Nereid's Horizons page states no spin, and the ETL, finding none, left it still; the validator's
comment read that as "Nereid has no spin". Its rotation is measured: Kepler's K2 light curve gives
11.594 +/- 0.017 hours, confirming earlier ground-based periods (Kiss et al. 2016, MNRAS 457, 2908;
arXiv:1601.02395). Its spec now carries that day, as Eris's carries Bernstein et al.'s, and with no
known pole it turns about its orbit normal, as Eris, Haumea and Makemake do. The free-spinner check
accepts it (11.594 hours against a 360-day orbit).
A new validator: a moon without a lock must have a day unless it tumbles, and only Hyperion
("Rotational period = Chaotic") does. Nereid, left without one, fails it: "Moon nereid is drawn not
turning, and is not known to tumble". The renderer spec's example of a body left still was Titan,
said to have no period on Horizons, though it carries its orbit's; it is Hyperion now, and
BodyRecord.rotationPeriodHours says where each kind of period comes from.
Measured: the solar ETL passes; in bodies.json only Hyperion has no rotationPeriodHours; live on
:4301 Nereid's marker turns 60.000 degrees in a sixth of its day. Test: Nereid, as shipped, turns 60
degrees in 1.93 hours. Guarded mutant, the day removed from its spec and run through the solar
ETL: the validator fails, and the suite on the data it wrote fails that test and only it.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
SenrokaiandClaude Opus 5.5
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