报告题目：A Planet with Two Suns

报告人：江群峰（香港大学）

报告摘要：Planets orbiting two suns — known as circumbinary planets — have long captured the imagination of both scientists and the public, perhaps most famously through Tatooine in Star Wars. But such worlds are not just fiction: more than half of all stars in our Galaxy live in binary systems, making circumbinary planets essential to any complete picture of how planets form, survive, and potentially host life. For most of astronomical history, these worlds remained out of reach. It was only in 2011, with NASA's Kepler mission, that the first transiting circumbinary planet, Kepler-16b, was discovered. Today, a small but growing population of such planets has been detected, and many of their orbital properties have now been precisely characterized. Yet a fundamental puzzle remains: how do these planets form and survive in such a dynamically hostile environment, where two stars constantly perturb their orbits?

In this talk, I will introduce the basic picture of circumbinary planets and present my MPhil work addressing this question. By combining analytical theory with N-body simulations, we provide the first complete measurements of free eccentricity, a quantity that reveals the planet's intrinsic orbital excitation, across the entire known population. We find that most circumbinary planets lie remarkably close to their dynamical stability limits, with strikingly low free eccentricities. Based on this result, we propose that an eccentricity-dependent stability filter has sculpted the population we see today, and demonstrate via statistical tests and Monte Carlo simulations that this single mechanism is sufficient to reshape the eccentricity distribution of planets around single stars into the distribution observed for circumbinary planets. The hypothesis makes several testable predictions, including a major production channel for free-floating planets, transient electromagnetic signals, and the formation of circumstellar planets in binary systems — all within reach of upcoming surveys. I will close by briefly extending the same framework to the Pluto–Charon system, where our results pose a new challenge to the leading formation theory of its small satellites.

报告时间：2026年4月23日上午10:00

报告地点：紫台2号楼208室

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