Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0501h&link_type=abstract
American Astronomical Society, DPS meeting #40, #5.01; Bulletin of the American Astronomical Society, Vol. 40, p.393
Astronomy and Astrophysics
Astronomy
Scientific paper
Comet 8P/Tuttle was successfully observed with the Arecibo S-band radar during its close (0.25 AU) Earth passage in early January 2008. This is only the third comet, and the first Halley-type, to have its nucleus imaged by radar. Delay-Doppler images with 300-meter resolution were obtained on four consecutive nights (Jan 2-5). These have yielded preliminary estimates for the size, shape, rotation period, and radar albedo of the nucleus and produced the surprising finding that Tuttle is a highly bifurcated object. The nucleus consists of two lobes, the larger of which is clearly elongated. The central cleft between the lobes is so deep as to suggest that Tuttle is a contact binary. The nucleus appears to be a principal-axis rotator, and we have a firm rotation period estimate of 11.4 hours. Preliminary modeling suggests a modest ( 30 deg) Earthward tilt for the spin axis, which gives a long-axis dimension of 10 km for the nucleus. The short-axis width (perpendicular to the binary axis) is about 4 km. Combining these dimensions with the radar cross section of 4.8 km2 gives a radar albedo of 14%, the highest ever measured for a comet nucleus and indicative of a relatively well compacted surface. A more systematic nucleus shape modeling is underway, which should improve our estimates of the nucleus properties. In addition to the nucleus echo, we found a broadband Doppler echo from large (> cm), slow-moving (few cm/s) coma grains. The 4.9 km2 radar cross section of this component indicates that Tuttle is a prolific source of large grains, which is consistent with its parentage of a meteor stream (the Ursids).
Giorgini Jon D.
Harmon John K.
Howell Ellen S.
Magri Christopher
Nolan Michael C.
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