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)
Aab-Bab Mass Center0.0........................
Aab Mass Center~464670.343114.5...............
Castor Aa0.0050.02520.499?2.15?2.3......<1
Castor Ab0.0170.02520.499?0.65?<1......<1
H.Z. Aab~5.88.50?...............
Bab Mass Center~614670.343114.5...............
Castor Ba0.00570.008020.01?1.7?1.6......<1
Castor Bb0.0240.008020.01?0.4?<1......<1
H.Z. Bab~45.50?...............


NOTE: This animation attempts to relate the complicated orbits (and possible habitable zones) of star groups Aab and Bab in the Castor system to their respective centers of mass. To enlarge the display, the orbits have been arbitrarily rotated by 45 degrees. Aljthough known inclinations of the AabBab orbital system and of their component orbits (from the perspective of an observer on Earth) are displayed, the orbital inclination of any planet that may be discovered someday in this star system would likely be different from those of the habitable zone orbits depicted here. (For the purposes of this animation, the masses of stars Aa, Ab, Ba, and Bb are assumed to be 2.15, 0.65, 1.7, and 0.4 Solar, respectively.) The outer binary pair of stars (Castor Cab or YY Geminorum) is currently separated from the inner quadruple of bright stars by over 1,100 AUs (73" at a HIPPARCOS distance estimate of 51.6), and so lies outside the view of this animation.

Stars Aab are separated from its nearest binary companions Bab by around 107 AUs (6.805" of a semi-major axis at a HIPPARCOS distance estimate of 51.6 ly) in an orbit that takes 467 years to complete. The two binary pairs move in an eccentric orbit (e= 0.343) that is inclined by 114.5 from the perspective of an observer on Earth (Wulff D. Heintz, 1988).

Stars Aa and Ab have a combined luminosity of over 34 times that of Sol's. They are separated on average by only 0.022 AUs (of a semi-major axis). Their highly eccentric orbit (e= 0.499) takes only 9.21 days to complete (Joel Stebbins, 1914, pp. 465-466; and Heber D. Curtis, 1906). Currently, the circumbinary orbit of an Earth-like planet (with liquid water) around Stars Aab may be centered just beyond 6.0 AU -- just outside the orbital distance of Jupiter in the Solar System. Astronomers would find it very difficult to detect an Earth-type planet in the water zone of any star in this system using present methods.

Stars Ba and Bb have a combined visual luminosity of more than 14 times that of Sol's. They are separated on average by only 0.03 AUs (of a semi-major axis). Their highly circular orbit (e= 0.01) takes only 2.93 days to complete (Joel Stebbins, 1914, pp. 465-466; and Heber D. Curtis, 1906), and suggests synchronous rotation (Schmitt et al, 1994, page 850). Currently, the circumbinary orbit of an Earth-like planet (with liquid water) around Stars Aab may be centered around 4 AU -- on the outer edge of the Main Asteroid Belt in the Solar System.


 

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