needed to detect these possible planets. The Large Synoptic Survey Telescope (LSST) will carry out an unbiased, large area (around 18,000 deg$^2$), deep (limiting magnitude of individual frames of 24.5) survey (the "wide-fast-deep" survey) of the southern sky beginning in 2022, and is therefore an important tool to search for these hypothesized planets. Here we explore the effectiveness of LSST as a search platform for these possible planets. Assuming the current baseline cadence (which includes the wide-fast-deep survey plus additional coverage) we estimate that LSST will confidently detect or rule out the existence of Planet X in 61\% of the entire sky. At orbital distances up to $\sim$75 au, Planet X could simply be found in the normal nightly moving object processing; at larger distances, it will require custom data processing. We also discuss the implications of a non-detection of Planet X in LSST data.

• The paper quantifies LSST’s high survey efficiency, predicting detection probabilities over 61% for Planet X within its coverage area.
• It examines critical detection factors including distance and motion, highlighting the need for specialized data processing for objects beyond 75 au.
• The findings suggest that LSST observations will play a crucial role in refining models of solar system formation and the dynamics of distant objects.

Detectability of Planet X Using the Large Synoptic Survey Telescope

The paper by Trilling et al. provides an analysis of the potential for the Large Synoptic Survey Telescope (LSST) to either detect or rule out the existence of hypothesized planetary-mass objects in the far outer Solar System, collectively referred to as Planet X. These objects have been proposed to account for peculiarities observed in the orbital properties of certain distant Kuiper Belt Objects (KBOs). Several studies have suggested the gravitational influence of one or more previously undetected planets could explain these anomalies.

Summary of Research

The premise for this investigation arises from the hypothesis that anomalies observed in the orbits of distant KBOs could be influenced by as-yet-undetected planetary mass objects. Previous research, including studies by Trujillo, Sheppard, Batygin, Brown, and others, suggests possible masses and orbital characteristics for these bodies, situating them well beyond the known boundaries of our solar system. Particularly, these objects may possess masses similar to super-Earths and exhibit semi-major axes that extend from 380 to over 980 au.

The LSST, with its wide field of view and deep survey capabilities, is slated to begin operations in 2022. Its wide-fast-deep (WFD) survey will cover approximately 18,000 square degrees of the southern sky and catalog objects down to a limiting magnitude of 24.5. This extensive coverage, together with the cadence of the observations, positions LSST as a key instrument in potentially identifying Planet X.

Key Findings

• Detection Probability: The paper calculates that LSST should detect or rule out the existence of Planet X over 61% of the sky. This is contingent upon the object being within the LSST's survey area and above its detection threshold.
• Distance Considerations: The rate of motion on the sky and distance from Earth are pivotal factors affecting detection. Objects within 75 au could be detected using standard processing techniques as their motion would be sufficiently fast. However, objects beyond this range would require tailored data analysis methods to account for slower motion.
• Survey Efficiency: The baseline cadence utilized in LSST simulations suggests high coverage efficiency. Some 96.9% of LSST pointings meet the operational requirements to facilitate detection—an important factor when considering the logistical constraints of systematic sky surveys.

Implications and Future Directions

The paper outlines significant implications for planetary science. If LSST does detect Planet X, it would substantiate claims about massive perturbing bodies in the outer solar system. Conversely, a non-detection would necessitate reevaluating the statistical models of current KBO orbital anomalies; this could involve questioning the current hypotheses or investigating other explanations, perhaps involving past stellar perturbations.

Furthermore, the success of LSST in this search will inform the broader astronomical endeavor of characterizing distant objects within our own solar system and beyond. In particular, any findings would impact theoretical models of solar system formation and dynamics.

Conclusion

The paper by Trilling et al. systematically evaluates LSST's ability to detect hypothesized distant planets in the solar system. Through rigorous analysis of observational capabilities and sky coverage, it affirms LSST's potential role in advancing our understanding of solar system architecture. The results underscore the utility of LSST in astronomical surveys, setting the stage for further refinement in search strategies and data processing approaches, particularly for slowly moving, dim objects like Planet X. As LSST operations commence, its findings will prove crucial in either confirming or reshaping our conception of the solar system's distant reaches.