An Exomoon Survey of 70 Cool Giant Exoplanets and the New Candidate Kepler-1708 b-i

Abstract: Exomoons represent a crucial missing puzzle piece in our efforts to understand extrasolar planetary systems. To address this deficiency, we here describe an exomoon survey of 70 cool, giant transiting exoplanet candidates found by Kepler. We identify only one which exhibits a moon-like signal that passes a battery of vetting tests: Kepler-1708 b. We show that Kepler-1708 b is a statistically validated Jupiter-sized planet orbiting a Sun-like quiescent star at ~1.6AU. The signal of the exomoon candidate, Kepler-1708 b-i, is a 4.8-sigma effect and is persistent across different instrumental detrending methods, with a 1% false-positive probability via injection-recovery. Kepler-1708 b-i is ~2.6 Earth radii and is located in an approximately coplanar orbit at ~12 planetary radii from its ~1.6AU Jupiter-sized host. Future observations will be necessary to validate or reject the candidate.

• The paper presents a survey of 70 cool giant exoplanets using advanced photodynamical models to detect exomoon candidates.
• It reports a 4.8-sigma signal on Kepler-1708 b with a low false-positive probability of about 1%, indicating a strong candidate exomoon.
• The discovery challenges current exomoon formation theories and highlights the need for follow-up observations with instruments like JWST.

Overview of "An Exomoon Survey of 70 Cool Giant Exoplanets and the New Candidate Kepler-1708 b-i"

In the quest to enhance our understanding of extrasolar planetary systems, the study of exomoons provides a fascinating frontier. The paper "An Exomoon Survey of 70 Cool Giant Exoplanets and the New Candidate Kepler-1708 b-i" authored by Kipping et al., is a step forward in this domain, where the authors conducted a dedicated survey to detect exomoons around a carefully curated sample of 70 cool, giant exoplanets. This paper is a methodical investigation leveraging transit data from the Kepler mission to identify potential exomoon candidates using advanced photodynamical models.

Key Findings

The authors focused on a population of cool, giant exoplanets, as these are theorized to be promising hosts for expansive satellite systems akin to those seen around Jupiter and Saturn. These exoplanets were long-period transiting candidates predominantly residing beyond 1 AU from their stars, making their detection biased due to longer observation periods required.

From their robust vetting processes applied to detrended Kepler light curves, only one of the surveyed targets, the planet Kepler-1708 b, displayed significant evidence suggesting the presence of an exomoon, provisionally named Kepler-1708 b-i. This candidate manifests a notable 4.8-sigma signal distinguishable across diverse detrending methods, suggesting a low false-positive probability of approximately 1%. Kepler-1708 b-i was inferred to be a relatively large exomoon, with a radius of about 2.6 Earth radii, orbiting its 1.6 AU distant host planet.

Implications

The identification of Kepler-1708 b-i, if validated, would signal a significant stride in exomoon discovery, echoing the earlier tantalizing hint of Kepler-1625b-i. This detection challenges the current theoretical frameworks that primarily predict smaller moons for giant exoplanets. The potential existence of such a large exomoon raises important questions regarding the formation scenarios of massive satellites and their subsequent orbital evolution, including formation through a circumplanetary disk or capture.

Future Directions

While the study offers a strong candidate exomoon, it is underscored by the need for additional observational verification to substantiate the claim. The authors propose that future transits of Kepler-1708 b, expected to be observable with forthcoming astronomical facilities like JWST, could offer critical tests of this exomoon's presence via TTVs or direct moon transits. Enhanced precision and sensitivity available with these platforms could provide the evidence needed to confirm Kepler-1708 b-i as a genuine exomoon.

In conclusion, the paper provides a compelling case for the existence of an exomoon around a distant giant planet, while emphasizing the importance of continued observations to confirm the claimed detection. The survey methods and rigorous statistical analysis highlighted in this work could serve as a robust blueprint for future exomoon detection campaigns.