YZ Ceti is a recently discovered star with three known planets (b,c and d) orbiting very close to it. Although some types of mean motion resonance, or near resonance, are quite common e.g. 2:1 or 3:2 conjunction ratios, this one is a bit different.

The orbit periods in days are:

YZ Ceti b = 1.96876 d

YZ Ceti c = 3.06008 d

YZ Ceti d = 4.65627 d

This gives these conjunction periods:

c-d = 8.9266052 d

b-c = 5.5204368 d

b-d = 3.4109931 d

(Note the first two digits on each line.)

Nearest matching period:

34 c-d = 303.50457 d

55 b-c = 303.62403 d

89 b-d = 303.57838 d

34,55 and 89 are Fibonacci numbers.

Therefore the conjunction ratios are linked to the golden ratio (Phi).

Phi = 1.618034

(c-d) / (b-c) = 1.6170106

(b-c) / (b-d) = 1.618425

Data source: exoplanets.eu