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Chesley, S.

Publications and source records attributed to Chesley, S..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The Nucleus of Comet 9P-Tempel 1: Shape and Geology from Two Flybys

The nucleus of comet Tempel 1 has been investigated at close range during two spacecraft missions separated by one comet orbit of the Sun, 5 1/2 years. The combined imaging covers 70% of the surface of this object which has a mean radius of 2.83 +/- 0.1 km. The surface can be divided into two terrain types: rough, pitted terrain and smoother regions of varying local topography. The rough surface has round depressions from resolution limits (10 m/pixel) up to 1 km across, spanning forms from crisp steep-walled pits, to subtle albedo rings, to topographic rings, with all ranges of morphologic gradation. Three gravitationally low regions of the comet have smoother terrain, parts of which appear to be deposits from minimally modified flows, with other parts likely to be heavily eroded portions of multiple layer piles. Changes observed between the two missions are primarily due to backwasting of scarps bounding one of these probable flow deposits. This style of erosion is also suggested by remnant mesa forms in other areas of smoother terrain. The two distinct terrains suggest either an evolutionary change in processes, topographically- controlled processes, or a continuing interaction of erosion and deposition.

geological↗
NASA NTRS2011

Comet Ephemerides for the EPOXI and Stardust-NExT Flybys

The recently successful flybys of Comet 103P/Hartley 2 by the Deep Impact spacecraft and Comet 9P/Tempel 1 by the Stardust spacecraft each presented different challenges from the perspective of comet ephemeris prediction and spacecraft targeting. Hartley 2 is a small, highly active comet, with nongravitational accelerations that proved very difficult to model, requiring some amount of "cometchasing" by the spacecraft navigators. In contrast, Tempel 1 is a far larger and less active comet. It showed very stable ephemeris behavior and at flyby was within 1-sigma of predictions issued more than a year prior to encounter. This happenstance was fortuitous because the Stardust spacecraft had very little fuel margin available for comet ephemeris errors.

non-gravitational accelerations↗
NASA NTRS2011

Deep Impact, Stardust-NExT and the Behavior of Comet 9P/Tempel 1 from 1997 to 2010

We present observational data for Comet 9P/Tempel 1 taken from 1997 through 2010 in an international collaboration in support of the Deep Impact and Stardust-NExT missions. The data were obtained to characterize the nucleus prior to the Deep Impact 2005 encounter, and to enable us to understand the rotation state in order to make a time of arrival adjustment in February 2010 that would allow us to image at least 25% of the nucleus seen by the Deep Impact spacecraft to better than 80 m/pixel, and to image the crater made during the encounter, if possible. In total, approx.500 whole or partial nights were allocated to this project at 14 observatories worldwide, utilizing 25 telescopes. Seventy percent of these nights yielded useful data. The data were used to determine the linear phase coefficient for the comet in the R-band to be 0.045 +/- 0.001 mag/deg from 1deg to 16deg. Cometary activity was observed to begin inbound near r approx. 4.0 AU and the activity ended near r approx. 4.6 AU as seen from the heliocentric secular light curves, water-sublimation models and from dust dynamical modeling. The light curve exhibits a significant pre- and post-perihelion brightness and activity asymmetry. There was a secular decrease in activity between the 2000 and 2005 perihelion passages of approx. 20%. The post-perihelion light curve cannot be easily explained by a simple decrease in solar insolation or observing geometry. CN emission was detected in the comet at 2.43 AU pre-perihelion, and by r = 2.24 AU emission from C2 and C3 were evident. In December 2004 the production rate of CN increased from 1.8 x 10(exp 23) mol/s to Q(sub CN) = 2.75 x 10(exp 23) mol/s in early January 2005 and 9.3 x 10(exp 24) mol/s on June 6, 2005 at r = 1.53 AU.

Meech, K. J.↗