Comet Tempel

Another meteor shower known as the Leonid occurs every year in November, caused by the tail of comet Tempel-Tuttle, which passes through the inner solar system every 32-33 years. Such a year was 1998 on November 17 and 18, 1998, observers on Earth saw as many as 200 meteors an hour. The shower was so intense that it generated widespread concern about the dismp-tion of global telecommunications and the possible damage or destmction of space telescopes. Partly as a result of careful preparation by satellite and telescope engineers, however, concerns afpeared to be minimal. 

NASA s most recent comet missions are Deep Impact and Rosetta. Deep Impact was launched on January 12, 2005, with Comet Tempel 1 as its target. The spacecraft encountered Tempel 1 on July 3, 2005, at which time it released a 770-pound (350 kg) copper projectile at the comet. Cameras and spectrometers on the spacecraft photographed and collected samples of materials ejected from the comet nucleus and relayed that information to scientists on Earth. Rosetta was launched on March 2, 2004, with Comet 67P/Churyumov-Gerasimenko as its target. The spacecraft will orbit the comet and make observations for about two years as the comet approaches the Sun. It will also release a small package of instruments that make the first-ever landing on the surface of a comet. 

A more recent mission, Deep Impact (2005), was designed to understand the Comet Tempel 1, by impacting it with a 370-kg mass Impactor and collect/analyze the Comet dust. The Impactor, also equipped with its own scientific equipment, was successfully powered by Li-SOCI2 batteries for one day, for navigation and science and communication, prior to the impact. The batteries were made by SAFT with 216 D-cells (9S24P) housed within a single mechanically and thermally coupled aluminum structure. 

Comet Tempel 1 was discovered in 1867 by E. Tempel. At the time of discovery, the comet was 0.7 AU from the Earth and 1.6 AU from the Sun. Currently, Tempel 1 has an orbital period of 5.5 years and a perihelion distance of roughly 1.5 AU. With an orbital eccentricity of 0.5, Tempel 1 s orbit lies between the orbits of Mars and Jupiter. These values varied in the past and will change in the future because of close approaches with the planet Jupiter. It therefore belongs to the group of short period comets. 

Comet Tempel 1 was selected as a target for a space mission with an impactor (see Fig. 5.5). It was also expected that due to the numerous and frequent perihelion passages, its surface and upper crust might have been considerably restructured. 

The Deep Impact mission revealed many details of the properties of comet Tern-pel 1. The spacecraft arrived at comet Tempel 1 on July 4, 2005 to impact it with a 370 kg mass. The spacecraft was launched from Earth in January, 2004. The im-pactor was a battery powered spacecraft that operated only for one day. Images from the comet were obtained till few seconds before the collision. The closest approach of the main spacecraft to the comet was 500 km. The flyby spacecraft monitored the impact. 

Dale, D., Pacult, R., and Reinhard, R., The Joint NASA/ESA Cometary Mission to Comets Halley and Tempel 2, European Space Agency Report No. ESA SP-153, Paris Cedex, France, pp. 3-5, October 1979. 

Mission Deep Impact In July 2005, NASA steered a projectile, about 370 kg in weight, at the comet 9F/Tempel (dimensions 4x4x14km), in order to obtain more exact information on its structure and composition. The impact was visible from Earth the Rosetta spacecraft discussed above also sent pictures to Earth. The dust/ice ratio determined after the impact is very probably greater than unity, so that comets are probably icy dustballs rather than (as had previously been surmised) dirty snowballs . The density of the cometary nucleus, which seems to consist of porous material, is roughly equal to that of ice. The impact set free around 19 GJ of... 

The densities of comets Halley and Tempel 2 were estimated to be 0.3 g cm 3, consistent with highly porous objects. However, comet 81 P/Wild2, imaged by the Stardust spacecraft in 2004, appears to be a more coherent object, implying that it has a higher density, -0.6 gcm 3. 

Images of comet nuclei taken during various spacecraft encounters illustrate both similarities and differences. Figure 12.2 compares images of comets Borrelly (taken by Deep Space 1 in 2001), Wild2 (taken by Stardust in 2004), and Tempel 1 (taken by Deep Impact in... 

Also, observations of crystalline silicates in the comets Halley (Swamy etal. 1988) and Tempel 1 (Harker et al. 2005) suggest that a large fraction of cometary dust was processed or formed in the hot inner regions of the protoplanetary disk and transported to the region where the comets formed. 

Both the analysis of Comet Wild 2 dust particles (Brownlee et al. 2006) and infrared spectroscopy of dust particles from comets Halley, Hale-Bopp, and Tempel 1 (Lisse et al. 2006) have shown that crystalline silicates are common constituents of comets. The presence of crystalline silicates in comets indicates that the crystallization of amorphous interstellar silicates occurred in the comet-forming region... 

Nucleus composed of rock, dust, ices, frozen gases often described as dirty snowballs, however the ices are covered by dark dust and rocks. The nuclei are irregularly shaped and the diameters range from several 100 m to some dozens of km. Up to now only the nuclei of the comets Halley (Fig. 5.3), Borrelly, Wild and Tempel 1 have been investigated by satellite missions and photographed directly. 

Schulz et al., 2006 [300] reported on the detection of water ice grains after the DEEP IMPACT onto Comet 9P/Tempel 1. 

Schulz, R., Owens, A., Rodriguez-Pascual, P.M., Lumb, D., Erd, C., Stiiwe, J.A. Detection of water ice grains after the DEEP IMPACT onto Comet 9P/Tempel 1. Astron. Astrophys. 448, 53-56 (2006)... 

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