Editing Orbital resonance (section)

=== Naiad:Thalassa 73:69 resonance ===
Neptune's innermost moon, [[Naiad (moon)|Naiad]], is in a 73:69 fourth-order resonance with the next outward moon, [[Thalassa (moon)|Thalassa]]. As it orbits Neptune, the more inclined Naiad successively passes Thalassa twice from above and then twice from below, in a cycle that repeats every ~21.5 Earth days. The two moons are about 3540&nbsp;km apart when they pass each other. Although their orbital radii differ by only 1850&nbsp;km, Naiad swings ~2800&nbsp;km above or below Thalassa's orbital plane at closest approach. As is common, this resonance stabilizes the orbits by maximizing separation at conjunction, but it is unusual for the role played by orbital inclination in facilitating this avoidance in a case where eccentricities are minimal.<ref name="JPLnews2019">{{cite web |url=https://www.jpl.nasa.gov/news/news.php?feature=7540 |title=NASA Finds Neptune Moons Locked in 'Dance of Avoidance' |date=14 November 2019 |website=Jet Propulsion Laboratory |access-date=15 November 2019}}</ref><ref name="Brozovic2019">{{cite journal |last1=Brozović |first1=M. |last2=Showalter |first2=M. R. |last3=Jacobson |first3=R. A. |last4=French |first4=R. S. |last5=Lissauer |first5=J. J. |last6=de Pater |first6=I. |title=Orbits and resonances of the regular moons of Neptune |date=31 October 2019 |journal=Icarus |volume=338 |issue=2 |pages=113462 |arxiv=1910.13612 |doi=10.1016/j.icarus.2019.113462 |bibcode=2020Icar..33813462B |s2cid=204960799}}</ref>{{NoteTag |The nature of this resonance (ignoring subtleties like libration and precession) can be crudely obtained from the orbital periods as follows. From Showalter ''et al.'', 2019,<ref name="Showalter2019">{{cite journal |last1=Showalter |first1=M. R. |last2=de Pater |first2=I. |last3=Lissauer |first3=J. J. |last4=French |first4=R. S. |url=https://www.spacetelescope.org/static/archives/releases/science_papers/heic1904/heic1904a.pdf |title=The seventh inner moon of Neptune |journal=Nature |volume=566 |issue=7744 |year=2019 |pages=350–353 |doi=10.1038/s41586-019-0909-9 |pmc=6424524 |pmid=30787452 |bibcode=2019Natur.566..350S}}</ref> the periods of Naiad (Pn) and Thalassa (Pt) are 0.294396 and 0.311484 days, respectively. From these, the period between conjunctions can be calculated as 5.366 days (1/[1/Pn – 1/Pt]), which is 18.23 (≈ 18.25) orbits of Naiad and 17.23 (≈ 17.25) orbits of Thalassa. Thus, after four conjunction periods, 73 orbits of Naiad and 69 orbits of Thalassa have elapsed, and the original configuration will be restored.}}