Tempel 1
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Tempel 1 is a periodic comet (formally designated 9P/Tempel 1). It was discovered on April 3, 1867 by Ernst Wilhelm Leberecht Tempel, an astronomer working in Marseille. At the time of discovery, it approached perihelion once every 5.68 years. It was subsequently observed in 1873 and in 1879. However, Tempel 1's orbit occasionally brings it sufficiently close to Jupiter that its orbit is altered and its orbital period consequently changes. This event occurred in 1881, lengthening the orbital period to 6.5 years. Perihelion also changed, increasing by 50 million kilometers, rendering the comet far less visible from Earth. As a result, astronomers lost trace of the comet and surmised that it had disintegrated. Tempel 1 was re-discovered in the 1960s after American astronomer Brian G. Marsden performed precise calculations of the comet's orbit, taking into account Jupiter's perturbations. Its current orbital period equals 5.5 years.
Tempel 1 is not a bright comet; its maximum magnitude so far has been 11, far below naked eye visibility. Its size is believed to be 14 by 4 kilometers (8.7 by 2.5 miles), based on measurements taken by the Hubble Space Telescope in visible light and the Spitzer Space Telescope in infrared light. Combining these observations also revealed a low albedo of only 4%. A two-day rotation rate was also determined.
Deep Impact space mission
On July 4, 2005 at 05:52 UTC (01:52 EDT), Tempel 1 was impacted by the NASA Deep Impact probe. Earth-bound and space telescopes observed brightening of several magnitude after the impact while Deep Impact's observation section recorded a bright spray from the impact site.
The exact details of the crater that was formed are not yet known. It is believed that the crater could be up to 200 meters in diameter and 30-50 meters deep, but the crater could be much smaller depending on the composition and structure of Tempel 1. The purpose of the Deep Impact mission is to study the interior composition of a cometary nucleus.
