Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass Estimate (Solar)	Diameter (Solar)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
Cab Mass Center	0.000	...	...	...	...	...	...	...	...
Castor Ca	0.009	0.00223	~0	?	0.6	<1	...	...	<1
Castor Cb	0.009	0.00223	~0	?	0.6	<1	...	...	<1
H.Z. Cab	0.23	0.101	0	?	...	...	...	...	...

NOTE: This animation attempts to relate the orbits and possible habitable zone of stars Ca and Cb in the Castor system to their center of mass. For the purposes of this animation, the masses of stars Aa and Ab are assumed to be 2.3 and 0.6 Solar, respectively. The inner two binary pairs of stars (Castor Aab and Bab) are currently separated from stars Cab by over 1,100 AUs (73" at a HIPPARCOS distance estimate of 51.6), and so lie outside the view of this animation.

Stars Ca and Cb have a combined visual luminosity that is only 5.1 percent of Sol's. They are separated on average by only 0.018 AUs (of a semi-major axis). Their highly circular orbit (e~ 0) takes only about 19.5 hours (0.814 days) to complete (Schmitt et al, 1994; Struve and Ebbighausen, 1959; and Joy and Sanford, 1926) and lies very nearly in the line of sight of an observer on Earth and so eclipse each other as they revolve (like CM Draconis Aab). Currently, the circumbinary orbit of an Earth-like planet (with liquid water) around Stars Cab may be centered around 0.23 AU -- well within the orbital distance of Mercury in the Solar System.