Has Earth ever been a super-puff planet?

ABSTRACT Building on the hypothesis that a planet passing through a large comet's fragment chain can capture a large number of fragments to form a planetary shell, we examine three challenging cases: (1) shell formation in planets located very close to their host stars, (2) the simultaneous formation of multiple shells in resonant chain systems, and (3) the possibility that Earth itself may have been a super-puff planet in recent past. Studying Kepler-18c, d, Kepler-223d, and TOI-1420b, planets that are very close to their stars, we demonstrate that fragment chains can plausibly form shells, rings, and even shell-ring composites. We show that small variations in eccentricity among breakup clusters can produce a multichain configuration capable of simultaneously forming shells around the resonant Kepler-51b, c, d system. To assess the plausibility of Earth itself as a super-puff planet, we consider two supporting global signatures: (1) ancient Egyptian records, as relayed to Herodotus, describe four instances of sunrise and sunset reversing direction over a period of 11 340 yr; and (2) abrupt climate shifts during the glacial–interglacial cycle, particularly the Younger and Older Dryas periods, that are consistent with the expected dynamics of shell formation and collapse. These findings challenge conventional models of super-puff formation by introducing a transient, observable, and repeatable mechanism for shell-induced radius inflation with potential precedent within our own Solar system. This study highlights the need for further research into shell-ring composite structures, multichain comet interactions, and the ‘super-puff Earth’ hypothesis, as it could radically impact scientific understanding of Earth.