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Table 6

Properties of comet 8P/Tuttle derived from our Spitzer Space Telescope observations.

Nucleus
Shape Two spheres in contact (binary)
Size of each sphere 2.7 ± 0.1 km and 1.1 ± 0.1 km (radii)
Pole orientation RA = 285 ± 12° and Dec = +20 ± 5°
Geometric albedo 0.042 ± 0.008 (R-band)

Roughness and thermal inertia
Valid combinations η = 0.7 and I = 0–100 J K−1 m−2 s−1∕2
or η = 0.8 and I = 0 J K−1 m−2 s−1∕2

Production rates
Water 1.1 ± 0.2 × 1028 s−1 (1.6 AU pre-peri.)
Active fraction ≈9%
Dust ɛfρ 310 ± 34 cm (1.6 AU pre-perihelion)
325 ± 36 cm (2.2 AU post-perihelion)

Dust properties
Tdust 258 ± 10 K (1.6 AU pre-perihelion)
Grain size ≈10 μm (diameter)
Composition Amorphous pyroxene

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