Millimoontides

Millimoontides is a term used to describe extremely small tides produced by the Moon's gravity on planetary bodies. The word blends milli- (one thousandth) with moontide, and in some discussions it refers to tidal amplitudes around one thousandth of a typical Earth lunar tide.

The concept arises in tidal theory as a way to discuss micro-tidal responses in bodies lacking substantial oceans, where solid-body tidal deformations dominate. In models, the millimoontide amplitude depends on gravitational forcing, the body's rigidity and internal structure (Love numbers), the size and distance of the perturbing body, and the presence or absence of liquids.

Measurement is challenging; current spacecraft instrumentation can detect centimeter-scale deformations on some bodies, but millimoontides would be near the detection limit. Research relies on precise orbital dynamics, laser altimetry, radar interferometry, or spacecraft tracking; in practice, it remains largely theoretical or used as a conceptual unit in simulations.

Outside of scientific literature, the term has appeared in science fiction and popular writing to describe minute tidal effects, such as the faint flexing of an asteroid shell or icy moon. Some researchers prefer other terms like microtide or nano-tide, and there is no formal standard.